Serovars, Antimicrobial Resistance and Conjugative R Plasmids of Salmonella Isolated from Human During the Period of 1966-1986 in Tokyo

Abstract

We examined 4, 739 isolates of Salmonella isolated from patients with gastroenteritis during the period of 1966-1986 in Tokyo for the incidences of serovars, antibiotic resistance and conjugative R plasmids. The period of study was divided into three: 1966-73 (early period), 1974-79 (middle period), and 1980-86 (late period). The predominant serovars were S. typhimurium (34.3%), Infantis (5.6%), Panama (4.9%) in the middle period, S. typhimurium (31.7%), Paratyphi B (9.4%), Litchfield (7.3%) in the late period. These results were consistent with serovars of isolates from healthy citizens. The frequency of resistant isolates was as high as 86.9% in the early period, mostly streptomycin (SM)-and tetracycline (TC)-resistant isolates, but decreased significantly in the middle and the late periods, to 53.3 and 39.4%, respectively. The percentages of ampicillin (ABPC)-, chloramphenicol (CP)-, and kanamycin (KM)-resistant isolates increased in the late period. Strains carrying conjugative R plasmids were isolated as frequently as 57.8% of the total isolates in 1973, but as less frequently as 6.7% in 1981 indicating that the rate was roughly proportional to the incidence of the drug resistant isolates. The rate, however, increased gradually after 1981. The predominant resistance pattern of the R plasmids was TC-resistance in the early period, gradually changed into multiple and finally to AP-, CP-, KM-, SM-, TC-and sulfonamides-resistance in the late period.