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

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

JOURNAL=Frontiers in Microbiology

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2020.545591

DOI=10.3389/fmicb.2020.545591

ISSN=1664-302X

ABSTRACT=<p>The emergence of third-generation cephalosporin resistance in <italic>Escherichia coli</italic> is increasing at an alarming rate in many countries. Thus, the aim of this study was to analyze co-infecting <italic>bla</italic><sub>CTX-M</sub>-producing pathogenic <italic>E. coli</italic> isolates linked to three school outbreaks. Among 66 <italic>E. coli</italic> 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 <italic>bla</italic><sub>CTX-M</sub> 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 <italic>bla</italic><sub>CTX-M-14</sub> gene and all ETEC isolates the <italic>bla</italic><sub>CTX-M-15</sub> 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 <italic>bla</italic><sub>CTX-M-15</sub> located on IncK plasmids associated with the Δ<italic>bla</italic><sub>TEM</sub>-<italic>bla</italic><sub>CTX-M-15</sub>-<italic>orf477</italic> transposon. The representative EAEC O44 isolates carried <italic>bla</italic><sub>CTX-M-14</sub> on the chromosome, which was surrounded by the IS<italic>Ecp1</italic>-<italic>bla</italic><sub>CTX-M-14</sub>-<italic>IS903</italic> transposon. To the best of our knowledge, this is the first report of co-infection with chromosomally located <italic>bla</italic><sub>CTX-M-14</sub> and plasmid-encoding <italic>bla</italic><sub>CTX-M-15</sub> in pathogenic <italic>E. coli</italic>. Our findings indicate that resistance genes in clinical isolates can spread through concurrent combinations of chromosomes and plasmids.</p>