Outer membrane protein A (OmpA) as a potential therapeutic target for Acinetobacter baumannii infection

High-throughput single-cell analysis reveals Omp38-specific monoclonal antibodies that protect against Acinetobacter baumannii infection

Infections caused by Acinetobacter baumannii (A. baumannii) have emerged as a global public health concern because of high pathogenicity of this bacterium. Monoclonal antibodies (mAbs) have a lower likelihood of promoting drug resistance and offer targeted treatment, thereby reducing potential adverse effects; however, the therapeutic potential of mAbs targeting A. baumannii has not been fully characterized. In this study, mAbs against the outer membrane proteins (OMPs) of A. baumannii were isolated in a high-throughput manner. The ability of Omp38-specific mAbs to bind to A. baumannii strains from diverse sources was confirmed via enzyme-linked immunosorbent assay (ELISA). Intravenous administration of the Omp38-specific mAbs significantly improved the survival rate and reduced the bacterial load in a mouse model of lethal A. baumannii infection. Flow cytometry and ELISA confirmed that immune cell infiltration and cytokine production, respectively, decreased in a mouse model of sublethal A. baumannii infection. In addition, analysis of the Omp38-mAb C3 binding conformation revealed the potential mechanism of broad-spectrum binding activity of this mAb against A. baumannii. Taken together, these findings indicate that mAbs against Omp38 facilitate bacterial clearance from host, minimize inflammatory mediator release and reduce host damage, highlighting the potential of Omp38-specific mAbs in the clinical treatment of A. baumannii infection.

Microbiome signatures of virulence in the oral-gut-brain axis influence Parkinson's disease and cognitive decline pathophysiology

The human microbiome is increasingly recognized for its crucial role in the development and progression of neurodegenerative diseases. While the gut-brain axis has been extensively studied, the contribution of the oral microbiome and gut-oral tropism in neurodegeneration has been largely overlooked. Cognitive impairment (CI) is common in neurodegenerative diseases and develops on a spectrum. In Parkinson's Disease (PD) patients, CI is one of the most common non-motor symptoms but its mechanistic development across the spectrum remains unclear, complicating early diagnosis of at-risk individuals. Here, we generated 228 shotgun metagenomics samples of the gut and oral microbiomes across PD patients with mild cognitive impairment (PD-MCI) or dementia (PDD), and a healthy cohort, to study the role of gut and oral microbiomes on CI in PD. In addition to revealing compositional and functional signatures, the role of pathobionts, and dysregulated metabolic pathways of the oral and gut microbiome in PD-MCI and PDD, we also revealed the importance of oral-gut translocation in increasing abundance of virulence factors in PD and CI. The oral-gut virulence was further integrated with saliva metaproteomics and demonstrated their potential role in dysfunction of host immunity and brain endothelial cells. Our findings highlight the significance of the oral-gut-brain axis and underscore its potential for discovering novel biomarkers for PD and CI.

Proteomic profile of multidrug-resistant Serratia marcescens under meropenem challenge

Serratia marcescens is an opportunistic bacterium implicated in the prevalence of serious nosocomial infections and increased outbreaks in Intensive Care Units (ICUs) and Neonatal Intensive Care Units (NICUs). S. marcescens strains are resistant to several antimicrobial classes and express numerous virulence factors that promote pathogenicity. In the present study, the proteomic profile of the multidrug-resistant (MDR) S. marcescens clinical isolate challenged with the antimicrobial meropenem was evaluated. The proteins obtained were analyzed using liquid chromatography coupled with tandem mass spectrometry (LC-MSE). A total of 199 induced proteins were identified revealing that multidrug-resistant S. marcescens promotes increasing of proteins related to energy metabolism and efflux pump and decreases synthesis of proteins related to oxidative stress response and cell mobility upon meropenem challenge, shedding some light on the relationship between expressed proteins and bacterial pathogenicity after antimicrobial induction.

Acinetobacter baumannii: A comprehensive review of global epidemiology, clinical implications, host interactions, mechanisms of antimicrobial resistance and mitigation strategies

Since the discovery of Acinetobacter baumannii, it has emerged as a significant global health threat due to its increasing prevalence in healthcare settings and remarkable ability to develop resistance to various antibiotics. This detailed review addresses global epidemiology, emphasizing the worldwide distribution of carbapenem-resistant A. baumannii (CRAb), which is particularly prevalent in high-density healthcare settings and regions with intensive antibiotic usage, such as India. Clinically, A. baumannii infection poses serious health challenges, with mortality rates ranging from 30 % to 75 % for multidrug-resistant (MDR) strains. The review highlights the clinical impact and disease spectrum of A. baumannii, associated with pneumonia, wound infections, bloodstream infections, and, urinary tract infections with a strong association to invasive medical procedures and devices. Additionally, it discusses human-pathogen interactions by exploring various mechanisms, persistence in hospital environments, and survival under harsh conditions. The review further elaborates on different resistance mechanisms, focusing broadly on antibiotic degradation, altered drug targets, reduced drug permeability, and efflux systems, which facilitate the survival and persistence of A. baumannii. Finally, it evaluates strategies to combat AMR, emphasizing infection control measures, antimicrobial stewardship, and the urgent need for innovative therapeutic approaches such as phage therapy and new antibiotic development. The review calls for concerted, collaborative efforts among researchers, healthcare professionals, and public health authorities to mitigate the global threat posed by MDR A. baumannii strains.

Whole-genome analysis of escherichia coli isolated from captive giant pandas (ailuropoda melanoleuca) at the Dujiangyan base of the China conservation and research center for the giant panda, Sichuan, China

The giant panda (Ailuropoda melanoleuca) is a rare and vulnerable species facing threats from bacterial infections. The extensive use of antibiotics in disease prevention has raised concerns about antibiotic resistance, which reduces treatment efficacy and poses environmental and public health risks. This study aims to analyze the resistance profiles of Escherichia coli (E. coli) in captive pandas, providing insights into the antibiotic resistance genes within their gut microbiota. Twenty-two E. coli isolates were obtained from the feces of 22 captive giant pandas, and whole-genome sequencing was conducted. Sequence types and evolutionary relationships were determined through Multi-Locus Sequence Typing (MLST) and core genome Multi-Locus Sequence Typing (cgMLST), while virulence and resistance genes were identified. Core genome SNP analysis was performed to establish genetic relationships, and AST was conducted to evaluate antibiotic resistance profiles. Whole-genome sequencing revealed 15 distinct sequence types (STs), with ST48 (22.7%, 5 isolates) and ST212 (18.2%, 4 isolates) identified as the dominant lineages. Further resolution using cgMLST revealed that ST48 encompassed multiple cgSTs distributed across different evolutionary branches, while all ST212 isolates belonged to a single cgST. These results demonstrate the utility of cgMLST in resolving genetic diversity and isolate relationships within dominant lineages. Core genome SNP-based phylogenetic analysis grouped isolates with similar serotypes and STs, including a pathogenic cluster closely related to a panda-derived E. coli isolate (AMSHJX04). A total of 88 virulence genes (average 52 per isolate) were widespread, including those involved in iron acquisition systems (yagZ/Y), fimbriae-associated genes (fimA/H), and type II secretion systems (gspM/K). Antimicrobial susceptibility testing (AST) showed 59.1% resistance to ciprofloxacin, 18.2% to norfloxacin, and 13.6% to tetracycline, while all isolates remained sensitive to gentamicin and amikacin. Resistance profiling identified 78 resistance genes, primarily efflux pumps (acrB/D, emrA/B) and tetracycline-related mutations (emrK/Y). The gut microbiota of captive giant pandas harbors multiple antibiotic resistance genes, indicating a risk of resistance gene spread. Diverse sequence types, virulence genes, and phylogenetic relationships reveal the genetic complexity of E. coli in this species. Some isolates showed genetic similarities to pathogenic E. coli, emphasizing the need for continuous bacterial monitoring. This threatens antibiotic efficacy, increases infection risks, and complicates health management, underscoring the urgency of addressing resistance in panda conservation.

Characterization of proteins present in the biofilm matrix and outer membrane vesicles of Histophilus somni during iron-sufficient and iron-restricted growth: identification of potential protective antigens through in silico analyses

There is limited efficacy in vaccines currently available to prevent some animal diseases of bacterial origin, such as bovine respiratory disease caused by Histophilus somni. Protective efficacy can potentially be improved if bacterial antigens that are expressed in the host are included in vaccines. During H. somni infection in the bovine host, biofilms become established, and the availability of essential iron is restricted. To investigate further, the protein composition of spontaneously released outer membrane vesicles (OMVs) during iron-sufficient and iron-restricted growth and the proteins expressed in the biofilm matrix were analyzed and compared. Proteomic analysis revealed a dramatic physiological change in H. somni as it transitioned from the planktonic form to the biofilm mode of growth. All transferrin-binding proteins (Tbps) previously identified in H. somni were detected in the OMVs, suggesting that OMVs could induce antibodies to these proteins. Two TbpA-like proteins and seven total proteins were present in the OMVs only when iron was restricted, indicating the expression of these Tbps was differentially regulated. More proteins associated with quorum-sensing (QS) signaling were detected in the biofilm matrix compared with proteins in the OMVs, supporting a link between QS and biofilm formation. Proteins ACA31267.1 (OmpA) and ACA32419.1 (TonB-dependent receptor) were present in the OMV and biofilm matrix and predicted to be potential protective antigens using an immuno-bioinformatic approach. Overall, the results support the development of novel vaccines that contain OMVs obtained from bacteria grown to simulate the in vivo environment, and possibly biofilm matrix, to prevent diseases caused by bacterial pathogens.IMPORTANCEBovine respiratory disease (BRD) is the most economically important disease affecting the cattle industry. Available BRD vaccines consist of killed bacteria but are not very effective. Poor vaccine efficacy may be because the phenotype of bacteria in the host differs from the phenotype of cultured bacteria. Following host infection, virulent bacteria can express transferrin-binding proteins (Tbps) not expressed in culture medium but are required to sequester iron from host proteins. During chronic infections, such as BRD, bacteria can form a biofilm consisting of novel protein and polysaccharide antigens. The unique proteins expressed on outer membrane vesicles (OMVs) of Histophilus somni (a BRD pathogen) in the absence of iron and as a biofilm were identified and characterized. At least two TbpA-like proteins were expressed in OMVs only under iron-limiting conditions. Quorum-sensing-associated proteins were identified in the H. somni biofilm matrix. In silico analysis identified potential protein targets for vaccine development.

