Development of reduced vancomycin susceptibility in methicillin-susceptible Staphylococcus aureus.
BACKGROUND
Most cases of reduced vancomycin susceptibility in Staphylococcus aureus reported in the literature have been in methicillin-resistant strains. We report the development of reduced vancomycin susceptibility in a series of clonally related, methicillin-susceptible S. aureus (MSSA) clinical isolates. This isogenic series permitted us to determine whether the evolution of reduced vancomycin susceptibility in MSSA is similar to that seen in MRSA.


METHODS
Differences in vancomycin population analysis profiles; chemical autolysis; vancomycin, oxacillin, and daptomycin minimum inhibitory concentrations; and bactericidal activities were examined.


RESULTS
Progressive vancomycin resistance correlated with increasing daptomycin nonsusceptibility. Chemical autolysis and the bactericidal activity of vancomycin, oxacillin, and daptomycin were reduced in the final, vancomycin-intermediate S. aureus isolate, compared with the vancomycin-susceptible MSSA progenitor.


CONCLUSIONS
Clinicians should recognize that reduced vancomycin susceptibility can occur in S. aureus irrespective of background methicillin susceptibility and that development of intermediate vancomycin susceptibility in MSSA may result in increased tolerance to several classes of anti-staphylococcal antibiotics.
Pillai
Satish K
SK
Division of Infectious Diseases, Beth Israel Deaconess Medical Center, and Harvard Medical School, Boston, Massachusetts 02215, USA. spillai@bidmc.harvard.edu
Wennersten
Christine
C
Venkataraman
Lata
L
Eliopoulos
George M
GM
Moellering
Robert C
RC
Karchmer
Adolf W
AW
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001433:Bacteriolysis; D015169:Colony Count, Microbial; D017576:Daptomycin / Q000494:pharmacology; D006801:Humans; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability; D017830:Octoxynol / Q000633:toxicity; D010068:Oxacillin / Q000494:pharmacology; D013203:Staphylococcal Infections / Q000382:microbiology; D013211:Staphylococcus aureus / Q000145:classification / Q000187:drug effects* / Q000302:isolation & purification; D014640:Vancomycin / Q000494:pharmacology*; D020713:Vancomycin Resistance
D000900:Anti-Bacterial Agents; D014640:Vancomycin; D017830:Octoxynol; D017576:Daptomycin; D010068:Oxacillin