Virulence alterations in staphylococcus aureus upon treatment with the sub-inhibitory concentrations of antibiotics

Beta-Lactam Antibiotics Promote Extracellular Vesicle Production of Staphylococcus aureus Through ROS-Mediated Lipid Metabolic Reprogramming

Bacterial extracellular vesicles (EVs) are natural reservoirs of biological active substances. They exhibit promising application in developing bioproducts such as vaccine, drug-delivery system and anticancer agent. However, the low yield of naturally secreted EVs during bacterial growth is a bottleneck factor that restricts EV applications. In this study, we showed that sub-minimum inhibitory concentration (MIC) of β-lactams boosted EV production in various Staphylococcus aureus strains. The expression of penicillin-binding protein (PBP) genes increased after β-lactam treatment, and the inactivation of alternative PBPs promoted EV secretion of S. aureus. We also demonstrated that sub-MIC β-lactams promoted EV production via a reactive oxygen species (ROS)-dependent pathway. Deletion of redundant pbp genes enhanced oxacillin (OXA)-stimulated ROS levels. Transcriptomic and lipidomic analyses revealed that OXA-induced ROS triggered lipid metabolic reprogramming in S. aureus. Particularly, ROS promoted lipid peroxidation (LPO) and increased the biosynthesis of phosphatidic acid (PA) and lipoteichoic acid (LTA) that contributed to EV generation. Furthermore, OXA treatment altered the diversity of EV-loaded proteins. OXA-treated ∆ agr /OXAEVs induced stronger Dengue EDIII-specific antibodies in BALB/c mice than did ∆ agrEVs. Overall, this study provided mechanic insights into β-lactam-promoted EV production in S. aureus, and highlighted the potential strategies to prepare EVs for various applications.

Integrated transcriptomics and metabolomics study on the biofilm formation of Haemophilus influenzae by the stimulation of amoxicillin-clavulanate at subinhibitory concentration

Exposure to subinhibitory concentrations of β-lactam antibiotics has been shown to induce the biofilm formation of microorganisms, but the underlying mechanisms remain poorly understood. This study aims to explore the effect of different concentrations of amoxicillin-clavulanate, the most commonly used antibiotic in pediatrics, on the biofilm formation of Haemophilus influenza (H. influenzae) in vitro and to explore the underlying mechanisms. The effect of amoxicillin-clavulanate on the in vitro biofilm formation was assessed by crystal violet assay, colony counts, MTT colorimetric method, scanning electron microscopy, and confocal laser scanning microscopy. Integrated transcriptomics and metabolomics analyses were performed to identify key genes and metabolites. Our findings revealed that 1/2 MIC of amoxicillin-clavulanate significantly enhanced H. influenzae ATCC 49247 biofilm formation in vitro, while simultaneously reducing culturable bacterial counts and metabolic activity of biofilm-embedded bacteria. When exposed to 1/2 MIC of amoxicillin-clavulanate, the biofilm ultrastructure was altered, with an increase in biofilm structure, a decrease in bacteria embedded within the biofilms with abnormal bacterial morphology. Transcriptomics identified 118 differentially expressed genes (DEGs), comprising 62 upregulated and 56 downregulated genes. Metabolomics identified 21 differentially expressed metabolites (DEMs), with 13 upregulated and 8 downregulated. Integrated transcriptomics and metabolomics implicated amino sugar and nucleotide sugar metabolism as a key regulatory pathway. This study has provided novel insights into the relationship between a commonly prescribed pediatric antibiotic and H. influenzae biofilm formation, elucidating the underlying mechanisms, emphasizing the critical importance of judicious antibiotic use and clinical consideration of subinhibitory antibiotic effects, particularly in pediatric populations.

Subminimum inhibitory concentrations of rifampicin attenuate methicillin-resistant staphylococcus aureus virulence by suppressing SaeRS two-component system and arginine metabolism-related pathways

OBJECTIVES

Methicillin-resistant Staphylococcus aureus (MRSA) poses a significant threat to global public health, prompting the exploration of alternative strategies to mitigate its virulence. This study investigates the impact of subminimum inhibitory concentrations (sub-MICs) of rifampicin on MRSA virulence, aiming to provide insights for optimizing antibiotic treatment strategies.

METHODS

Enzyme-linked immunosorbent assay and western blot analysis were used to assess α-hemolysin expression. Transcriptomic sequencing and RT-qPCR analyzed gene expression changes in MRSA treated with sub-MICs of rifampicin. Mutant strains (ΔsaeR and ΔargGH) were constructed to validate the roles of the SaeRS system and arginine metabolism. Thermal shift assays evaluated the interaction between L-arginine and SaeR protein. In vivo murine models and Galleria mellonella infection models were used to assess the anti-virulence effects of rifampicin.

RESULTS

Our findings reveal that sub-MICs of rifampicin significantly reduce the expression of MRSA α-hemolysin. Transcriptomic sequencing and RT-qPCR analysis suggest a dual-pathway mechanism, wherein rifampicin suppresses virulence by indirectly inhibiting the SaeRS two-component system and disrupting arginine metabolism-related pathways. The construction of a saeR knockout mutant (ΔsaeR) and an arginine biosynthesis deficient mutant (ΔargGH) further supports this mechanism. Notably, exogenous l-arginine supplementation reverses rifampicin's inhibitory effect on α-hemolysin expression, underscoring the pivotal role of l-arginine metabolism in MRSA virulence regulation. Thermal shift assays demonstrate a direct interaction between l-arginine and SaeR protein, elucidating the intricate interplay between metabolic pathways and virulence regulation. In vivo studies confirm that sub-MICs of rifampicin attenuate the severity of skin abscesses in a murine model, improve survival rates in bloodstream infection models, and mitigate inflammation in both skin and lung tissues.

CONCLUSION

This study highlights the potential of rifampicin as an anti-virulence agent and pave the way for the development of innovative therapeutic strategies targeting MRSA infections.

Multidrug resistance in group B Streptococcus causing urinary tract infection exposes an erythromycin-driven protective effect against oxidative stress

Multidrug resistance has been reported in group B Streptococcus (GBS) from various origins, but rates among urinary tract infection (UTI) isolates are largely unknown. Erythromycin, a second-line antibiotic for GBS for which high rates of resistance have been reported, was recently shown to support the resistance of Staphylococcus to oxidative stress. To survey multidrug-resistant (MDR) GBS from UTI and to investigate the effect of erythromycin exposure on the bacteria's ability to resist oxidative stress, we determined the antibacterial activity of 18 antibiotics against 292 GBS UTI isolates by disc diffusion and used in vitro growth assays of MDR GBS exposed to erythromycin to examine relative resistance to oxidative stress in the form of H2O2. A high proportion of all 292 GBS isolates (33.6%) were MDR, reflecting high rates of resistance to four antibiotics: azithromycin (44.5%), clindamycin (26%), erythromycin (36.3%) and tetracycline (81.5%); however, no resistance was detected for any other antibiotics tested. Rates of resistance were not significantly different when analysed according to clinical origins (acute and recurrent UTI, asymptomatic bacteriuria). The growth of MDR GBS was attenuated and severely inhibited by exposure to erythromycin and H2O2, respectively. Surprisingly, exposure of MDR GBS to erythromycin significantly relieved the severe growth inhibitory effect of H2O2, signifying a partial rescue effect of the antibiotic. The GBS isolates in this study exhibit high levels of multidrug resistance without an association between resistance and clinical origin. Exposure of MDR GBS to erythromycin can partially counteract the severe growth inhibitory effect from H2O2.

Exacerbation of virulence of multi-drug resistant Escherichia coli O104:H4 by subinhibitory concentrations of ampicillin

Little is known about how subinhibitory concentrations of antibiotics to which bacteria are resistant affect bacterial virulence. In this study, the effect of subinhibitory concentrations of ampicillin on the virulence of E. coli O104:H4 was analyzed. Bacteria were pre-exposed to 0.1, 0.3, or 0.5 mg/mL of ampicillin in LB media and incubated for 4 h at 37 °C. Transformation capacity (using plasmids and PCR-amplified DNA sequences), swarming motility, biofilm production, curli formation, and virulence gene expression were determined. Ampicillin increased the transformation of E. coli O104:H4, with the highest number of transformants (>104 CFU/ng DNA; p ≤ 0.05) detected after exposure to DNA sequences of spectinomycin. In addition, bacteria pre-treated with 0.5 mg/mL of ampicillin exhibited higher swarming motility (7.6 cm, vs 6.0 cm for control; p ≤ 0.05) and biofilm production (up to 1.9-fold; p ≤ 0.05) when subsequently exposed to 0.1 and 0.3 mg/mL of antibiotic compared with the control. Also, significant overexpression of the virulence-related genes flhC (≤16.1-fold), fliA (≤22.1-fold), csgA (≤3.6-fold), csgD (≤9.1-fold), stx2a (≤32.2-fold), and the antibiotic resistance gene blaTEM-1 (≤5.5-fold) was observed. In conclusion, ampicillin-resistant E. coli O104:H4 increased the expression of its virulence factors when exposed to most subinhibitory concentrations of ampicillin analyzed in this study.

