A total of 173 isolates of S. typhi identified by PCR were characterized by antibiogram profile, MIC determination, plasmid profile and PFGE analysis. 36% of the isolates (63) were found to be resistant to one or more antibiotics. Of these 20% (35) were resistant to Chloramphenicol (C) and Trimethoprim Sulphamethoxazol (Tm Su) and also 4 isolates were resistant to amoxycillin (Ax)/gentamycin (Gycefotaxime (Cx) in addition to C and Tm Su. Higher MICs to Tm Su and Ciprofloxacin.were demonstrated using E-strips (Biodisk). Isolates resistant to C and Tm Su had MIC higher than 32 and 4/176 μg/ml respectively. 3 strains from moderately sensitive group and 2 from sensitive group against Ciprofloxacin showed MICs in the range of 0.5 to 1.5 μg/ml which is higher than 0.25 μg/ml reported so far from India. 36 of these strains were phage typed and most of them belonged to phage group EI (17) and (A3). One isolate was in phage group E, while 11 isolates were untypeable and 3 were Vi negative. Most of the resistant strains were in the phage type ET. Representative strains (both sensitive & resistant) were screened for the presence of plasmids in the range of 4-55 kb were present in most of the resistant as well as sensitive strains while plasmids of 90-180 kb were present in exclusively MDR strains. Pulsed-Field Gel Electrophoresis analysis of 20 (both sensitive & resistant) isolates showed heterogeneity in PFGE patterns among drug sensitive strains while homogeneity among MDR strains except in one case. Comparative analysis of PFGE patterns suggested that considerable genetic diversity exists among Salmonella strains.
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