| The objective of this study was to determine whether original isolates from hospitalized patients who develop a primary episode of vancomycin susceptible Staphylococcus aureus (VSSA) bacteremia strain are identical from a molecular perspective to subsequent isolates recovered from the same patient. A very small percentage of these patients had developed vancomycin intermediate Staphylococcus aureus (VISA) bacteremia upon reinfection. A total of 40 samples from 15 patients were collected from Mount Sinai Medical Center between 2002 and 2007. The samples were fingerprinted to determine strain relatedness using repetitive sequence based polymerase chain reaction (rep-PCR) technique (DiversiLab System bioMerieux, Inc., Durham, NC). The isolates were separated by a 30 day difference, i.e. those whose date of isolation was >30 days and those <=30 days. Nine out of 15 patients had recurrent infection with the same isolate (H, F, L, M, A, B, J, I and N). Of the 9, only 4 had dates of isolation that were <=30 days. Isolates from the remaining five patients, (F, L, J, I and N), whose date of isolation was >30 days, were identical to their primary isolate upon reinfection. I and N isolates did not show similarity with those of F, L and J. However, there was a great similarity between VISA isolates of patients I and N. Four patients (H, F, L, and M) had a large circulating group of isolates with >=95% similarity. There were two smaller groups, A and B and O and J, that were similar between patients. The remaining six patients (C, K, G, D, O and E) did not show reinfection with the same isolate. Two patients (O and E) were completely different upon reinfection. All 15 patients had in common; a serious debilitating underlying diseases such as: cancer, diabetes, endocardititis or end stage renal disease with hemodialysis. All these conditions coupled with vancomycin therapy made these patients prone to reinfection. As described by Charles, et al., (2004) vancomycin therapy predisposes one to hVISA and VISA. However, in this study, vancomycin therapy did not play a significant role because only a small percentage of the staphylococcal isolates tested positive for increased vancomycin resistance (Table 1). Overall, this study found that a significant number of isolates were molecularly identical to the original vancomycin susceptible strain. Therefore utilizing vancomycin to treat primary Staphylococcus aureus does not seem to play a major role in inducing resistance to vancomycin. |
