“Emergence of Resistance to Third Generation Cephalosporins (C3G) in Shigella flexneri (Sf) Isolates in Argentina”

M. GALAS; H. A. SAKA; R. MELANO; F. PASTERAN; M. RAPOPORT; H. LOPARDO; M. MARTINEZ; J. MULKI; C. CULASSO; I. MARQUEF; M. TURCO; S. GRENON; A. ROSSI.

Toronto, Canadá

Conferencia; 40th Interscience Conference on Antimicrobial Agents and Chemotherapy (ICAAC); 2000

American Society for Microbiology

During 1997-99, according to WHONET-Argentina Network for antimicrobial susceptibility surveillance (33 institutions), elevated levels of resistance (%) to ampicillin-AM (90%), cotrimoxazole-CO (68% and chloramphenicol-CH (72%) were observed among Sf isolates (n=3334). Since first detection of TGC resistance in Argentina in this genus in 1997 to date, such resistance was found in 7 Sf. In order to estimate the TGC resistance mechanisms, antimicrobial susceptibility (diffusion and agar dilution, according to NCCLS), isoelectric focusing (IEF), PCR determinations and conjugation assays were performed. Strain 3260 3127 3186 3244 Hpp22 Hp63 20091 State Cordoba Bs As Bs As Salta Misiones Chaco Bs As MIC µg/mL FT 1 1 32 64 32 512 128 FC .015 .015 .03 .06 .03 < .03 .03 CA .5 2 2 4 2 4 4 CC < .03 < .03 .06 .12 .06 < .03 .12 AM 512 1024 > 1024 > 1024 > 1024  1024 > 1024 CH 64 1 1 32 128 64 > 128 CO 512 .12 512 512 512 256 512 IEF1 7.6 5.4 + 7.6 5.4 + 7.9 5.4 + 7.9 5.4 + 7.9 5.4 + 7.9 5.4 + 8.4 5.4 + 7.9 PCR posotive SHV TEM; SHV TEM; CTX-M TEM; CTX-M TEM; CTX-M TEM; CTX-M TEM; CTX-M TEM; CTX-M  FT: cefotaxime; FC: FT + clavulanate (4 µg/mL); CA: ceftazidime; CC: CA + clavulanate (4 µg/mL).1 Underlined IEF indicates activity over TGC. Nor ciprofloxacin, nitrofurantoin neither fosfomycin resistance was detected. Resistance to TGC was unequivocal in 5/7 strains, with FT more affected than CA. Among these strains the ESBL (n) estimated were CTX-M-2 (4) and CTX.M-derived (pI=8.4) (1). In the remaining 2/7 strains, both TGC were poorly affected and SHV2 was estimated. Current NCCLS breakpoint for FT and CA failed to detect strains with SHV2, by both, diffusion and dilution methods. In all cases the resistance could be transferred. Emergence of TGC resistance could be the result of the use of these drugs against multi-resistant strains during the last years. Antimicrobial susceptibility surveillance of Sf is mandatory.