Biological Activities of Leonotis ocymifolia (Burm.f.) and Its Antibacterial Activities Against ESKAPE Pathogens

Background/Objectives: The rise in antibiotic-resistant ESKAPE pathogens, which are responsible for severe and hard-to-treat infections, highlights the urgent need for alternative therapeutic agents. While species in the Leonotis genus have demonstrated antimicrobial potential, limited research exists on Leonotis ocymifolia. This study evaluated the phytochemical profiles and antioxidant, antibacterial, and antibiofilm activities of L. ocymifolia leaf and stem extracts. Methods: Acidified acetone and hexane were used for extraction, followed by liquid-liquid fractionation with dichloromethane (DCM), ethyl acetate, and butanol. Phytochemicals were profiled using thin-layer chromatography (TLC), while polyphenolic content and antioxidant activity were determined using colorimetric and DPPH assays, respectively. Antibacterial activity was assessed via bioautography and micro-broth dilution assays. Antibiofilm activities were evaluated using crystal violet staining, and metabolic activity was assessed using tetrazolium salt as a cell viability indicator. Results: Ethyl acetate fractions had the highest phenolic (98.15 ± 9.63 mg GAE/g) and tannin contents (108.28 ± 8.78 mg GAE/g), with strong DPPH scavenging activity (79-90% at 250 µg/mL). DCM extracts had potent antibacterial activity, with a minimum inhibitory concentration (MIC) of 0.31-0.625 mg/mL against Pseudomonas aeruginosa, Escherichia coli, and Klebsiella pneumoniae. Antibiofilm assays revealed over 50% inhibition across biofilm formation phases, with DCM leaf extracts disrupting biofilms by inhibiting microbial metabolism. Conclusions: This study highlights L. ocymifolia as a promising source of bioactive compounds with significant antioxidant and antibacterial properties. The DCM and ethyl acetate extracts demonstrated high polyphenol content and effective biofilm inhibition. Further studies are warranted to isolate bioactive compounds and elucidate their mechanisms of action.

Encapsulation nanoarchitectonics of glabridin with sophorolipid micelles for addressing biofilm hazards via extracellular polymeric substance permeation and srtA gene suppression

BACKGROUND

Biofilm, a common drug-resistant phenotype of Staphylococcus aureus (S. aureus), demonstrates significant drug resistance and recurrence due to its extracellular polymeric substance (EPS) barrier and subsequent bacterial migration. Hence, there is an urgent need for effective solutions to mitigate the hazards posed by biofilms.

RESULT

This study developed a stable, low-toxicity multifunctional nanomicelle, GLA@SOL/EYL, by encapsulating glabridin (GLA) using sophorolipid (SOL) and egg yolk lecithin (EYL). Optimizations were performed for the hydration medium, the ratio of carrier materials to GLA, and EYL additions. GLA@SOL/EYL exhibited a particle size of 122.1 ± 0.8 nm and a surface potential of -66.4 ± 1.7 mV, endowing it with the ability to permeate biofilms EPS effectively. GLA@SOL/EYL encapsulated 98.3 ± 1.2 % of GLA and demonstrated a slow-release effect, significantly enhancing the bioavailability of GLA. The addition of EYL reduced the hemolytic toxicity of GLA@SOL/EYL and improved its encapsulation rate and stability. GLA@SOL/EYL reduced the minimum inhibitory concentration of GLA to 8 μg/mL and extended its inhibitory effect at low concentrations by rapidly disrupting the structural integrity of S. aureus. GLA@SOL/EYL may penetrate biofilms to disperse EPS and remove twice as much biofilm as GLA alone, thereby eliminating 99.99 % of S. aureus within biofilms, compared to 99 % bactericidal efficacy of GLA. Additionally, GLA@SOL/EYL inhibited 63.8 ± 1.8 % of biofilm formation by affecting the expression of the srtA gene, thereby reducing the expression of cell wall-anchoring protein genes. In contrast, the biofilm inhibition rates of GLA and blank micelles were less than 10 %.

CONCLUSION

GLA@SOL/EYL utilizes the nanoparticle effect to penetrate biofilms and deliver antimicrobial GLA. The SOL disperses the biofilm matrix while GLA is released to kill S. aureus, preventing bacterial dissemination and colonization. Thus, GLA@SOL/EYL presents an innovative strategy for effectively eradicating S. aureus biofilms and preventing new hazards in a one-step approach.

Ultrasound-Mediated Antibiotic Delivery to In Vivo Biofilm Infections: A Review

Bacterial biofilms are a significant concern in various medical contexts due to their resilience to our immune system as well as antibiotic therapy. Biofilms often require surgical removal and frequently lead to recurrent or chronic infections. Therefore, there is an urgent need for improved strategies to treat biofilm infections. Ultrasound-mediated drug delivery is a technique that combines ultrasound application, often with the administration of acoustically-active agents, to enhance drug delivery to specific target tissues or cells within the body. This method involves using ultrasound waves to assist in the transportation or activation of medications, improving their penetration, distribution, and efficacy at the desired site. The advantages of ultrasound-mediated drug delivery include targeted and localized delivery, reduced systemic side effects, and improved efficacy of the drug at lower doses. This review scrutinizes recent advances in the application of ultrasound-mediated drug delivery for treating biofilm infections, focusing on in vivo studies. We examine the strengths and limitations of this technology in the context of wound infections, device-associated infections, lung infections and abscesses, and discuss current gaps in knowledge and clinical translation considerations.

Bacterial outer membrane vesicles increase polymyxin resistance in Pseudomonas aeruginosa while inhibiting its quorum sensing

The persistent emergence of multidrug-resistant bacterial pathogens is leading to a decline in the therapeutic efficacy of antibiotics, with Pseudomonas aeruginosa (P. aeruginosa) emerging as a notable threat. We investigated the antibiotic resistance and quorum sensing (QS) system of P. aeruginosa, with a particular focused on outer membrane vesicles (OMVs) and polymyxin B as the last line of antibiotic defense. Our findings indicate that OMVs increase the resistance of P. aeruginosa to polymyxin B. The overall gene transcription levels within P. aeruginosa also reveal that OMVs can reduce the efficacy of polymyxin B. However, both OMVs and sublethal concentrations of polymyxin B suppressed the transcription levels of genes associated with the QS system. Furthermore, OMVs and polymyxin B acted in concert on the QS system of P. aeruginosa to produce a more potent inhibitory effect. This suppression was evidenced by a decrease in the secretion of virulence factors, impaired bacterial motility, and a notable decline in the ability to form biofilms. These results reveal that OMVs enhance the resistance of P. aeruginosa to polymyxin B, yet they collaborate with polymyxin B to inhibit the QS system. Our research contribute to a deeper understanding of the resistance mechanisms of P. aeruginosa in the environment, and provide new insights into the reduction of bacterial infections caused by P. aeruginosa through the QS system.

Antimicrobial Sub-MIC induces Staphylococcus aureus biofilm formation without affecting the bacterial count

BACKGROUND

Biofilm formation is an essential virulence factor that creates a highly protected growth mode for Staphylococcus aureus (S. aureus) to survive in any hostile environment. Antibiotic sub-minimal inhibitory concentration (sub-MIC) may modulate the biofilm formation ability of bacterial pathogens, thereby affecting bacterial pathogenesis and infection outcomes. Intense antimicrobial therapy to treat biofilm-associated infections can control the pathogenic infection aggravation but cannot guarantee its complete eradication.

OBJECTIVE

This study aimed to assess the sub-MICs effect of 5 different antimicrobial classes on biofilm-forming capacity among Staphylococcus aureus clinical isolates using three different biofilm quantitation techniques.

