Escherichia coli Producing CMY-2 β-Lactamase in Retail Chicken, Pittsburgh, Pennsylvania, USA

To the Editor: Rates of resistance to various antimicrobial drugs are rapidly increasing in Escherichia coli, not only in health care settings but also in the community. The food supply is suspected as a potential source of antimicrobial-resistant E. coli strains, which include cephalosporin-resistant E. coli found in retail meat products and other types of food (1). We reported a high prevalence of cephalosporin-resistant E. coli, most of which produced CMY-2 β-lactamase, among retail poultry products in Pittsburgh, Pennsylvania, USA during 2006–2007 (2). CMY-2 is the most commonly acquired ampicillin C (AmpC)–type β-lactamase found in E. coli that cause human infections (3). The aim of this study was to investigate whether cephalosporin-resistant E. coli are present in retail raw meat and ready-to-eat meat products in our area 5 years after our previous study and defi ne subtypes of concern. A convenience sampling of 104 raw ground meat products from 3 local grocery stores in Pittsburgh was performed during February–April 2011. Items purchased were samples of all available deli counter ground meat, all fresh sausages prepared in stores at the deli counter, and selected uncooked commercially packaged fresh and frozen sausages. Types of meat items were chicken (n = 22), turkey (n = 10), lamb (n = 2), pork (n = 43), and beef (n = 27). Approximately 10 g of each sample was excised and suspended in 10 mL of nutrient broth. After being incubated overnight at 37°C, 10 μL of broth was plated on MacConkey agar plates containing 2 mg/L of cefotaxime or ceftazidime, and the plates were incubated overnight at 37°C. Lactose-fermenting colonies were identifi ed as E. coli by using standard biochemical methods, which included sulfi de indole motility, growth on triple sugar iron medium, oxidase activity testing, and the API20E system (bioMérieux, Durham, NC, USA) as needed. Antimicrobial drug susceptibility was determined by using the disk diffusion method (AB Biodisk, Solna, Sweden) according to the manufacturer's instructions and interpreted according to the criteria of the Clinical and Laboratory Standards Institute (4). Isolates were screened for extended-spectrum β-lactamase (ESBL) production by using the double-disk diffusion method and for acquired ampC-type β-lactamase genes by using multiplex PCR (4,5). Phylogenetic groups (A, B1, B2, and D) were determined as reported (6). Screening for sequence type (ST) 131 was conducted by using PCR and confi rmed by using multilocus sequence typing (7,8). Pulsed-fi eld gel electrophoresis was performed to determine …