Multilocus sequence typing and bla(ESBL) characterization of extended-spectrum beta-lactamase-producing Escherichia coli isolated from healthy humans and swine in Northern Thailand

PURPOSE: Here, we investigated the genetic relationships and characteristics of extended- spectrum beta-lactamase-producing Escherichia coli (ESBL-E. coli) isolates from healthy hosts, humans in the community and swine among the livestock of Amphor Mueang, Lamphun Province, Thailand. PATIENTS AND METHODS: Four hundred and nine rectal swabs were collected from healthy people and swine. A total of 212 ESBL-E. coli was isolated and phenotypically confirmed by a combination disk method. Putative ESBL-encoding genes, including bla(CTX-M), bla(TEM), and bla(SHV), were examined by multiplex-PCR. Randomly selected 42 ESBL-E. coli isolates were whole genome sequenced to characterize the ESBL-encoding genes and identify additional antimicrobial resistance genes. The genetic relatedness of 212 ESBL-E. coli was investigated by multilocus sequence typing. RESULTS: Overall, bla(CTX-M) was the dominant ESBL-encoding gene found in 95.75% of the isolates, followed by bla(TEM) (60.85%) and bla(SHV) (2.40%). While bla(CTX-M-55) was the most common bla(ESBL) subgroup found in this study. Whole genome sequencing showed a total of 15 different antimicrobial resistance genes other than bla(ESBL), including sul, qnr, aph(3ʹ)-Ia, among the selected 42 ESBL-E. coli isolates. Over half of the ESBL-E. coli (56.60%) carried bla(CTX-M) co-existing with bla(TEM). The most common sequence types (STs) identified from human isolates were ST131, ST101, and ST70 while those isolated from swine were ST10, ST48, and ST131. ST131 strains carrying bla(CTX-M) were the major isolated ESBL-E. coli strains, supporting a previous study that considered this strain truly pathogenic. Noticeably, 66.51% of ESBL-E. coli strains shared 19 identical STs, including a host-restricted ST131 between humans and swine, suggesting that transmission between these two hosts might be possible. CONCLUSION: Proof of a direct transfer of ESBL-E. coli from animals to humans, or vice versa, is required for further elucidation. The ESBL-E. coli isolated from both types of healthy hosts may serve as a reservoir for community-acquired antimicrobial resistance.