Current and novel therapies for management of Acinetobacter baumannii-associated pneumonia

Acinetobacter baumannii is a common pathogen associated with hospital-acquired pneumonia showing increased resistance to carbapenem and colistin antibiotics nowadays. Infections with A. baumannii cause high patient fatalities due to their capability to evade current antimicrobial therapies, emphasizing the urgency of developing viable therapeutics to treat A. baumannii-associated pneumonia. In this review, we explore current and novel therapeutic options for overcoming therapeutic failure when dealing with A. baumannii-associated pneumonia. Among them, antibiotic combination therapy administering several drugs simultaneously or alternately, is one promising approach for optimizing therapeutic success. However, it has been associated with inconsistent and inconclusive therapeutic outcomes across different studies. Therefore, it is critical to undertake additional clinical trials to ascertain the clinical effectiveness of different antibiotic combinations. We also discuss the prospective roles of novel antimicrobial therapies including antimicrobial peptides, bacteriophage-based therapy, repurposed drugs, naturally-occurring compounds, nanoparticle-based therapy, anti-virulence strategies, immunotherapy, photodynamic and sonodynamic therapy, for utilizing them as additional alternative therapy while tackling A. baumannii-associated pneumonia. Importantly, these innovative therapies further require pharmacokinetic and pharmacodynamic evaluation for safety, stability, immunogenicity, toxicity, and tolerability before they can be clinically approved as an alternative rescue therapy for A. baumannii-associated pulmonary infections.

Biological VFAs production from proteinaceous wastewater varied with protein type: The role of protein exposed enzyme cleavage sites and hydrolysates biotransformation capacity

Proteinaceous wastewater contains various proteins, which can be valorized to biobased volatile fatty acids (VFAs), important substrates for the synthesis of biodegradable plastics, biodiesel, bioelectricity, etc., but the influence of protein type on VFAs has never been documented. It was found that among the five proteinaceous wastewater proteins investigated, ovalbumin and casein produced the most and the least VFAs, respectively. The mechanism investigation shows that proteins with higher VFAs production had higher functional microorganism abundance and key enzyme activity in the reaction system due to their more enzyme cleavage sites and looser secondary structure, which made it easier for more hydrolase to bind, causing more protein hydrolysis. Also, metaproteomics and amino acid composition analyses revealed that the hydrolysates of proteins with higher VFAs had more isoleucine and proline, which were needed for the synthesis of recognizing and binding proteins (oligopeptide permease subunit A (OppA) and dipeptide permease (Dpp)) of acidogens and beneficial for transporters (Dpp subunit F/Opp subunit F), more hydrolysates (amino acids) were therefore transported into the cell. Further investigation indicates that more electron acceptor and electron donor paired amino acids were in the hydrolysates, facilitating the Stickland reaction and promoting intracellular amino acids bio-transformation to VFAs.

Identification of virulence genes and clade-specific markers through pan-genomic analysis of Leptospira

Leptospirosis is an emerging zoonotic and neglected disease across the world causing huge loss of life and economy. In this study, we did whole genome sequencing of one Leptospira isolate and a comparative genomic analysis with 69 other species of Leptospira available in RefSeq database provided insight into taxonomic and evolutionary relationship between species. AAI and whole genome based phylogenomic analysis established 3 clusters of Leptospira i.e. pathogenic, intermediate and saprophytic correlating with level of virulence of species. Leptospira has large closed core genome of 1038 genes and an open pan genome with 20,822 genes. The mobilome related genes were found mainly in pan-genome of pathogenic clade. A total of 498 genes have been identified as virulomes, with 329 virulent genes exhibiting presence/absence in various Leptospira species contributing to each species specific virulence profile. The hierarchical clustering of the congregated pathogenic genes yielded five groups, each with a distinct pattern of predominant genes that were either unique or common among clades, indicating lineage uniqueness. Most of the virulent gene pool identified were significantly enriched in COG functional categories of Nucleotide transport and metabolism, Intracellular trafficking, secretion and vesicular transport, cell motility and amino acid transport & metabolism. Pathogenic leptospires exhibit fewer clade-specific genes than non-pathogenic and intermediate leptospires, indicating gene loss and gain events in the evolution of pathogenic leptospires from non-pathogenic. The study's clade-specific and virulent genes can be utilised as markers for defining clade and associated virulence levels in any new Leptospira isolates. Wet-lab validation of virulent genes will help in accurately targeting pathogenic pathways of Leptospira and controlling leptospirosis.

Evaluation of Immunostimulatory Effects of Bacterial Lysate Proteins on THP-1 Macrophages: Pro-inflammatory Cytokine Response and Proteomic Profiling

Bacterial lysate proteins (BLPs) serve as potential immunostimulants, recognized by pattern recognition receptors (PRRs) on immune cells, eliciting a robust immune response. In this study, THP-1 macrophages were treated with varying doses of BLPs derived from Streptococcus pyogenes (SP), Streptococcus agalactiae (SA), and Serratia marcescens (SM). The results showed significant increases (p  < 0.05) in pro-inflammatory cytokines such as TNF-α, IL-1β, IL-6, IL-12, granulocyte macrophage-colony stimulating factor (GM-CSF), eotaxin, and macrophage inflammatory protein (MIP)-1α, except for 5 µg of all BLPs for TNF-α and eotaxin, and 5 µg of SP for IL-12 production. No significant differences were found between the corresponding doses of SP and SA or SP and SM, except for GM-CSF in all doses, while SA and SM only showed a difference at the 5 µg dose for GM-CSF. Furthermore, there were no significant differences between the 10 and 20 µg doses of all BLPs, indicating that doses higher than 10 µg do not significantly enhance the pro-inflammatory response. Combination doses of SP + SM and SA + SM did not show significant differences, except for IL-1β, suggesting no synergistic effect. Cytotoxicity was observed to increase with higher BLP concentrations in a dose-dependent manner, with combinations of SP + SM and SA + SM exhibiting greater cytotoxicity than the individual BLPs. Proteomic analysis of BLPs identified immunostimulatory proteins, including heat shock proteins (HSPs; ClpB, DnaK, and GroEL), metabolic enzymes (glyceraldehyde 3-phosphate dehydrogenase (GAPDH), enolase, and arginine deiminase (ADI)), and surface and secreted proteins (ESAT-6-like protein, CRISPR-associated endonuclease Cas9, OmpA, porin OmpC, and serralysin), which are involved in immune modulation, bacterial clearance, and immune evasion. This study underscores the potential of bacterial proteins as vaccine adjuvants or supplementary therapies; however, further research is essential to find a balance between immune activation and inflammation reduction to develop safer and more effective immunostimulants.

Acinetobacter baumannii OmpA hinders host autophagy via the CaMKK2-reliant AMPK-pathway

Outer membrane protein A (OmpA) plays a vital role in the interactions between Acinetobacter baumannii and host cells. Autophagy is a defense mechanism that hinders the intracellular replication of bacteria, thereby safeguarding cells against microbial infections. While it has been observed that A. baumannii triggers cellular autophagy, the precise role of its virulence protein OmpA in this process remains uncertain. In this study, we investigated the effects of A. baumannii OmpA (AbOmpA) on autophagy and explored the underlying molecular mechanisms. We found that AbOmpA exerted its autophagy-suppressive effect through inhibition of CaMKK2 phosphorylation. Compared to the wild-type strain, the ompA-deletion mutant strain displayed considerably enhanced autophagy induction, via the AMPK-ULK1 pathway. AbOmpA hindered starvation-induced autophagy, while A. baumannii-Omp33 (AbOmp33) and Escherichia coli-OmpA (EcOmpA) did not. Importantly, we confirmed that exogenous AbOmpA suppressed autophagy through the CaMKK2-AMPK-ULK1 pathway during A. baumannii infection. These findings reveal a novel mechanism for AbOmpA-mediated autophagy evasion, providing new insights into the pathogenesis of A. baumannii infection.IMPORTANCEAcinetobacter baumannii is a significant clinical pathogen notorious for causing infections in hospitals. Its outer membrane protein A acts as a virulence factor and helps the bacteria evade host defenses. Autophagy is a defense mechanism that hinders the intracellular replication of bacteria. While it has been observed that A. baumannii triggers cellular autophagy, the precise role of its AbOmpA in this process remains uncertain. Our studies demonstrate the AbOmpA of A. baumannii inhibits the cellular defense process, autophagy, through the CaMKK2-AMPK-ULK1 signaling cascade, thereby enhancing bacterial survival. This insight into how AbOmpA bypasses autophagy sheds light on A. baumannii infection's novel virulence strategy and suggests possible treatments.

Fast Encapsulation of Microbes into Dissolvable Hydrogel Beads Enables High-Throughput Microbial Single-Cell RNA Sequencing of Clinical Microbiome Samples

Microbial single-cell RNA-seq (mscRNA-seq) can achieve resolution at the cellular level, enhancing the understanding of microbial communities. However, current high-throughput mscRNA-seq methods are limited by multiple centrifugation steps, which can lead to microbial loss and bias. smGel-seq is reported, a high-throughput single-microbe RNA sequencing method for clinical microbiome samples that employs hydrogel beads to encapsulate individual microbes to reduce microbial loss and input requirements. In this method, a novel microchannel array device is implemented for encapsulating single microbe in dissolvable hydrogel beads (smDHBs), along with an optimized automated microfluidic platform to co-encapsulate barcoded beads and smDHBs, enabling high-throughput barcoding of individual microbes. smGel-seq significantly increases the microbial recovery rate in a gut microbiome sample from 8.8% to 91.8%. Furthermore, this method successfully processes clinical microbiome samples with microbial inputs 20 times lower than those required by previous methods. Notably, smGel-seq enables the first mscRNA-seq in a clinical sputum microbiome sample, revealing a specific microbial subpopulation that may play a key role in environmental adaptability, antibiotic resistance, and pathogenicity. These results highlight the compatibility of smGel-seq with clinical microbiome samples and demonstrate its potential for widespread application in diverse clinical and research settings.

