STUDY OF MINIMAL INHIBITORY CONCENTRATIONS AND MULTIPLE DRUG RESISTANCE PLASMIDS IN SALMONELLA TYPHI.

S. typhi isolated from blood cultures were tested for minimal inhibitory concentrations of antimicrobial drugs using an simple easily fabricated multiple inoculator. Multiple drug resistant S. typhi were inhibited by high concentrations of ampicillin, sulphamethoxazole, trimethoprim and chloramphenicol (> 128 mg/L) suggestive of R factor mediated resistance. They showed presence of a single large plasmid with molecular weight ranging from 85 to 110 megadaltons. Sensitive S. typhi isolates were inhibited by lower concentrations of antimicrobial and did not show evidence of any plasmid. All isolates were equally sensitive to extremely low concentrations of ceftazidime, cefuroxime, ciprofloxacin, norfloxacin and gentamicin (< 0.5 mg/L).