Evaluation of the ability of Acinetobacter baumannii to form biofilms on six different biomedical relevant surfaces

An integrative review on the risk factors, prevention, and control strategies for carbapenem-resistant Acinetobacter baumannii colonization in critically ill patients

The presence of carbapenem-resistant Acinetobacter baumannii (CRAb) has become one of the leading causes of life-threatening, hospital-acquired infections globally, especially with a notable prevalence in intensive care units (ICUs). The cross-transmission of microorganisms between patients and the hospital setting is crucial in the development of CRAb colonization and subsequent infections. Recent studies indicate that colonization typically precedes infection, suggesting the effectiveness and necessity of preventing CRAb colonization as a primary method to lower infection risks. As CRAb infections tend to draw more attention due to their severe symptoms and poor outcomes, understanding the link between colonization and infection is equally vital. To establish a foundation for prevention and control strategies against CRAb colonization in ICUs, we present a comprehensive review of research pertaining to CRAb in ICUs. This encompasses an analysis of the resistance mechanisms and epidemiological characteristics of CRAb, a discussion on associated risk factors, adverse outcomes, and an evaluation of detection methods and preventive strategies.

Multidrug resistant Acinetobacter baumannii: A study on its pathogenesis and therapeutics

The overuse of antibiotics has led to the global dissemination of Acinetobacter baumannii, an increasingly challenging nosocomial pathogen. This review explores the medical significance along with the diverse resistance ability of A. baumannii. Intensive care units (ICUs) serve as a breeding ground for A. baumannii, as these settings harbour vulnerable patients and facilitate the spread of opportunistic microorganisms. A. baumannii belongs to the ESKAPE group of bacterial pathogens that are major contributors to antibiotic-resistant infections. The pathogenic nature of A. baumannii is particularly evident in seriously ill patients, causing pneumonia, wound infections, and other healthcare-associated infections. Historically considered benign, A. baumannii is a global threat due to its propensity for rapid acquisition of multidrug resistance phenotypes. The genus Acinetobacter was formally recognized in 1968 following a comprehensive survey by Baumann et al., highlighting the relationship between previously identified species and consolidating them under the name Acinetobacter. A. baumannii is characterized by its Gram-negative nature, dependence on oxygen, positive catalase activity, lack of oxidase activity, inability to ferment sugars, and non-motility. The DNA G+C content of Acinetobacter species falls within a specific range. For diagnostic purposes, A. baumannii can be cultured on specific agar media, producing distinct colonies. The genus Acinetobacter comprises numerous species those are associated with bloodstream infections with high mortality rates. Therefore, A. baumannii poses a significant challenge to global healthcare due to its multidrug resistance and ability to cause various infections. A comprehensive understanding of the mechanisms underlying its resistance acquisition and pathogenicity is essential for combating this healthcare-associated pathogen effectively.

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.

Handwashing sinks as reservoirs of carbapenem-resistant Acinetobacter baumannii in the intensive care unit: a prospective multicenter study

Introduction

The extent to which sinks are contaminated by carbapenem-resistant Acinetobacter baumannii (CRAB) in intensive care units (ICUs) and the association between these contaminated sinks and hospital-acquired CRAB infections during the non-cluster period remains largely unknown. Here, we performed a prospective multicenter study in 16 ICUs at 11 tertiary hospitals in Chengdu, China.

Methods

We sampled sinks, collected CRAB clinical isolates, and conducted whole-genome sequencing and analysis.

Results

A total of 789 swabs were collected from 158 sinks, and 16 CRAB isolates were recovered from 16 sinks, resulting in a contamination rate of 10.16%. Twenty-seven clinical isolates were collected during the study period. The majority (97.67%, 42/43) of the CRAB isolates belonged to ST2, and 36 (83.72%) of them had both bla OXA-23 and bla OXA-66. The 43 strains belonged to 12 clones. One certain clone caused multiple contaminations of seven sinks in one GICU. Two clones of ST2 bla OXA-23 and bla OXA-66-carrying sink strains were likely the sources of the two clusters in the two GICUs, respectively. Five ST2 bla OXA-23-carrying isolates were found to be common clones but were recovered from two hospitals.

Conclusion

The contamination rate of CRAB in handwashing sinks is high in some local ICUs, and the contaminated sinks can serve as environmental reservoirs for CRAB clusters.

Fluopsin C Promotes Biofilm Removal of XDR Acinetobacter baumannii and Presents an Additive Effect with Polymyxin B on Planktonic Cells

Acinetobacter baumannii emerged as one of the most important pathogens for the development of new antimicrobials due to the worldwide detection of isolates resistant to all commercial antibiotics, especially in nosocomial infections. Biofilm formation enhances A. baumannii survival by impairing antimicrobial action, being an important target for new antimicrobials. Fluopsin C (FlpC) is an organocupric secondary metabolite with broad-spectrum antimicrobial activity. This study aimed to evaluate the antibiofilm activity of FlpC in established biofilms of extensively drug-resistant A. baumannii (XDRAb) and the effects of its combination with polymyxin B (PolB) on planktonic cells. XDRAb susceptibility profiles were determined by Vitek 2 Compact, disk diffusion, and broth microdilution. FlpC and PolB interaction was assessed using the microdilution checkerboard method and time-kill kinetics. Biofilms of XDRAb characterization and removal by FlpC exposure were assessed by biomass staining with crystal violet. Confocal Laser Scanning Microscopy was used to determine the temporal removal of the biofilms using DAPI, and cell viability using live/dead staining. The minimum inhibitory concentration (MIC) of FlpC on XDRAb was 3.5 µg mL-1. Combining FlpC + PolB culminated in an additive effect, increasing bacterial susceptibility to both antibiotics. FlpC-treated 24 h biofilms reached a major biomass removal of 92.40 ± 3.38% (isolate 230) using 7.0 µg mL-1 FlpC. Biomass removal occurred significantly over time through the dispersion of the extracellular matrix and decreasing cell number and viability. This is the first report of FlpC's activity on XDRAb and the compound showed a promissory response on planktonic and sessile cells, making it a candidate for the development of a new antimicrobial product.

Deciphering the impact of Acinetobacter baumannii on human health, and exploration of natural compounds as efflux pump inhibitors to treat multidrug resistance

Acinetobacter baumannii is an ESKAPE pathogen and threatens human health by generating infections with high fatality rates. A. baumannii leads to a spectrum of infections such as skin and wound infections, endocarditis, meningitis pneumonia, septicaemia and urinary tract infections. Recently, strains of A. baumannii have emerged as multidrug-resistant (MDR), meaning they are resistant to at least three different classes of antibiotics. MDR development is primarily intensified by widespread antibiotic misuse and inadequate stewardship. The World Health Organization (WHO) declared A. baumannii a precarious MDR species. A. baumannii maintains the MDR phenotype via a diverse array of antimicrobial metabolite-hydrolysing enzymes, efflux of antibiotics, impermeability and antibiotic target modification, thereby complicating treatment. Hence, a deeper understanding of the resistance mechanisms employed by MDR A. baumannii can give possible approaches to treat antimicrobial resistance. Resistance-nodulation-cell division (RND) efflux pumps have been identified as the key contributors to MDR determinants, owing to their capacity to force a broad spectrum of chemical substances out of the bacterial cell. Though synthetic inhibitors have been reported previously, their efficacy and safety are of debate. As resistance-modifying agents, phytochemicals are ideal choices. These natural compounds could eliminate the bacteria or interact with pathogenicity events and reduce the bacteria's ability to evolve resistance. This review aims to highlight the mechanism behind the multidrug resistance in A. baumannii and elucidate the utility of natural compounds as efflux pump inhibitors to deal with the infections caused by A. baumannii.

