Co-infection With Chromosomally-Located bla CTX-M-14 and Plasmid-Encoding bla CTX-M-15 in Pathogenic Escherichia coli in the Republic of Korea

Jungsun Park; Eunkyung Shin; Ae Kyung Park; Soojin Kim; Hyun Ju Jeong; Jin Seok Kim; Young-Hee Jin; Nan Joo Park; Jeong-Hoon Chun; Kyujam Hwang; Kwang Jun Lee; Junyoung Kim

doi:10.3389/fmicb.2020.545591

Co-infection With Chromosomally-Located bla _CTX-M-14 and Plasmid-Encoding bla _CTX-M-15 in Pathogenic Escherichia coli in the Republic of Korea

Front Microbiol. 2020 Nov 11:11:545591. doi: 10.3389/fmicb.2020.545591. eCollection 2020.

Authors

Affiliations

¹ Division of Bacterial Diseases, Center for Laboratory Control of Infectious Diseases, Korea Centers for Disease Control and Prevention, Chungju, South Korea.
² Infectious Diseases Team, Seoul Metropolitan Government Research Institute of Public Health and Environment, Seoul, South Korea.
³ Microbiology Team, Gyeonggi-do Institute of Health and Environment, Suwon, South Korea.
⁴ Division of Antimicrobial Resistance, National Institute of Health, Center for Infectious Diseases Research, Centers for Disease Control and Prevention, Chungcheongbuk-do, South Korea.

Abstract

The emergence of third-generation cephalosporin resistance in Escherichia coli is increasing at an alarming rate in many countries. Thus, the aim of this study was to analyze co-infecting bla _CTX-M-producing pathogenic E. coli isolates linked to three school outbreaks. Among 66 E. coli isolates, 44 were identified as ETEC O25, an ETEC isolate serotype was O2, and the other 21 were confirmed as EAEC O44. Interestingly, six patients were co-infected with EAEC O44 and ETEC O25. For these isolates, molecular analysis [antibiotic susceptibility testing, identification of the β-lactamase gene, multilocus sequence typing (MLST), and pulsed-field gel electrophoresis (PFGE)] was performed for further characterization. In addition, the transmission capacity of bla _CTX-M genes was examined by conjugation experiments. Whole-genome sequencing (WGS) was performed on representative EAEC O44 and ETEC O25 isolates associated with co-infection and single-infection. All isolates were resistant to cefotaxime and ceftriaxone. All EAEC isolates carried the bla _CTX-M-14 gene and all ETEC isolates the bla _CTX-M-15 gene, as detected by multiplex PCR and sequencing analysis. Sequence type and PFGE results indicated three different patterns depending on the O serotype. WGS results of representative isolates revealed that the ETEC O25 strains harbored bla _CTX-M-15 located on IncK plasmids associated with the Δbla _TEM-bla _CTX-M-15-orf477 transposon. The representative EAEC O44 isolates carried bla _CTX-M-14 on the chromosome, which was surrounded by the ISEcp1-bla _CTX-M-14-IS903 transposon. To the best of our knowledge, this is the first report of co-infection with chromosomally located bla _CTX-M-14 and plasmid-encoding bla _CTX-M-15 in pathogenic E. coli. Our findings indicate that resistance genes in clinical isolates can spread through concurrent combinations of chromosomes and plasmids.

Keywords: CTX-M; chromosomally-located blaCTX-M-14; co-infection; pathogenic Escherichia coli; plasmid-encoding blaCTX-M-15.