Detection and epidemiology of plasmid-mediated AmpC ß-lactamase producing Escherichia coli in two Irish tertiary care hospitals.

ABSTRACT

This study determined the prevalence and distribution of plasmid-mediated AmpC (pAmpC) ß-lactamases in Irish Escherichia coli isolates. Clinical E. coli isolates (n=95) that were intermediate or resistant to cefoxitin and/or flagged by VITEK® 2 as potential AmpC-producers underwent confirmation using a MASTDISCS™ ESBL and AmpC Detection Kit. Multiplex PCR capable of detecting family-specific plasmid ampC genes was performed to detect the presence of these genes. Five PCR-negative isolates were selected for promoter analysis. PFGE and MLST were performed on E. coli isolates that harboured a plasmid ampC gene to determine their clonal relatedness. Plasmid ampC genes were detected in 19% (18/95) of phenotypic AmpC producing E. coli isolates. The CIT group was the most common plasmid family type (n=14); DHA (n=3) and ACC (n=1) groups were also detected. Promoter analysis showed that four isolates had multiple point mutations and one had a 1 bp insertion in the -10 box. PFGE demonstrated a polyclonal pattern for E. coli isolates. Furthermore, with the exception of two isolates with an identical sequence type (ST720), MLST analysis revealed that these isolates were not clonally related. This study revealed that there was a marked prevalence of pAmpC E. coli among phenotypic AmpC producing E. coli isolates but no evidence of cross-transmission of a single strain. Establishing the prevalence and clonality of these organisms is important in order to implement evidence-based infection control measures that reduce the spread of pAmpC ß-lactamase resistance in the hospital environment.