Exploring the occurrence of Listeria in biofilms and deciphering the bacterial community in a frozen vegetable producing environment

The establishment of Listeria (L.) monocytogenes within food processing environments constitutes a significant public health concern. This versatile bacterium demonstrates an exceptional capacity to endure challenging environmental conditions in the food processing environment, where contamination of food products regularly occurs. The diverse repertoire of stress resistance genes, the potential to colonize biofilms, and the support of a co-existing microbiota have been proposed as root causes for the survival of L. monocytogenes in food processing environments. In this study, 71 sites were sampled after cleaning and disinfection in a European frozen vegetable processing facility, where L. monocytogenes in-house clones persisted for years. L. monocytogenes and L. innocua were detected by a culture-dependent method at 14 sampling sites, primarily on conveyor belts and associated parts. The presence of biofilms, as determined by the quantification of bacterial load and the analysis of extracellular matrix components (carbohydrates, proteins, extracellular DNA) was confirmed at nine sites (12.7%). In two cases, L. innocua was detected in a biofilm. Furthermore, we explored the resident microbial community in the processing environment and on biofilm-positive sites, as well as the co-occurrence of bacterial taxa with Listeria by 16S rRNA gene sequencing. Pseudomonas, Acinetobacter, and Exiguobacterium dominated the microbial community of the processing environment. Using differential abundance analysis, amplicon sequence variants (ASVs) assigned to Enterobacterales (Enterobacter, Serratia, unclassified Enterobacteriaceae) and Carnobacterium were found to be significantly higher abundant in Listeria-positive samples. Several Pseudomonas ASVs were less abundant in Listeria-positive compared to Listeria-negative samples. Acinetobacter, Pseudomonas, Janthinobacterium, Brevundimonas, and Exiguobacterium were key players in the microbial community in biofilms, and Exiguobacterium and Janthinobacterium were more relatively abundant in biofilms. Further, the microbial composition varied between the different areas and the surface materials.

Current treatment strategies for targeting virulence factors and biofilm formation in Acinetobacter baumannii

A higher prevalence of Acinetobacter baumannii infections and mortality rate has been reported recently in hospital-acquired infections (HAI). The biofilm-forming capability of A. baumannii makes it an extremely dangerous pathogen, especially in device-associated hospital-acquired infections (DA-HAI), thereby it resists the penetration of antibiotics. Further, the transmission of the SARS-CoV-2 virus was exacerbated in DA-HAI during the epidemic. This review specifically examines the complex interconnections between several components and genes that play a role in the biofilm formation and the development of infections. The current review provides insights into innovative treatments and therapeutic approaches to combat A. baumannii biofilm-related infections, thereby ultimately improving patient outcomes and reducing the burden of HAI.

Biofilm formation of the food spoiler Brochothrix thermosphacta on different industrial surface materials using a biofilm reactor

Brochothrix thermosphacta is considered as a major food spoiler bacteria. This study evaluates biofilm formation by B. thermosphacta CD337(2) - a strong biofilm producer strain - on three food industry materials (polycarbonate (PC), polystyrene (PS), and stainless steel (SS)). Biofilms were continuously grown under flow at 25 °C in BHI broth in a modified CDC biofilm reactor. Bacterial cells were enumerated by plate counting, and biofilm spatial organization was deciphered by combining confocal laser scanning microscopy and image analysis. The biofilms had the same growth kinetics on all three materials and reach 8log CFU/cm2 as maximal concentration. Highly structured biofilms were observed on PC and PS, but less structured ones on SS. This difference was confirmed by structural quantification analysis using the image analysis software tool BiofilmQ. Biofilm on SS show less roughness, density, thickness and volume. The biofilm 3D structure seemed to be related to the coupon topography and roughness. The materials used in this study do not affect biofilm growth. However, their roughness and topography affect the biofilm architecture, which could influence biofilm behaviour.

Exploring the evolutionary and pathogenic role of Acinetobacter baumannii biofilm-associated protein (Bap) through in silico structural modeling

Acinetobacter species encode for extracellularly secreted Biofilm-associated protein (Bap), a multi-domain protein with variable molecular weights reaching several hundred kilodaltons. Bap is crucial for the development of multi-dimensional structures of mature biofilms. In our investigation, we analyzed 7338 sequences of A. baumannii from the NCBI database and found that Bap or Bap-like protein (BLP) was present in 6422 (87.52%) isolates. Further classification revealed that 12.12% carried Type-1 Bap, 68.44% had Type-2, 6.91% had Type-3, 0.05% had Type-6 or SDF-Type, and 12.51% lacked Bap or BLP. The majority of isolates with Type-1, Type-2, and Type-3 Bap belonged to ST1, ST2, and ST25, respectively. Phylogenetic analysis suggested that Type-1 Bap is the most ancient, while Type-3 and SDF-Type have evolved recently. Studying the interaction of predicted Bap structures with human CEACAM-1 and PIgR showed that Bap with its BIg13 and BIg6 domains interact with the N-terminal domain of CEACAM-1, involving Arg43 and Glu40, involved in CEACAM-1 dimerization. Also, we found that recently evolved Type-3 and SDF-Type Bap showed greater interaction with CEACAM-1 and PIgR. It can be asserted that the evolution of Bap has conferred enhanced virulence characteristics to A. baumannii with increased interaction with CEACAM-1 and PIgR. Using in silico approaches, this study explores the evolutionary, physicochemical, and structural features of A. baumannii Bap and unravels its crucial role in mediating interaction with human CEACAM-1 and PIgR through detailed structure modelling. These findings advance our understanding of A. baumannii Bap and highlight its role in pathogenesis.

Treatment and Management of Acinetobacter Pneumonia: Lessons Learned from Recent World Event

Acinetobacter pneumonia is a significant healthcare-associated infection that poses a considerable challenge to clinicians due to its multidrug-resistant nature. Recent world events, such as the COVID-19 pandemic, have highlighted the need for effective treatment and management strategies for Acinetobacter pneumonia. In this review, we discuss lessons learned from recent world events, particularly the COVID-19 pandemic, in the context of the treatment and management of Acinetobacter pneumonia. We performed an extensive literature review to uncover studies and information pertinent to the topic. The COVID-19 pandemic underscored the importance of infection control measures in healthcare settings, including proper hand hygiene, isolation protocols, and personal protective equipment use, to prevent the spread of multidrug-resistant pathogens like Acinetobacter. Additionally, the pandemic highlighted the crucial role of antimicrobial stewardship programs in optimizing antibiotic use and curbing the emergence of resistance. Advances in diagnostic techniques, such as rapid molecular testing, have also proven valuable in identifying Acinetobacter infections promptly. Furthermore, due to the limited availability of antibiotics for treating infections caused A. baumannii, alternative strategies are needed like the use of antimicrobial peptides, bacteriophages and their enzymes, nanoparticles, photodynamic and chelate therapy. Recent world events, particularly the COVID-19 pandemic, have provided valuable insights into the treatment and management of Acinetobacter pneumonia. These lessons emphasize the significance of infection control, antimicrobial stewardship, and early diagnostics in combating this challenging infection.

Co-regulation of biofilm formation and antimicrobial resistance in Acinetobacter baumannii: from mechanisms to therapeutic strategies

In recent years, multidrug-resistant Acinetobacter baumannii has emerged globally as a major threat to the healthcare system. It is now listed by the World Health Organization as a priority one for the need of new therapeutic agents. A. baumannii has the capacity to develop robust biofilms on biotic and abiotic surfaces. Biofilm development allows these bacteria to resist various environmental stressors, including antibiotics and lack of nutrients or water, which in turn allows the persistence of A. baumannii in the hospital environment and further outbreaks. Investigation into therapeutic alternatives that will act on both biofilm formation and antimicrobial resistance (AMR) is sorely needed. The aim of the present review is to critically discuss the various mechanisms by which AMR and biofilm formation may be co-regulated in A. baumannii in an attempt to shed light on paths towards novel therapeutic opportunities. After discussing the clinical importance of A. baumannii, this critical review highlights biofilm-formation genes that may be associated with the co-regulation of AMR. Particularly worthy of consideration are genes regulating the quorum sensing system AbaI/AbaR, AbOmpA (OmpA protein), Bap (biofilm-associated protein), the two-component regulatory system BfmRS, the PER-1 β-lactamase, EpsA, and PTK. Finally, this review discusses ongoing experimental therapeutic strategies to fight A. baumannii infections, namely vaccine development, quorum sensing interference, nanoparticles, metal ions, natural products, antimicrobial peptides, and phage therapy. A better understanding of the mechanisms that co-regulate biofilm formation and AMR will help identify new therapeutic targets, as combined approaches may confer synergistic benefits for effective and safer treatments.

The microbiology and pathogenesis of nonfermenting Gram-negative infections

PURPOSE OF REVIEW

This review provides an overview of most recent evidence about pathogenesis traits and virulence factors contributing to successful colonization or infection by P. aeruginosa , A. baumannii , S. maltophilia and B. cepacia complex, among the most clinically relevant nonfermenting Gram-negative bacteria (NFGNB).

