Antimicrobial drug resistance and resistance factor transfer among clinical isolates of salmonellae in Iran.

508 salmonella strains isolated during 1983-1986 in Tehran, Iran from cases of diarrhoea in children less than 5 were tested for sensitivity to 10 antimicrobial drugs and their ability to transfer the resistance determinants. Salmonella typhimurium and S. havana were most common (45.7% and 30.9%, respectively) followed by S. typhi (2.9%) and S. larochelle (2.4%). The antimicrobial agents used were chloramphenicol (C), gentamicin (G), tetracycline (T), ampicillin (A), cephalothin (Cf), trimethoprim-sulfamethoxazole (SXT), kanamycin (K), nalidixic acid (Na), streptomycin (S), and furoxone (F). 91% of the salmonellae isolates contained resistance determinants, of which 89.6% were resistant to more than one agent. Strains resistant to 4-7 drugs comprised 85.6% of the total isolates. Ampicillin resistance was found in 85.4% and nalidixic acid in 2.7%. 58 different patterns of resistance to the antimicrobial agents used were observed, of which C/T/A/SXT/K/S and C/T/A/SXT/K/S/Cf were the most frequently encountered. 71.9% of the resistant strains contained transferable resistance factors and S. typhimurium had the highest rate of transfer (80.8%). Resistance to chloramphenicol had the highest rate of transfer among the agents used (77.4%) and streptomycin the lowest (20.0%). The pattern most frequently transferred was C/T/A/SXT/K (41.9%).