Fecal carriage and shedding density of CTX-M extended-spectrum β-lactamase-producing Escherichia coli in cattle, chickens, and pigs: Implications for environmental contamination and food production

Abstract

The number and proportion of CTX-M positive Escherichia coli organisms were determined in feces from cattle, chickens, and pigs in the United Kingdom to provide a better understanding of the risk of the dissemination of extended-spectrum β-lactamase (ESBL) bacteria to humans from food animal sources. Samples of bovine (n = 35) and swine (n = 20) feces were collected from farms, and chicken cecal contents (n = 32) were collected from abattoirs. There was wide variation in the number of CTX-M-positive E. coli organisms detected; the median (range) CFU/g were 100 (100 × 106 to 1 × 106), 5,350 (100 × 106 to 3.1 × 106), and 2,800 (100 × 105 to 4.7 × 105) for cattle, chickens, and pigs, respectively. The percentages of E. coli isolates that were CTX-M positive also varied widely; median (range) values were 0.013% (0.001 to 1%) for cattle, 0.0197% (0.00001 to 28.18%) for chickens, and 0.121% (0.0002 to 5.88%) for pigs. The proportion of animals designated high-density shedders (>1 × 104 CFU/g) of CTX-M E. coli was 3/35, 15/32, and 8/20 for cattle, chickens, and pigs, respectively. We postulate that high levels of CTX-M E. coli in feces facilitate the dissemination of blaCTX-M genes during the rearing of animals for food, and that the absolute numbers of CTX-M bacteria should be given greater consideration in epidemiological studies when assessing the risks of food-borne transmission. © 2011, American Society for Microbiology.