RECENT FINDINGS

The growing clinical importance of NFGNB as important opportunistic pathogens causing difficult-to-treat infections in a fragile patients' population in stressed by numerous studies. Identification of novel virulence factors and deciphering of their mechanisms of action have greatly furthered our understanding of NFGNB pathogenesis, revealing that each pathogen-specific armamentarium of virulence factors (adhesins, motility, capsule, biofilm, lipopolysaccharide, exotoxins, exoenzymes, secretion systems, siderophores) can be likely responsible for the difference in the pathophysiology even in the context of a similar infection site. Emerging evidence of the immunomodulatory effect of some virulence factors is also acknowledged.

SUMMARY

NFGNB continue to be a serious global problem as cause of life-threatening opportunistic infections, owing to a highly heterogeneous content of virulence factors and their extensive number of intrinsic resistance mechanisms. Further efforts in development of novel effective antimicrobials and of alternative strategies targeting key virulence factors are warranted.

Synergistic Role of Biofilm-Associated Genes and Efflux Pump Genes in Tigecycline Resistance of Acinetobacter baumannii

BACKGROUND Previous research reported that the resistance mechanism of Acinetobacter baumannii resistance to tigecycline was mainly related to the overexpression of the AdeABC efflux pump system. Biofilm formation is a notable pathogenesis of A. baumannii infections and antibiotic resistance. Our study explores the latent relevance of biofilm-associated genes and efflux pump genes in A. baumannii tigecycline resistance. MATERIAL AND METHODS A total of 78 clinical samples were collected from October 2018 to October 2019. Seventy-two clinically isolated A. baumannii strains were divided into a tigecycline-resistant Acinetobacter baumannii (TR-AN) group and tigecycline-sensitive Acinetobacter baumannii (TS-AN) group by tigecycline minimum inhibitory concentration tests. The biofilm formation of the 2 groups was observed using crystal violet staining. Furthermore, biofilm-related genes and efflux pump genes were analyzed by RT-PCR. RESULTS The biofilm-forming rate of the TR-AN group was 82.2%, and that of the TS-AN group was 14.8%. The biofilm synthesis gene bfs was 91.3% positive in the TR-AN group, significantly higher than in the TS-AN group at the transcription level (P<0.05). The minimum inhibitory concentration of tigecycline was higher in the TR-AN group with biofilm formation than in the TR-AN group without biofilm formation (P<0.05). The efflux pump AdeB gene was 95.2% positive in the TR-AN group with biofilm formation and 38.7% positive in the TR-AN group without biofilm formation. CONCLUSIONS The biofilm formation of A. baumannii may be positively related to tigecycline resistance ability because of the co-expression of the bfs gene and the AdeB efflux pump gene. The enhanced transcription level of bfs and AdeB promotes biofilm formation to improve the resistance of A. baumannii to tigecycline.

Phenotypical and molecular characterization of Acinetobacter spp. isolated from a pharmaceutical facility

Characterizing microorganisms according to different criteria is useful when investigating sources of microbiological contamination in the pharmaceutical industry. The aim of this study was to characterize 38 Acinetobacter baumannii complex strains isolated from a biopharmaceutical industry by 16S rRNA sequencing, matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF/MS), multilocus sequence typing (MLST), antimicrobial susceptibility profile, biofilm formation, and sensibility to disinfectants. Thirty-three (86.9%) strains were identified by 16S rRNA gene sequencing as A. seifertii/pitti/nosocomialis/lactucae, four (10.5%) as A. baumannii, and one (2.6%) as A. vivianii/courvalini. MALDI-TOF/MS did not identify one strain, and incorrectly identified 30/37 (81.1%) strains as A. baumannii. Strains were assigned to 12 different STs, of which nine were newly defined in this study (STs 2091-2099). Twenty-six (68.4%) strains showed resistance to amikacin and gentamicin. Thirty-three (86.8%) strains were classified as moderately or strongly adherent on polystyrene. Alcohol 70%/15 min and quaternary ammonium 0.08%/20 min were not able to eliminate the biofilm formed, but sodium hypochlorite 0.1%/15 min was efficient. In conclusion, improved methods are needed to improve the identification of Acinetobacter strains in pharmaceutical industries. This organism is of particular concern as it forms recalcitrant biofilms, leading to persistence in the manufacturing environment and increased risk of product contamination.

Swine farm groundwater is a hidden hotspot for antibiotic-resistant pathogenic Acinetobacter

Acinetobacter is present in the livestock environment, but little is known about their antibiotic resistance and pathogenic species in the farm groundwater. Here we investigated antibiotic resistance of Acinetobacter in the swine farm groundwater (JZPG) and residential groundwater (JZG) of a swine farming village, in comparison to a nearby (3.5 km) non-farming village (WTG) using metagenomic and culture-based approaches. Results showed that the abundance of antibiotic resistome in some JZG and all JZPG (~3.4 copies/16S rRNA gene) was higher than that in WTG (~0.7 copies/16S rRNA gene), indicating the influence of farming activities on both groundwater types. Acinetobacter accounted for ~95.7% of the bacteria in JZG and JZPG, but only ~8.0% in WTG. They were potential hosts of ~95.6% of the resistome in farm affected groundwater, which includes 99 ARG subtypes against 23 antibiotic classes. These ARGs were associated with diverse intrinsic and acquired resistance mechanisms, and the predominant ARGs were tetracyclines and fluoroquinolones resistance genes. Metagenomic binning analysis elucidated that non-baumannii Acinetobacter including A. oleivorans, A. beijerinckii, A. seifertii, A. bereziniae and A. modestus might pose environmental risks because of multidrug resistance, pathogenicity and massive existence in the groundwater. Antibiotic susceptibility tests showed that the isolated strains were resistant to multiple antibiotics including sulfamethoxazole (resistance ratio: 96.2%), levofloxacin (42.5%), gatifloxacin (39.0%), ciprofloxacin (32.6%), tetracycline (32.0%), doxycycline (29.0%) and ampicillin (12.0%) as well as last-resort polymyxin B (31.7%), colistin (24.1%) and tigecycline (4.1%). The findings highlight potential prevalence of groundwater-borne antibiotic-resistant pathogenic Acinetobacter in the livestock environment.

Phenotypic and genomic comparison of dominant and nondominant sequence-type of Acinetobacter baumannii isolated in China

A. baumannii is a common clinical pathogen that often causes pneumonia and bloodstream infections in ICU patients. Sequence types (ST) are used to investigate the distribution and spread of A. baumannii. Biological characteristics such as virulence and resistance may play a role in A. baumannii becoming a specific dominant ST(DST,ST191, ST195 and ST208) strain. To characterize the biological, genetic, and transcriptomic differences between the DST and non-dominant ST(NST,ST462 and ST547,etc.) strains in A. baumannii, we performed several biological experiments and genetic, and transcriptomic analyses. The DST group displayed more resistance ability to desiccation, oxidation, multiple antibiotics, and complement killing than the NST group. However, the latter had higher biofilm formation ability than the former. The genomic analysis showed the DST group exhibited more capsule-related and aminoglycoside-resistant genes. Besides, GO analysis indicated that functions involved in lipid biosynthetic, transport, and the metabolic process were up-regulated in the DST group, while KEGG analysis manifested that the two-component system related to potassium ion transport and pili were down-regulated. In short, resistance to desiccation, oxidation, multiple antibiotics, and serum complement killing are important reasons for the formation of DST. Genes related to capsule synthesis and lipid biosynthesis and metabolism play an important role at the molecular level in the formation of DST.

Multidrug-Resistant Acinetobacter: Detection of ESBL, MBL, bla NDM-1 Genotype, and Biofilm Formation at a Tertiary Care Hospital in Eastern Nepal

Background

The Acinetobacter species is an important hospital-acquired pathogen. The rapid development of resistance to multiple drugs and the ability to form biofilm make these bacteria more adaptable to survive in healthcare facilities, thus posing a challenge to their effective management.

Objective

This study aimed to characterize clinical isolates of Acinetobacter spp and to study their antimicrobial susceptibility patterns and ability to form biofilm. Resistant Acinetobacter was further analyzed for the detection of extended-spectrum β-lactamases (ESBLs), metallo β-lactamases (MBLs), carbapenemase production, and presence of blaNDM-1 gene.

