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RESISTANCE PROFILE OF Bacteroides fragilis STRAINS FROM DIFFERENT
SOURCES
Souza, W.G.S., Silveira, A.P.M., Domingues, R.M.C.P. & Ferreira*, M.C.S.
Instituto de Microbiologia Prof. Paulo de Góes - UFRJ - Rio de Janeiro, RJ,
Brasil
The epidemiology of antimicrobial resistance of clinical isolates and human intestinal specimens of Bacteroides fragilis , seems to have assumed great importance in the last few years since this micro-organism, like other components of B. fragilis group, can be responsible for resistance determinants spreading. The endogenous origin of B. fragilis and their possible role in exogenous infections, justify the determination of antimicrobial sensibility of human intestinal specimens and polluted aquatic environment strains. So, the purpose of this study was to determine the antimicrobial resistance profile of
38 clinical B. fragilis isolates in the eighties and nineties and also 8 fecal and 10 polluted aquatic environment B. fragilis strains. The susceptibilities tests were performed by E test (AB Biodisk) to penicillin (PG), cefoxitin (FX), imipenem (IP), meropenem (MP), clindamycin (CM), chloramphenicol (CL) and metronidazole (MZ) using the breakpoints established by the NCCLS
(1993) in Wilkins-Chalgren agar enriched with 5% sheep blood. The following values of MIC 50 and MIC 90 were observed for clinical isolates: in the eighties PG 12 and 256, FX 4 and 8, IP 0,047 and 0,125, MP 0,094 and 0,19,
CM 1 and 4, CL 3 and 4, MZ 0,5 and 1,5. Yet in the nineties we could observe:
PG 6 and 12, FX 4 and 12, IP 0,032 and 0,094, MP 0,094 and 0,125, CM 1,5 and 8, CL 3 and 4, MZ 0,5 and 2. So, the resistance to PG showed a high level as we expected in the eighties (92,86%) and also in the nineties (88,46%), although the MIC 90 decreased from 256 to 12. The analysis of MIC 90 deserves special attention by showing the potentiality of the resistance level increase to CM and FX since from one decade to another the values changed from 4 to 8 mg/ml and 8 to 12 mg/ml, respectively. Such analysis could also demonstrate that the susceptibility profile to metronidazole, chloramphenicol, imipenem and meropenem still remains stable. All human intestinal and polluted aquatic environment strains were resistant to penicillin and susceptible to cefoxitin, imipenem, chloranpheniocol and metronidazole. A strain isolated of polluted aquatic environmet showed a MIC of 6mg/ml to meropenem.
Grants: CNPq, CEPG, FUJB, PRONEX and FINEB-BID

The epidemiology of antimicrobial resistance of clinical isolates and human intestinal specimens of
Bacteroides fragilis seems, in the last years has assumed great importance since this micro- organism, like the other components of B. fragilis group, can be responsible for resistance

determinants spreading. The purpose of this study was to obtain the antimicrobial resistance profile of 48 clinical and faecal B. fragilis strains isolated in the eighties and nineties. The susceptibilities tests were performed by the E test to penicillin-PG, cefoxitin-FX, imipenem-IP, meropenem-MP, clindamycin-CM, chloranfenicol-CL and metronidazole-MZ (AB Biodisk) using the breakpoints established by the National Committee for Clinical Laboratory Standards (NCCLS,
1993) in
Wilkins-Chalgren enriched with 5% blood sheep. The following values of MIC50 and
MIC90 were observed for clinical isolates: in the eighties PG 12, 256; FX 4, 8; IP 0,047,
0,125; MP 0,094, 0,19;
CM 1,4; CL 3,4 and MZ 0,5, 1,5. Yet in the nineties we could observe: PG 6,12;
FX 4,12; IP
0,032, 0,094; MP 0,094, 0,125; CM 1,5, 8; CL 3,4 and 0,5, 2. So, the resistance to PG showed high level as we expected in the eighties (92,86%) and also in the nineties
(88,46%). The analysis of MIC90 deserve special attention by showing the potentiality of the resistance level increase to
CM and FX since from one decade to another the values changed from 4 to 8 mg/ml and 8 to 12 mg/ml, respectively. Such analysis could also demonstrate the susceptibility profile to metronidazole, chloranfenicol, imipenem and meropenem stillremainstable.
ENGLISH SUMMARY
The necessity for recording the changes in the susceptibility profile among anaerobes strains, mainly Bacteroides fragilis, a potential responsible for gene of resistance spreading raise objections in the aspect of the methodology. We decide to evaluate two methods: disk elution and E test, both against agar dilution (reference test) in 19 strains isolated from different clinical sources, using for all

antibiotics the breakpoints established by NCCLS
(1993). We could observe the following correlation percentage between disk elution and agar dilution:
66,7% cefoxitina; 73,7% clindamycin; 61,0% chloranfenicol; 84,0% penicillin and 89,5% metronidazol. In relation to E test compared with agar dilution we could find: 93,75% cefoxitin;
73,7% clindamycin; 55,6% chloranfenicol; 94,7% penicillin and 100% metronidazol. Although the disk elution was a reasonable option in anaerobe susceptibility assay, E test seems to offer many advantages to B. fragilis susceptibility since good correlation was found in regard to reference method - agar dilution, however, the cost limits the regular application.