METHODS

In this study, the effects of 5 different antimicrobial agents, namely, azithromycin, gentamicin, ciprofloxacin, doxycycline, and imipenem, at sub-MICs of 12.5%, 25%, and 50% were tested on 5 different clinical isolates of S. aureus. The biofilms formed in the absence and presence of different antimicrobial sub-MICs were then assessed using the following three different techniques: the crystal violet (CV) staining method, the quantitative PCR (qPCR) method, and the spread plate method (SPM).

RESULTS

Biofilm formation was significantly induced in 64% of the tested conditions using the CV technique. On the other hand, the qPCR quantifying the total bacterial count and the SPM quantifying the viable bacterial count showed significant induction only in 24% and 17.3%, respectively (Fig. 1). The difference between CV and the other techniques indicates an increase in biofilm biomass without an increase in bacterial growth. As expected, sub-MICs did not reduce the viable cell count, as shown by the SPM. The CV staining method revealed that sub-MICs of imipenem and ciprofloxacin had the highest significance rate (80%) showing an inductive effect on the biofilm development. On the other hand, doxycycline, azithromycin, and gentamicin displayed lower significance rates of 73%, 53%, and 47%, respectively.

CONCLUSION

Exposure to sub-MIC doses of antimicrobial agents induces the biofilm-forming capacity of S. aureus via increasing the total biomass without significantly affecting the bacterial growth of viable count.

Host and antibiotic jointly select for greater virulence in Staphylococcus aureus

Widespread antibiotic usage has resulted in the rapid evolution of drug-resistant bacterial pathogens and poses significant threats to public health. Resolving how pathogens respond to antibiotics under different contexts is critical for understanding disease emergence and evolution going forward. The impact of antibiotics has been demonstrated most directly through in vitro pathogen passaging experiments. Independent from antibiotic selection, interactions with hosts have also altered the evolutionary trajectories and fitness landscapes of pathogens, shaping infectious disease outcomes. However, it is unclear how interactions between hosts and antibiotics impact the evolution of pathogen virulence. Here, we evolved and re-sequenced Staphylococcus aureus, a major bacterial pathogen, varying exposure to host and antibiotics to tease apart the contributions of these selective pressures on pathogen adaptation. After 12 passages, S. aureus evolving in Caenorhabditis elegans nematodes exposed to a sub-minimum inhibitory concentration of antibiotic (oxacillin) became highly virulent, regardless of whether the ancestral pathogen was methicillin-resistant (MRSA) or methicillin-sensitive (MSSA). Host and antibiotic exposure selected for reduced drug susceptibility in MSSA lineages while increasing MRSA total growth outside hosts. We identified mutations in genes involved in complex regulatory networks linking virulence and metabolism, including codY , agr , and gdpP , suggesting that rapid adaptation to infect hosts may have pleiotropic effects. In particular, MSSA populations under selection from host and antibiotic accumulated mutations in the global regulator gene codY , which controls biofilm formation in S. aureus. These populations had indeed evolved more robust biofilms-a trait linked to both virulence and antibiotic resistance-suggesting evolution of one trait can confer multiple adaptive benefits. Despite evolving in similar environments, MRSA and MSSA populations proceeded on divergent evolutionary paths, with MSSA populations exhibiting more similarities across replicate populations. Our results underscore the importance of considering multiple and concurrent selective pressures as drivers of pervasive pathogen traits.

Can photocatalysis inhibit interspecies bacterial cooperation to quench the formation of robust complex bacterial biofilms in water environments?

Bacterial biofilms pose significant a public health risk as an environmental reservoir for opportunistic aquatic bacterial pathogens. Understanding the interspecies roles of complex bacterial biofilms under different stimuli and regulatory mechanisms of stress responses is the key to controlling their dissemination. Herein, two-species mixture (TSM) biofilms (Staphylococcus aureus and Pseudomonas aeruginosa) were constructed in a flowthrough reactor. Compared with the single-species biofilms, the TSM biofilm had higher growth activity to reach maturity faster, forming a staggered community structure. Moreover, the TSM biofilm exhibited greatly improved resistance to different antibiotics (16-128 times higher), especially to those that act on protein synthesis and cell membrane integrity, when compared to single planktonic microorganisms. In the presence of stimuli, photocatalysis effectively inactivated the TSM biofilm within 10 h, a 4-fold shorter inactivation time compared to UVC irradiation. In addition, photocatalysis effectively depleted the extracellular polymers of the TSM biofilm and inhibited secretion of their interspecies quorum sensing signaling molecule autoinducer-2 (AI-2). However, the expression of AI-2 induced related virulence factors, and biofilm growth-related genes were initially up-regulated 3 - 10 fold for the TSM biofilm within the first 2 - 4 h of photocatalysis, followed by significant down-regulation. Furthermore, the addition of the AI-2 precursor 4,5-dihydroxy-2,3-pentanedione effectively delayed the photocatalytic inactivation efficiency of the TSM biofilm compared to the control. These results suggest that photocatalysis can effectively inactivate biofilms by inhibiting interspecies cooperation by quenching AI-2 in the TSM biofilm. This work sheds light on controlling biofilms in public health engineering systems.

Potential antivirulence and antibiofilm activities of sub-MIC of oxacillin against MDR S. aureus isolates: an in-vitro and in-vivo study

BACKGROUND

Multi-drug resistant Staphylococcus aureus is one of the most common causes of nosocomial and community-acquired infections, with high morbidity and mortality. Treatment of such infections is particularly problematic; hence, it is complicated by antibiotic resistance, and there is currently no reliable vaccine. Furthermore, it is well known that S. aureus produces an exceptionally large number of virulence factors that worsen infection. Consequently, the urgent need for anti-virulent agents that inhibit biofilm formation and virulence factors has gained momentum. Therefore, we focused our attention on an already-approved antibiotic and explored whether changing the dosage would still result in the intended anti-virulence effect.

METHODS

In the present study, we determined the antibiotic resistance patterns and the MICs of oxacillin against 70 MDR S. aureus isolates. We also investigated the effect of sub-MICs of oxacillin (at 1/4 and 1/8 MICs) on biofilm formation using the crystal violet assay, the phenol-sulphuric acid method, and confocal laser scanning microscopy (CLSM). We examined the effect of sub-MICs on virulence factors and bacterial morphology using quantitative reverse transcription polymerase chain reaction (qRT-PCR) and electron microscopy, respectively. Moreover, we studied the effect of sub-MICs of oxacillin (OX) in-vivo using a wound infection model.

RESULTS

Oxacillin at 1/2 MIC showed a significant decrease in bacterial viability, while 1/4 and 1/8 MICs had negligible effects on treated bacterial isolates. Treatment of MDR isolates with 1/4 or 1/8 MICs of oxacillin significantly reduced biofilm formation (64% and 40%, respectively). The treated MDR S. aureus with sub-MICs of OX exhibited a dramatic reduction in several virulence factors, including protease, hemolysin, coagulase, and toxic shock syndrome toxin-1 (TSST-1) production. The sub-MICs of OX significantly decreased (P < 0.05) the gene expression of biofilm and virulence-associated genes such as agrA, icaA, coa, and tst. Furthermore, oxacillin at sub-MICs dramatically accelerated wound healing, according to the recorded scoring of histological parameters.

CONCLUSION

The treatment of MDR S. aureus with sub-MICs of oxacillin can help in combating the bacterial resistance and may be considered a promising approach to attenuating the severity of S. aureus infections due to the unique anti-biofilm and anti-virulence activities.

