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Isolation of antimicrobial-resistant Escherichia coli from retail meats purchased in Greater Washington, DC, USA

https://doi.org/10.1016/S0168-1605(02)00508-1Get rights and content

Abstract

Four hundred and seventy-two generic Escherichia coli isolates were recovered from ground and whole retail beef, chicken, pork, and turkey obtained from Greater Washington, DC, USA during the years 1998 to 2000. Many of the isolates displayed resistance to tetracycline (59%), sulfamethoxazole (45%), streptomycin (44%), cephalothin (38%) and ampicillin (35%). Resistance was also observed, but to a lesser extent, to gentamicin (12%), nalidixic acid (8%), chloramphenicol (6%), ceftiofur (4%) and ceftriaxone (1%). Sixteen percent of the isolates displayed resistance to one antimicrobial, followed by 23% to two, 23% to three, 12% to four, 7% to five, 3% to six, 2% to seven and 2% to eight. Three E. coli isolates were shown to possess Shiga toxin genes (stx2) via PCR; all were O non-typeable and were recovered from ground beef samples purchased on the same day at the same supermarket. One of the Shiga toxin-producing E. coli (STEC) isolates was susceptible to each of the antimicrobials tested, whereas one displayed resistance to cephalothin and sulfamethoxazole, and one displayed resistance to ampicillin, cephalothin, gentamicin, streptomycin, sulfamethoxazole and tetracycline. Findings from this study indicate that retail raw meats may often be contaminated with antimicrobial-resistant E. coli.

Introduction

The use of antimicrobial agents in any venue, including therapeutically in human and veterinary medicine, or as prophylaxis for growth promotion in animal husbandry, ultimately exerts selective pressure favorable for the propagation of antimicrobial-resistant bacteria (Witte, 1998). Resistant bacteria from the intestines of food animals may be transferred to retail meat products resulting from fecal contamination during various stages of the slaughter process (e.g., evisceration) and subsequent handling of animal tissue (Jackson et al., 2001). As a likely consequence, antimicrobial resistance phenotypes have been documented for zoonotic pathogens including Salmonella spp. (White et al., 2001), Campylobacter spp. (Sáenz et al., 2000) and Escherichia coli (Sáenz et al., 2001) isolated from retail beef, chicken, and pork.

E. coli are common inhabitants of the intestinal tracts of animals and man. Pathogenic strains of E. coli, however, are an important cause of foodborne illness. In the United States, foodborne Shiga toxin-producing E. coli (STEC) and non-STEC are estimated to each year cause approximately 94,000 and 79,000 illnesses, respectively (Mead et al., 1999). Moreover, because E. coli are readily capable of transferring resistance genes to other bacteria (Zhao et al., 2001b), they may be important in the dissemination of antimicrobial resistance among intestinal microflora and other foodborne pathogens.

Continued surveillance of the antimicrobial susceptibility profiles of foodborne pathogens, including E. coli, has been strongly recommended to identify emerging antimicrobial-resistant phenotypes within the food production continuum (World Health Organization, 1997). There is, nevertheless, a relative paucity of data concerning the extent of antimicrobial resistance among foodborne E. coli. In this study, E. coli were isolated from retail beef, chicken, turkey, and pork purchased in Greater Washington, DC, USA during 1998 to 2000. A total of 472 isolates were assayed for the presence of Shiga toxin genes and susceptibility to 11 antimicrobials of human and veterinary importance. The objective was to further characterize antimicrobial resistance among E. coli from retail meats.

Section snippets

Sample collection and processing

A total of 1025 raw meat samples were purchased from retail supermarkets in Greater Washington, DC (Table 1). For ground meats, 200 samples (50 beef, 51 chicken, 49 pork, and 50 turkey) were purchased from stores representing three supermarket chains between June and September 1998. Ground poultry samples were processed and packed at one of four poultry processing plants, ground pork samples were processed and packed at one pork processing plant, and ground beef samples were ground and packaged

Results and discussion

On average, the incidence of E. coli in ground meat samples was significantly higher (P<0.05) than in whole meat samples (Table 1). Identical techniques were used for the isolation of E. coli from whole and ground meat samples, thus, differences in the incidence of E. coli were most likely due to other factors. Because a much larger amount of surface area is present in ground meats, bacteria from grinding machinery and trimmings may be distributed throughout these products. For instance, during

Acknowledgements

We thank Cuiwei Zhao, Juan De Villena, Robert Sudler, Emily Yeh, and Shenghui Cui for the help with sample collection and processing. We also thank Robert Walker, Shabbir Simjee, Steven Foley, and Janice Derr for the comments that improved various aspects of the manuscript prior to submission.

Support was provided in part by a grant from the Maryland Agricultural Experimental Station, and by the University of Maryland/Food and Drug Administration Joint Institute for Food Safety and Applied

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