Materials and Methods

A total of 324 Acinetobacter species were isolated from various clinical specimens which were submitted to the Department of Microbiology, B.P. Koirala Institute of Health Sciences, Dharan, Nepal, and were studied for antibiotic susceptibility testing, detection of ESBL and MBL production, and formerly biofilm formation was performed by standard microbiological methods. PCR was carried out to determine the presence of the blaNDM-1 gene.

Results

The predominant Acinetobacter species isolated was A calcoaceticus-baumannii Complex (Acb complex) 167 (51.5%). Among those, all A. species 128 (40%) were multidrug resistant (MDR). In which 13 (4.0%) were ESBL producers, 70 (61.9%) were MBL, and 12 (10.6%) were carbapenemases producers. The blaNDM1 gene was present in 33 isolates. Thirty-seven percent (121/324) of isolates formed biofilm. The majority of A. species were resistant to cefotaxime 73.8% (239) and cefepime 74.4% (241). A significant proportion of biofilm producers were MDR (p < 0.001).

Conclusion

Drug-resistant Acinetobacter formed a substantial proportion of this hospital's samples with a large presence of the bla NDM-1 gene. A matter of great concern is the association of multidrug-resistant phenotype with biofilm formation. This situation warranted stringent surveillance and adherence to infection prevention and control practices.

Mushroom-shaped structures formed in Acinetobacter baumannii biofilms grown in a roller bioreactor are associated with quorum sensing-dependent Csu-pilus assembly

There is currently a need to develop simple biofilm models that facilitate investigation of the architecture/biology of mature bacterial biofilms in a consistent/standardized manner given their environmental and clinical importance and the need for new anti-biofilm interventions. This study introduces a novel biofilm culture system termed the rolling biofilm bioreactor (RBB). This easily operated system allows adherent microbial cells to be repeatedly exposed to air/solid/liquid interfaces optimizing biofilm growth. The RBB was exploited to investigate biofilm formation in Acinetobacter baumannii. High levels of A. baumannii biofilm biomass reproducibly accumulate in the RBB and, importantly, undergo a maturation step to form large mushroom-shaped structures that had not been observed in other models. Based on image analysis of biofilm development and genetic manipulation, we show how N-acylhomoserine lactone-dependent quorum sensing (QS) impacts on biofilm differentiation, composition and antibiotic tolerance. Our results indicate that extracellular DNA (eDNA) is a key matrix component in mature Acinetobacter biofilms as the mushroom-like structures consist of dense cellular masses encased in an eDNA mesh. Moreover, this study reveals the contribution of QS to A. baumannii biofilm differentiation through Csu pilus assembly regulation. Understanding the mechanisms of structural development of mature biofilms helps to identify new biofilm eradication and removal strategies.

Effectiveness of ozone generated by a dielectric barrier discharge plasma reactor against multidrug-resistant pathogens and Clostridioides difficile spores

The contaminated healthcare environment plays an important role in the spread of multidrug-resistant organisms (MDROs) and Clostridioides difficile. This study aimed to evaluate the antimicrobial effects of ozone generated by a dielectric barrier discharge (DBD) plasma reactor on various materials that were contaminated by vancomycin-resistant Enterococcus faecium (VRE), carbapenem-resistant Klebsiella pneumoniae (CRE), carbapenem-resistant Pseudomonas aeruginosa (CRPA), carbapenem-resistant Acinetobacter baumannii (CRAB) and C. difficile spores. Various materials contaminated by VRE, CRE, CRPA, CRAB and C. difficile spores were treated with different ozone concentrations and exposure times. Atomic force microscopy (AFM) demonstrated bacterial surface modifications following ozone treatment. When an ozone dosage of 500 ppm for 15 min was applied to VRE and CRAB, about 2 or more log₁₀ reduction was observed in stainless steel, fabric and wood, and a 1–2 log₁₀ reduction in glass and plastic. Spores of C. difficile were more resistant to ozone than were all other tested organisms. On AFM, the bacterial cells, following ozone treatment, were swollen and distorted. The ozone generated by the DBD plasma reactor provided a simple and valuable decontamination tool for the MDROs and C. difficile spores, which are known as common pathogens in healthcare-associated infections.

Investigation the effects of silver nanoparticles and gold nanoparticles on expression of bap and csu genes in biofilm formation of Acinetobacter baumannii

Background and Objectives

Acinetobacter baumannii is one of the main pathogens of the hospital and causes various infections. csu A/BABCDE involved in the initial surface attachment during biofilm formation and bap gene produces specific proteins at the cell surface that play a direct role in formation of biofilm and the infectivity of this bacterium. The aim of this study was to investigate the effect of silver nanoparticles and gold nanoparticles on the expression of bap and csu genes in the Acinetobacter baumannii biofilm formation.

Materials and Methods

The susceptibility test was performed to determine the MIC of silver nanoparticles, gold nanoparticles and gold-vancomycin nanoparticles performed by broth dilution method on A. baumannii strains. The ability of biofilms formation in strains treated by MIC of silver nanoparticles and gold-vancomycin nanoparticles were evaluated by microtiter plate method and A. baumannii ATCC19606 used as control. Expression of the csu and bap genes were determinded by measuring the cognate mRNA level by real-time PCR.

Results

In present study, gold nanoparticles could not prevent the growth and biofilm formation of A. baumannii strains. The MIC concentration of silver nanoparticles and vancomycin- gold nanoparticles were 6.25 μg/ml and 0.625 μg/ml respectively and MBC concenteration of nanoparticles for 70% of strain was 12.5 μg/ml and 1.25 μg/ml respectively. Real-time PCR and data analysis, determined that the expression of bap, csuC and csuE genes in A. baumannii strains treated with MIC concentration (6.25 μg/ml) of silver nanoparticles decreased compared to control groups. Also, the expression of csuC and csuE genes in strains treated with MIC concentration (0.625 μg/ml) of vancomycin -gold nanoparticles increased, however the expression of bap was decreased compared to the control groups.

Conclusion

Due to the inhibitory effect of silver nanoparticles and gold-vancomycin nanoparticles against A. baumannii biofilm formation and genes expression, they can probably be used for prevent of biofilm formation in medical instrument or can be use for treatment of infections with or without antibiotic.

Inanimate Surfaces as a Source of Hospital Infections Caused by Fungi, Bacteria and Viruses with Particular Emphasis on SARS-CoV-2

The carriers of nosocomial infections are the hands of medical personnel and inanimate surfaces. Both hands and surfaces may be contaminated as a result of contact with the patient, their body fluids, and touching contaminated surfaces in the patient's surroundings. Visually clean inanimate surfaces are an important source of pathogens. Microorganisms have properties thanks to which they can survive in unfavorable conditions, from a few days to several months. Bacteria, viruses and fungi are able to transmit from inanimate surfaces to the skin of the patient and the medical staff. These pathogens include SARS-CoV-2, which can survive on various types of inanimate surfaces, being a potential source of infection. By following the recommendations related to washing and disinfecting hands and surfaces, and using appropriate washing and disinfecting agents with a broad biocidal spectrum, high material compatibility and the shortest duration of action, we contribute to breaking the chain of nosocomial infections.

Evaluating the Effectiveness of Hospital Antiseptics on Multidrug-Resistant Acinetobacter baumannii: Understanding the Relationship between Microbicide and Antibiotic Resistance

Acinetobacter baumannii hospital infections are difficult to treat due to the rapid emergence of multidrug-resistant (MDR) strains. In addition, A. baumannii can survive in numerous adverse environments, including in the presence of common hospital antiseptics. We hypothesized that in addition to accumulating drug resistance determinants, MDR A. baumannii strains also accumulate mutations that allow for greater microbicide tolerance when compared to pan-susceptible (PS) strains. To test this hypothesis, we compared the survival of five MDR and five PS patient isolates when exposed to bleach, ethanol, quaternary ammonium compounds, chlorhexidine gluconate, and povidone. We evaluated bacteria in a free-living planktonic state and under biofilm conditions. Each disinfectant eliminated 99.9% of planktonic bacteria, but this was not the case for bacterial biofilms. Next, we characterized strains for the presence of the known microbicide-resistance genes cepA, qacEΔ1, qacE, and qacA. MDR strains did not survive more than PS strains in the presence of microbicides, but microbicide-resistant strains had higher survival rates under some conditions. Interestingly, the PS strains were more likely to possess microbicide-resistance genes. Microbicide resistance remains an important topic in healthcare and may be independent of antimicrobial resistance. Hospitals should consider stricter isolation precautions that take pan-susceptible strains into account.