Anti-virulence potential of iclaprim, a novel folic acid synthesis inhibitor, against Staphylococcus aureus

Infections caused by Staphylococcus aureus pose a significant global public problem. Therefore, new antibiotics and therapeutic strategies are needed to combat this pathogen. This investigation delves into the effects of iclaprim, a newly discovered inhibitor of folic acid synthesis, on S. aureus virulence. The phenotypic and genotypic effects of iclaprim were thoroughly examined in relation to virulence factors, biofilm formation, and dispersal, as well as partial virulence-encoding genes associated with exoproteins, adherence, and regulation in S. aureus MW2, N315, and ATCC 25923. Then, the in vivo effectiveness of iclaprim on S. aureus pathogenicity was explored by a Galleria mellonella larvae infection model. The use of iclaprim at sub-inhibitory concentrations (sub-MICs) resulted in a reduction of α-hemolysin (Hla) production and a differential effect on the activity of coagulase in S. aureus strains. The results of biofilm formation and eradication assay showed that iclaprim was highly effective in depolymerizing the mature biofilm of S. aureus strains at concentrations of 1 MIC or greater, however, inhibited the biofilm-forming ability of only strains N315 and ATCC 25923 at sub-MICs. Interestingly, treatment of strains with sub-MICs of iclaprim resulted in significant stimulation or suppression of most virulence-encoding genes expression. Iclaprim did not affect the production of δ-hemolysin or staphylococcal protein A (SpA), nor did it impact the total activity of proteases, nucleases, and lipases. In vivo testing showed that sub-MICs of iclaprim significantly improves infected larvae survival. The present study offered valuable insights towards a better understating of the influence of iclaprim on different strains of S. aureus. The findings suggest that iclaprim may have potential as an anti-virulence and antibiofilm agent, thus potentially mitigating the pathogenicity of S. aureus and improving clinical outcomes associated with infections caused by this pathogen. KEY POINTS: • Iclaprim effectively inhibits α-hemolysin production and biofilm formation in a strain-dependent manner and was an excellent depolymerizing agent of mature biofilm • Iclaprim affected the mRNA expression of virulence-encoding genes associated with exoproteins, adherence, and regulation • In vivo study in G. mellonella larvae challenged with S. aureus exhibited that iclaprim improves larvae survival.

Microbiological Characteristics of Clinically Isolated Staphylococcus aureus with Different Hemolytic Phenotypes in China

Purpose

This study aimed to investigate the microbiological characteristics of clinically isolated Staphylococcus aureus with different hemolytic phenotypes in China.

Materials and Methods

Using the three-point inoculation method, the hemolytic phenotypes of 1295 clinically isolated S. aureus strains were detected and categorized. Antimicrobial susceptibility testing of all strains was performed using a VITEK 2 Compact System. After sample size matching, plasma coagulase activity, catalase activity, mRNA expression of hemolysin genes (hla, hlb, hlc, and hld), biofilm formation, growth kinetics, inflammatory response of macrophages and cytotoxicity of S. aureus with different hemolytic phenotypes using the rabbit plasma kit, the catalase test on slides, qRT-PCR, crystal violet staining, the microcultivation assay, the ELISA kits, and the CCK-8 assay, respectively.

Results

Seven categories of hemolytic phenotypes were identified. Accordingly, strains were categorized into seven different groups, including S. aureus with complete hemolytic phenotype (SCHP), S. aureus with weak hemolytic phenotype (SWHP), S. aureus with incomplete hemolytic phenotype 1 (SIHP-1), SIHP-2, SIHP-3, SIHP-4 and SIHP-5, the last three of which were reported for the first time. Except for the hemolytic phenotype, all seven groups differed in clinical isolation rates, antibiotic resistance profile, plasma coagulase activity, mRNA expression of hemolysin genes, biofilm formation, growth kinetics, inflammatory response of macrophages, and cytotoxicity.

Conclusion

S. aureus with different hemolytic phenotypes have distinctive microbiological characteristics. Clinical microbiologists need to be vigilant about the hemolytic phenotypes when culturing S. aureus strains, and actively enhance communication with clinicians to optimize the treatment of infection.

Sub-inhibitory concentrations of tetrabromobisphenol A induce the biofilm formation of methicillin-resistant Staphylococcus aureus

Biofilm formation by methicillin-resistant Staphylococcus aureus (MRSA) on indwelling medical devices complicates the treatment of infection. Tetrabromobisphenol A (TBBPA), a synthetic, lipophilic, halogenated aromatic compound widely used as an additive in plastics and electronic products, has raised environmental concerns due to its potential for bioaccumulation. This study investigated the impact of sub-inhibitory concentrations of TBBPA on MRSA biofilm formation. Crystal violet staining and confocal laser scanning microscopy analysis demonstrated that 1/8 MIC (0.5 µg/mL) of TBBPA significantly stimulated MRSA biofilm formation (P < 0.0001). MTT assays indicated that the metabolic activity within the biofilms increased by 15.60-40.85% compared to untreated controls. Dot blot immunoassay, autolysis assay, and extracellular DNA (eDNA) quantification further revealed TBBPA enhanced the production of polysaccharide intercellular adhesin (PIA) and eDNA, which are key biofilm components. Additionally, TBBPA was found to enhance the production of staphyloxanthin, facilitating MRSA survival under oxidative conditions and in human whole blood. RT-qPCR analysis showed that TBBPA significantly upregulated genes associated with biofilm formation (icaA, atlA, sarA), staphyloxanthin biosynthesis (crtM and sigB), and oxidative stress responses (sodA and katA). These findings suggest that TBBPA promotes MRSA biofilm development and enhances bacterial resistance to adverse conditions, thereby potentially exacerbating risks to human health.

Potential antivirulence activity of sub-inhibitory concentrations of ciprofloxacin against Proteus mirabilis isolates: an in-vitro and in-vivo study

BACKGROUND

Proteus mirabilis is a significant nosocomial pathogen that is frequently associated with a wide range of infections, necessitating heightened attention to mitigate potential health risks. Hence, this study was performed to investigate the impact of sub-minimum inhibitory concentrations (MICs) of ciprofloxacin (CIP) on Proteus mirabilis clinical isolates.

METHODS

The sub-MICs of CIP were selected using the growth curve approach. The untreated and treated isolates with sub-MICs of CIP were assessed for their biofilm development, motilities on agar, and other virulence factors. The cell morphology of untreated and treated isolates with sub-MIC of CIP was explored using electron microscope. Moreover, the expression levels of the virulence genes in isolates were measured using quantitative real-time PCR.

RESULTS

Data revealed that sub-MICs of CIP significantly (p < 0.05), in a concentration-dependent manner, inhibited biofilm formation and other virulence factors in the selected isolates. Electron microscope analysis showed cell enlargement and various abnormalities in the cell wall and membrane integrity.

CONCLUSION

Sub-MICs of CIP exhibited inhibition of virulence and alterations in morphological integrity against P. mirabilis isolates.

Myricetin Acts as an Inhibitor of Type II NADH Dehydrogenase from Staphylococcus aureus

BACKGROUND

Staphylococcus aureus is a common pathogenic microorganism in humans and animals. Type II NADH oxidoreductase (NDH-2) is the only NADH:quinone oxidoreductase present in this organism and represents a promising target for the development of anti-staphylococcal drugs. Recently, myricetin, a natural flavonoid from vegetables and fruits, was found to be a potential inhibitor of NDH-2 of S. aureus. The objective of this study was to evaluate the inhibitory properties of myricetin against NDH-2 and its impact on the growth and expression of virulence factors in S. aureus.

RESULTS

A screening method was established to identify effective inhibitors of NDH-2, based on heterologously expressed S. aureus NDH-2. Myricetin was found to be an effective inhibitor of NDH-2 with a half maximal inhibitory concentration (IC50) of 2 μM. In silico predictions and enzyme inhibition kinetics further characterized myricetin as a competitive inhibitor of NDH-2 with respect to the substrate menadione (MK). The minimum inhibitory concentrations (MICs) of myricetin against S. aureus strains ranged from 64 to 128 μg/mL. Time-kill assays showed that myricetin was a bactericidal agent against S. aureus. In line with being a competitive inhibitor of the NDH-2 substrate MK, the anti-staphylococcal activity of myricetin was antagonized by MK-4. In addition, myricetin was found to inhibit the gene expression of enterotoxin SeA and reduce the hemolytic activity induced by S. aureus culture on rabbit erythrocytes in a dose-dependent manner.

CONCLUSIONS

Myricetin was newly discovered to be a competitive inhibitor of S. aureus NDH-2 in relation to the substrate MK. This discovery offers a fresh perspective on the anti-staphylococcal activity of myricetin.

