Analysis of gyrA mutations related to quinolone resistance in Escherichia coli isolates originating from pet, human, vegetable and ice in Bangkok and vicinity.

Escherichia coli was used to investigate quinolone resistance and mutations in gyrA gene of E. coli isolated from pet (dog and cat), human (pet's owner), vegetable and edible ice in Bangkok and vicinity. Susceptibility test for nalidixic acid (NA) showed similar percent resistance among the sample sources but a lower ciprofloxacin (CIP) resistance was found particularly in human source. Mutations within quinolone resistance determining region of gyrA gene analyzed using non-radioactive single-strand conformation polymorphism (SSCP) and sequencing showed 10 different SSCP patterns. E. coli isolates from pet, vegetable and ice showed more variety of patterns than strains isolated from human. Four out of 10 SSCP patterns were identified as having mutations in amino acids positions 83 (Ser to Leu) and position 87 (Asp to Asn). These mutations were observed only in NA-resistant strains and combined mutations were observed only in E. coli isolated from humans and pets. As only 24% of NA- and CIP-resistant E coli isolates contained gyrA mutations, other quinolone resistant mechanisms may be involved. Nevertheless, gyrA mutations may be used to monitor nalidixid acid resistance in E. coli.

Antimicrobial susceptibility patterns and phage types of Salmonella typhi from Vietnam.

A retrospective study of the patterns of antimicrobial susceptibility and phage types of 111 Salmonella typhi strains isolated in 1996 from Vietnam was carried out. The strains were tested for susceptibility to chloramphenicol, ampicillin, tetracycline, trimethoprim-sulfamethoxazole, nalidixic acid, ceftazidime, ceftriaxone and ciprofloxacin. Simultaneous resistance to chloramphenicol, ampicillin, tetracycline and trimethoprim-sulfamethoxazole were present in 84 strains (75.7%). Nalidixic acid resistance was only observed in 2 multidrug-resistant strains (1.8%). Twenty-one strains (18.9%) were completely susceptible to all drugs tested. All 111 strains were susceptible to ceftazidime, ceftriaxone and cipropfloxacin. The MIC values for chloramphenicol, ampicillin and trimethoprim-sulfamethoxazole corresponded with the results by disk diffusion method. On Vi phage-typing, 5 different phage types (28, A, D1, E1 and M1) were found in 12 strains (10.8%). However, most S. typhi strains were indistinguishable by this typing technique because they were degraded Vi-positive or untypeable Vi-positive strains (35.1% and 54.1%, respectively). There were no correlations between antimicrobial resistance patterns and phage types in the tested S. typhi strains in this study.