Whole-Genome Sequencing of a Colistin-Resistant Acinetobacter baumannii Strain Isolated at a Tertiary Health Facility in Pretoria, South Africa

BACKGROUND

Acinetobacter baumannii's (A. baumannii) growing resistance to all available antibiotics is of concern. The study describes a colistin-resistant A. baumannii isolated at a clinical facility from a tracheal aspirate sample. Furthermore, it determines the isolates' niche establishment ability within the tertiary health facility.

METHODS

An antimicrobial susceptibility test, conventional PCR, quantitative real-time PCR, phenotypic evaluation of the efflux pump, and whole-genome sequencing and analysis were performed on the isolate.

RESULTS

The antimicrobial susceptibility pattern revealed a resistance to piperacillin/tazobactam, ceftazidime, cefepime, cefotaxime/ceftriaxone, imipenem, meropenem, gentamycin, ciprofloxacin, trimethoprim/sulfamethoxazole, tigecycline, and colistin. A broth microdilution test confirmed the colistin resistance. Conventional PCR and quantitative real-time PCR investigations revealed the presence of adeB, adeR, and adeS, while mcr-1 was not detected. A MIC of 0.38 µg/mL and 0.25 µg/mL was recorded before and after exposure to an AdeABC efflux pump inhibitor. The whole-genome sequence analysis of antimicrobial resistance-associated genes detected beta-lactam: blaOXA-66; blaOXA-23; blaADC-25; blaADC-73; blaA1; blaA2, and blaMBL; aminoglycoside: aph(6)-Id; aph(3″)-Ib; ant(3″)-IIa and armA) and a colistin resistance-associated gene lpsB. The whole-genome sequence virulence analysis revealed a biofilm formation system and cell-cell adhesion-associated genes: bap, bfmR, bfmS, csuA, csuA/B, csuB, csuC, csuD, csuE, pgaA, pgaB, pgaC, and pgaD; and quorum sensing-associated genes: abaI and abaR and iron acquisition system associated genes: barA, barB, basA, basB, basC, basD, basF, basG, basH, basI, basJ, bauA, bauB, bauC, bauD, bauE, bauF, and entE. A sequence type classification based on the Pasteur scheme revealed that the isolate belongs to sequence type ST2.

CONCLUSIONS

The mosaic of the virulence factors coupled with the resistance-associated genes and the phenotypic resistance profile highlights the risk that this strain is at this South African tertiary health facility.

Genetic analysis of Acenitobacter bumannii associated with viral respiratory infections

In this study, samples were collected from Corona patients who were in isolation units for Corona virus patients, where samples were taken (from the nasal passage, mouth and sputum) and the samples were transferred by a liquid nutrient medium to the laboratory and kept at -2 temperature until they were cultivated on the medium of the Maconkey and saved In the incubator for 24 hours to observe the types of bacteria present , The samples were also cultured on Chrom agar Base Acinetobacter bacteria (which is a selective medium).It is difficult to distinguish it phenotypically from other bacteria, The phenotypic detection of A. bumannii bacteria, biochemical tests, and then molecular detection using ITS-specific primer were also performed and molecular detection using SP4-specific primer were also performed . A molecular assay for the CipA gene that encodes for the production of an enzyme complementary-inhibitor and Plg-binding protein of A. baumannii (Cip A) was also performed and The molecular assay for the Peptidase M10, metallopeptidase-specific primer gene was also performe. As the most important virulence factors in A. bumannii , Because the two enzymes played an important role in the pathogenesis of these bacteria . 

Convergence of Biofilm Formation and Antibiotic Resistance in Acinetobacter baumannii Infection

Acinetobacter baumannii (A. baumannii) is a leading cause of nosocomial infections as this pathogen has certain attributes that facilitate the subversion of natural defenses of the human body. A. baumannii acquires antibiotic resistance determinants easily and can thrive on both biotic and abiotic surfaces. Different resistance mechanisms or determinants, both transmissible and non-transmissible, have aided in this victory over antibiotics. In addition, the propensity to form biofilms (communities of organism attached to a surface) allows the organism to persist in hospitals on various medical surfaces (cardiac valves, artificial joints, catheters, endotracheal tubes, and ventilators) and also evade antibiotics simply by shielding the bacteria and increasing its ability to acquire foreign genetic material through lateral gene transfer. The biofilm formation rate in A. baumannii is higher than in other species. Recent research has shown how A. baumannii biofilm-forming capacity exerts its effect on resistance phenotypes, development of resistome, and dissemination of resistance genes within biofilms by conjugation or transformation, thereby making biofilm a hotspot for genetic exchange. Various genes control the formation of A. baumannii biofilms and a beneficial relationship between biofilm formation and "antimicrobial resistance" (AMR) exists in the organism. This review discusses these various attributes of the organism that act independently or synergistically to cause hospital infections. Evolution of AMR in A. baumannii, resistance mechanisms including both transmissible (hydrolyzing enzymes) and non-transmissible (efflux pumps and chromosomal mutations) are presented. Intrinsic factors [biofilm-associated protein, outer membrane protein A, chaperon-usher pilus, iron uptake mechanism, poly-β-(1, 6)-N-acetyl glucosamine, BfmS/BfmR two-component system, PER-1, quorum sensing] involved in biofilm production, extrinsic factors (surface property, growth temperature, growth medium) associated with the process, the impact of biofilms on high antimicrobial tolerance and regulation of the process, gene transfer within the biofilm, are elaborated. The infections associated with colonization of A. baumannii on medical devices are discussed. Each important device-related infection is dealt with and both adult and pediatric studies are separately mentioned. Furthermore, the strategies of preventing A. baumannii biofilms with antibiotic combinations, quorum sensing quenchers, natural products, efflux pump inhibitors, antimicrobial peptides, nanoparticles, and phage therapy are enumerated.

Molecular Study of Acinetobacter baumannii that Lacking Some Essentials Genes Responsible of Toxin-Antitoxin System

Acinetobacter genus has various species that are widespread in different environments and can exist in non-living environment samples as well. Acinetobacter baumannii (A. baumannii) is known to be one of the main causes of nosocomial infection. Few studies have examined the possibility of the presence of this opportunistic pathogen in non-living environment samples. In this study, A. baumannii strain cl-2 was isolated from dishwasher basket samples and it was identified by 16S ribosomal RNA sequencing analysis. The present study also investigated the presence of some important genes responsible for toxin-antitoxin (TA) systems necessary for the resistance of this bacterium in improper environmental conditions. Additionally, attempts were made to study some essential virulence factors, such as hemolysin, lipase, protease, and lecithinase production, as well as biofilm formation and surface motility. The findings revealed that the isolate belongs to the A. baumannii strain cl-2. The isolate was deposed in the National Center for Biotechnology Information, (NCBI) and the data can be accessed via the NCBI accession number (MW642251). The results of screening the TA system by higBA, mazEF, and relBE genes showed the isolate did not contain these genes. The hemolysin toxin activity (phenotypic test) was performed by using the streaking and spot methods on blood agar. It was found that the A. baumannii strain cl-2 had the ability to hemolyze red blood cells and produce lecithinase and protease enzymes. Finally, it was revealed that the A. baumannii strain cl-2 had surface motility based on the concentric diffusion ring of growth observed on Luria Broth agar (0.3%). In conclusion, the isolates under study showed association patterns between their ability to produce hemolysin, lipase, lecithinase, as well as protease, and other virulence factors, including surface motility and biofilm formation.

Acinetobacter baumannii: Virulence Strategies and Host Defense Mechanisms

Acinetobacter baumannii is a highly antibiotic-resistant bacterial pathogen known to cause severe life-threatening infections, including pneumonia, meningitis, and sepsis. Recent emergence of this bacterium as a serious nosocomial pathogen has led to categorization of A. baumannii as a "high-priority" pathogen by the World Health Organization (WHO), for which research efforts are urgently required to develop therapeutic interventions. Some of the properties that make A. baumannii a serious pathogen include its capacity to tolerate high levels of stress and enhanced expression of efflux pumps that enable high degrees of antibiotic resistance. Virulence mechanisms employed by A. baumannii to establish successful infection and host responses elicited against A. baumannii to counter the infection are discussed in detail in this article.