α-Pinene: Inhibitor of Acinetobacter baumannii biofilms and potential therapeutic agent for pneumonia

Acinetobacter baumannii is a Gram-negative bacterium whose biofilm formation and mechanisms contribute to its persistent infectivity and drug resistance in clinical settings. Inhibition or disruption of biofilms might hold the key to resolving the issue of drug resistance in A. baumannii. α-Pinene, a bicyclic terpene olefin derived from the essential oils of plants, exhibits multiple biological activities, including antimicrobial, antioxidant, and anti-inflammatory effects. In this investigation, we discovered that α-Pinene had powerful antimicrobial activity against A. baumannii 390015, and its minimum inhibitory concentration was 0.625 μL/mL. In vitro experiments demonstrated that α-Pinene exerted an inhibitory effect on biofilm formation and impacted the production of extracellular polymers and the twitching motility of A. baumannii. Moreover, qRT-PCR experiments in combination with proteomic validation revealed that bmfR, csuAB, ompA, and bap were down-regulated in A. baumannii after the action of α-Pinene. In vivo experiments indicated that α-Pinene decreased the expression of inflammatory factors, including interleukin 6 (IL-6) and tumor necrosis factor-α (TNF-α) in tissues. Additionally, the expression levels of JNK, P38, and ERK in the downstream pathways of TRAF6 were evaluated, and it was found that α-Pinene decreased the expression levels of JNK, P38, and ERK. Notably, the expression levels of these markers increased as the concentration of α-Pinene decreased. These findings suggest that α-Pinene can inhibit biofilm formation in A. baumannii and mitigate inflammation, highlighting its therapeutic potential for A. baumannii infections.

Isolation and characterization of a protective monoclonal antibody targeting outer membrane protein (OmpA) against tuberculosis

Tuberculosis (TB) caused by Mycobacterium tuberculosis (Mtb) complex is an important zoonotic infectious disease around the world, and the One Health approach is an essential strategy for TB prevention and control. The abundant surface antigens present on the cell wall of Mtb can induce protective antibodies; however, its full characterization remains incomplete. Previous research has shown that antibodies targeting surface proteins can enhance host defense mechanisms. Therefore, identifying antigens that stimulate the production of protective antibodies is essential. In this study, we focused on a select antigen, outer membrane protein (OmpA), located on the outer membrane of Mtb. By screening for antibodies with protective effects in phagocytosis and intracellular killing in vitro, we identified a protective antibody targeting OmpA. We prepared an antibody, designated as 1E1, belonging to the IgG2b isotype, which exhibited high titers of 1:2,048,000. Further research demonstrated that antibody-induced protection was achieved by promoting opsonophagocytosis in a dose-dependent manner, enhancing phagosome-lysosome fusion, and inhibiting mycobacterial intracellular growth. These findings were corroborated in vivo, with a reduction in bacterial loads of approximately 0.7 log observed in the preventive group and almost 1.0 log in the therapeutic group of mice treated with the antibodies, compared to the negative control group. Cytotoxicity assays, animal toxicity analyses, and pharmacokinetic evaluations confirmed the safety and sustained effectiveness of the antibody in vivo. These findings indicate that OmpA can elicit protective antibodies and may serve as a treatment strategy for drug-resistant TB and a promising antigen for TB vaccine development.

IMPORTANCE

In this study, we identified a protective antibody targeting the outer membrane protein (OmpA) of Mycobacterium tuberculosis. This monoclonal antibody (MAb) belongs to the IgG2b isotype and exhibits high titers of 1:2,048,000 to the antigen. The cell infection assays demonstrated that antibody protection was achieved by promoting opsonophagocytosis in a dose-dependent manner, enhancing phagosome-lysosome fusion, and inhibiting mycobacterial intracellular growth in vitro and ex vivo. Cytotoxicity assays, animal toxicity analyses, and pharmacokinetic evaluations confirmed the safety and sustained effectiveness of the antibody in vivo. Furthermore, the mAb 1E1 can reduce the organs' bacterial burdens and pathological damages in the prevention mouse model as well as the treatment models. Above all, in this study, we found a novel mAb named 1E1 with IgG2b isotype targeting OmpA can have protection against tuberculosis (TB) in mice, which may serve as a treatment strategy for drug-resistant TB and a promising antigen for TB vaccine development.

Bacteriophage induces modifications in outer membrane protein expression and antibiotic susceptibility in Acinetobacter baumannii

Bacteriophages, the most abundant biological agents targeting bacteria, offer a promising alternative to antibiotics for combating multi-drug resistant pathogens like Acinetobacter baumannii. However, the rapid development of bacteriophage resistance poses a significant challenge. This study highlights the contribution of outer membrane proteins (OMPs) in the emergence of bacteriophage resistance in A. baumannii. The bacteriophage-sensitive and resistant isolates were studied for their native OMP profiles. Bacteriophage-tolerant A. baumannii were generated by infecting bacteria with bacteriophages and sub-culturing the survivors, and their expression of OMP and virulence was further characterized. These tolerant strains had significantly downregulated omp genes and under-expressed OMPs. Phenotypic changes like reduced adsorption to phages, deviant growth rates, biofilm-forming capacities, higher survival in limiting conditions, higher motility, and higher alkaline protease production were observed in the phage-tolerant strains equipped with better survival and virulent properties. The tolerant strains were re-sensitized to antibiotics they previously resisted. The significantly under-expressed OMPs in phage-tolerant strains were identified as OmpA and other OMPs similar to OmpA. This study could identify certain OMPs significantly under-expressed on bacteriophage exposure. The tolerant bacteria had altered phenotypic properties in addition to the development of phage resistance and the re-sensitisation to antibiotics, which paved the way for the future of phage therapeutics.

Exploring the evolution of Acinetobacter baumannii and Pseudomonas aeruginosa resistance during the COVID-19 era

Aim

In our study, we aim to compare the resistance profiles of Acinetobacter baumannii and Pseudomonas aeruginosa isolates from intensive care unit (ICU) patients before and during the COVID-19 pandemic.

Materials

The study involved adult patients monitored in the ICUs of a secondary-level hospital from January 2019 to December 2022. Isolates of A. baumannii and P. aeruginosa were obtained from blood, urine, and respiratory samples. Identification and antibiotic susceptibility tests were conducted using the disk diffusion method and the VITEK 2 system.

Results

The average age of the patients was 61.3 ± 21.9 years (range: 18-95), with a majority of 1306 (51.6%) being male. During the pandemic, A. baumannii isolates showed a significant increase in resistance rates for several antibiotics compared to the pre-pandemic period: imipenem (96% vs 35.1%), amikacin (84.1% vs 14.4%), ciprofloxacin (96.9% vs 36.9%), trimethoprim-sulfamethoxazole (66.4% vs 27%), and ceftazidime (96.5% vs 33.3%) (all with P < .001). However, there was no significant change in colistin resistance rates in these isolates (0.9% vs 0%; P = .307). Similarly, Pseudomonas aeruginosa isolates exhibited significant increases in resistance rates during the pandemic compared to the pre-pandemic period: imipenem (51.5% vs 18.8%; P < .001), colistin (4.9% vs 0.6%; P = .009), amikacin (23.5% vs 4.4%; P < .001), ciprofloxacin (53.3% vs 13.8%; P < .001), and ceftazidime (39.2% vs 12.7%; P < .001).

Conclusion

Our results demonstrate a significant increase in antibiotic resistance levels in Acinetobacter and Pseudomonas strains associated with hospital-acquired infections or colonization during the COVID-19 pandemic.

Current innovations in mRNA vaccines for targeting multidrug-resistant ESKAPE pathogens

The prevalence of multidrug-resistant (MDR) ESKAPE pathogens, including Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa, represents a critical global public health challenge. In response, mRNA vaccines offer an adaptable and scalable platform for immunotherapy against ESKAPE pathogens by encoding specific antigens that stimulate B-cell-driven antibody production and CD8+ T-cell-mediated cytotoxicity, effectively neutralizing these pathogens and combating resistance. This review examines recent advancements and ongoing challenges in the development of mRNA vaccines targeting MDR ESKAPE pathogens. We explore antigen selection, the nuances of mRNA vaccine technology, and the complex interactions between bacterial infections and antibiotic resistance. By assessing the potential efficacy of mRNA vaccines and addressing key barriers to their paraclinical implementation, this review highlights the promising function of mRNA-based immunization in combating MDR ESKAPE pathogens.

Epitope-Based Vaccines: The Next Generation of Promising Vaccines Against Bacterial Infection

The increasing resistance of bacteria to antibiotics has underscored the need for new drugs or vaccines to prevent bacterial infections. Reducing multidrug resistance is a key objective of the WHO's One Health initiative. Epitopes, the key parts of antigen molecules that determine their specificity, directly stimulate the body to produce specific humoral and/or cellular immune responses. Epitope-based vaccines, which combine dominant epitopes in a rational manner, induce a more efficient and specific immune response than the original antigen. While these vaccines face significant challenges, such as epitope escape or low immunogenicity, they offer advantages including minimal adverse reactions, improved efficacy, and optimized protection. As a result, epitope-based vaccines are considered a promising next-generation approach to combating bacterial infections. This review summarizes the latest advancements, challenges, and future prospects of epitope-based vaccines targeting bacteria, with a focus on their development workflow and application in antibiotic-resistant pathogens with high mortality rates, including Staphylococcus aureus, Streptococcus pneumoniae, Streptococcus pyogenes, Klebsiella pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa. The goal of this review is to provide insights into next-generation vaccination strategies to combat bacterial infections associated with antibiotic resistance and high mortality rates.