Sub-inhibitory concentrations of ceftriaxone induce morphological alterations and PIA-independent biofilm formation in Staphylococcus aureus

The exposure of bacteria to sub-inhibitory concentrations of antibiotics is of biological significance since it can occur in vivo under many circumstances, including low-dose treatment, poor adherence to a regimen, poor drug penetration, drug-drug interactions, and antibiotic resistance of the pathogen. In this study, we investigated the effects of subinhibitory concentrations of four antibiotics: ampicillin, ceftriaxone, gentamicin, and norfloxacin, which are commonly used in clinical settings and on cell morphology and biofilm formation in Staphylococcus aureus as one of the leading causes of nosocomial and biofilm-associated infections. Nine clinical S. aureus biofilm-producing isolates and two known biofilm-producing reference strains, S. aureus ATCC 29213 and S. aureus ATCC 6538, were used in this study. Sub-MICs of beta-lactam antibiotics (ampicillin and ceftriaxone) significantly induced biofilm formation in S. aureus ATCC 29213 and S. aureus ATCC 6538 and in six clinical isolates out of the nine selected isolates when compared with the antibiotic-free control group (P < 0.05), with an approximately 2- to 2.5-fold increase. Gentamicin and norfloxacin induced biofilms in S. aureus ATCC 29213 and S. aureus ATCC 6538, while gentamicin and norfloxacin induced biofilms only in three and two of the nine tested isolates, respectively (P < 0.05). The chemical nature of the biofilm matrix produced by half the MIC of ceftriaxone in the six isolates that showed increased biofilm was all non-polysaccharide in composition (PIA-independent). Gene expression of biofilm-encoding genes atl and sarA in biofilms of the two tested strains (S. aureus ATCC 6538) and clinical strain (S. aureus 16) showed a significant upregulation after exposure to half MIC of ceftriaxone. Additionally, the bacterial cell morphological changes in planktonic cells caused by half MIC of ceftriaxone were evaluated by scanning electron microscopy, which demonstrated a significant cell enlargement when compared with the antibiotic-free control (P < 0.05), and some deformed cells were also noticed. In S. aureus clinical isolates, sub-MICs of ampicillin, ceftriaxone, gentamicin, and norfloxacin may stimulate substantial production of biofilm, which could have important clinical significance and make infection treatment challenges. Further, in vivo research is needed to fully comprehend how sub-MIC of antibiotics can affect biofilm formation in clinical settings. Additionally, more research is required to reveal the clinical implications of the morphological alterations in S. aureus brought on by exposure to ceftriaxone at concentrations below its MIC.

Ciprofloxacin enhances the biofilm formation of Staphylococcus aureus via an agrC-dependent mechanism

Staphylococcus aureus readily forms biofilms on host tissues and medical devices, enabling its persistence in chronic infections and resistance to antibiotic therapy. The accessory gene regulator (Agr) quorum sensing system plays a key role in regulating S. aureus biofilm formation. This study reveals the widely used fluoroquinolone antibiotic, ciprofloxacin, strongly stimulates biofilm formation in methicillin-resistant S. aureus, methicillin-sensitive S. aureus, and clinical isolates with diverse genetic backgrounds. Crystal violet staining indicated that ciprofloxacin induced a remarkable 12.46- to 15.19-fold increase in biofilm biomass. Confocal laser scanning microscopy revealed that ciprofloxacin induced denser biofilms. Phenotypic assays suggest that ciprofloxacin may enhance polysaccharide intercellular adhesin production, inhibit autolysis, and reduce proteolysis during the biofilm development, thus promoting initial adhesion and enhancing biofilm stability. Mechanistically, ciprofloxacin significantly alters the expression of various biofilm-related genes (icaA, icaD, fnbA, fnbB, eap, emp) and regulators (agrA, saeR). Gene knockout experiments revealed that deletion of agrC, rather than saeRS, abolishes the ciprofloxacin-induced enhancement of biofilm formation, underscoring the key role of agrC. Thermal shift assays showed ciprofloxacin binds purified AgrC protein, thereby inhibiting the Agr system. Molecular docking results further support the potential interaction between ciprofloxacin and AgrC. In summary, subinhibitory concentrations of ciprofloxacin stimulate S. aureus biofilm formation via an agrC-dependent pathway. This inductive effect may facilitate local infection establishment and bacterial persistence, ultimately leading to therapeutic failure.

Need for standardization in sub-lethal antibiotics research

While monitoring and managing resistant and persistent microbes is of utmost importance and should not be glossed over, one must also focus on mitigating the microbe's ability to cause harm. Exploring the concept of lowering or even suppressing the microbe's virulence with sub-Minimum Inhibitory Concentration (MIC) antibiotics holds promise and warrants further investigation. At present, such antibiotic concentrations have mostly been studied to cover the side-effects of gradient exposure, overlooking the possibility of utilizing them to influence not only bacterial virulence, but also colonization, fitness and collateral sensitivities. This review focuses on conflicting findings of studies demonstrating both increased and decreased virulence in microbes under sub-MIC antibiotic exposure. It identifies lack of standardization in this field of research as one of the main culprits for discordant results across numerous studies on virulence. It critically discusses important terminology related to bacterial traits and existing methods to determine MIC and sub-MIC ranges. Lastly, possible directions toward standardized sub-MIC profiling and thereby tailored treatment options in the future are explored.

A novel small-molecule compound S-342-3 effectively inhibits the biofilm formation of Staphylococcus aureus

IMPORTANCE

Biofilms are an important virulence factor in Staphylococcus aureus and are characterized by a structured microbial community consisting of bacterial cells and a secreted extracellular polymeric matrix. Inhibition of biofilm formation is an effective measure to control S. aureus infection. Here, we have synthesized a small molecule compound S-342-3, which exhibits potent inhibition of biofilm formation in both MRSA and MSSA. Further investigations revealed that S-342-3 exerts inhibitory effects on biofilm formation by reducing the production of polysaccharide intercellular adhesin and preventing bacterial adhesion. Our study has confirmed that the inhibitory effect of S-342-3 on biofilm is achieved by downregulating the expression of genes responsible for biofilm formation. In addition, S-342-3 is non-toxic to Galleria mellonella larvae and A549 cells. Consequently, this study demonstrates the efficacy of a biologically safe compound S-342-3 in inhibiting biofilm formation in S. aureus, thereby providing a promising antibiofilm agent for further research.

Antimicrobial peptidase lysostaphin at subinhibitory concentrations modulates staphylococcal adherence, biofilm formation, and toxin production

BACKGROUND

The ability of antimicrobial agents to affect microbial adherence to eukaryotic cell surfaces is a promising antivirulence strategy for combating the global threat of antimicrobial resistance. Inadequate use of antimicrobials has led to widespread instances of suboptimal antibiotic concentrations around infection sites. Therefore, we aimed to examine the varying effect of an antimicrobial peptidase lysostaphin (APLss) on staphylococcal adherence to host cells, biofilm biomass formation, and toxin production as a probable method for mitigating staphylococcal virulence.

RESULTS

Initially, soluble expression in E. coli and subsequent purification by immobilized-Ni2+ affinity chromatography (IMAC) enabled us to successfully produce a large quantity of highly pure ~ 28-kDa His-tagged mature APLss. The purified protein exhibited potent inhibitory effects against both methicillin-sensitive and methicillin-resistant staphylococcal strains, with minimal inhibitory concentrations (MICs) ranging from 1 to 2 µg/mL, and ultrastructural analysis revealed that APLss-induced concentration-specific changes in the morphological architecture of staphylococcal surface membranes. Furthermore, spectrophotometric and fluorescence microscopy revealed that incubating staphylococcal strains with sub-MIC and MIC of APLss significantly inhibited staphylococcal adherence to human vaginal epithelial cells and biofilm biomass formation. Ultimately, transcriptional investigations revealed that APLss inhibited the expression of agrA (quorum sensing effector) and other virulence genes related to toxin synthesis.

CONCLUSIONS

Overall, APLss dose-dependently inhibited adhesion to host cell surfaces and staphylococcal-associated virulence factors, warranting further investigation as a potential anti-staphylococcal agent with an antiadhesive mechanism of action using in vivo models of staphylococcal toxic shock syndrome.

Synergy of Antibiotics and Antibiofilm Agents against Methicillin-Resistant Staphylococcus aureus Biofilms

Methicillin-resistant Staphylococcus aureus (MRSA) infections are some of the most common antibiotic-resistant infections, often exacerbated by the formation of biofilms. Here, we evaluated six compounds, three common antibiotics used against MRSA and three antibiofilm compounds, in nine combinations to investigate the mechanisms of synergistic eradication of MRSA biofilms. Using metabolic assessment, colony enumeration, confocal fluorescence microscopy, and scanning electron microscopy, we identified two promising combinations of antibiotics with antibiofilm agents against preformed MRSA biofilms. The broad-spectrum protease, proteinase K, and membrane-targeting antibiotic, daptomycin, worked in synergy against MRSA biofilms by manipulating the protein content, increasing access to the cell membrane of biofilm bacteria. We also found that the combination of cationic peptide, IDR-1018, with the cell wall cross-linking inhibitor, vancomycin, exhibited synergy against MRSA biofilms by causing bacterial damage and preventing repair. Our findings identify synergistic combinations of antibiotics and antibiofilm agents, providing insight into mechanisms that may be explored further for the development of effective treatments against MRSA biofilm.

