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2000, Cilt 30, Sayı 3-4, Sayfa(lar) 077-084
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Species Level Identification and Investigation of Resistance to Vancomycin and Some Other Antibiotics in Enterococcus Strains
Seyed Reza Moaddab, Kurtuluş Töreci
İstanbul Üniversitesi, İstanbul Tıp Fakültesi, Mikrobiyoloji ve Klinik Mikrobiyoloji Anabilim Dalı, İstanbul
Keywords: Enterococcus, vancomycin, antibiotic resistance

Five hundred and one stool specimens from 316 inpatients, 143 of whom had received vancomycin and 173 had not, were collected in Stuart transport medium and inoculated onto Slanetz-Bartley Enterococcus agar with and without vancomycin within 24 hours. 198 enterococcus spp. were isolated from stool culture. One hundred strains isolated from various clinical specimens as etiological agents in the laboratories of the Department of Microbiology and Clinical Microbiology were added to 198 stool isolates after confirmation of their identifications.

The identifications of these 298 strains down to the species level were performed by classical methods and by API Rapid ID 32 Strep when necessary. Vancomycin susceptibility of these strains was investigated by agar dilution method according to the NCCLS recommendations, the susceptibility to vancomycin and some other antibiotics by the disk diffusion method, highlevel resistance to gentamicin, streptomycin, penicillin and ampicillin by the growth on agar containing specific concentrations of these antibiotics, and beta-lactamase production by nitrocefin sticks.

Out of 298 Enterococcus strains, 176 were identified as E.faecalis, 96 as E.faecium, 15 as E.avium, 9 as E.raffinosus, 1 as E.durans and 1 as E.hirae.

All of 100 strains isolated from clinical specimens were found susceptible to vancomycin (MIC ≤ 4μg/ml). Eleven of the 198 strains isolated from stools of inpatients were found to be moderately susceptible to vancomycin (MIC: 8 μg/ml for 5 and 16 μg/ml for 6 strains) and the rest of these strains were found to be susceptible (MIC ≤ 4μg/ml). MIC50 and MIC90 were 1 μg/ml and 2 μg/ml, respectively. One of the vancomycin-moderately susceptible strains was E.faecalis and the remaining 10 strains were E.faecium. All vancomycin-moderately susceptible isolates were isolated in both media with or without vancomycin. These results were interpreted as addition of vancomycin to isolation medium would not increase the isolation rate of vancomycin-moderately sensitive or vancomycin-resistant strains. It was also observed that vancomycin usage in our hospital did not result in the intestinal colonization of vancomycin-resistant enterococci.

By the disk diffusion tests, 89 of 298 strains were found to be resistant to erithromycin, 83 to penicillin, 67 to ampicillin, 25 to ciprofloxacin, 20 to norfloxacin and 8 to nitrofurantoin. No resistance was observed to vancomycin or teicoplanin. Out of the 11 strains which were found as vancomycin-moderately susceptible by the agar dilution method, 6 were found to be moderately susceptible and 5 susceptible to vancomycin by the disk diffusion tests.

Fifty four strains exhibited high-level resistance to streptomycin (2000 μg/ml) and 39 strains exhibited highlevel resistance to gentamicin (500 μg/ml). Twenty one of these strains had high-level resistance to both aminoglycosides. Twenty eight strains were resistant to 100 μg/ml, and 24 of them to 200 μg/ml penicillin. Thirty three strains were resistant to 50 μg/ml, and 22 of them to 100 μg/ml ampicillin. Thirteen strains had high-level resistance to at least one aminoglycoside and one betalactam antibiotic.

No beta-lactamase production was detected in 298 strains.

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