A review of gut failure as a cause and consequence of critical illness

In critical illness, all elements of gut function are perturbed. Dysbiosis develops as the gut microbial community loses taxonomic diversity and new virulence factors appear. Intestinal permeability increases, allowing for translocation of bacteria and/or bacterial products. Epithelial function is altered at a cellular level and homeostasis of the epithelial monolayer is compromised by increased intestinal epithelial cell death and decreased proliferation. Gut immunity is impaired with simultaneous activation of maladaptive pro- and anti-inflammatory signals leading to both tissue damage and susceptibility to infections. Additionally, splanchnic vasoconstriction leads to decreased blood flow with local ischemic changes. Together, these interrelated elements of gastrointestinal dysfunction drive and then perpetuate multi-organ dysfunction syndrome. Despite the clear importance of maintaining gut homeostasis, there are very few reliable measures of gut function in critical illness. Further, while multiple therapeutic strategies have been proposed, most have not been shown to conclusively demonstrate benefit, and care is still largely supportive. The key role of the gut in critical illness was the subject of the tenth Perioperative Quality Initiative meeting, a conference to summarize the current state of the literature and identify key knowledge gaps for future study. This review is the product of that conference.

Development of an enzyme-linked immunosorbent assay (ELISA) for determining neutrophil elastase (NE) - a potential useful marker of multi-organ damage observed in COVID-19 and post-Covid-19 (PCS)

Background

The ongoing post-COVID-19 syndrome (PCS) epidemic, causing complications of diverse etiology, necessitates the search for new diagnostic markers and the development of widely accessible methods for their detection. This would enable the prognosis of PCS progression and faster implementation of targeted treatments. One potential marker is neutrophil elastase (NE), whose elevated levels in the blood during PCS may result from organ damage caused by increased secretion of severe inflammatory mediators or amyloidosis resulting from the interaction of NE with SARS-CoV-2. The aim of this publication is to present a step-by-step method for designing an enzymatic ELISA test, enabling the quantitative assessment of NE in the blood serum of patients.

Methods

NE was measured using the designed ELISA test.

Results

The study outlines all the steps necessary for designing and optimizing the ELISA test, including the selection of standards, primary and secondary antibodies, and their dilutions. Using the test, elevated NE levels were demonstrated in patients with advanced-stage diabetic nephropathy after symptomatic COVID-19, compared to a relative group of patients sampled before COVID-19.

Conclusion

The undertaken efforts enabled the development of a test with high performance parameters (initially set sensitivity: ≥40 pg/μL; intra-assay precision: 7%; inter-assay precision <20%). No significant cross-reactivity with other tested proteins was observed. Serial dilution of plasma samples resulted in a proportional decrease in signal intensity.

Natural peptides and their synthetic congeners acting against Acinetobacter baumannii through the membrane and cell wall: latest progress

Acinetobacter baumannii is one of the deadliest Gram-negative bacteria (GNB), responsible for 2-10% of hospital-acquired infections. Several antibiotics are used to control the growth of A. baumannii. However, in recent decades, the abuse and misuse of antibiotics to treat non-microbial diseases have led to the emergence of multidrug-resistant A. baumannii strains. A. baumannii possesses a complex cell wall structure. Cell wall-targeting agents remain the center of antibiotic drug discovery. Notably, the antibacterial drug discovery intends to target the membrane of the bacteria, offering several advantages over antibiotics targeting intracellular systems, as membrane-targeting agents do not have to travel through the plasma membrane to reach the cytoplasmic targets. Microorganisms, insects, and mammals produce antimicrobial peptides as their first line of defense to protect themselves from pathogens and predators. Importantly, antimicrobial peptides are considered potential alternatives to antibiotics. This communication summarises the recently identified peptides of natural origin and their synthetic congeners acting against the A. baumannii membrane by cell wall disruption.

Rani F, Alattraqchi AG, Ismail S, A. Rahman NI, Cleary DW, Clarke SC, Yeo CC. Whole-genome sequencing of Acinetobacter baumannii clinical isolates from a tertiary hospital in Terengganu, Malaysia (2011-2020), revealed the predominance of the Global Clone 2 lineage

Carbapenem-resistant Acinetobacter baumannii is recognized by the World Health Organization (WHO) as one of the top priority pathogens. Despite its public health importance, genomic data of clinical isolates from Malaysia remain scarce. In this study, whole-genome sequencing was performed on 126 A. baumannii isolates collected from the main tertiary hospital in the state of Terengganu, Malaysia, over a 10-year period (2011-2020). Antimicrobial susceptibilities determined for 20 antibiotics belonging to 8 classes showed that 77.0% (n=97/126) of the isolates were categorized as multidrug resistant (MDR), with all MDR isolates being carbapenem resistant. Multilocus sequence typing analysis categorized the Terengganu A. baumannii clinical isolates into 34 Pasteur and 44 Oxford sequence types (STs), with ST2Pasteur of the Global Clone 2 lineage identified as the dominant ST (n=76/126; 60.3%). The ST2Pasteur isolates could be subdivided into six Oxford STs with the majority being ST195Oxford (n=35) and ST208Oxford (n=17). Various antimicrobial resistance genes were identified with the bla OXA-23-encoded carbapenemase being the predominant acquired carbapenemase gene (n=90/126; 71.4%). Plasmid-encoded rep genes were identified in nearly all (n=122/126; 96.8%) of the isolates with the majority being Rep_3 family (n=121). Various virulence factors were identified, highlighting the pathogenic nature of this bacterium. Only 14/126 (11.1%) of the isolates were positive for the carriage of CRISPR-Cas arrays with none of the prevalent ST2Pasteur isolates harbouring them. This study provided a genomic snapshot of the A. baumannii isolates obtained from a single tertiary healthcare centre in Malaysia over a 10-year period and showed the predominance of a single closely related ST2Pasteur lineage, indicating the entrenchment of this clone in the hospital.

K. pneumoniae ghosts serve as a novel vaccine formulation to enhance immune responses of A. baumannii subunit vaccine in mice

Acinetobacter baumannii (A. baumannii) is a prominent nosocomial pathogen, posing a significant threat to public health. Urgent efforts are required to develop a safe and effective vaccine. Bacterial ghosts (BGs), comprising empty bacterial cell envelopes, offer a promising platform for vaccine adjuvant development. In the present study, Klebsiella pneumoniae (K. pneumoniae, KP) ghosts were generated via PhiX-174 lysis gene E-mediated inactivation. The present study results demonstrated that KP ghosts greatly promoted maturation and activation of BMDCs by upregulating the expression of surface molecules (CD40, CD80, CD86 and MHCII) and improving the secretion of cytokines (IL-1β, TNF-α and IL-12p70). In addition, to assess the immunogenicity and protective efficacy of the vaccine candidate, C57BL/6 mice were immunized with either A. baumannii OmpA or A. baumannii OmpA plus KP ghosts. The results showed that OmpA plus KP ghosts elicited higher levels of specific IgG antibody responses compared to OmpA alone. Furthermore, OmpA plus KP ghosts also increased lymphocyte proliferation and expression of the early activation marker CD69 on T cells, augmented frequency of central memory T cells (TCM) and IFN-γ+CD4+ T cells with production of increased IFN-γ in response to OmpA stimulation, as compared to OmpA alone. Furthermore, post-challenge with A. baumannii, mice immunized with OmpA plus KP ghosts exhibit a higher survival rate and lower bacterial loads in the spleen and lungs compared to those immunized with OmpA alone. In conclusion, these findings underscore the potential of KP ghosts as a candidate vaccine formulation or immunomodulators for designing a novel vaccine against A. baumannii infection.

Fragment optimized chalcone derivatives targeting OmpA protein as a therapeutic approach against multidrug resistant Acinetobacter baumannii

Acinetobacter baumannii is a notorious pathogen associated with life-threatening infections, with its outer membrane protein A (OmpA) being a key contributor to its pathogenicity by targeting epithelial cell apoptosis. The study presents an in silico analysis of chalcone derivatives as potential therapeutic agents against the outer membrane protein A (OmpA) of Acinetobacter baumannii. We performed molecular docking to evaluate the binding interactions, revealing that isobavachalcone exhibited the highest binding affinity. Further fragment optimization (FOI) of isobavachalcone improved its binding energy. Additionally, ADMET (absorption, distribution, metabolism, excretion, and toxicity) analysis was conducted to assess the pharmacokinetic properties of the compounds. Antigenicity and allergenicity of the protein show that this protein is virulent and antigenic. Moreover, molecular docking was performed and the result shows that isobavachalcone showed the highest binding energy at -6.7 kcal/mol. Furthermore, for a more potent compound, fragment optimization was performed and led to a new lead compound fragment optimized isobavachalcone (FOI) which shows increased binding energy -6 kcal/mol. ADMET and toxicity analysis was performed of both the compounds isobavachalcone and FOI which revealed favorable pharmacokinetic profiles for both compounds, but toxicity analysis showed discrepancies, with the isobavachalcone exhibiting toxicity but FOI compound showing no detectable toxicity. This underscores the importance of structure optimization in drug development. Overall, chalcone derivatives show promise as antibacterial agents against A. baumannii, with computational analyses aiding in compound selection and optimization. While both isobavachalcone and its FOI showed favorable pharmacokinetics, in vivo and in vitro validation is needed to confirm their therapeutic potential.