The effect and mechanism of iodophors on the adhesion and virulence of Staphylococcus aureus biofilms attached to artificial joint materials

BACKGROUND

Iodophors are known to be a treatment for biofilm-related periprosthetic joint infection. However, the efficacy and mechanism of eradicating biofilms from different artificial joint materials after iodophor treatment are unknown. This study was conducted to understand the effect and mechanism of iodophors with respect to the adhesion and virulence of Staphylococcus aureus biofilms attached to artificial joint materials.

METHODS

Biofilms of Staphylococcus aureus strains were grown on titanium alloy, cobalt chromium molybdenum and polyethylene coupons, which are commonly used materials for artificial joints, for 24 h. Afterward, all coupons were divided into experimental and control groups: (1) exposed to a 0.5 ± 0.05% iodophor for 5 min and (2) exposed to phosphate-buffered saline for 5 min. To gauge the level of biofilm, colony forming units (CFU), live/dead staining confocal microscopy and crystal violet staining were used. Meanwhile, the expression of icaACDR and clfA, which are related to virulence and adhesion, was examined in both the experimental and control groups.

RESULTS

A roughly three-log decrease in CFU/cm2 was seen in the viable plate count compared to the control group. Confocal imaging and crystal violet staining verified the CFU data. Moreover, the expression of icaACDR was reduced on three different orthopaedic implant materials, and the expression of clfA was also inhibited on titanium alloy coupons exposed to the iodophor.

CONCLUSIONS

Our results indicated that exposure to an iodophor for 5 min could significantly eliminate biofilms. When Staphylococcus aureus that had adhered to these three materials, which were used for artificial joints, was treated with an iodophor for 5 min, the expression of icaACDR was significantly reduced. This provides strong evidence for clinically clearing periprosthetic joint infections without removing the artificial joints.

Biological effect abundance analysis of hemolytic pathogens based on engineered biomimetic sensor

Conventional pathogen detection strategies based on the molecular structure or chemical characteristics of biomarkers can only provide the "physical abundance" of microorganisms, but cannot reflect the "biological effect abundance" in the true sense. To address this issue, we report an erythrocyte membrane-encapsulated biomimetic sensor cascaded with CRISPR-Cas12a (EMSCC). Taking hemolytic pathogens as the target model, we first constructed an erythrocyte membrane-encapsulated biomimetic sensor (EMS). Only hemolytic pathogens with biological effects can disrupt the erythrocyte membrane (EM), resulting in signal generation. Then the signal was amplified by cascading CRISPR-Cas12a, and more than 6.67 × 104-fold improvement in detection sensitivity compared to traditional erythrocyte hemolysis assay was achieved. Notably, compared with polymerase chain reaction (PCR) or enzyme linked immunosorbent assay (ELISA)-based quantification methods, EMSCC can sensitively respond to the pathogenicity change of pathogens. For the detection of simulated clinical samples based on EMSCC, we obtained an accuracy of 95% in 40 samples, demonstrating its potential clinical value.

Small-Molecule Compound CY-158-11 Inhibits Staphylococcus aureus Biofilm Formation

Staphylococcus aureus is an important human pathogen and brings about many community-acquired, hospital-acquired, and biofilm-associated infections worldwide. It tends to form biofilms, triggering the release of toxins and initiating resistance mechanisms. As a result of the development of S. aureus tolerance to antibiotics, there are few drugs can availably control biofilm-associated infections. In this study, we synthesized a novel small-molecule compound CY-158-11 (C22H14Cl2NO2Se2) and proved its inhibitory effect on the biofilm formation of S. aureus at a subinhibitory concentration (1/8 MIC). The subinhibitory concentration of CY-158-11 not only did not affect the growth of bacteria but also had no toxicity to A549 cells or G. mellonella. Total biofilm biomass was investigated by crystal violet staining, and the results were confirmed by SYTO 9 and PI staining through confocal laser scanning microscopy. Moreover, CY-158-11 effectively prevented initial attachment and repressed the production of PIA instead of autolysis. RT-qPCR analysis also exhibited significant suppression of the genes involved in biofilm formation. Taken together, CY-158-11 exerted its inhibitory effects against the biofilm formation in S. aureus by inhibiting cell adhesion and the expression of icaA related to PIA production. IMPORTANCE Most bacteria exist in the form of biofilms, often strongly adherent to various surfaces, causing bacterial resistance and chronic infections. In general, antibacterial drugs are not effective against biofilms. The small-molecule compound CY-158-11 inhibited the biofilm formation of S. aureus at a subinhibitory concentration. By hindering adhesion and PIA-mediated biofilm formation, CY-158-11 exhibits antibiofilm activity toward S. aureus. These findings point to a novel therapeutic agent for combating intractable S. aureus-biofilm-related infections.

Gum Arabic polysaccharide embedded L-cysteine capped copper oxide nanocarriers selectively inhibit fluconazole-resistant C. albicans biofilm and remove the toxic dye from wastewater

Copper oxide nanocarriers have attracted increasing interest in the scientific community, including antimicrobial applications. Candida biofilm developed causes serious clinical problems, leading to drug failure caused by its inherent drug tolerance. Nanocarriers are a good alternative approach to solving this challenge because of their excellent penetration power inside biofilms. Hence, main objectives of this research were to prepare gum arabic-embedded L-cysteine-capped copper oxide nanocarriers (GCCuO NCs) and tested against C. albicans and explore another application. To achieve the main research objectives, GCCuO NCs were synthesized and investigated for antibiofilm potency against C. albicans. Various methods were employed to measure antibiofilm potency such as biofilm assay etc., of NCs. The nano size of GCCuO NCs is advantageous for augmenting penetration power and retention into biofilms. GCCuO NCs at 100 μg/mL exhibited significant antibiofilm activity against the C. albicans DAY185 by switching of yeast-to-hyphae and gene perturbation. The level of CR dye adsorption was 58.96 % using 30 μg/mL of NCs. Based on effective C. albicans biofilm inhibition and CR dye adsorption capacity of NCs, it can be suggested that present research work opens an innovative path to treat biofilm-associated fungal infections, and these NCs can be used for environmental remedies.

Therapeutic potential of bacteriophage endolysins for infections caused by Gram-positive bacteria

Gram-positive (G⁺) bacterial infection is a great burden to both healthcare and community medical resources. As a result of the increasing prevalence of multidrug-resistant G⁺ bacteria such as methicillin-resistant Staphylococcus aureus (MRSA), novel antimicrobial agents must urgently be developed for the treatment of infections caused by G⁺ bacteria. Endolysins are bacteriophage (phage)-encoded enzymes that can specifically hydrolyze the bacterial cell wall and quickly kill bacteria. Bacterial resistance to endolysins is low. Therefore, endolysins are considered promising alternatives for solving the mounting resistance problem. In this review, endolysins derived from phages targeting G⁺ bacteria were classified based on their structural characteristics. The active mechanisms, efficacy, and advantages of endolysins as antibacterial drug candidates were summarized. Moreover, the remarkable potential of phage endolysins in the treatment of G⁺ bacterial infections was described. In addition, the safety of endolysins, challenges, and possible solutions were addressed. Notwithstanding the limitations of endolysins, the trends in development indicate that endolysin-based drugs will be approved in the near future. Overall, this review presents crucial information of the current progress involving endolysins as potential therapeutic agents, and it provides a guideline for biomaterial researchers who are devoting themselves to fighting against bacterial infections.

Omadacycline in treating community-based infections: a review and expert perspective

INTRODUCTION

Omadacycline is approved for the treatment of community-acquired bacterial pneumonia (CABP) and acute bacterial skin and soft tissue infection (ABSSSI). The integration of newer agents into clinical use involves understanding the nuances of clinical decision-making. This review will provide an in-depth focus on omadacycline in clinical practice.

AREAS COVERED

Literature review of omadacycline utilizing PubMed was performed to provide a comprehensive evaluation of omadacycline pharmacology, microbiology, registrational Phase 3 clinical trials, and post-marketing clinical studies. In addition, the immunomodulatory and other attributes of tetracycline class of antibiotics, of which omadacycline is a member, are reviewed, introducing the concept of antibiotic selection with attention to the bacterial pathogen and human host relationship.

EXPERT OPINION

Omadacycline builds upon the favorable attributes of tetracycline antibiotics and provides very reliable empiric coverage for both Staphylococcus aureus and Streptococcus spp. Clinicians require a more robust understanding of antibiotics, including omadacycline, in order to optimize patient outcomes, streamline care, and reduce medical costs.

