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 ␤-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 ؋ 10 6 to 1 ؋ 10 6 ), 5,350 (100 ؋ 10 6 to 3.1 ؋ 10 6 ), and 2,800 (100 ؋ 10 5 to 4.7 ؋ 10 5 ) 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 ؋ 10 4 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 bla CTX-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.The emergence and spread of extended-spectrum beta-lactamases (ESBLs), particularly among Enterobacteriaceae, is well recognized as a threat to the efficacy of extended-spectrum cephalosporins for the treatment of serious infections (8,11,14,31,35). During the last 5 years, ESBLs belonging to the CTX-M family of enzymes have been reported from many countries from a variety of different food-producing animals, including cattle, chickens, and pigs (17,21,22,25), and these animals are recognized as reservoirs of extended-spectrum ␤-lactamase producers (12). The presence of CTX-M ESBLs in United Kingdom cattle was first reported in 2005 and 2006 (20, 37). More recently, CTX-M ESBL-positive Escherichia coli has also been detected in United Kingdom poultry flocks (32).Epidemiological studies often use selective agar to ascertain and report the presence or absence of CTX-M-producing bacteria in samples; however, the number of bacteria present in samples is usually not reported. Fecal carriage is an important factor for the spread of CTX-M ESBL bacteria among both human communities (34) and animals (1, 12, 15, 24) and will be influenced by factors such as previous treatment with antimicrobials (2, 4, 6). The dissemination of CTX-M E. coli in food production units may occur via fecal cross-contamination between groups of animals (or individuals), and the contamination of food derived from animals may occur during processing in the abattoir. Previous studies have shown that the number of E. coli O157 organisms shed in feces is an important factor for dissemination during slaughter and carcass processing (29). Therefore, the aim of t...

Curing vector for IncI1 plasmids and its use to provide evidence for a metabolic burden of IncI1 CTX-M-1 plasmid pIFM3791 on Klebsiella pneumoniae

“…LREC215, a commensal E. coli isolated from a broiler chick (Horton et al, 2011), and LREC447, an avian pathogenic E. coli isolated from a broiler (Randall et al, 2012), were confirmed by PCR to carry a CTX-M group 1 gene on an IncI1-g plasmid and to be sensitive to kanamycin, a strong selectable marker present in pIFM27. Electrocompetent cells were transformed with curing vector pIFM27 with selection on kanamycin (50 mg l À1 ).…”

“…The strains and plasmids described in this study were either WT and originating from previous studies (Freire Martín et al, 2014;Horton et al, 2011;Randall et al, 2012), commercially available strains and plasmids or, in the case of pIFM26 (S1), a modification of previously described plasmid pAKE604 (El-Sayed et al, 2001), which differed from it only in the orientation of the restriction sites within its multiple cloning site. The strains were grown in LB medium and, when necessary for plasmid maintenance, in the presence of appropriate antibiotics.…”

“…Tetracycline was chosen as the intended recipients had been shown to be resistant during extensive characterization carried out as part of previous work (Freire Martín et al, 2014). Colonies of the appropriate colour (red for the S. enterica strains, purple for the K. pneumoniae strains) were re-streaked and checked for the presence of the incoming plasmid by CTX-M universal PCR (Horton et al, 2011) and plasmid profiling (Kado & Liu, 1981).…”

“…The CTX-M class of ESBLs has become the most prevalent type isolated from clinical settings (Livermore et al, 2007), and is increasingly common in community and veterinary isolates (Batchelor et al, 2005;Pitout et al, 2005). Awareness of the potential spread of this resistance in livestock has increased (Horton et al, 2011). Furthermore, recent genome sequencing data of human and food animal Escherichia coli isolates from the Netherlands indicate that the dissemination of resistance across reservoirs is caused by the expansion of successful plasmid lineages (de Been et al, 2014).…”

Genetic heterogeneity of CTX-M type extended-spectrum β-lactamase producing Escherichia coli strains from diverse sources in Saudi Arabia

“…The emergence of bla CTX-M has been detected in food animal populations [3], food products [4], and both domestic [5] and wild [6] animal species throughout the world. Saudi Arabia is one of many countries with higher rates of bacterial pathogens with ESBLs-producers in the clinical setting, mostly associated with CTX-M-types [7,8].…”