ESBL-Producing E. coli in Captive Black Bears: Molecular Characteristics and Risk of Dissemination

The emergence and global dissemination of extended-spectrum β-lactamase (ESBL)-producing <i>Escherichia coli</i> (ESBL-<i>E. coli</i>) represent a major public health concern. However, the characterization and capacity for horizontal gene transfer (HGT) of ESBL-<i>E. coli</i> in captive black bears remain substantially understudied. In the present study, 19 ESBL-<i>E. coli</i> strains were successfully identified (13.38%, 19/142). A total of 11 sequence types (STs) were identified from 19 ESBL-<i>E. coli</i> strains using MLST. This included eight known types (ST10, ST2690, ST208, ST695, ST4160, ST540, ST3865 and ST2792) and three new STs. Antimicrobial susceptibility testing demonstrated that all 19 ESBL-<i>E. coli</i> exhibited high resistance to KZ (100.00%), CRO (78.95%), and CTX (73.68%). Polymerase chain reaction (PCR) screening for 14 β-lactam antibiotic resistance genes (ARGs) and their variants revealed that <i>bla</i>_CTX-M was the most prevalent, followed by <i>bla</i>_SHV, <i>bla</i>_TEM, and <i>bla</i>_DHA. Furthermore, eight β-lactamase variants were detected, including five <i>bla</i>_CTX-M variants (<i>bla</i>_CTX-M-15, <i>bla</i>_CTX-M-3, <i>bla</i>_CTX-M-14, <i>bla</i>_CTX-M-55, and <i>bla</i>_CTX-M-27) and one variant each of <i>bla</i>_SHV-1, <i>bla</i>_TEM-1, and <i>bla</i>_DHA-14. Conjugation assays revealed that eight ESBL-<i>E. coli</i> strains were capable of conjugative transfer. Five plasmid types (IncFII, IncW, IncFrepB, IncY, and IncHI1) and three mobile genetic elements (MGEs) (<i>IS26</i>, <i>ISEcp1</i>, and <i>trbC</i>) were identified as co-transferred with <i>bla</i>_CTX-M. ESBL-<i>E. coli</i> poses a potential threat to captive black bears and may lead to further transmission. Consequently, the implementation of continuous surveillance and targeted interventions is imperative to prevent the transmission of ESBL-<i>E. coli</i>.