Relation between Salmonella typhimurium biotypes and drug resistance, Teheran, Iran (1962-1973)

According to the procedure of Cordano (1971), the identification of biotypes of 118 strains of Salmonella typhimurium isolated from stools or rectal swabs of patients with sporadic cases of diarrhoea on the Central Plateau during the period 1962-1973 revealed that: From 118 S. typhimurium, 65 (55-1%) were biotype "d", 50 (42-4%) were "a" and three (2-5%) were "b". The predominant biotype was "d", followed by the "a" biotype, and "b" was rarely encountered. Biotype "d" has existed since 1965, and after that date has increased. Biotype "a" existed from the beginning of the study, but has decreased during the period 1962-1973. Sensitivity tests were performed according to Bauer (1966). Biotypes "d" and "a" showed a high degree of resistance to tetracycline, chloramphenicol, streptomycin, triple-sulfa, ampicillin, furazolidone, kanamycin, neomycin, paromomycin, cephalothin and co-trimoxazole. All isolated biotypes "d" were multiple drug-resistant, while some of the strains of biotype "a" were resistant and some sensitive. All three biotypes "b" were sensitive to all drugs examined. Resistance to drugs for biotypes "d" and "a" increased with time. The predominant pattern of resistance for all biotypes was found to be resistance to eight drugs: tetracycline, chloramphenicol, streptomycin, triple-sulfa, ampicillin, kanamycin, neomycin and paromomycin (Tc, Cm, Sm, Su, Am, K, N, Par). Considering the relationship between resistance pattern and biotypes, the predominant pattern in biotype "d" was resistance to eight drugs (Tc, Cm, Sm, Su, Am, K, N, Par) (47-7%), and in biotype "a" was resistance to nine drugs, tetracycline, chloramphenicol, streptomycin, triple-sulfa, ampicillin, furazolidone, kanamycin, neomycin, paromomycin (Tc, Cm, Sm, Su, Am, Fx, K, N, Par) (28%).