[Show abstract][Hide abstract] ABSTRACT: Staphylococcus aureus, an important human pathogen, is particularly adept at producing biofilms on implanted medical devices. Although antibiotic treatment of nonsusceptible bacteria will not kill these strains, the consequences should be studied. The present study focuses on investigating the effect of vancomycin on biofilm formation by vancomycin-non-susceptible S. aureus. Biofilm adherence assays and scanning electron microscopy demonstrated that biofilm formation was significantly enhanced following vancomycin treatment. Bacterial autolysis of some subpopulations was observed and was confirmed by the live/dead staining and confocal laser scanning microscopy. A significant increase in polysaccharide intercellular adhesin (PIA) production was observed by measuring icaA transcript levels and in a semi-quantitative PIA assay in one resistant strain. We show that the release of extracellular DNA (eDNA) via cidA-mediated autolysis is a major contributor to vancomycin-enhanced biofilm formation. The addition of xenogeneic DNA could also significantly enhance biofilm formation by a PIA-overproducing S. aureus strain. The magnitude of the development of the biofilm depends on a balance between the amounts of eDNA and PIA. In conclusion, sublethal doses of cell wall-active antibiotics like vancomycin induce biofilm formation through an autolysis-dependent mechanism in vancomycin-non-susceptible S. aureus.
[Show abstract][Hide abstract] ABSTRACT: Pulsed-field gel electrophoresis (PFGE) analysis revealed that the genomes of some pathogenic Escherichia coli O157:H7 strains, including EDL933, were resistant to NotI digestion. An amino acid sequence comparison suggested that the z2389 gene carried on prophage CP-933R in strain EDL933 is likely to encode a C(5)-cytosine methyltransferase. The z2389-equivalent gene was found in the NotI-resistant strains tested, but it was not detected in the NotI-susceptible strains. PFGE analysis of the wild-type EDL933 strain and of a z2389 null mutant revealed that z2389 was associated with full genome protection against NotI digestion and partial protection against EagI digestion. In vitro methylation experiments with purified recombinant protein demonstrated that Z2389 is capable of methylating NotI and EagI sites. Sequencing of bisulfite-treated DNA indicated that the methylation occurred at the first cytosine residue of the NotI recognition sequence, whereas EagI sites remained unmethylated or were methylated at the first cytosine residue. Thus, z2389 encodes a DNA cytosine methyltransferase that confers full protection to NotI sites.
International journal of medical microbiology: IJMM 12/2009; 300(5):296-303. · 4.54 Impact Factor