VETERINARY MICROBIOLOGY Occurrence and Genetic Characteristics of Third-Generation Cephalosporin-Resistant Escherichia coli in Swiss Retail Meat Debora Vogt, 1 Gudrun Overesch, 1 Andrea Endimiani, 2 Alexandra Collaud, 1 Andreas Thomann, 1 and Vincent Perreten 1 Prevalence and genetic relatedness were determined for third-generation cephalosporin-resistant Escherichia coli (3GC-R-Ec) detected in Swiss beef, veal, pork, and poultry retail meat. Samples from meat-packing plants (MPPs) processing 70% of the slaughtered animals in Switzerland were purchased at different intervals between April and June 2013 and analyzed. Sixty-nine 3GC-R-Ec isolates were obtained and characterized by microarray, PCR/DNA sequencing, Multi Locus Sequence Typing (MLST), and plasmid replicon typing. Plasmids of selected strains were transformed by electroporation into E. coli TOP10 cells and analyzed by plasmid MLST. The prevalence of 3GC-R-Ec was 73.3% in chicken and 2% in beef meat. No 3GC-R-Ec were found in pork and veal. Overall, the bla CTX-M-1 (79.4%), bla CMY-2 (17.6%), bla CMY-4 (1.5%), and bla SHV-12 (1.5%) b-lactamase genes were detected, as well as other genes conferring resistance to chloramphenicol (cmlA1-like), sulfonamides (sul), tetracycline (tet), and trimethoprim (dfrA). The 3GC-R-Ec from chicken meat often harbored virulence genes associated with avian pathogens. Plasmid incompatibility (Inc) groups IncI1, IncFIB, IncFII, and IncB/O were the most frequent. A high rate of clonality (e.g., ST1304, ST38, and ST93) among isolates from the same MPPs suggests that strains persist at the plant and spread to meat at the carcass-processing stage. Additionally, the presence of the bla CTX-M-1 gene on an IncI1 plasmid sequence type 3 (IncI1/pST3) in genetically diverse strains indicates interstrain spread of an epidemic plasmid. The bla CMY-2 and bla CMY-4 genes were located on IncB/O plasmids. This study represents the first comprehensive assessment of 3GC-R-Ec in meat in Switzerland. It demonstrates the need for monitoring contaminants and for the adaptation of the Hazard Analysis and Critical Control Point concept to avoid the spread of multidrug-resistant bacteria through the food chain. Introduction S ince the introduction of third-generation cephalo- sporins, a large number of extended-spectrum b-lactamase (ESBL), chromosomally mediated, and plasmid-mediated AmpC b-lactamase (cAmpC and pAmpC) producers have emerged in Gram-negative bacteria, particularly in En- terobacteriaceae such as Escherichia coli. 14,49 ESBL enzymes belong to Ambler class A and are mainly represented by the SHV-, TEM-, and CTX-M-type families. The latter is the most frequent, with * 150 different types categorized into five groups. 45,53 ESBLs hydrolyze penicillins, first- to fourth- generation cephalosporins and monobactams, but they are in- hibited by the standard b-lactamase inhibitors (e.g., clavulanate and tazobactam). Plasmid-mediated AmpC b-lactamases belong to Ambler class C, hydrolyze penicillins and all cephalosporins (with the exception of the fourth-generation, e.g., cefepime), and are not inhibited by b-lactamase inhibitors. They are divided into six clusters, the most common being the CMY family. 32 E. coli is a normal inhabitant of the gut of humans and animals; however, certain E. coli have acquired different vir- ulence factors causing host-specific infections. Extraintestinal pathogenic E. coli (ExPEC) are responsible for colibacillosis in various animal species, including poultry (avian pathogenic E. coli [APEC]), 19 urinary tract infections (uropathogenic E. coli), and newborn meningitis (newborn meningitis-causing E. coli). 23 Enterotoxigenic E. coli can cause diarrhea in calves, 27 pigs, 24 and humans. Enterohemorrhagic E. coli (EHEC) can be commensal or pathogenic in cattle and have been of great interest as meat and vegetable contaminants, as they cause severe illness in humans. 42,55 E. coli are also responsible for wound infections, pneumonia, and septicemia in people. 14,25,49 1 Vetsuisse Faculty, Institute of Veterinary Bacteriology, University of Bern, Bern, Switzerland. 2 Faculty of Medicine, Institute for Infectious Diseases, University of Bern, Bern, Switzerland. MICROBIAL DRUG RESISTANCE Volume 00, Number 00, 2014 ª Mary Ann Liebert, Inc. DOI: 10.1089/mdr.2013.0210 1