Examining properties influencing infectious microbe associations with surfaces of four different thermoplastic radiation therapy masks

BACKGROUND

Previous testing revealed that four different microbes applied to face-only masks from Civco, Klarity Medical, Orfit, and Qfix demonstrated variation in the number recovered from each mask type after a 1-hour contact time. In all cases, the Orfit mask demonstrated the largest number of recovered microbes suggesting a preference by tested microbes to create associations with this mask type.

METHODS

The current study evaluated three physiochemical features of these thermoplastic masks to determine why the Orfit mask encouraged greater microbial associations. Measurements including water contact angle (WCA), surface topography, and available contact area were determined for each mask type, where feasible.

RESULTS

The Orfit mask exhibited the greatest difference in each of the 3 evaluated characteristics. Overall, it showed decreased hydrophobicity, increased surface roughness, and increased surface contact area. The WCA of both Orfit (50.8°) and Klarity (95.6°) masks showed decreased hydrophobicity when compared to native PCL (129.97°).

CONCLUSION

The Orfit mask's decreased hydrophobicity, increased roughness, and larger surface contact area appears to have contributed to its ability to support a larger number of microbe associations. The decreased hydrophobicity and altered topography of both Klarity and Orfit masks may have been due to their additional antimicrobial coatings.

Biocide resistance in Acinetobacter baumannii: appraising the mechanisms

A global upsurge in antibiotic-resistant Acinetobacter baumannii requires supervised selection of biocides and disinfectants to avert nosocomial infections by reducing its spread. Moreover, inadequate and improper biocides have been reported as a contributing factor in antimicrobial resistance. Regardless of the manner of administration, a biocidal concentration that does not kill the target bacteria creates a stress response, propagating the resistance mechanisms. This is an essential aspect of the disinfection programme and the overall bio-contamination management plan. Knowing the mechanisms of action of biocides and resistance modalities may open new avenues to discover novel agents. This review describes the mechanisms of action of some biocides, resistance mechanisms, and approaches to study susceptibility/resistance to these agents.

Phenotypic and Genotypic Characteristics of Biofilm Formation in Clinical Isolates of Acinetobacter baumannii

Background

Acinetobacter baumannii is an important pathogen in clinical infections, and biofilm formation is an effective way for A. baumannii to survive under external pressures. In this study, the aims were to examine the antimicrobial resistance, biofilm formation, and biofilm-specific resistance in clinical isolates of A. baumannii.

Materials and Methods

A total of 104 clinical A. baumannii isolates were collected from a large teaching hospital in Southwest China. The antibiotics susceptibilities were tested, and biofilm-forming ability was evaluated by crystal violet staining by confocal laser scanning microscopy (CLSM). Minimum inhibitory concentration (MIC), minimum bactericidal concentration (MBC), minimum biofilm inhibitory concentration (MBIC), and minimum biofilm eradication concentration (MBEC) of ciprofloxacin, meropenem, and ceftazidime were tested on selected strains by broth microdilution method. Biofilm-associated genes were detected by polymerase chain reaction (PCR), and expression of genes at planktonic stage and biofilm stage were analyzed by real-time reverse transcription PCR (RT-PCR).

Results

Multidrug-resistant (MDR) isolates accounted for 65.4%, but no strain was resistant to tigecycline and polymyxin B. Moreover, non-MDR strains tended to form stronger biofilms than MDR strains, and a negative correlation between biofilm-forming ability and resistance profiles to each of tested antimicrobials were observed. The MBECs and MBICs of ciprofloxacin, ceftazidime, and meropenem were evidently increased compared with MICs and MBCs among all tested strains. Additionally, the biofilm formation ability of the csuD-positive strains was stronger than that of the csuD-negative strains. The strains in MDR group had higher carrying rate of csuA and csuD genes than non-MDR group, while non-MDR strains possessed more ompA gene than MDR group. Finally, abaI gene was significantly up-regulated after biofilm formation.

Conclusion

These results revealed valuable data for the negative correlation between antimicrobial resistance and biofilm formation, as well as phenotypic and genotypic characteristics of biofilm formation in A. baumannii.

Phenotypic and genotypic characteristics of Acinetobacter baumannii enrolled in the relationship among antibiotic resistance, biofilm formation and motility

Acinetobacter baumannii is an important pathogen in clinical. The factors of biofilm formation, antibiotic resistance and motility contribute great to A. baumannii in persisting in stressed environment, and further leads to nosocomial infections. 70 A. baumannii clinical isolates were investigated for their clinical characteristics of infection. Among the tested strains, 54 (77.1%) isolates were obtained from ICUs, with the frequency of multidrug-resistance (MDR) at 55.7%, and that of extensively drug-resistance (XDR) at 31.4%. 97.1% of the clinical isolates could form biofilms, in which 4.3% possessed weak biofilm formation ability, while 41.4% and 51.4% were moderate and strong biofilm producers, respectively. A strong correlation between antibiotic resistance and biofilm formation ability was found that all the resistant strains could form biofilms, with the majority in moderate and strong levels, but 2.9% sensitive isolates had no such ability. However, the sensitive strains that could produce biofilms showed stronger biofilm formation capacity in the early stage before 24 h compared to the resistant isolates, though they became weaker afterwards. 24 biofilm-related genes and two bla_OXA genes were found in both biofilm-forming and non-biofilm-forming strains, but with higher prevalence in the strains that could produce biofilms. No correlation was detected between twitching motility with antibiotic susceptibility or biofilm formation. These results raised a viewpoint that examining timepoint is a key factor for determining the biofilm formation ability, and further highlighted the importance of the appropriate surveillance and control measures in preventing the emergence and transmission of MDR and XDR A. baumannii.

An overview of Acinetobacter baumannii pathogenesis: Motility, adherence and biofilm formation

The Gram-negative opportunistic pathogen Acinetobacter baumannii has gain notoriety in recent decades, primarily due to its propensity to cause nosocomial infections in critically ill patients. Its global spread, multi-drug resistance features and plethora of virulence factors make it a serious threat to public health worldwide. Though much effort has been expended in uncovering its successes, it continues to confound researchers due to its highly adaptive nature, mutating to meet the needs of a given environment. Its persistence in the clinical setting allows it to be in close proximity to a potential host, where contact can be made facilitating infection and colonization. In this article, we aim to provide a current overview of the bacterial virulence factors, specifically focusing on factors involved in the initial stages of infection, highlighting the role of adaptation facilitated by two-component systems and biofilm formation. Finally, the study of host-pathogen interactions using available animal models, their suitability, notable findings and some perspectives moving forward are also discussed.

Acinetobacter baumannii: Its Clinical Significance in Human and Veterinary Medicine

Acinetobacter baumannii is a Gram-negative, opportunistic pathogen, causing severe infections difficult to treat. The A. baumannii infection rate has increased year by year in human medicine and it is also considered as a major cause of nosocomial infections worldwide. This bacterium, also well known for its ability to form biofilms, has a strong environmental adaptability and the characteristics of multi-drug resistance. Indeed, strains showing fully resistant profiles represent a worrisome problem in clinical therapeutic treatment. Furthermore, A. baumannii-associated veterinary nosocomial infections has been reported in recent literature. Particularly, carbapenem-resistant A. baumannii can be considered an emerging opportunistic pathogen in human medicine as well as in veterinary medicine.

Outer membrane vesicles containing OmpA induce mitochondrial fragmentation to promote pathogenesis of Acinetobacter baumannii

Acinetobacter baumannii is a highly antibiotic resistant Gram-negative bacterium that causes life-threatening infections in humans with a very high mortality rate. A. baumannii is an extracellular pathogen with poorly understood virulence mechanisms. Here we report that A. baumannii employs the release of outer membrane vesicles (OMVs) containing the outer membrane protein A (OmpAAb) to promote bacterial pathogenesis and dissemination. OMVs containing OmpAAb are taken up by mammalian cells where they activate the host GTPase dynamin-related protein 1 (DRP1). OmpAAb mediated activation of DRP1 enhances its accumulation on mitochondria that causes mitochondrial fragmentation, elevation in reactive oxygen species (ROS) production and cell death. Loss of DRP1 rescues these phenotypes. Our data show that OmpAAb is sufficient to induce mitochondrial fragmentation and cytotoxicity since its expression in E. coli transfers its pathogenic properties to E. coli. A. baumannii infection in mice also induces mitochondrial damage in alveolar macrophages in an OmpAAb dependent manner. We finally show that OmpAAb is also required for systemic dissemination in the mouse lung infection model. In this study we uncover the mechanism of OmpAAb as a virulence factor in A. baumannii infections and further establish the host cell factor required for its pathogenic effects.