Transcriptome and Proteome of Methicillin-Resistant Staphylococcus aureus Small-Colony Variants Reveal Changed Metabolism and Increased Immune Evasion

Methicillin-resistant Staphylococcus aureus (MRSA) infection has become a public health crisis. Recently, we isolated small-colony variants (SCVs) of MRSA, which are characterized by slow growth, decreased virulence, increased antibiotic resistance, and immune evasion. In the present study, we provided proteomic and transcriptomic profiles of clinical MRSA sequence type 239 (ST239) normal strains and SCVs and attempted to identify the key genes or pathways closely related to SCV formation and survival. RNAs and proteins were extracted and subjected to RNA sequencing and mass spectrometry, and the transcriptome and proteome were evaluated via bioinformatic analysis. The results were verified by functional assays. In total, 822 differentially expressed genes (DEGs) and 773 differentially expressed proteins (DEPs) were identified; of these, 286 DEGs and DEPs were correlated and subjected to Kyoto Encyclopedia Genes and Genomes analysis. Some pathways were significant, including ABC transporters, ribosome biogenesis, and metabolic pathways such as glycolysis/gluconeogenesis and the citrate cycle (tricarboxylic acid [TCA] cycle). Based on these results, we found that the downregulation of ABC transporters and the TCA cycle pathway resulted in electron transport chain deficiencies and reduced ATP production in SCVs, leading to a dependence on glycolysis and its upregulation. In addition, the upregulation of capsule polysaccharides and the downregulation of surface proteins prevented phagocytosis and reduced the adhesion of host cells, contributing to immune evasion by SCVs. These findings contribute to a better understanding of the mechanisms of SCV formation and survival. IMPORTANCE Small-colony variants (SCVs) of Staphylococcus aureus have drawn increasing research attention. Owing to their slow growth, atypical colony morphology, and unusual metabolic characteristics, SCVs often cause confusion in the laboratory. Furthermore, clinical treatment of SCVs is challenging owing to their antibiotic resistance and immune evasion, leading to persistent and recurrent infections. However, the mechanisms underlying their formation remain unclear. In this study, we isolated SCVs of methicillin-resistant S. aureus and provided transcriptomic and proteomic profiles of normal strains and SCVs. Based on our analysis, glycolysis upregulation and TCA cycle downregulation affected the electron transport chain and energy supply, leading to slower metabolism. Moreover, capsular biosynthesis was increased, while the number of surface proteins decreased, thus promoting immune evasion by SCVs.

Antibiotics resistance evolution of isolated Vibrio parahaemolyticus from mariculture under the continuous culture of sub-inhibitory concentrations of Ulva fasciata hydroponic solution

The outbreak of vibriosis from Vibrio (V.) parahaemolyticus is widespread in the mariculture, and live macroalgae has been considered to be effective and eco-friendly approach for the control of vibriosis. Three V. parahaemolyticus strains with β-lactam antibiotics resistance (resistant to ampicillin (AM), amoxicillin (AMX)) were isolated from mariculture in study, and the antibiotics resistance evolution mechanism was examined at the sub-inhibitory concentration (SIC) of hydroponic solution of Ulva (U.) fasciata (HSUF). The HSUF with the highest density (20 g fresh weight U. fasciata L^-1) demonstrated the strongest inhibitory rates (47.0 %-65.8 %) on the three strains during the stable phase (8-24 h) of growth curve, which indicated that the HSUF (≤20 g L^-1) could be considered to be at SIC for V. parahaemolyticus strains. After continuous subculture of V. parahaemolyticus with three dilutes (1/2 (HT), 1/20 (MT) and 1/50 (LT)) of HSUF (20 g L^-1), all the strains of 20th generation were still resistant to AM and AMX. However, the LT condition reduced MIC of AM (2-16 times) and AMX (0-2 times) to strains, while MT and HT showed significantly various effect of β-lactam antibiotics resistance on different strains. The biofilm formation and ROS content of V. parahaemolyticus were almost positively correlated to the concentrations of HSUF. Transcriptome sequencing analysis of a representative strain showed that the lower concentrations of HSUF caused more down-regulated DEGs of the strains, and more down-regulated (vmeA, vmeB, sapA, mrdA) DEGs of strains were related to the pathway of β-lactam antibiotics resistance at LT condition. Thus, low concentration of HSUF was seemed to have better improvement for V. parahaemolyticus strains resistant to β-lactam antibiotics, which were mainly related to the impairment of biofilm formation, ROS and efflux pump.

Baicalein Inhibits the Staphylococcus aureus Biofilm and the LuxS/AI-2 System in vitro

Introduction

Staphylococcus aureus (S. aureus) is a common cause of mastitis in dairy cows, a condition that has a significant economic impact. S. aureus displays quorum sensing (QS) system-controlled virulence characteristics, like biofilm formation, that make therapy challenging. In order to effectively combat S. aureus, one potential technique is to interfere with quorum sensing.

Methods

This study evaluated the effects of different Baicalin (BAI) concentrations on the growth and the biofilm of S. aureus isolates, including the biofilm formation and mature biofilm clearance. The binding activity of BAI to LuxS was verified by molecular docking and kinetic simulations. The secondary structure of LuxS in the formulations was characterized using fluorescence quenching and Fourier transform infrared (FTIR) spectroscopy. Additionally, using fluorescence quantitative PCR, the impact of BAI on the transcript levels of the luxS and biofilm-related genes was investigated. The impact of BAI on LuxS at the level of protein expression was also confirmed by a Western blotting investigation.

Results

According to the docking experiments, they were able to engage with the amino acid residues in LuxS and BAI through hydrogen bonding. The results of molecular dynamics simulations and the binding free energy also confirmed the stability of the complex and supported the experimental results. BAI showed weak inhibitory activity against S. aureus but significantly reduced biofilm formation and disrupted mature biofilms. BAI also downregulated luxS and biofilm-associated genes' mRNA expression. Successful binding was confirmed using fluorescence quenching and FTIR.

Discussion

We thus report that BAI inhibits the S. aureus LuxS/AI-2 system for the first time, which raises the possibility that BAI could be employed as a possible antimicrobial drug to treat S. aureus strain-caused biofilms.

Evaluation of the Antibacterial Activity of Quinoxaline Derivative Compound Against Methicillin-Resistant Staphylococcus aureus

Background

While the frequency of methicillin-resistant Staphylococcus aureus (MRSA) continues to rise globally, there is a fear regarding an increase in vancomycin resistance among S. aureus strains. As far back as the 1960s, MRSA was one of the world's most prevalent antibiotic-resistant bacteria. Among hospitalized patients and community members, MRSA is the cause of a significant number of infections. As a result of its resistance to classical beta-lactam and, in some cases, vancomycin antibiotics, efforts must be made as soon as feasible to find a new approach to fighting MRSA.

Purpose

This study is designed to evaluate the antibacterial activity of quinoxaline derivative compound against MRSA in comparison with vancomycin as a reference drug.

Methods

Sixty MRSA isolates were subjected to susceptibility testing by broth microdilution method for quinoxaline derivative compound and vancomycin. Each drug's minimal inhibitory concentration (MIC) was determined and compared.

Results

Among the sixty MRSA isolates, most of the quinoxaline derivative compound MIC findings (56.7%) were 4 µg/mL compared to vancomycin MIC values (63.3%) of 4 µg/mL. In comparison, 20% of quinoxaline derivative compound MIC readings were 2 µg/mL, while the vancomycin MIC results were 6.7%. However, the overall proportion of MIC readings at ≤2 µg/mL for both antibacterial agents was equal (23.3%). None of the isolates were resistant to vancomycin.

Conclusion

This experiment revealed that most MRSA isolates were associated with low MICs (1-4 μg/mL) for quinoxaline derivative compound. Overall, the susceptibility of the quinoxaline derivative compound signifies a promising efficacy against MRSA and may set a novel treatment approach.

A vancomycin resistance-associated WalK(S221P) mutation attenuates the virulence of vancomycin-intermediate Staphylococcus aureus

INTRODUCTION

Vancomycin-intermediate Staphylococcus aureus (VISA) is typically associated with a decline in virulence. We previously reported a WalK(S221P) mutation that plays an important role in mediating vancomycin resistance in VISA XN108. Whether this mutation is implicated in bacterial virulence remains unknown.

