Molecular epidemiological analysis of Salmonella enterica serotype Derby infections in Hong Kong

Objectives: We aimed to study the antimicrobial susceptibilities and molecu lar epidemiology of Salmonella enterica serotype Derby, a unique and common salmonella serotype in Hong Kong, Methods: Salmonella Derby strains isolat ed from stools of patients in a large general hospital in Hong Kong from 19 89 to 1994 and From food samples isolated in the Public Health Laboratory w ere randomly selected and investigated for the antimicrobial susceptibiliti es by determining the minimal inhibitory concentrations of 19 antimicrobial agents and their relatedness using plasmid analysis, ribotyping, pulsed-fi eld gel electrophoresis (PFGE) and total DNA fingerprinting, Results: About 50% of the 127 isolates studied were susceptible to all the 19 antibiotics tested, although resistance to tetracycline (49%) and sulfamethoxazole (38 %) was high, Only 12% did not harbour any detectable plasmids, while the re st contained plasmids in 51 profiles, There were two predominant clones, on e comprising of 35% of isolates that could not be pulsotyped because discre te bands were not discernible after PFGE and another comprising 31% of isol ates that could be pulsotyped. The remaining 31% belonged to a variety of t ypes. Conclusions: Approximately 70% of S. Derby belonging to two clones we re endemic in the community, while the remaining isolates belonged to a var iety of types which were probably a result of sporadic infection. The sourc es of human infections were foods, since most isolates from foods also belo nged to the two endemic clones, Typing of S, Derby isolates from other sour ces such as animals or the environment would help elucidate how foods were contaminated, PFGE might not be universally applicable to all salmonella st rains. (C) 2001 The British Infection Society.