Comparative study of phenotypic and genotypic expression of virulence factors in colonizing and pathogenic carbapenem resistant Acinetobacter baumannii (CRAB)

Carbapenem resistant Acinetobacter baumannii has evolved as the most troublesome microorganism with multiple virulence factors. Biofilm formation, porins, micronutrient capturing mechanism and quorum sensing, provide protection against desiccation, host-pathogen killing and enhance its persistence. The conservation of these factors between colonizing and pathogenic carbapenem resistant A. baumannii has been barely investigated. We studied biofilm formation, desiccation survival, motility and hemolysis in pathogenic carbapenem resistant A. baumannii and colonizer carbapenem resistant A. baumannii from the hospital environment. The virulent genes pgaA, csuE, bap, ompA, abaI, pilA and bauA were detected by simplex-PCR and Quantitative Real-Time PCR was done for expressional studies. In-vivo survival percentage was studied by Galleria mellonella (wax moth) killing assay. Phenotypic characterization revealed that the biofilm formation and desiccation survival proportion was significantly higher in colonizer carbapenem resistant A. baumannii (p < 0.05). Twitching motility was found comparable (mean 0.5 to 1.5 cm). Surface associated motility varied widely. None showed hemolysis. The csuE, bap, ompA, abaI, pilA and bauA genes were detected in almost all the pathogenic and colonizer carbapenem resistant A. baumannii isolates while none harboured pgaA gene. The expression of bap, ompA and bauA gene was found significantly higher in pathogenic carbapenem resistant A. baumannii while expression of csuE and abaI gene was comparable in both. Overexpression of pilA gene was seen in those with higher surface associated motility. Pathogenic carbapenem resistant A. baumannii showed significantly higher pathogenicity in-vivo, as 100% of larvae died on 4th day post-infection. In conclusion high level expression of outer membrane proteins (ompA) and siderophores is significantly associated with the pathogenicity in carbapenem resistant A. baumannii isolated from infections, which can be a differentiating point from the colonizers. CLINICAL TRIAL: Not Applicable.

Development of a novel multi-epitope subunit mRNA vaccine candidate to combat Acinetobacter baumannii

Acinetobacter baumannii, an opportunistic bacterium prevalent in various environment, is a significant cause of nosocomial infections in ICUs. As the causative agent of pneumonia, septicemia, and meningitis, A. baumannii typically exhibits multidrug resistance and is associated with poor prognosis, thus led to a challenge for researchers in developing new treatment and prevention methods. This study involved the development of a novel multi-epitope mRNA vaccine for A. baumannii and validation of in silico approaches was conducted. We screened 11 immunodominant epitopes for cytotoxic T cells, 5 for helper T cells, and 10 for Linear B-cell based on promising candidate proteins omp33-36, ompA and ompW, the selection of these three proteins is based on reverse vaccinology screening and previous work by other researchers. All predicted epitopes demonstrated strong antigenicity, immunogenicity without posing any potential harm to humans. Additionally, high conservancy is required to cover different strains. All epitopes, as well as adjuvants, were constructed into a final vaccine, which was further assessed by calculating its physicochemical properties. Next, we docked the vaccine protein with immune receptors and analyzed the complexes with dynamic simulations to evaluate its affinity to receptors. At last, the constructed sequence is translated to an mRNA sequence. The results indicated the constructed vaccine is capability of eliciting robust humoral and cellular immune responses, making it a promising candidate for protection against the targeted pathogen.

Unseen Enemy: Mechanisms of Multidrug Antimicrobial Resistance in Gram-Negative ESKAPE Pathogens

Multidrug antimicrobial resistance (AMR) represents a formidable challenge in the therapy of infectious diseases, triggered by the particularly concerning gram-negative Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp. (ESKAPE) pathogens. Designated as a "priority" in 2017, these bacteria continue to pose a significant threat in 2024, particularly during the worldwide SARS-CoV-2 pandemic, where coinfections with ESKAPE members contributed to worsened patient outcomes. The declining effectiveness of current treatments against these pathogens has led to an increased disease burden and an increase in mortality rates globally. This review explores the sophisticated mechanisms driving AMR in gram-negative ESKAPE bacteria, focusing on Acinetobacter baumannii, Klebsiella pneumoniae, Pseudomonas aeruginosa, and Enterobacter spp. Key bacterial mechanisms contributing to resistance include limitations in drug uptake, production of antibiotic-degrading enzymes, alterations in drug target sites, and enhanced drug efflux systems. Comprehending these pathways is vital for formulating innovative therapeutic strategies and tackling the ongoing threat posed by these resistant pathogens.

Comparative genomic and phenotypic analysis of low- and high-virulent Acinetobacter baumannii strains: Insights into antimicrobial resistance and virulence potential

Multi-drug resistant Acinetobacter baumannii poses a significant threat to public health. This study investigated the genomic features and phenotypic characteristics of two clinical A. baumannii strains, KBN10P01317 (low-virulent) and KBN10P01599 (high-virulent), which share the same sequence type and antimicrobial susceptibility profile. The phenotypic characteristics of A. baumannii strains were assessed by antimicrobial susceptibility testing and virulence trait examination in vitro and in vivo. Whole-genome sequencing was conducted for comparative genomic analysis, and the expression of virulence-associated genes was analyzed using quantitative polymerase chain reaction. Our comparative genomic analysis revealed that KBN10P01599 harbored a larger genome with a greater number of antimicrobial resistance genes, including two copies of the critical resistance gene blaOXA-23, which might contribute to its higher minimum inhibitory concentration for carbapenems (64 μg/ml) compared to KBN10P01317 (32 μg/ml). Although both A. baumannii strains possessed the same repertoire of virulence-associated genes, KBN10P01599 exhibited significantly enhanced expression of quorum sensing (abaI/R) and biofilm formation genes (csuCDE, bap, and pgaA), correlating with its virulence traits, including increased surface motility, biofilm formation, and adherence to host cells. The differences in the expression of virulence-associated genes between the two strains were partly attributed to the transposition of insertion sequence elements. These findings provide valuable insights into the genetic basis of the virulence potential and antimicrobial resistance in A. baumannii, highlighting the evolutionary changes that may occur within strains of the same clone.

A peptide targeting outer membrane protein A of Acinetobacter baumannii exhibits antibacterial activity by reducing bacterial pathogenicity

The World Health Organization has classified multidrug-resistant (MDR) Acinetobacter baumannii as a significant threat to human health, necessitating the urgent discovery of new antibacterial drugs to combat bacterial resistance. Outer membrane protein A of A. baumannii (AbOmpA) is an outer membrane-anchored β-barrel-shaped pore protein that plays a critical role in bacterial adhesion, invasion, and biofilm formation. Therefore, AbOmpA is considered a key virulence factor of A. baumannii. Herein, we screened three phage display peptide libraries targeting AbOmpA and identified several peptides. Among them, P92 (amino acid sequence: QMGFMTSPKHSV) exhibited the highest binding affinity with AbOmpA, with a KD value of 7.84 nM. In vitro studies demonstrated that although P92 did not directly inhibit bacterial growth, it significantly reduced the invasion and adhesion capabilities of multiple clinical isolates of MDR A. baumannii and concentration-dependently inhibited biofilm formation by acting on OmpA. Furthermore, the polymerase chain reaction results confirmed a significant positive correlation between the antibacterial effect of P92 and OmpA expression levels. Encouragingly, P92 also displayed remarkable therapeutic efficacy against A. baumannii infection in various models, including an in vitro cell infection model, a mouse skin infection model, and a mouse sepsis model. These results highlight P92 as a novel and highly effective antimicrobial molecule specifically targeting the virulence factor AbOmpA.

In silico design of a novel hybrid epitope-based antigen harboring highly exposed immunogenic peptides of BamA, OmpA, and Omp34 against Acinetobacter baumannii

Acinetobacter baumannii, is among the highest priority bacteria according to the WHO categorization which necessitate the exploration of alternative strategies such as vaccination. OmpA, BamA, and Omp34 are assigned as appropriate antigens to serve in vaccine development against this pathogen. Experimentally validated exposed epitopes of OmpA and Omp34 along with selected exposed epitopes predicted by an integrative in silico approach were represented by the barrel domain of BamA as a scaffold. Among the 8 external loops of BamA, 5 loops were replaced with selected loops of OmpA and Omp34. The designed antigen was analyzed regarding the physicochemical properties, antigenicity, epitope retrieval, topology, structure, and safety. BamA is a two-domain OMP with a 16-stranded barrel in which L4, L6, and L7 were the longest loops of BamA in order. The designed antigen consisted of 478 amino acids with antigen probability of 0.7793. The novel antigen was a 16-stranded barrel. No identical 8-meric peptides were found in the human proteome against the designed antigen sequence. The designed construct was safe regarding the allergenicity, toxicity, and human proteome reactivity. The designed antigen could develop higher protection against A. baumannii in comparison to either OmpA, BamA, or Omp34 alone.

Antibacterial phenolic compounds from the flowering plants of Asia and the Pacific: coming to the light

CONTEXT

The emergence of pan-resistant bacteria requires the development of new antibiotics and antibiotic potentiators.

OBJECTIVE

This review identifies antibacterial phenolic compounds that have been identified in Asian and Pacific Angiosperms from 1945 to 2023 and analyzes their strengths and spectra of activity, distributions, molecular masses, solubilities, modes of action, structures-activities, as well as their synergistic effects with antibiotics, toxicities, and clinical potential.

METHODS

All data in this review was compiled from Google Scholar, PubMed, Science Direct, Web of Science, and library search; other sources were excluded. We used the following combination of keywords: 'Phenolic compound', 'Plants', and 'Antibacterial'. This produced 736 results. Each result was examined and articles that did not contain information relevant to the topic or coming from non-peer-reviewed journals were excluded. Each of the remaining 467 selected articles was read critically for the information that it contained.

RESULTS

Out of ∼350 antibacterial phenolic compounds identified, 44 were very strongly active, mainly targeting the cytoplasmic membrane of Gram-positive bacteria, and with a molecular mass between 200 and 400 g/mol. 2-Methoxy-7-methyljuglone, [6]-gingerol, anacardic acid, baicalin, vitexin, and malabaricone A and B have the potential to be developed as antibacterial leads.

CONCLUSIONS

Angiosperms from Asia and the Pacific provide a rich source of natural products with the potential to be developed as leads for treating bacterial infections.

