Morphological and Genetic Differences in Two Isogenic Staphylococcus aureus Strains with Decreased Susceptibilities to Vancomycin
AUTOR(ES)
Reipert, Andrea
FONTE
American Society for Microbiology
RESUMO
Many VISA (vancomycin intermediately resistant Staphylococcus aureus) strains are characterized by increased cell wall biosynthesis and decreased cross-linking of the peptide side chains, leading to accumulation of free d-alanyl-d-alanine termini in the peptidoglycan, which act as false target sites for vancomycin. A spontaneous mutant of methicillin-resistant VISA strain SA137/93A (vancomycin MIC [E-test], 8 μg/ml), called SA137/93G, showed increased resistance to vancomycin (MIC [E-test], 12 μg/ml). Analysis of the resistance profile of the mutant revealed a loss of β-lactam resistance with a concomitant increase in resistance to glycopeptides. In both strains, cell wall thickness was 1.4-fold greater than that of control isolates. However, cross-linking of the cell wall was drastically lower in SA137/93A than in SA137/93G. The sensitivity of strain SA137/93G to β-lactams was due to loss of the β-lactamase plasmid and a deletion that comprises 32.5 kb of the methicillin resistance cassette SCCmec, as well as 65.4 kb of chromosomal DNA. A spontaneous mutant of SA137/93G with higher sensitivity to vancomycin displayed a cell wall profile similar, in some respects, to that of an fmhB mutant. Results described here and elsewhere show that the only feature common to all VISA strains is a thickened cell wall, which may play a central role in the vancomycin resistance mechanism.
ACESSO AO ARTIGO
http://www.pubmedcentral.nih.gov/articlerender.fcgi?artid=151770Documentos Relacionados
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