A novel antibacterial compound decreases MRSA biofilm formation without the use of antibiotics in a murine model.

Despite significant advancements in material science, surgical site infection (SSI) rates remain high and prevention is key. This study aimed to demonstrate the in vivo safety and antibacterial efficacy of titanium implants treated with a novel broad-spectrum biocidal compound (DBG21) against methicillin-resistant Staphylococcus aureus (MRSA). Titanium (Ti) discs were covalently bound with DBG21. Untreated Ti discs were used as controls. All discs were implanted either untreated for 44 control mice or DBG21-treated for 44 treated mice. After implantation, 1 × 107 colony forming units (CFU) of MRSA were injected into the operating site. Mice were killed at 7 and 14 days to determine the number of adherent bacteria (biofilm) on implants and in the peri-implant surrounding tissues. Systemic and local toxicity were assessed. At both 7 and 14 days, DBG21-treated implants yielded a significant decrease in MRSA biofilm (3.6 median log10 CFU [99.97%] reduction [p < 0.001] and 1.9 median log10 CFU [98.7%] reduction [p = 0.037], respectively) and peri-implant surrounding tissues (2.7 median log10 CFU/g [99.8%] reduction [p < 0.001] and 5.6 median log10 CFU/g [99.9997%] reduction [p < 0.001], respectively). There were no significant differences between control and treated mice in terms of systemic and local toxicity. DBG-21 demonstrated a significant decrease in the number of biofilm bacteria without associated toxicity in a small animal implant model of SSI. Preventing biofilm formation has been recognized as a key element of preventing implant-related infections.

Complex Regulation of Gamma-Hemolysin Expression Impacts Staphylococcus aureus Virulence.

Staphylococcus aureus gamma-hemolysin CB (HlgCB) is a core-genome-encoded pore-forming toxin that targets the C5a receptor, similar to the phage-encoded Panton-Valentine leucocidin (PVL). Absolute quantification by mass spectrometry of HlgCB in 39 community-acquired pneumonia (CAP) isolates showed considerable variations in the HlgC and HlgB yields between isolates. Moreover, although HlgC and HlgB are encoded on a single operon, their levels were dissociated in 10% of the clinical strains studied. To decipher the molecular basis for the variation in hlgCB expression and protein production among strains, different regulation levels were analyzed in representative clinical isolates and reference strains. Both the HlgCB level and the HlgC/HlgB ratio were found to depend on hlgC promoter activity and mRNA processing and translation. Strikingly, only one single nucleotide polymorphism (SNP) in the 5' untranslated region (UTR) of hlgCB mRNA strongly impaired hlgC translation in the USA300 strain, leading to a strong decrease in the level of HlgC but not in HlgB. Finally, we found that high levels of HlgCB synthesis led to mortality in a rabbit model of pneumonia, correlated with the implication of the role of HlgCB in severe S. aureus CAP. Taken together, this work illustrates the complexity of virulence factor expression in clinical strains and demonstrates a butterfly effect where subtle genomic variations have a major impact on phenotype and virulence. IMPORTANCE S. aureus virulence in pneumonia results in its ability to produce several virulence factors, including the leucocidin PVL. Here, we demonstrate that HlgCB, another leucocidin, which targets the same receptors as PVL, highly contributes to S. aureus virulence in pvl-negative strains. In addition, considerable variations in HlgCB quantities are observed among clinical isolates from patients with CAP. Biomolecular analyses have revealed that a few SNPs in the promoter sequences and only one SNP in the 5' UTR of hlgCB mRNA induce the differential expression of hlgCB, drastically impacting hlgC mRNA translation. This work illustrates the subtlety of regulatory mechanisms in bacteria, especially the sometimes major effects on phenotypes of single nucleotide variation in noncoding regions.

In vitro antimicrobial activity of daptomycin alone and in adjunction with either amoxicillin, cefotaxime or rifampicin against the main pathogens responsible for bacterial meningitis in adults.

OBJECTIVES: As daptomycin adjunction is currently under clinical evaluation in the multicentre phase II AddaMAP study to improve the prognosis of pneumococcal meningitis, the present work aimed at evaluating the in vitro antimicrobial activity of daptomycin-based combinations against some of the most frequent species responsible for bacterial meningitis. METHODS: Clinically relevant strains of Streptococcus pneumoniae, Listeria monocytogenes, Haemophilus influenzae and Neisseria meningitidis were obtained from National Reference Centers. The antimicrobial activity of amoxicillin, cefotaxime and rifampicin, either alone or in association with daptomycin, was explored through the determination of minimum inhibitory concentration (MIC) and fractional inhibitory concentration index (FICI) as well as time-kill assay (TKA) using the broth microdilution method. RESULTS: All species taken together, the adjunction of daptomycin had no deleterious impact on the antimicrobial activity of amoxicillin, cefotaxime or rifampicin in vitro. Regarding Gram-positive bacteria, FICI and TKA analysis confirmed a global improvement of growth inhibition and bactericidal activity due to the adjunction of daptomycin. The synergistic effect prevailed for L. monocytogenes as demonstrated by FICI mainly <0.5 and a dynamic TKA-based synergy rate >50%. In addition, daptomycin-based associations did not modify the activity of ß-lactam antibiotics or rifampicin against Gram-negative bacteria, notably N. meningitidis. CONCLUSION: These results bring comforting evidence towards the clinical potential of daptomycin adjunction in the treatment of bacterial meningitis, which supports the ongoing AddaMAP clinical trial.