Chitosan oligosaccharide efficiently inhibits Cronobacter sakazakii biofilm by interacting with out membrane protein A for regulating CpxRA-mediated cellulose production pathway

Chitosan oligosaccharide (COS) can efficiently inhibit Cronobacter sakazakii (C. sakazakii) biofilm independent on antibacterial activity. However, the mechanism is still unclear. In this study, the role of out membrane protein A (OmpA) and its downstream CpxRA-mediated cellulose production pathway in COS's inhibition on C. sakazakii biofilm were explored. The spectroscopic results were shown that COS could interact with OmpA, and this changed OmpA's second structure and spatial conformation as well as cell membrane permeability and COS uptake. C. sakazakii ΔOmpA strain under COS treatment had a lower cell membrane permeability and COS uptake rate. The interaction between OmpA and COS could further initiate CpxRA system. The regulon cpxP expression level was therefore up-regulated. The deletion of the response regulator cpxR gene reduced inhibitory effect of COS on biofilm. CpxRA system inhibited expression of csgD and adrA, which coded diguanylate cyclase to generate cyclic diguanosine monophosphate (c-di-GMP). The expression of bcsAB was then down-regulated by c-di-GMP, and the cellulose production as well as biofilm were reduced. The addition of exogenous c-di-GMP could mitigate the inhibition of COS on C. sakazakii biofilm. These results not only help to elucidate biofilm inhibition mechanism of COS, but also provided a basis for developing anti-biofilm agents targeted OmpA.

Transcriptomic investigations of polymyxins and colistin/sulbactam combination against carbapenem-resistant Acinetobacter baumannii

Carbapenem-resistant Acinetobacter baumannii (CRAB) is a Priority 1 (Critical) pathogen urgently requiring new antibiotics. Polymyxins are a last-line option against CRAB-associated infections. This transcriptomic study utilized a CRAB strain to investigate mechanisms of bacterial killing with polymyxin B, colistin, colistin B, and colistin/sulbactam combination therapy. After 4 h of 2 mg/L polymyxin monotherapy, all polymyxins exhibited common transcriptomic responses which primarily involved disruption to amino acid and fatty acid metabolism. Of the three monotherapies, polymyxin B induced the greatest number of differentially expressed genes (DEGs), including for genes involved with fatty acid metabolism. Gene disturbances with colistin and colistin B were highly similar (89 % common genes for colistin B), though effects on gene expression were generally lower (0-1.5-fold in most cases) with colistin B. Colistin alone (2 mg/L) or combined with sulbactam (64 mg/L) resulted in rapid membrane disruption as early as 1 h. Transcriptomic analysis of this combination revealed that the effects were driven by colistin, which included disturbances in fatty acid synthesis and catabolism, and inhibition of nutrient uptake. Combination therapy produced substantially higher fold changes in 72 % of DEGs shared with monotherapy, leading to substantially greater reductions in fatty acid biosynthesis and increases in biofilm, cell wall, and phospholipid synthesis. This indicates synergistic bacterial killing with the colistin/sulbactam combination results from a systematic increase in perturbation of many genes associated with bacterial metabolism. These mechanistic insights enhance our understanding of bacterial responses to polymyxin mono- and combination therapy and will assist to optimize polymyxin use in patients.

Genetic Characterization of Multidrug-Resistant Acinetobacter baumannii and Synergy Assessment of Antimicrobial Combinations

Background/Objectives: A. baumannii is a prominent nosocomial pathogen due to its drug-resistant phenotype, representing a public health problem. In this study, the aim was to determine the effect of different antimicrobial combinations against selected multidrug-resistant (MDR) or extensive drug-resistant (XDR) isolates of A. baumannii. Methods: MDR or XDR A. baumannii isolates were characterized by assessing genes associated with drug resistance, efflux pumps, porin expression, and biofilm formation. The activities of antimicrobial combinations including tigecycline, ampicillin/sulbactam, meropenem, levofloxacin, and colistin were evaluated using checkerboard and time-to-kill assays on isolates with different susceptibility profiles and genetic characteristics. Results: Genetic characterization of MDR/XDR strains (n = 100) included analysis of OXA-24/40 gene carbapenemase (98%), genes encoding aminoglycoside-modifying enzymes (44%), and parC gene mutations (10%). AdeIJK, AdeABC, and AdeFGH efflux pumps were overexpressed in 17-34% of isolates. Omp33-36, OmpA, and CarO membrane porins were under-expressed in 50-76% of isolates; CarO was overexpressed in 22% of isolates. Isolates showed low biofilm production (11%). Synergistic activity was observed with levofloxacin-ampicillin/sulbactam and meropenem-colistin, which were able to inhibit bacterial growth. Conclusions: Genetic characteristics of A. baumannii were highly variable among the strains. Synergistic activity was observed with meropenem-colistin and levofloxacin-ampicillin/sulbactam combinations in the checkerboard method, but not in the time-to-kill assays. These discrepancies among both methods indicate that further studies are needed to determine the best therapeutic combination for treating infections by A. baumannii.

Comprehensive Approaches to Combatting Acinetobacter baumannii Biofilms: From Biofilm Structure to Phage-Based Therapies

Acinetobacter baumannii-a multidrug-resistant (MDR) pathogen that causes, for example, skin and soft tissue wounds; urinary tract infections; pneumonia; bacteremia; and endocarditis, particularly due to its ability to form robust biofilms-poses a significant challenge in clinical settings. This structure protects the bacteria from immune responses and antibiotic treatments, making infections difficult to eradicate. Given the rise in antibiotic resistance, alternative therapeutic approaches are urgently needed. Bacteriophage-based strategies have emerged as a promising solution for combating A. baumannii biofilms. Phages, which are viruses that specifically infect bacteria, offer a targeted and effective means of disrupting biofilm and lysing bacterial cells. This review explores the current advancements in bacteriophage therapy, focusing on its potential for treating A. baumannii biofilm-related infections. We described the mechanisms by which phages interact with biofilms, the challenges in phage therapy implementation, and the strategies being developed to enhance its efficacy (phage cocktails, engineered phages, combination therapies with antibiotics). Understanding the role of bacteriophages in both biofilm disruption and in inhibition of its forming could pave the way for innovative treatments in combating MDR A. baumannii infections as well as the prevention of their development.

Structural characterization of the POTRA domains from A. baumannii reveals new conformations in BamA

Recent studies have demonstrated BamA, the central component of the β-barrel assembly machinery (BAM), as an important therapeutic target to combat infections caused by Acinetobacter baumannii and other Gram-negative pathogens. Homology modeling indicates BamA in A. baumannii consists of five polypeptide transport-associated (POTRA) domains and a β-barrel membrane domain. We characterized the POTRA domains of BamA from A. baumannii in solution using size-exclusion chromatography small angle X-ray scattering (SEC-SAXS) analysis and determined crystal structures in two conformational states that are drastically different than those previously observed in BamA from other bacteria, indicating that the POTRA domains are even more conformationally dynamic than has been observed previously. Molecular dynamics simulations of the POTRA domains from A. baumannii and Escherichia coli allowed us to identify key structural features that contribute to the observed novel states. Together, these studies expand on our current understanding of the conformational plasticity within BamA across differing bacterial species.

In vitro antibacterial activity of photoactivated flavonoid glycosides against Acinetobacter baumannii

Acinetobacter baumannii's extensive antibiotic resistance makes its infections difficult to treat, so effective strategies to fight this bacterium are urgently needed. This study aims to evaluate the effectiveness of antimicrobial photodynamic therapy (aPDT) mediated by Rutin-Gal(III) complex and Quercetin against A. baumannii. Absorbance spectra, fluorescence spectra, and minimum inhibitory concentration (MIC) of Rutin-Gal(III) complex and Quercetin were determined. The intracellular reactive oxygen species (ROS), extracellular polymeric substances (EPS), cell membrane permeability, expression of ompA and blaOXA-23, anti-biofilm activity, and anti-metabolic activity of Rutin-Gal(III) complex- and Quercetin-mediated aPDT were measured. Rutin-Gal(III) complex and Quercetin revealed absorption peaks in the visible spectra. Quercetin and Rutin-Gal(III) complex displayed fluorescence peaks at 524 nm and 540 nm, respectively. MIC values for the Rutin-Gal(III) complex and Quercetin were 64 µg/mL and 256 µg/mL, respectively. Quercetin- and Rutin-Gal(III) complex-mediated aPDT significantly reduced the colony forming units/mL (58.4% and 67.5%), EPS synthesis (47.4% and 56.5%), metabolic activity (30.5% and 36.3%), ompA (5.5- and 10.5-fold), and blaOXA-23 (4.1-fold and 7.8-fold) genes expression (respectively; all P < 0.05). Quercetin- and Rutin-Gal(III) complex-mediated aPDT enhanced notable biofilm degradation (36.2% and 40.6%), ROS production (2.55- and 2.90-folds), and membrane permeability (10.8- and 9.6-folds) (respectively; all P < 0.05). The findings indicate that Rutin-Gal(III) complex- and Quercetin-mediated aPDT exhibits antibacterial properties and could serve as a valuable adjunctive strategy to conventional antibiotic treatments for A. baumannii infections. One limitation of this study is that it was conducted solely on the standard strain; testing on clinical isolates would allow for more reliable interpretation of the results.

