The role of horizontal gene transfer in the dissemination of extended-spectrum beta-lactamase–producing Escherichia coli and Klebsiella pneumoniae isolates in an endemic setting

Abstract

The contribution of horizontal gene transmission (HGT) in the emergence and spread of extended-spectrum beta-lactamase (ESBL)–producing Gram-negative bacteria during periods of endemicity is unclear. Over a 12-month period, rectal colonization with SHV-5– and SHV-12–producing Escherichia coli and Klebsiella pneumoniae was quantified among a cohort of residents in a long-term care facility. Demographic and clinical data were collected on colonized residents. Transferability of SHV-encoding plasmids and pulsed-field gel electrophoresis were performed to quantify the contribution of HGT and cross-transmission, respectively. A total of 25 (12%) of 214 enrolled patients were colonized with 11 SHV-5– and 17 SVH-12–producing E. coli and K. pneumoniae. Clonally related isolates were detected among multiple residents residing on the same and different wards. Among 12 clonally distinct isolates, HGT of SHV-5– and SHV-12–encoding plasmids was identified among 6 (50%) isolates. HGT among clonally distinct strains contributes to the transmission dynamics of these ESBL-producing Gram-negative bacteria and should be considered when evaluating the spread of these pathogens.