Plasmid-mediated resistance to ciprofloxacin and cefotaxime in clinical isolates of Salmonella enterica serotype Enteritidis in Hong Kong.

To characterize the genetic determinants involved in the reduced susceptibility to ciprofloxacin and cefotaxime in Salmonella enterica serotype Enteritidis clinical isolates obtained from four patients in summer 2003 in Hong Kong. Three Salmonella Enteritidis isolates from blood culture and one from stool were collected due to their increased resistance to ciprofloxacin and cefotaxime. PFGE analysis was used to investigate their genetic relatedness. Conjugation experiments were employed to show if the genetic determinants involved were plasmid-mediated. MICs of various antimicrobials were determined by VITEK 2 and Etest. Based on the susceptibility and conjugation experiment results, previously described PCR methods were employed to detect sequences homologous to qnr and bla(CTX-M) suspected to be involved in the reduced susceptibility to ciprofloxacin and cefotaxime, respectively. PFGE analysis showed that the four Salmonella isolates were clonally unrelated. The presence of a qnr-like gene and the CTX-M allele bla(CTX-M-14) on four different transferable plasmids harboured by the four isolates was confirmed. This is the first report of transferable fluoroquinolone resistance due to a new qnr allele, which appeared to be linked to bla(CTX-M-14), in isolates of Salmonella Enteritidis in Hong Kong.