Recent Advances in the Pursuit of an Effective Acinetobacter baumannii Vaccine

Acinetobacter baumannii has been a major cause of nosocomial infections for decades. The absence of an available vaccine coupled with emerging multidrug resistance has prevented the medical community from effectively controlling this human pathogen. Furthermore, the ongoing pandemic caused by SARS-CoV-2 has increased the risk of hospitalized patients developing ventilator-associated pneumonia caused by bacterial opportunists including A. baumannii. The shortage of antibiotics in the development pipeline prompted the World Health Organization to designate A. baumannii a top priority for the development of new medical countermeasures, such as a vaccine. There are a number of important considerations associated with the development of an A. baumannii vaccine, including strain characteristics, diverse disease manifestations, and target population. In the past decade, research efforts have revealed a number of promising new immunization strategies that could culminate in a safe and protective vaccine against A. baumannii. In this review, we highlight the recent progress in the development of A. baumannii vaccines, discuss potential challenges, and propose future directions to achieve an effective intervention against this human pathogen.

Nosocomial pathogen biofilms on biomaterials: Different growth medium conditions and components of biofilms produced in vitro

BACKGROUND/PURPOSE (S)

Nosocomial pathogens can develop biofilms on hospital surfaces and medical devices; however, few studies have focused on the evaluation of mono-and dual-species biofilms developed by nosocomial pathogens under different growth conditions.

METHODS

This study investigated biofilm development by nosocomial pathogens (Acinetobacter baumannii, Staphylococcus aureus, Escherichia coli, and Pseudomonas aeruginosa) on biomaterials in different culture media and their components of the extracellular matrix biofilm.

RESULTS

The mono-species biofilms showed cell densities from 7.50 to 9.27 Log₁₀ CFU/cm² on natural rubber latex type I (NLTI) and from 7.58 to 8.79 Log₁₀ CFU/cm² on stainless steel (SS). Dual-species biofilms consisted of S. aureus + P. aeruginosa (7.87-8.27 Log₁₀ CFU/cm² in TSBP and TSBME onto SS; p < 0.05), E. coli + P. aeruginosa (8.32-8.86 Log₁₀ CFU/cm² in TSBME onto SS and TSBP onto NLTI; p < 0.05), and S. aureus + E. coli (7.82 Log₁₀ CFU/cm² in TSBME onto SS; p < 0.05). Furthermore, biofilm detachment after proteinase K treatment was 5.54-32.81% compared to 7.95-24.15% after DNase I treatment in the mono-dual species biofilm matrix. Epifluorescence microscopy and scanning electron microscopy (SEM) enabled visualizing the bacteria and extracellular polymeric substances of biofilms on SS and NLTI.

CONCLUSION

Nosocomial pathogens can develop biofilms on biomaterials. Mono-species biofilms of Gram-negative bacteria showed lower densities than dual-species biofilms in TSBME and TSBP. Additionally, dual-species biofilms showed a higher concentration of proteins and eDNA in the extracellular matrix.

Insights Into Mechanisms of Biofilm Formation in Acinetobacter baumannii and Implications for Uropathogenesis

Multidrug resistant Acinetobacter baumannii is a serious healthcare threat. In fact, the Center for Disease Control recently reported that carbapenem-resistant A. baumannii is responsible for more than 8,500 infections, 700 deaths, and $281 million in healthcare costs annually in the United States with few, if any, treatment options available, leading to its designation as a pathogen of urgent concern and a priority for novel antimicrobial development. It is hypothesized that biofilms are, at least in part, responsible for the high prevalence of A. baumannii nosocomial and recurrent infections because they frequently contaminate hospital surfaces and patient indwelling devices; therefore, there has been a recent push for mechanistic understanding of biofilm formation, maturation and dispersal. However, most research has focused on A. baumannii pneumonia and bloodstream infections, despite a recent retrospective study showing that 17.1% of A. baumannii isolates compiled from clinical studies over the last two decades were obtained from urinary samples. This highlights that A. baumannii is an underappreciated uropathogen. The following minireview will examine our current understanding of A. baumannii biofilm formation and how this influences urinary tract colonization and pathogenesis.

Pan-Drug Resistant Acinetobacter baumannii, but Not Other Strains, Are Resistant to the Bee Venom Peptide Mellitin

Acinetobacter baumannii is a prevalent pathogen in hospital settings with increasing importance in infections associated with biofilm production. Due to a rapid increase in its drug resistance and the failure of commonly available antibiotics to treat A. baumannii infections, this bacterium has become a critical public health issue. For these multi-drug resistant A. baumannii, polymyxin antibiotics are considered the only option for the treatment of severe infections. Concerning, several polymyxin-resistant A. baumannii strains have been isolated over the last few years. This study utilized pan drug-resistant (PDR) strains of A. baumannii isolated in Brazil, along with susceptible (S) and extreme drug-resistant (XDR) strains in order to evaluate the in vitro activity of melittin, an antimicrobial peptide, in comparison to polymyxin and another antibiotic, imipenem. From a broth microdilution method, the determined minimum inhibitory concentration showed that S and XDR strains were susceptible to melittin. In contrast, PDR A. baumannii was resistant to all treatments. Treatment with the peptide was also observed to inhibit biofilm formation of a susceptible strain and appeared to cause permanent membrane damage. A subpopulation of PDR showed membrane damage, however, it was not sufficient to stop bacterial growth, suggesting that alterations involved with antibiotic resistance could also influence melittin resistance. Presumably, mutations in the PDR that have arisen to confer resistance to widely used therapeutics also confer resistance to melittin. Our results demonstrate the potential of melittin to be used in the control of bacterial infections and suggest that antimicrobial peptides can serve as the basis for the development of new treatments.

Insights into Acinetobacter baumannii: A Review of Microbiological, Virulence, and Resistance Traits in a Threatening Nosocomial Pathogen

Being a multidrug-resistant and an invasive pathogen, Acinetobacter baumannii is one of the major causes of nosocomial infections in the current healthcare system. It has been recognized as an agent of pneumonia, septicemia, meningitis, urinary tract and wound infections, and is associated with high mortality. Pathogenesis in A. baumannii infections is an outcome of multiple virulence factors, including porins, capsules, and cell wall lipopolysaccharide, enzymes, biofilm production, motility, and iron-acquisition systems, among others. Such virulence factors help the organism to resist stressful environmental conditions and enable development of severe infections. Parallel to increased prevalence of infections caused by A. baumannii, challenging and diverse resistance mechanisms in this pathogen are well recognized, with major classes of antibiotics becoming minimally effective. Through a wide array of antibiotic-hydrolyzing enzymes, efflux pump changes, impermeability, and antibiotic target mutations, A. baumannii models a unique ability to maintain a multidrug-resistant phenotype, further complicating treatment. Understanding mechanisms behind diseases, virulence, and resistance acquisition are central to infectious disease knowledge about A. baumannii. The aims of this review are to highlight infections and disease-producing factors in A. baumannii and to touch base on mechanisms of resistance to various antibiotic classes.

Recent progress in experimental and human disease-associated multi-species biofilms

Human bodies are colonized by trillions of microorganisms, which are often referred to as human microbiota and play important roles in human health. Next generation sequencing studies have established links between the genetic content of human microbiota and various human diseases. However, it remains largely unknown about the spatial organizations and interspecies interactions of individual species within the human microbiota. Bacterial cells tend to form surface-attached biofilms in many natural environments, which enable intercellular communications and interactions in a microbial ecosystem. In this review, we summarize the recent progresses on the experimental and human disease-associated multi-species biofilm studies. We hypothesize that engineering biofilm structures and interspecies interactions might provide a tool for manipulating the composition and function of human microbiota.

