Extensive dissemination of CTX-M-producing Escherichia coli with multidrug resistance to ‘critically important’ antibiotics among food animals in Hong Kong, 2008–10

Results: In total, 2106 faecal specimens from 398 cats, 460 chickens, 368 dogs, 210 cattle, 214 pigs and 456 rodents were cultured. The faecal carriage rate of extended-spectrum b-lactamase (ESBL)-producing E. coli was highest in pigs (63.6%, 136/214) and lowest in rodents (4.2%, 19/456). The faecal ESBL-producing E. coli carriage rate for food-producing animals (53.6%, 474/884) was significantly higher than that for cats/dogs (14.0%, 107/766; P,0.01) and wild rodents (4.2%, 19/456; P,0.01). ESBL-producing isolates from food animals often (33% –81%) had multidrug (≥4) resistance to amikacin, chloramphenicol, ciprofloxacin, co-trimoxazole, gentamicin, nalidixic acid, netilmicin, nitrofurantoin and tetracycline. Most (91.2%) of the ESBL-producing isolates had CTX-M-type enzymes. A total of 10 alleles (3, 13, 14, 15, 24, 27, 28, 55, 65 and 98) from two CTX-M families (M1 and M9) were found. PFGE showed that the CTX-M-producing isolates were genetically diverse. Conclusions: This study shows that food animals are a major reservoir of E. coli with multidrug resistance to many antibiotics that are ranked as critically important in human medicine.