Susceptibility of enterococcal isolates from Riyadh city hospitals to some antimicrobial agents

A total of 138 clinical enterococcal isolates were collected from three major hospitals in Riyadh city, namely King Khalid University Hospitals [KKUH, 59]. King Faisal Specialist Hospital and Research Center [KFSH and RC, 25] and King Fahad National Guard Hospital [KFNGH, 54]. The identity of the genus was checked and the isolates were identified to the species level to E. faecalis [108], E. faecium [26] and other Enterococcus species [4]. Using agar disk diffusion method, the isolates demonstrated high susceptibility to ampicillin [99.3%], sulfamethoxa.zole-trimethoprim [95%], vancomycin [89.1%], chloramphenicol [86.2%], and penicillin G [85.5%]. Moderate susceptibility was shown to rifampin [58.7%]. Low susceptibility was expressed to ciprofloxacin [37.7%] and tetracycline [30.4%], whereas very low susceptibility was shown to erythromycin [7.2%]. Except for rifampin which showed higher efficacy against E. faecium, the latter had relatively lower susceptibility to antimicrobials compared with E. faecalis isolates Minimum inhibitory concentration [MIC] data showed that 4 E. faecalis [3.7%] and 12 E. faecium [46.15%] isolates had MIC > 16 micro g/ml for penicillin. Among these, only one E. faecalis isolate and two E. faecium isolates had MICs of 16 micro g/ml for ampicillin. None of the 16 penicillin resistant isolates could be identified as beta-lactamase positive. Three [2.8%] of E. faecalis isolates and 10 [38.5%] of E. faecium isolates with an overall percentage of 9.4% had MICs of vancomycin greater than the breakpoint of resistance [32 micro g/ml]. All these 13 isolates were also resistant to teicoplanin, expressing Van A phenotype. MICs data revealed no susceptible isolates to ciprofloxacin and erythromycin and resistance the rates were 28.2% and 44%, respectively. For these two antimicrobial agents, discrepancy between the results of the two methods with respect to the susceptibility and resistance was evident. The MIC results, confirm the very high susceptibility of the isolates to sulfamethoxazole-trimethoprim combination. The results were discussed in the light of the available literatures and demonstrate the usefulness of ampicillin as a drug of choice and the alarming situation for vancomycin that needs attention

Response of high level gentamicin resistant enterococci to penicillin and gentamicin combination

In the present study the incidence of high level resistance [HLR] to gentamicin [MIC >/= 500 micro g/ml] was determined for 138 clinical enterococcal isolates, representing 108 E. faecalis, 26 E. faecium and 4 other Enterococcus spp. A 28.3% of the isolates, comprising 42.3% of E. faecium and 25.9% of E. faecalis isolates were found to be HLR to gentamicin. A 5% of the isolates were resistant to 2000 micro g/ml of gentamicin, representing one [0.9%] of E.faecalis isolates and 7[23%] of E. faecium isolates. Eight selected isolates were used to evaluate the bactericidal activity of penicillin-gentamicin combination by the time-kill curve method. Bactericidal synergy for the combination was obtained for two E. faecium isolates [No. 16 and 32] whereas a synergistic bacteriostatic activity was observed for a third E. faecium isolate [No.35], despite their resistance to penicillin alone. No synergy was obtained for the other two E.faecalis isolates [No.19 and 32]. No synergy was obtained for the other non-E. faecium isolates. Although penicillin alone was bactericidal, the two E. faecalis isolates [No.2 and 137] did not show synergistic bactericidal activity for the combination, irrespective of the level of resistance to gentamicin [No. 2 is not HLR but 137 is]. For the other Enterococcus raffinosus [isolate], although it was not HLR to gentamicin and being susceptible to penicillin neither bactericidal effect for penicillin nor for the combination was observed