Emergence of plasmid-mediated quinolone resistance genes in Enterobacteriaceae isolated from chickens in China.

increase in the number of different qnr-positive serotypes was observed in 2007, although the total number of positive isolates was evenly distributed between 2003 and 2007 (Table 1). The qnrS1 variant was highly prevalent in Salmonella Corvallis supporting the results recently published from Denmark, the Netherlands and the UK. 2,6,8 The Danish study included a restricted set of Salmonella Corvallis isolates originating from Thailand and Denmark from different hosts. 2 Most isolates were typed using PFGE and a high similarity between isolates within each serotype positive for qnr genes was observed in this study (data not shown). The Salmonella Enteritidis isolates had identical PFGE profiles and the 27 Salmonella Corvallis isolates were divided between 11 different but closely related PFGE types. Four PFGE types included 20 of the Salmonella Corvallis isolates, and the remaining PFGE types were represented by one isolate each and differed from other PFGE types by one small band below 33 kb (data not shown). Seven of the nine Salmonella Typhimurium were divided between two closely related PFGE types, and the remaining two isolates had two different profiles that differed by very few bands from the other PFGE types. Salmonella Typhimurium isolates were furthermore typed by multilocus variable number tandem repeat analysis (MLVA). 9 All isolates positive for qnr genes differed at only one locus, the STTR5 locus. Loci STTR6 and STTR10 were not present, whereas STTR3 and STTR9 had fragment sizes of 516 and 162 bp, respectively (data not shown). This is in concordance with data from the UK and indicates a close relationship between qnrS1-positive Salmonella Typhimurium isolated from humans in Denmark and the UK. 8 The Far East has been proposed as the common origin since Salmonella Typhimurium from the UK with this MLVA type were isolated from tourists returning from Asia. 8 This is supported by our study, since 44% of Danish qnrS-positive Salmonella Typhimurium were isolated from tourists returning from Asia and travel history was unknown for the remaining patients. The most predominant co-resistance among all qnr-positive isolates was sulphonamide, streptomycin and tetracycline (Table 1). None of the isolates had the extended-spectrum b-lactamase (ESBL) phenotype, but one isolate had the AmpC phenotype as detected by the combination disc method. In conclusion, we found that qnr genes were present in 66% of Salmonella isolates selected on the basis of decreased susceptibility to ciprofloxacin and low-level resistance to nalidixic acid. Our study supports recent …