Carriage of extended-spectrum β-lactamases in pig farmers is associated with occurrence in pigs

Abstract

Livestock may serve as a reservoir for extended-spectrum β-lactamase-producing Enterobacteriaceae (ESBL-PE). The objectives of this study were to determine the prevalence of carriage with ESBL-PE in pig farmers, family members and employees, and its association with carriage in pigs. Rectal swabs were taken from 2388 pigs (398 pooled samples) on 40 pig farms and faecal samples were obtained from 142 humans living or working on 34 of these farms. Presence of ESBL-PE was determined by selective plating (agar). ESBL genes were analysed by PCR or microarray analysis, and gene sequencing. Genotypes and plasmids were determined by multilocus sequence typing and PCR-based replicon typing for selected isolates. ESBL genes were detected in Escherichia coli from eight humans (6%) (bla<inf>CTX-M-1</inf>, n = 6; bla<inf>TEM-52</inf>, n = 1 and bla<inf>CTX-M-14</inf>, n = 1) on six farms. In 157 pig isolates (107 pooled samples) on 18 farms (45%) ESBL genes were detected (bla<inf>CTX-M-1</inf>, n = 12; bla<inf>TEM-52</inf>, n = 6; and bla<inf>CTX-M-14</inf>, n = 3). Human and pig isolates within the same farm harboured similar ESBL gene types and had identical sequence and plasmid types on two farms (e.g. E. coli ST-453, bla<inf>CTX-M-1</inf>, IncI1), suggesting clonal transmission. For the remaining farms, sequence types, but not plasmid types, differed. Human ESBL carriage was associated with average number of hours working on the farm per week (OR = 1.04, 95% CI 1.02-1.06) and presence of ESBLs in pigs (OR = 12.5, 95% CI 1.4-111.7). Daily exposure to pigs carrying ESBL-PE is associated with ESBL carriage in humans.