Abstract

Extended-spectrum β-lactamase (ESBL) producing Escherichia coli is one of the most important drug resistant pathogen of clinical infection and is of global concern. CTX-M-55 type ESBL that has D240G amino acid substitution to confer ceftazidime resistance is often isolated from not only clinical patients, but also livestocks and retail meats. This study revealed molecular epidemiology and characteristics of CTX-M-55 producing E. coli isolated from medical facilities in Japan with less than 300 beds. Among the isolates possessing bla_CTX-M-55, antimicrobial susceptibility was examined, and resistant genes, sequence type, and incompatibility type of its plasmids were determined by next-generation sequencing. The proportion of E. coli harboring bla_CTX-M-55 ESBL was 12.5% (8/64) of the CTX-M-1 group ESBL genes positive isolates. Four and six isolates were resistant to fosfomycin and ciprofloxacin, respectively. Results of the whole genome sequencing for bla_CTX-M-55 positive strains, sequence type and plasmid incompatibility were dominant as ST131 and IncF, respectively. Further, two isolates determind as ST131 were likely to be isolated from the same facility, and are identical. This finding suggests that continuous surveillance for CTX-M-55 producing E. coli ST131 is needed. Moreover, the presence of floR gene in clinical strain implied that ingestion of contaminated meat and/or contact of livestocks transferred CTX-M-55 producing E. coli to community human. Additionally, the spread of fosA possessing E. coli combined with bla_CTX-M-55 may restrict therapeutic options against patients of urinary tract infection on which β-lactam has no therapeutic effect. In conclusion, this is the first study on the epidemiology and characteristics of CTX-M-55 ESBL producing E. coli isolates from regional medical facilities with less than 300 beds in Japan. These results show that CTX-M-55 producing E. coli originates from a different clone such as pandemic and veterinary clone.