Objective: The aim of this study was to explore the occurrence and molecular characterization of extended-spectrum β-lactamases (ESBL), plasmid-mediated AmpC β-lactamase (pAmpC) and carbapenemases among ESBL-producing multidrug resistant (MDR) Escherichia coli from dogs and cats in the United States.
Methods: Of 2443 E.coli isolated from dogs and cats collected between August 2009 and January 2013, 68 isolates were confirmed as ESBL-producing MDR ones. PCR and sequencing were performed to identify β-lactamases and plasmid-mediated quinolone resistance (PMQR) genes, and shed light on the virulence gene profiles, phylogenetic groups and ST types.
Results: Phylogenic group D and B2 accounted for 69.1% of the isolates. 50 (73.5%) isolates carried CTX-M ESBL gene, and the most predominant specific CTX-M subtype identified was bla CTX−M−15 ( n = 33), followed by bla CTX−M−1 ( n = 32), bla CTX−M−123 ( n = 27), bla CTX−M−9 ( n = 19) and bla CTX−M−14 ( n = 19), and bla CTX−M−123 was firstly reported in E. coli isolates in the United States alone or in association. Other β-lactamase genes bla TEM, bla SHV, bla OXA−48, and bla CMY−2 were detected in 41.2, 29.4, 19.1, and 17.6% of 68 ESBL-producing MDR isolates, respectively. The bla TEM and bla SHV genes were classfied as ESBLs with the exception of the bla TEM−1 gene. Additionally, 42.6% (29/68) of isolates co-expressed bla CTX−M−15 and PMQR gene aac(6′ )-Ib-c. The overall occurrence of virulence genes ranged from 11.8 ( ireA) to 88.2% ( malX), and most of virulence genes were less frequent among CTX-M-producing isolates than non-CTX-M isolates with the exception of malX and iutA. The 68 isolates analyzed were assigned to 31 STs with six being novel. Three pandemic clonal lineages ST131 ( n = 10), ST648 ( n = 9), and ST405 ( n = 9) accounted for more than 41% of the investigated isolates, and ST648 and ST405 of phylogenetic D were firstly reported in E. coli from dogs and cats in the United States.
Conclusion: bla CTX−M−123 of ESBLs and carbapenemase bla OXA−48 were firstly reported in ESBL-producing MDR E.coli from dogs and cats in the United States, and ST131, ST648, and ST405 were the predominant clonal groups.