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Preventing the contamination of ground beef with pathogens such as E. coli O157:H7, that can lead to outbreaks of foodborne illness linked to consumption of hamburger, is a high priority for the meat industry as well as consumers. Meat from cow/bull processing plants makes up a significant proportion of ground beef. We have established that the prevalence of E. coli O157:H7 on the hides of fed cattle is high, that often pre-evisceration carcasses become contaminated with E. coli O157:H7. Yet little is known about the prevalence of E. coli O157:H7 on the hides and carcasses of cull cows and bulls. This experiment was designed to assess the prevalence and levels of E. coli O157:H7, Salmonella, Listeria, and aerobic plate count on the hides and carcasses of cull cows and bulls and to determine the multi drug resistance of Salmonella isolates.
Salmonella have been found on the hides of fed beef cattle at higher rates than in feces. We found hide prevalence to vary from 27.7% in the winter to 91.6% and 97.7% in the summer and fall, respectively (Barkocy-Gallagher et al., 2003). Salmonella enterica serovars Typhimurium and Newport are two of the top three disease-causing Salmonella serovars. Multi drug-resistant (MDR) Salmonella, such as S. Typhimurium with the ACSSuT resistance pattern (resistant to ampicillin, chloramphenicol, streptomycin, sulfisoxazole, tetracycline), and S. Newport with the MDR-AmpC resistance pattern (resistant to at least 9 antibiotics including: amoxicillin/clavulonic acid, ampicillin, cephalothin, ceftiofur, cefoxitin, chloramphenicol, streptomycin, sulfamethoxazole, tetracycline and show decreased susceptibility to ceftriaxone) were two of the most common multi drug-resistant Salmonella phenotypes in 2002 (CDC, 2004). During 1997-2001, the number of laboratory-confirmed S. Newport infections reported to the CDC increased from 1,584 (5%) of 34,608 reported Salmonella infections to 3,152 (10%) of 31,607 (Anon., 2002).
The increase in the number of S. Newport infections appears to be associated with the emergence and rapid dissemination of the multi drug-resistant strains of MDR-AmpC Newport (Anon., 2002). These strains are noted for their resistance to extended spectrum cephalosporins (ESCs) such as ceftriaxone or cephalothin. Recent studies indicate that plasmid mediated ESC resistance can be readily transferred between E. coli and Salmonella isolates (Poppe et al., 2005). Thus, the need to assess the levels of S. Typhimurium and S. Newport on hides and carcasses, and to characterize their antimicrobial resistance profiles, is evident.
L. monocytogenes is commonly associated with human listeriosis. Listeriosis is a serious infection, affecting primarily pregnant women, newborns, and adults with weakened immune systems, that is caused by eating food contaminated with the bacteria and the overt form of the disease has a mortality rate greater than 25 percent. L. monocytogenes has 11 serovars, but just three (1/2a, 1/2b, and 4b) are responsible for over 98% of reported human listeriosis cases. Major outbreaks of Listeria have been caused by L. monocytogenes 4b. Listeria has been considered a problem associated with ready-to-eat (RTE) foods, but recently, the producers of RTE products have started to require their suppliers to certify raw materials are free of Listeria. Thus, there is a need to assess the prevalence of this pathogen on the hides and carcasses of animals at slaughter.
The stated objectives for this work were:
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