Acinetobacter baumannii Is a Risk Factor for Lower Respiratory Tract Infections in Children and Adolescents With a Tracheostomy

BACKGROUND

Lower respiratory tract infections (LRIs) are a major cause of hospitalization for children and adolescents with a tracheostomy. The aim of this study was to identify risk factors for LRI.

METHODS

In this retrospective study, we assessed the number of LRI and hospitalizations for LRI from 2004 to 2014 at the University Hospital Muenster Pediatric Department. We analyzed associations between LRI and clinical findings, and we cultured pathogens in tracheal aspirates (TAs) during noninfection periods. Univariable and multivariable negative, binomial regression analyses were applied to identify associations between possible risk factors and LRI.

RESULTS

Seventy-eight patients had 148 LRI, of which 99 were treated in hospital. The median number of LRI per year was 0.4. Six-hundred thirteen pathogens were detected in 315 specimens; Staphylococcus aureus (22.5%), Pseudomonas aeruginosa (14.8%) and Haemophilus influenzae (6.2%) were most frequently detected. Acinetobacter baumannii is an independent risk factor for LRI (rate ratio, 1.792; P = 0.030) and hospital admissions for LRI (rate ratio, 1.917; P = 0.011).

CONCLUSIONS

Children with a tracheostomy have frequent LRI. A. baumannii but not P. aeruginosa or S. aureus in TA is a risk factor for LRI in children with a long-term tracheostomy. This supports repetitive culture of TA for microbiologic workup to identify children and adolescents with an increased risk for LRI.

Analysis of Acinetobacter baumannii survival in liquid media and on solid matrices as well as effect of disinfectants

BACKGROUND

Acinetobacter baumannii is a cause of healthcare-associated infections and has considerable potential to survive on inanimate hospital surfaces under hostile conditions (e.g. disinfection or desiccation).

AIM

To learn more about its survival strategy and capacity to persist in liquid media and on surfaces mimicking hospital environments.

METHODS

The effect of temperature, nutrient deprivation, permanence on inanimate surfaces, and exposure to disinfectants on the survival of four A. baumannii strains (ATCC 19606^T and three clinical isolates) was studied by monitoring the number of total and viable cells using fluorescent microscopy and of culturable cells by standard cultures.

FINDINGS

Bacterial survival was differentially affected by temperature (cells maintained at 20°C remained culturable at least within 30 days) and physical environment (desiccation favoured cell resistance to stress at 37°C). Moreover, persistence was associated with two adaptation patterns: one linked to entry into the viable but non-culturable state, whereas the other apparently followed a bust-and-boom model. During a study on the effect of disinfectant (commercial bleach and quaternary ammonium compounds), it was found that treatment with these antibacterial compounds did not eliminate A. baumannii populations and provoked the reduction of culturable populations, although a fraction of cells remained culturable.

CONCLUSION

The ability to persist for long periods on different surfaces, mimicking those usually found in hospitals, along with A. baumannii's capacity to survive after a disinfection process may account for the recurrent outbreaks in intensive care units.

Tug of war between Acinetobacter baumannii and host immune responses

Acinetobacter baumannii is an emerging nosocomial, opportunistic pathogen with growing clinical significance. Acinetobacter baumannii has an exceptional ability to rapidly develop drug resistance and to adhere to abiotic surfaces, including medical equipment, significantly promoting bacterial spread and also limiting our ability to control A. baumannii infections. Consequently, A. baumannii is frequently responsible for ventilator-associated pneumonia in clinical settings. In order to develop an effective treatment strategy, understanding host-pathogen interactions during A. baumannii infection is crucial. Various A. baumannii virulence factors have been identified as targets of host innate pattern-recognition receptors, which leads to activation of downstream inflammasomes to develop inflammatory responses, and the recruitment of innate immune effectors against A. baumannii infection. To counteract host immune attack, A. baumannii regulates its expression of different virulence factors. This review summarizes the significance of mechanisms of host-bacteria interaction, as well as different bacteria and host defense mechanisms during A. baumannii infection.

Bacterial Biofilms on Extracorporeal Membrane Oxygenation Catheters

Despite the advantages of extracorporeal membrane oxygenation (ECMO), secondary catheter infection remains a major concern during ECMO support. In this study, to clarify the mechanism of ECMO catheter-related infection, we evaluated the impact of infection on biofilm formation on the surfaces of ECMO catheters, and we investigated clinical factors associated with biofilm formation. Catheters used for ECMO were prospectively collected aseptically from the femoral vein, internal jugular vein, and femoral artery of 81 patients with acute cardiorespiratory failure between January 2015 and October 2016. Prepared catheter sections were investigated by fluorescence microscopy, confocal scanning laser microscopy, transmission electron microscopy, and using semiquantitative culture methods. Of the 81 patients, 51 were assigned to the infection group and 30 to a control group. Biofilms were identified in 43.1% patients in the infection group, and in 20% controls (p = 0.034). Extracorporeal membrane oxygenation flow, systemic infection, and carbapenem-resistant Acinetobacter baumannii (CRAB) infection were associated with biofilm formation in a univariate analysis (odds ratio [OR]: 1.00, 95% confidence interval [CI]: 1.00-1.00, p = 0.007; OR: 3.03, 95% CI: 1.06-8.69, p = 0.039; OR: 9.60, 95% CI: 2.94-31.30, p < 0.001, respectively). However, of these factors, only CRAB infection was found to independently predict the presence of a biofilm by a multivariate logistic regression analysis (OR: 9.60, 95% CI: 2.94-31.30; p < 0.001). Biofilms were more prevalent in patients with an infection than in uninfected controls. Carbapenem-resistant A. baumannii infection was identified as an independent risk factor for biofilm formation on ECMO catheters.

Acinetobacter baumannii biofilms: effects of physicochemical factors, virulence, antibiotic resistance determinants, gene regulation, and future antimicrobial treatments

Acinetobacter baumannii is a leading cause of nosocomial infections due to its increased antibiotic resistance and virulence. The ability of A. baumannii to form biofilms contributes to its survival in adverse environmental conditions including hospital environments and medical devices. A. baumannii has undoubtedly propelled the interest of biomedical researchers due to its broad range of associated infections especially in hospital intensive care units. The interplay among microbial physicochemistry, alterations in the phenotype and genotypic determinants, and the impact of existing ecological niche and the chemistry of antimicrobial agents has led to enhanced biofilm formation resulting in limited access of drugs to their specific targets. Understanding the triggers to biofilm formation is a step towards limiting and containing biofilm-associated infections and development of biofilm-specific countermeasures. The present review therefore focused on explaining the impact of environmental factors, antimicrobial resistance, gene alteration and regulation, and the prevailing microbial ecology in A. baumannii biofilm formation and gives insights into prospective anti-infective treatments.

The structure of PilA from Acinetobacter baumannii AB5075 suggests a mechanism for functional specialization in Acinetobacter type IV pili

Type IV pili (T4P) are bacterial appendages composed of protein subunits, called pilins, noncovalently assembled into helical fibers. T4P are essential, in many bacterial species, for processes as diverse as twitching motility, natural competence, biofilm or microcolony formation, and host cell adhesion. The genes encoding type IV pili are found universally in the Gram-negative, aerobic, nonflagellated, and pathogenic coccobacillus Acinetobacter baumannii, but there is considerable variation in PilA, the major protein subunit, both in amino acid sequence and in glycosylation patterns. Here we report the X-ray crystal structure of PilA from AB5075, a recently characterized, highly virulent isolate, at 1.9 Å resolution and compare it to homologues from A. baumannii strains ACICU and BIDMC57, which are C-terminally glycosylated. These structural comparisons revealed that PilA^AB5075 exhibits a distinctly electronegative surface chemistry. To understand the functional consequences of this change in surface electrostatics, we complemented a ΔpilA knockout strain with divergent pilA genes from ACICU, BIDMC57, and AB5075. The resulting transgenic strains showed differential twitching motility and biofilm formation while maintaining the ability to adhere to epithelial cells. PilA^AB5075 and PilA^ACICU, although structurally similar, promote different characteristics, favoring twitching motility and biofilm formation, respectively. These results support a model in which differences in pilus electrostatics affect the equilibrium of microcolony formation, which in turn alters the balance between motility and biofilm formation in Acinetobacter.