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

Abstract

To assess the occurrence of faecal carriage of Escherichia coli with resistance to 'critically important' antibiotics in various animals. Rectal or cloacal swabs were obtained weekly from cattle, pigs, chickens, cats, dogs and wild rodents over a 2 year period. Plain and antibiotic-containing medium was used for bacterial isolation. Selected isolates were characterized by molecular methods. 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 β-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. 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.