Extended-Spectrum β-Lactamase– and AmpC-Producing Enterobacteria in Healthy Broiler Chickens, Germany

Felix Reich, Viktoria Atanassova, and Günter Klein

Author affiliations: University of Veterinary Medicine Hannover, Hannover, Germany

Abstract

During 2010, we evaluated the presence of extended-spectrum β-lactamase– and AmpC-producing enterobacteria in broiler chickens at slaughter. Samples (70 carcasses and 51 ceca) from 4 flocks were analyzed by direct plating and after enrichment. Extended-spectrum β-lactamase producers were found in 88.6% and 72.5% of carcasses and ceca, respectively; AmpC producers were found in 52.9% and 56.9% of carcasses and ceca, respectively. Most isolates were identified as Escherichia coli; Enterobacter cloacae (cecum) and Proteus mirabilis (carcass) were found in 2 samples each. Molecular characterization revealed the domination of CTX-M genes; plasmidic AmpC was CIT-like. Phylogenetic grouping of E. coli showed types A (31.5%), B1 (20.2%), B2 (13.5%), and D (34.8%). These findings provide evidence that healthy broilers in Germany are a source for the dissemination of transmissible resistance mechanisms in enterobacteria brought from the rearing environment into the food chain during slaughtering.

Antimicrobial drug resistance is a threat for therapy failure in human medicine. The presence of enterobacteria, especially Escherichia coli that produces extended-spectrum β-lactamases (ESBLs), has increased during past decades in terms of the worldwide distribution of such resistance traits and of the evolution of different genes (1). Resistance genes of the ESBL type are mostly plasmid associated and therefore can spread among bacteria. Although chromosomal AmpC genes exist in several enterobacteria and E. coli, plasmid-bound types also exist that can be transferred among bacteria. These types can lead to the overall distribution of antimicrobial resistance, although the carrier bacteria are not pathogenic per se but might lead to opportunistic infections in predisposed patients because ESBL-producing E. coli are associated with, for example, urinary tract infection and severe systemic disease. E. coli infections can be nosocomial, community acquired, or foodborne. The main ESBL types are TEM, SHV, and CTX-M. Rates of CTX-M infections have increased during the last decade compared with rates of TEM and SHV infections. These enzymes confer resistance to β-lactam antibacterial drugs, particularly cephalosporins, and may be accompanied by co-resistance to drugs of other classes (1,2). Because of the ESBL resistance and associated co-resistance, empiric oral antibacterial therapy appears to be limited, especially in the community setting (3,4).
Sources of infection can be diverse. In addition to human sources of transmission in hospitals and communities, animals pose a reservoir for different pathogenic bacteria with zoonotic potential. Especially with food-producing animals, animals and humans are directly linked. Foodborne pathogens usually do not result in clinical infection of the animal host. Thus identification of sources is possible only by extensive field research in primary production and regular testing of end products. ESBL-producing enterobacteria were shown in different sources of food-producing animals at the farm and from products (5–7).
Several studies have focused on the characterization of ESBL or AmpC producers from food-production animals by testing flocks at the farm; others have focused only on fecal samples at later production steps (8–11). Less is known about the actual prevalence or diversity within single healthy broiler flocks at the slaughterhouse and the effect on meat contamination. The processing of meat contributes to overall transmission of bacteria from contamination during slaughtering and dressing, including transmission of resistant bacteria introduced at slaughter by colonized animals onto the meat product.
Our objective was to assess the prevalence of ESBL and AmpC producers in the broiler chicken–production chain in Germany in different species of the Enterobacteriaceae family. We focused on individual broiler flocks at the slaughterhouse level to show the introduction of enterobacteria to the slaughtering operation and transmission to the product. In addition to determining different resistance phenotypes and molecular characterization of the isolates, we evaluated the number of presumptive ESBL producers found in meat.