Novel chiral phthalimides: Antimicrobial evaluation and docking study against Acinetobacter baumannii's OmpA protein

Antibiotics have been a vital component in the fight against microbial diseases for over 75 years, saving countless lives. However, the global rise of multi-drug-resistance (MDR) bacterial infections is pushing us closer to a post-antibiotic era where common infections may once again become lethal. To combat MDR Acinetobacter baumannii, we investigated chiral phthalimides and used molecular docking to identify potential targets. Outer membrane protein A (OmpA) is crucial for A. baumannii resistant to antibiotics, making it a pathogen of great concern due to its high mortality rate and limited treatment options. In this study, we evaluated three distinct compounds against the OmpA protein: FIA (2-(1,3-dioxoindolin-2yl)-3-phenylpropanoic acid), FIC (2-(1,3-dioxoindolin-2yl)-4-(methylthio) butanoic acid), and FII (3-(1,3-dioxoindolin-2yl)-3-phenylpropanoic acid). Molecular docking results showed that these three compounds exhibited strong interactions with the OmpA protein. Molecular dynamics (MD) simulation analysis further confirmed the stability and binding efficacy of these compounds with OmpA. Their antimicrobial activities were assessed using the agar well diffusion method, revealing that FIA had an optimal zone of inhibition of 24 mm. Additionally, the minimum inhibitory concentrations (MIC) of these compounds were determined, demonstrating their bactericidal properties against A. baumannii, with MICs of 11 μg/μL for FIA, 46 μg/μL for FIC, and 375 μg/μL for FII. In vitro cytotoxicity data indicated that none of the three compounds were hemolytic when exposed to human red blood cells. This finding is particularly significant as it highlights the superior efficacy of FIA against A. baumannii compared to the other compounds. With thorough pharmacokinetic validations, these chiral phthalimides are promising alternative therapeutic options for treating infections caused by A. baumannii, offering new hope in the face of rising antibiotic resistance.

Limonene encapsulated alginate/collagen as antibiofilm drug against Acinetobacter baumannii

This work examined the antibacterial and antibiofilm properties of alginate/collagen nanoparticles containing limonene. The multi-drug resistant (MDR) strains were screened, and the morphological features of the produced nanoparticles were determined utilizing SEM, DLS, and FTIR. Additionally, the encapsulation effectiveness, stability, and drug release were assessed. The levels of OmpA and Bap biofilm genes were assessed using qRT-PCR. At the same time, the antibacterial and cytotoxic activities of the nanoparticles were evaluated using well diffusion and MTT techniques, respectively. LAC nanoparticles measuring 300 ± 9.6 nm in size, 83.64 ± 0.19% encapsulation efficiency, and 60-day stability at 4 °C were synthesized. The biological investigation demonstrated that LAC nanoparticles had potent antibacterial capabilities. This was shown by their ability to significantly decrease the transcription of OmpA and Bap biofilm genes at a statistically significant level of p ≤ 0.05. The nanoparticles exhibited reduced antibiotic resistance compared to free limonene and alginate/collagen. Compared to limonene, LAC nanoparticles exhibited negligible cytotoxicity against HEK-293 at doses ranging from 1.56 to 100 µg/mL (p ≤ 0.01). The findings underscore the potential of LAC nanoparticles as a breakthrough in the fight against highly resistant pathogens. The potent antibacterial effects of LAC nanoparticles versus Acinetobacter baumannii (A. baumannii) MDR strains, considered highly resistant pathogens of significant concern, could inspire new strategies in antibacterial research.

A New Bacterial Chassis for Enhanced Surface Display of Recombinant Proteins

Introduction

Bacterial surface display is a valuable biotechnology technique for presenting proteins and molecules on the outer surface of bacterial cells. However, it has limitations, including potential toxicity to host bacteria and variability in display efficiency. To address these issues, we investigated the removal of abundant non-essential outer membrane proteins (OMPs) in E. coli as a new strategy to improve the surface display of recombinant proteins.

Methods

We targeted OmpA, a highly prevalent OMP in E. coli, using the lambda red method. We successfully knocked out ompA in two E. coli strains, K-12 MG1655 and E. coli BL-21, which have broad research and therapeutic applications. We then combined ompA knockout strains and two OMPs with three therapeutic proteins including an anti-toxin enzyme (ClbS), interleukin 18 (IL-18) for activating cytotoxic T cells and an anti- CTLA4 nanobody (αCTLA4) for immune checkpoint blockade.

Results

A total of six different display constructs were tested for their display levels by flow cytometry, showing that the ompA knockout strains increased the percentage as well as the levels of display in bacteria compared to those of isogenic wild-type strains.

Conclusions

By removing non-essential, highly abundant surface proteins, we develop an efficient platform for displaying enzymes and antibodies, with potential industrial and therapeutic applications. Additionally, the enhanced therapeutic efficacy opens possibilities for live bacteria-based therapeutics, expanding the technology's relevance in the field.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12195-024-00819-w.

Nisin-relevant antimicrobial peptides: synthesis strategies and applications

Small pentacyclic peptides, represented by nisin, have been successfully utilized as preservatives in the food industry and have evolved into a paradigm for understanding the genetic structure, expression, and control of genes created by lantibiotics. Due to the ever-increasing antibiotic resistance, nisin-relevant antimicrobial peptides have received much attention, which calls for a summarization of their synthesis, modification and applications. In this review, we first provided a timeline of select highlights in nisin biosynthesis and engineering. Then, we outlined the current developments in nisin synthesis. We also provided an overview of the engineering, screening, and production of nisin-relevant antimicrobial peptides based on enzyme alteration, substrate modification, and sequence mining. Furthermore, an updated summary of applications of nisin-relevant antimicrobial peptides has been developed for food applications. Finally, this study offers insights into emerging technologies, limitations and the future development of nisin-relevant antimicrobial peptides for pathogen inhibition, food preservatives, and improved health.

Polyvinylpyrrolidone capped silver nanoparticles enhance the autophagic clearance of Acinetobacter baumannii from human pulmonary cells

Acinetobacter baumannii, an opportunistic pathogen has shown an upsurge in its multi-drug resistant isolates. OmpA of A. baumannii induces incomplete autophagy and apoptosis in host cells. Various therapeutic alternatives are under investigation against A. baumannii. Here, the major emphasis has been laid on comparing the efficacy of AgNP with different capping agents. OmpA targeted lead, Ivermectin capped AgNP (IVM-AgNP) has been compared with the antibacterial polyvinylpyrrolidone capped AgNP (PVP-AgNP) for their role in the modulations of host autophagy. Upregulation of p62 and LC3B confirmed by real-time PCR analysis indicated an increased autophagic flux upon the treatment with AgNPs. The elongation and closure of autophagic vacuoles was also supported by upregulated Atg genes (Atg4, Atg3, Atg5) in A. baumannii infected cells after treatment with AgNP. Autophagic flux increased on treatment with PVP-AgNP as suggested by the rise in mcherryLC3B fluorescence in A549 cells treated with PVP-AgNP as compared to the GFP-LC3B of IVM-AgNP. This suggests that PVP-AgNP treatment more effectively promotes the elongation and maturation stages of autophagy by increasing autophagic flux. These results indicate that capped AgNPs have the efficiency to revert the incomplete autophagy induced by A. baumannii back to normal autophagic levels.

Impact of AbaI mutation on virulence, biofilm development, and antibiotic susceptibility in Acinetobacter baumannii

The quorum sensing (QS) system mediated by the abaI gene in Acinetobacter baumannii is crucial for various physiological and pathogenic processes. In this study, we constructed a stable markerless abaI knockout mutant (ΔabaI) strain using a pEXKm5-based allele replacement method to investigate the impact of abaI on A. baumannii. Proteomic analysis revealed significant alterations in protein expression between the wild type (WT) and ΔabaI mutant strains, particularly in proteins associated with membrane structure, antibiotic resistance, and virulence. Notably, the downregulation of key outer membrane proteins such as SurA, OmpA, OmpW, and BamA suggests potential vulnerabilities in outer membrane integrity, which correlate with structural abnormalities in the ΔabaI mutant strain, including irregular cell shapes and compromised membrane integrity, observed by scanning and transmission electron microscopy. Furthermore, diminished expression of regulatory proteins such as OmpR and GacA-GacS highlights the broader regulatory networks affected by abaI deletion. Functional assays revealed impaired biofilm formation and surface-associated motility in the mutant strain, indicative of altered colonization capabilities. Interestingly, the mutant showed a complex antibiotic susceptibility profile. While it demonstrated increased susceptibility to membrane-targeting antibiotics, its response to beta-lactams was more nuanced. Despite increased expression of metallo-beta-lactamase (MBL) superfamily proteins and DcaP-like protein, the mutant unexpectedly showed lower MICs for carbapenems (imipenem and meropenem) compared to the wild-type strain. This suggests that abaI deletion affects antibiotic susceptibility through multiple, potentially competing mechanisms. Further investigation is needed to fully elucidate the interplay between quorum sensing, antibiotic resistance genes, and overall antibiotic susceptibility in A. baumannii. Our findings underscore the multifaceted role of the abaI gene in modulating various cellular processes and highlight its significance in A. baumannii physiology, pathogenesis, and antibiotic resistance. Targeting the abaI QS system may offer novel therapeutic strategies for this clinically significant pathogen.

Clinical and microbiological features of a cohort of patients with Acinetobacter baumannii bloodstream infections

PURPOSE

Acinetobacter baumannii is emerging as a pathogen that is a focus of global concern due to the frequent occurrence of the strains those are extensively resistant to antibiotics. This study was aimed to analyze the clinical and microbiological characteristics of a cohort of patients with A. baumannii bloodstream infections (BSIs) in western China.

METHODS

A retrospective study of the patients at West China Hospital of Sichuan University with A. baumannii BSIs between Jan, 2018 and May, 2023 was conducted. Antimicrobial susceptibility of A. baumannii isolates was tested by microdilution broth method. Whole-genome sequencing and genetic analysis were also performed for these isolates.

RESULTS

Among the 117 patients included, longer intensive care unit stay, higher mortality, and more frequent invasive procedures and use of more than 3 classes of antibiotics were observed among the carbapenem-resistant A. baumannii (CRAB)-infected group (n = 76), compared to the carbapenem-susceptible A. baumannii (CSAB)-infected group (n = 41, all P ≤ 0.001). Twenty-four sequence types (STs) were determined for the 117 isolates, and 98.7% (75/76) of CRAB were identified as ST2. Compared to non-ST2 isolates, ST2 isolates exhibited higher antibiotic resistance, and carried more resistance and virulence genes (P < 0.05). In addition, 80 (68.4%) isolates were CRISPR-positive, showed higher antibiotic susceptibility, and harbored less resistance and virulence genes, in comparison to CRISPR-negative ones (P < 0.05). Phylogenetic clustering based on coregenome SNPs indicated a sporadic occurrence of clonal transmission.