OBJECTIVES

This study aimed to investigate the effect of WalK(S221P) mutation on the virulence of VISA and the underlying mechanism of this effect.

METHODS

The influence of WalK(S221P) mutation on VISA virulence and its underlying mechanism were explored using animal models, RNA-seq analysis, RT-qPCR, hemolytic assay, slide coagulase test, Western blot, β-galactosidase assay, and electrophoresis mobility shift assay (EMSA).

RESULTS

Compared with XN108, WalK(S221P)-reverted strain XN108-R exacerbated cutaneous infections with increased lesion size and extensive inflammatory infiltration in mouse models. The bacterial loads of S. aureus XN108-R in murine kidney increased compared with those of XN108. RNA-seq analysis showed upregulation of a set of virulence genes in XN108-R, which exhibited greater hemolytic and stronger coagulase activities compared with XN108. Introduction of WalK(S221P) to methicillin-resistant S. aureus USA300 and methicillin-susceptible strain Newman increased the vancomycin resistance of the mutants, which exhibited reduced hemolytic activities and decreased expression levels of many virulence factors compared with their progenitors. WalK(S221P) mutation weakened agr promoter-controlled β-galactosidase activity. EMSA results showed that WalK-phosphorylated WalR could directly bind to the agr promoter region, whereas WalK(S221P)-activated WalR reduced binding to the target promoter. Inactivation of agr in S. aureus did not affect their vancomycin susceptibility but mitigated the virulence alterations caused by WalK(S221P) mutation.

CONCLUSION

The results of our study indicate that WalK(S221P) mutation can enhance vancomycin resistance in S. aureus of diverse genetic backgrounds. WalK(S221P)- bearing S. aureus strains exhibit reduced virulence. WalK(S221P) mutation may directly impair the activation of the agr system by WalR, thereby decreasing the expression of virulence factors in VISA.

Non-antibiotic strategies for prevention and treatment of internalized Staphylococcus aureus

Staphylococcus aureus (S. aureus) infections are often difficult to cure completely. One of the main reasons for this difficulty is that S. aureus can be internalized into cells after infecting tissue. Because conventional antibiotics and immune cells have difficulty entering cells, the bacteria can survive long enough to cause recurrent infections, which poses a serious burden in healthcare settings because repeated infections drastically increase treatment costs. Therefore, preventing and treating S. aureus internalization is becoming a research hotspot. S. aureus internalization can essentially be divided into three phases: (1) S. aureus binds to the extracellular matrix (ECM), (2) fibronectin (Fn) receptors mediate S. aureus internalization into cells, and (3) intracellular S. aureus and persistence into cells. Different phases require different treatments. Many studies have reported on different treatments at different phases of bacterial infection. In the first and second phases, the latest research results show that the cell wall-anchored protein vaccine and some microbial agents can inhibit the adhesion of S. aureus to host cells. In the third phase, nanoparticles, photochemical internalization (PCI), cell-penetrating peptides (CPPs), antimicrobial peptides (AMPs), and bacteriophage therapy can effectively eliminate bacteria from cells. In this paper, the recent progress in the infection process and the prevention and treatment of S. aureus internalization is summarized by reviewing a large number of studies.

Daptomycin exerts differential immunomodulatory effects on host responses against methicillin-resistant Staphylococcus aureus biofilms

BACKGROUND

Daptomycin (DAP) is indicated for difficult-to-treat Gram-positive infections, especially those caused by methicillin-resistant S. aureus (MRSA). Exposure of S. aureus to sub-inhibitory concentrations (sub-MICs) of antibiotics have been shown to alter cell morphology or biofilm formation.

OBJECTIVES

To investigate the influence of DAP biofilm sub-MICs on the damage caused by human polymorphonuclear neutrophils (PMNs) against MRSA biofilms and the potential immunomodulatory activity of DAP on human monocytes (MNCs) exposed to MRSA biofilms.

METHODS

DAP activity against biofilms and the impact of DAP on the PMNs-induced biofilm damage were evaluated by the XTT reduction assay, whereas pathogen recognition, signal transduction and cytokine modulation of DAP on MNCs in response to MRSA biofilms were assessed by RT-PCR and ELISA methodology.

RESULTS

The MIC50 of DAP to MRSA biofilms was 16 to 32 mg/L. Pre-treatment of MRSA to 1, 2 or 4 mg/L DAP caused a synergistic effect on PMN-mediated biofilm damage, being dependent on the effector-to-target ratio. MNCs responded to MRSA biofilms and DAP through Toll like receptor 2 (TLR2) upregulation and increased NLRP3 inflammasome production. DAP caused 2.5-fold greater TLR2 mRNA levels than those caused by MRSA biofilms. A predominantly inflammatory response was induced by either component, causing the release of significantly increased IFN-γ, TNF-α, IL-8 and IL-6 levels by MNCs exposed to the combination treatment. MRSA biofilms alone or combined with DAP caused low amounts of IL-10 production, but increased IL-1β levels.

CONCLUSIONS

DAP may condition MNCs towards an inflammatory response through TLR2 engagement and NLRP3 inflammasome activation, possibly controlling biofilm-associated pathogenicity.

Antivirulence Agent as an Adjuvant of β-Lactam Antibiotics in Treating Staphylococcal Infections

Staphylococcus aureus can cause a plethora of life-threatening infections. Antibiotics have been extensively used to treat S. aureus infections. However, when antibiotics are used at sub-inhibitory concentrations, especially for β-lactam antibiotics, they may enhance staphylococcal pathogenicity and exacerbate the infection. The combination of antivirulence agents and antibiotics may be a novel approach to controlling antibiotic-induced S. aureus pathogenicity. We have illustrated that under in vitro conditions, antivirulence agent M21, when administered concurrently with ampicillin, suppressed the expression and production of virulence factors induced by ampicillin. In a mouse peritonitis model, M21 reduced bacterial load irrespective of administration of ampicillin. In a bacteremia model, combinatorial treatment consisting of ampicillin or ceftazidime and M21 increased the survival rate of mice and reduced cytokine abundance, suggesting the suppression of antibiotic-induced virulence by M21. Different from traditional antibiotic adjuvants, an antivirulence agent may not synergistically inhibit bacterial growth in vitro, but effectively benefit the host in vivo. Collectively, our findings from this study demonstrated the benefits of antivirulence–antibiotic combinatorial treatment against S. aureus infections and provide a new perspective on the development of antibiotic adjuvants.

Commensal Bacillus subtilis from cow milk inhibits Staphylococcus aureus biofilm formation and mastitis in mice

The colonization and virulence production of Staphylococcus aureus (S. aureus), a known pathogen that induces mastitis, depend on its quorum-sensing (QS) system and biofilm formation. It has been reported that Bacillus can inhibit the QS system of S. aureus, thereby reducing S. aureus colonization in the intestine. However, whether Bacillus affects S. aureus biofilm formation and consequent colonization during mastitis is still unknown. In this study, the differences in the colonization of S. aureus and Bacillus were first analyzed by isolating and culturing bacteria from milk samples. It was found that the colonization of Bacillus and S. aureus in cow mammary glands was negatively correlated. Secondly, we found that although Bacillus did not affect S. aureus growth, it inhibited the biofilm formation of S. aureus by interfering its QS signaling. The most significant anti-biofilm effect was found in Bacillus subtilis H28 (B. subtilis H28). Finally, we found that B. subtilis H28 treatment alleviated S. aureus-induced mastitis in a mice model. Our results rerealed that bovine milk derived commensal Bacillus inhibited S. aureus colonization and alleviated S. aureus-induced mastitis by influencing biofilm formation, suggesting a potential targeted strategy to limit the colonization of S. aureus in vivo.

Antibiotics and ECMO in the Adult Population-Persistent Challenges and Practical Guides

Extracorporeal membrane oxygenation (ECMO) is an emerging treatment modality associated with a high frequency of antibiotic use. However, several covariables emerge during ECMO implementation, potentially jeopardizing the success of antimicrobial therapy. These variables include but are not limited to: the increased volume of distribution, altered clearance, and adsorption into circuit components, in addition to complex interactions of antibiotics in critical care illness. Furthermore, ECMO complicates the assessment of antibiotic effectiveness as fever, or other signs may not be easily detected, the immunogenicity of the circuit affects procalcitonin levels and other inflammatory markers while disrupting the immune system. We provided a review of pharmacokinetics and pharmacodynamics during ECMO, emphasizing practical application and review of patient-, illness-, and ECMO hardware-related factors.