Rising incidence of Staphylococcus aureus with reduced susceptibility to vancomycin and susceptibility to antibiotics: a global analysis 2004–2009

In vitro susceptibility of Staphylococcus aureus and Staphylococcus epidermidis isolated from prosthetic joint infections

“…7 Both MRSA and MRSE strains are also usually resistant to other antibiotics, and although vancomycin remains the elective therapy for these cases, its efficacy has been declining over the last few years. 8,9 For this reason, other antibiotics have recently been considered as alternatives to vancomycin. [10][11][12][13][14][15] Despite these facts, antimicrobial susceptibility remains extremely variable among these microorganisms, making it necessary to perform individual susceptibility studies for each strain to select the best antibiotic combination for treatment.…”

Comparison of Commercial Antimicrobial Susceptibility Test Methods for Testing of Staphylococcus aureus and Enterococci against Vancomycin, Daptomycin, and Linezolid

“…In 2006, the Clinical and Laboratories Standards Institute (CLSI) adjusted the susceptibility and resistance breakpoints for vancomycin MICs against S. aureus: the breakpoint for susceptible (S) results was lowered from Յ4 g/ml to Յ2 g/ml, the breakpoint for intermediate (I) results was changed from 8 to 16 g/ml to 4 to 8 g/ml, and the breakpoint for resistant (R) results was changed from Ն32 g/ml to Ն16 g/ml (7,8). However, clinical failures with vancomycin treatment for MRSA bacteremia still occur with isolates having MICs within the susceptible range (9)(10)(11)(12). Recognized clinical treatment failure with vancomycin has prompted the use of high-dose vancomycin treatment regimens and the use of alternate antimicrobial agents (12)(13)(14)(15).…”

Is Vancomycin MIC “Creep” Method Dependent? Analysis of Methicillin-Resistant Staphylococcus aureus Susceptibility Trends in Blood Isolates from North East Scotland from 2006 to 2010

“…This has been demonstrated by the emergence of strains of intermediate resistance, i.e., hetero-VISA (vancomycin-intermediate S. aureus) and VISA strains, and of increasing proportions of MRSA isolates with high MICs within the susceptible range, the so-called vancomycin MIC "creep" (13,17,28,30). The creep phenomenon has not been reported consistently (7,13,28), but it is concerning because vancomycin still remains the cornerstone of therapy for many serious MRSA infections (7,14).…”

“…Studies evaluating whether an in vitro vancomycin MIC can be used to predict clinical success or failure have not been able to give definitive answers (7,15,26). Equally, since outcomes often remain poor despite a vancomycin MIC in the susceptible range (MIC of Յ2 mg/liter), there has been a suggestion of lowering the clinical breakpoints further (5), and a shift in MIC population distributions may have important implications for the incidence of treatment failure beyond individual risk assessment.…”

“…In many of the reported studies looking at in vitro susceptibility data, MIC testing was performed retrospectively on isolates retrieved from storage, not at the time of isolation of the organism, and often this is not made explicitly clear (1,7,8,10,12,13,15,16,18,19,25,27,28,30,31,32,34,35). It has been demonstrated that certain organisms can become more susceptible when stored (3,22), and it is possible that this phenomenon, together with differing methodologies, may explain some of the conflicting results in the literature (9).…”