Clonal diversity of CTX-M-producing, multidrug-resistant Escherichia coli from rodents

This territory-wide study investigated the occurrence of faecal carriage of extended-spectrum β-lactamase (ESBL)-producing Escherichia coli among wild rodents from the 18 districts in Hong Kong. Individual rectal swabs were obtained from the trapped animals and cultured in plain and selective media. A total of 965 wild rodents [148 chestnut spiny rats (Niviventer fulvescens), 326 Indo-Chinese forest rats (Rattus andamanensis), 452 brown rats (Rattus norvegicus) and 39 black rats (Rattus rattus)] were sampled. ESBL carriage was 0 % in chestnut spiny rats, 0.6 % in Indo-Chinese forest rats, 7.7 % in black rats and 13.9 % in brown rats. Among brown rats, the prevalence of ESBL carriage differed markedly by geographical location: absent in two districts, low (7-10 %) in six districts, moderate (11-19 %) in seven districts and high (21-50 %) in three districts. Nonetheless, there was no correlation between the prevalence of ESBL in brown rats and human population density in the 18 districts. CTX-M-type enzymes were detected in 92.0 % of the ESBL-producing isolates, of which 83.1 % were resistant to three or more non-β-lactam drugs. The CTX-M producing isolates were genetically diverse but a large proportion (47.8 %) were included in six successful clones that are strongly associated with human diseases and CTX-M dissemination, viz. sequence type complex [STC]10/phylogroup A, STC23/phylogroup B1, STC38/phylogroup D, STC155/phylogroup B1, ST405/phylogroup D and ST131/phylogroup B2. In conclusion, our results show that brown rats often carry potentially zoonotic clones of CTX-M producing, multidrug-resistant E. coli. The potential for rats to be a source of CTX-M producing E. coli for humans deserves further consideration.