Molecular Epidemiology and Characteristics of CTX-M-55 Extended-Spectrum β-Lactamase-Producing Escherichia coli From Guangzhou, China

Abstract

In recent years, the CTX-M-55 extended-spectrum β-lactamase (ESBL)-positive rate has gradually increased in the clinic. To identify the molecular epidemiology and characteristics of <i>bla</i> _CTX-M _-55-positive isolates, a total of 374 non-repetitive ESBL-producing <i>Escherichia coli</i> strains were collected from patients in two hospitals in Guangzhou, and 89 <i>bla</i> _CTX-M _-55-positive isolates were selected by CTX-M-1-group PCR amplification and confirmed by DNA sequencing. Whole-genome sequencing was used to analyze the resistance phenotype, plasmid types, phylogenetic relationships and genetic environment of the <i>bla</i> _CTX-M _-55 gene. Conjugation experiments and PCR were performed to confirm whether the plasmid harboring <i>bla</i> _CTX-M-55 gene could be transferred. The results showed that all <i>bla</i> _CTX-M-55-positive isolates were resistant to ceftriaxone, and 88.76 and 76.40% were resistant to ceftazidime and cefepime, respectively. The resistance rates to levofloxacin and sulfamethoxazole were 66.29 and 59.55%, respectively. However, the sensitivity rate of piperacillin/tazobactam, amoxicillin/clavulanate, and amikacin exceeded 90%. All <i>bla</i> _CTX-M-55-positive isolates were sensitive to carbapenems. Thirty-two STs were detected in the <i>bla</i> _CTX-M-55-positive isolates, among which the detection rate of ST1193 was relatively high (19.10%, 17/89), and other ST types were scattered. It remains to be seen whether ST1193 carrying the <i>bla</i> _CTX-M _-55 gene can become a popular clone strain in this region in the future. The plasmid types carrying the <i>bla</i> _CTX-M _-55 gene included IncI1, IncFII, IncFIC, IncFIB, IncHI2, IncI2, and IncX/Y, among which the IncI1 and IncFII plasmids were the main plasmids, accounting for 37.80 and 28.09%, respectively. Among them, 11 strains of the IncI1 plasmid existed in ST1193 strains. The <i>bla</i> _CTX-M _-55 gene was found on chromosomes of 13 isolates, and seemed to be increasing annually. Up to five distinct types of genetic environments surrounding the <i>bla</i> _CTX-M _-55 gene were analyzed. The most common structure was type II "IS<i>Ecp1</i>-<i>bla</i> _CTX-M _-55-ORF477." In conclusion, whether ST1193, which carries <i>bla</i> _CTX-M _-55 gene, will be an epidemic clone of this region in the future remains to be concerned. The plasmids IncI1 and IncFII, and mobile elements such as IS<i>Ecp1</i> and IS<i>26</i> may be the main factors leading to the spread and prevalence of CTX-M-55 genotypes.