CONCLUSION

Our findings demonstrate a high frequency of ST2 among A. baumannii causing BSIs, and high antibiotic susceptibility of non-ST2 and CRISPR-positive isolates. It is necessary to strengthen the surveillance of this pathogen.

Acinetobacter baumannii OmpA-like porins: functional characterization of bacterial physiology, antibiotic-resistance, and virulence

Acinetobacter baumannii is a critical opportunistic pathogen associated with nosocomial infections. The high rates of antibiotic-resistance acquisition make most antibiotics ineffective. Thus, new medical countermeasures are urgently needed. Outer membrane proteins (OMPs) are prime candidates for developing novel drug targets and antibacterial strategies. However, there are substantial gaps in our knowledge of A. baumannii OMPs. This study reports the impact of OmpA-like protein on bacterial physiology and virulence in A. baumannii strain AB5075. We found that PsaB (ABUW_0505) negatively correlates to stress tolerance, while ArfA (ABUW_2730) significantly affects bacterial stiffness, cell shape, and cell envelope thickness. Furthermore, we expand our knowledge on YiaD (ABUW_3045), demonstrating structural and virulence roles of this porin, in addition to meropenem resistance. This study provides solid foundations for understanding how uncharacterized OMPs contribute to A. baumannii's physiological and pathological processes, aiding the development of innovative therapeutic strategies against A. baumannii infections.

In Silico Analysis and Development of the Secretory Expression of D-Psicose-3-Epimerase in Escherichia coli

D-psicose-3-epimerase (DPEase), a key enzyme for D-psicose production, has been successfully expressed in Escherichia coli with high yield. However, intracellular expression results in high downstream processing costs and greater risk of lipopolysaccharide (LPS) contamination during cell disruption. The secretory expression of DPEase could minimize the number of purification steps and prevent LPS contamination, but achieving the secretion expression of DPEase in E. coli is challenging and has not been reported due to certain limitations. This study addresses these challenges by enhancing the secretion of DPEase in E. coli through computational predictions and structural analyses. Signal peptide prediction identified PelB as the most effective signal peptide for DPEase localization and enhanced solubility. Supplementary strategies included the addition of 0.1% (v/v) Triton X-100 to promote protein secretion, resulting in higher extracellular DPEase (0.5 unit/mL). Low-temperature expression (20 °C) mitigated the formation of inclusion bodies, thus enhancing DPEase solubility. Our findings highlight the pivotal role of signal peptide selection in modulating DPEase solubility and activity, offering valuable insights for protein expression and secretion studies, especially for rare sugar production. Ongoing exploration of alternative signal peptides and refinement of secretion strategies promise further enhancement in enzyme secretion efficiency and process safety, paving the way for broader applications in biotechnology.

Pharmaceutical industrial wastewater exhibiting the co-occurrence of biofilm-forming genes in the multidrug-resistant bacterial community poses a novel environmental threat

The interaction of the environment with the effluent of wastewater treatment plants, having antibiotics, multidrug-resistant (MDR) bacteria, and biofilm-forming genes (BFGs), has vast environmental risks. Antibiotic pollution bottlenecks environmental bacteria and has the potential to significantly lower the biodiversity of environmental bacteria, causing an alteration in ecological equilibrium. It can induce selective pressure for antibiotic resistance (AR) and can transform the non-resistant environmental bacteria into a resistant form through HGT. This study investigated the occurrence of MDR bacteria, showing phenotypic and genotypic characteristics of biofilm. The bacteria were isolated from the pharmaceutical wastewater treatment plants (WWTPs) of Dehradun and Haridwar (India), located in the pharmaceutical areas. The findings of this study demonstrate the coexistence of BFGs and MDR clinical bacteria in the vicinity of pharmaceutical industrial wastewater treatment plants. A total of 47 bacteria were isolated from both WWTPs and tested for antibiotic resistance to 13 different antibiotics; 16 isolates (34.04 %) tested positive for MDR. 5 (31.25 %) of these 16 MDR isolates were producing biofilm and identified as Pseudomonas aeruginosa, Acinetobacter baumannii, Escherichia coli, Klebsiella pneumoniae, and Burkholderia cepacia. The targeted BFGs in this study were ompA, bap and pslA. The most common co-occurring gene was ompA (80 %), with pslA (40 %) being the least common. A. baumannii contains all three targeted genes, whereas B. cepacia only has bap. Except for B. cepacia, all the biofilm-forming MDR isolates show AR to all the tested antibiotics and prove that the biofilm enhances the AR potential. The samples of both wastewater treatment plants also showed the occurrence of tetracycline, ampicillin, erythromycin and chloramphenicol, along with high levels of BOD, COD, PO4-3, NO3-, heavy metals and organic pollutants. The co-occurrence of MDR and biofilm-forming tendency in the clinical strain of bacteria and its environmental dissemination may have an array of hazardous impacts on human and environmental health.

Functional analysis of OmpA and its contribution to pathogenesis of Edwardsiella tarda

Outer membrane protein A (OmpA), a major component of outer membrane proteins in gram-negative bacteria, is considered to be an important virulence factor in various pathogenic bacteria, but its underlying mechanisms involved in pathogenic process of Edwardsiella tarda has not yet been fully elucidated. E. tarda is an important facultative intracellular pathogen with a broad host range. This bacterium could survive and replicate in macrophages as an escape mechanism from the host defense. To address the functions of OmpA and its potential roles in the pathogenesis of E. tarda, ΔompA mutant strain and ΔompA-C complementary strain were constructed by the allelic exchange method in this study. Here, we demonstrate that the abilities of motility, biofilm formation and adherence to RAW264.7 cells of ΔompA were significantly impaired, although there was no difference in growth between wild-type (WT) strain and ΔompA. Moreover, inactivation of ompA rendered E. tarda more sensitive to oxidative, heat shock and osmotic stress, which simulate the in vivo conditions that E. tarda encounters within the intramacrophage environment. Consist with this observation, ΔompA was also found to be markedly attenuated for growth within macrophages. In addition, compared with the WT strain, ΔompA activated macrophages to release more inflammatory mediators, including tumor necrosis factor alpha (TNF-α), reactive oxygen species (ROS) and nitric oxide (NO). However, flow cytometry analysis revealed that ΔompA induced less apoptosis of RAW264.7 cells as compared with WT strain, characterized by decreased Annexin V binding and the activation of caspase-3. Overall, our findings suggest an importance of OmpA to E. tarda and provide the first comprehensive insight into its functions and potential roles in the pathogenesis of E. tarda, including its effect on interaction with macrophages.

Reassessment of the genetic basis of natural rifampin resistance in the genus Rickettsia

Rickettsia, a genus of obligate intracellular bacteria, includes species that cause significant human diseases. This study challenges previous claims that the Leucine-973 residue in the RNA polymerase beta subunit is the primary determinant of rifampin resistance in Rickettsia. We investigated a previously untested Rickettsia species, R. lusitaniae, from the Transitional group and found it susceptible to rifampin, despite possessing the Leu-973 residue. Interestingly, we observed the conservation of this residue in several rifampin-susceptible species across most Rickettsia phylogenetic groups. Comparative genomics revealed potential alternative resistance mechanisms, including additional amino acid variants that could hinder rifampin binding and genes that could facilitate rifampin detoxification through efflux pumps. Importantly, the evolutionary history of Rickettsia genomes indicates that the emergence of natural rifampin resistance is phylogenetically constrained within the genus, originating from ancient genetic features shared among a unique set of closely related Rickettsia species. Phylogenetic patterns appear to be the most reliable predictors of natural rifampin resistance, which is confined to a distinct monophyletic subclade known as Massiliae. The distinctive features of the RNA polymerase beta subunit in certain untested Rickettsia species suggest that R. raoultii, R. amblyommatis, R. gravesii, and R. kotlanii may also be naturally rifampin-resistant species.

Design of multi-epitope vaccine candidate based on OmpA, CarO and ZnuD proteins against multi-drug resistant Acinetobacter baumannii

Acinetobacter baumannii has been identified as a major cause of nosocomial infections. Acinetobacter infections are often difficult to treat with multidrug resistant phenotypes. One of the most effective ways to combat infectious diseases is through vaccination. In this study, an attempt was made to select the most protective and potent immunostimulatory epitopes based on the epitope-rich domains of the ZnuD, OmpA and CarO proteins of Acinetobacter baumannii to design a vaccine that can protect against this infection. After predicting the epitope of B- and T-cells, seven antigenic regions of three proteins CarO, ZnuD and OmpA, were selected. These regions were bound by a GGGS linker. The binding affinity and molecular interactions of the vaccine with the immune receptors TLR2 and TLR4 were studied using molecular docking analysis. This vaccine design was subjected to in silico immune simulations using C-ImmSim. The designed vaccine was highly antigenic, non-allergenic and stable. TLR2 and TLR4 were selected to analyze the ability of the modeled chimeric protein to interact with immune system receptors. The results showed strong interaction between the designed protein vaccine with TLR2 (-18.8 kcal mol-1) and TLR4 (-15.1 kcal mol-1). To verify the stability of the interactions and the structure of the designed protein, molecular dynamics (MD) simulations were performed for 200 ns. Various analyses using MD showed that the protein structure is stable alone and in interaction with TLR2 and TLR4. The ability of the vaccine candidate protein to stimulate the immune system to produce the necessary cytokines and antibodies against Acinetobacter baumannii was also demonstrated by the ability of the protein designed using the C-ImmSim web server to induce an immune response. Therefore, the designed protein vaccine may be a suitable candidate for in vivo as well as in vitro studies against Acinetobacter baumannii infections.