Prevalence of integrons in antibiotic-resistant Salmonella spp. in Hong Kong.

Of the 834 Salmonella spp. isolates collected from 2002 to 2004 in the New Territories East Cluster hospitals in Hong Kong, 21% were resistant to 3-14 antibiotics and 30% were resistant to nalidixic acid with reduced susceptibility to ciprofloxacin. A class 1 integron was present in 105 (13%) isolates, of which more than 50% were Salmonella Typhimurium. Class 2 or 3 integrons were not detected in any of the isolates. DNA sequencing showed that there were 16 different integrons, of which the most common, detected in 40% of isolates, was dfrA12-orfF-aadA2. Almost half of the isolates had lost the qacEdelta1-sulI 3' conserved segment (3'CS). Four isolates had an orf513 gene downstream of the 3'CS. There was probably one predominant clone among each heterogeneous population of integron-harboring S. Typhimurium, S. Virchow, and S. Derby isolates in our community. This is the first thorough study of the prevalence and characteristics of integrons in Salmonella isolates in Hong Kong and the first to report a class 1 integron in S. Birkenhead, S. Landwasser, S. Litchfield, and S. Reading.