ABSTRACT
The Gram-positive cocci (GPC), Staphylococcus aureus, Streptococcus pneumoniae, Enterococcus faecalis and Enterococcus faecium, have become important causes of community and nosocomial-acquired infections. The prevalence of multiple resistant isolates to standard antimicrobial drugs has significantly increased over the past decades. Few prospective studies have been performed in Puerto Rico (PR) concerning the GPC antimicrobial susceptibilities pattern. The purpose of this study was to evaluate the in vitro susceptibility of GPC clinical isolates from PR to selected standard antibiotics and to the new antimicrobial agents, linezolid (LZ), quinupristin/dalfopristin (Q/D) and gemifloxacin (GM). The in vitro susceptibility utilizing disk diffusion and Etest methods to selected antibiotics was determined for a total of 429 isolates obtained during a period of 5 months from the Puerto Rico Medical Center Bacteriology Laboratory. The distribution of GPC collected was as follows: 213 S. aureus isolates, 162 E. faecalis, 16 E. faecium and 38 S. pneumoniae. The results of the susceptibility test demonstrated: 1) that in S. aureus, 100 per cent of the isolates were susceptible to vancomycin (VAN), LZ and Q/D; 93 per cent to GM; and 61 per cent to methicillin/oxacillin; 2) in S. pneumoniae, 100 per cent were susceptible to LN and GM; 87 per cent to Q/D; and 53 per cent to penicillin; 3) in E. faecalis, 99 per cent were susceptible to ampicillin; 93 per cent to LZ; 79 per cent to GM; 78.6 per cent to VAN; and 0 per cent to Q/D. Sixty eight and 66 per cent of the E. faecalis isolates were susceptible to gentamicin and streptomycin respectively; and 4) in E. faecium, 100 per cent were susceptible to LZ; 94 per cent to Q/D; 69 per cent to GM; 37.5 per cent to VAN and 20 per cent to ampicillin. In E. faecium isolates, 50 per cent and 31 per cent were susceptible to gentamicin and streptomycin, respectively. Of the vancomycin resistant enterococci, 88.9 per cent and 21 per cent of E. faecium and faecalis showed VanA phenotypic resistance, respectively...