Background

Highly publicized outbreaks of food-borne illness since 1993, primarily caused by bacteria such as E. coli O157:H7, Salmonella spp. and Listeria monocytogenes, elicited intense consumer concern about meat safety. In response, regulatory authorities, researchers and the beef industry-initiated efforts to implement food safety management systems that would improve microbiological quality. The USDA Food Safety and Inspection Service (FSIS) began initiating new regulatory requirements during the mid-1990s. Packers were required to knife-trim carcasses to remove all visible contaminants, comply with written sanitation standard operating procedures (SSOP), implement Hazard Analysis Critical Control Point (HACCP) systems, and meet microbiological performance criteria and standards for E. coli and Salmonella as a means to verify HACCP effectiveness and pathogen reduction. Researchers and beef packers/processors have addressed consumer food safety concerns by developing a variety of methods that are now implemented, or are being further developed, to reduce numbers of bacteria on beef and beef products and improve microbiological safety. 

These microbiological decontamination technologies include:

• Animal cleaning
• Chemical dehairing at slaughter
• Spot-cleaning of carcasses by knife-trimming or steam/hot water vacuuming; and
• Spraying/washing/rinsing of carcasses before evisceration and/or before chilling, with water, chemical solutions and/or steam or hot water. 

Enhanced sensitivity tests have shown that the prevalence of E. coli 0157:H7 in live cattle and the environment is much higher in fecal and carcass samples than researchers had originally thought. The main objective of this study was to identify effective mitigation strategies that can be used by producers to reduce the carriage and shedding of E. coli O157 in market-ready feedlot cattle.

Methodology

Dr. Keith Belk, Colorado State University researcher, tested:

1. Lactobacillus acidophilus probiotic (Bovamine Culture Complex Probiotic, Nutrition Physiology Corp.); 
2. Neomycin sulfate (NEOMIX®, Pharmacia & Upjohn Company); and  
3. An E. coli O157:H7 bacterin (FDAH Vaccine, Fort Dodge Animal Health). 

Seven variations on the treatments were studied in addition to the control group – the three interventions mentioned above were tested singularly and four treatments applied the intervention strategies in combination. The study was conducted in a commercial feedlot located in Eastern Colorado from March 1, 2003 through May 26, 2003. Researchers collected 1,172 fecal and hide samples from 24 pens of cattle with approximately 200 head of (925 lb) cattle per pen. 

Findings

The table below shows the effects of each treatment on E. coli 0157 hide and fecal prevalence.

Fecal Samples:  In the cattle control group, 45.8 percent of the fecal samples tested positive for E. coli O157. After treatment with neomycin sulfate, no fecal samples tested positive for E. coli O157. The Lactobacillus acidophilus and the bacterin vaccine, when administered singularly, resulted in only 13.3 and 14.7 percent of positive tests, respectively. Only 1.3 percent of fecal samples tested positive for E. coli O157 after a combined treatment of neomycin sulfate and Lactobacillus acidophilus. 

Hide Samples:  In the cattle control group, 40.3 percent of hide samples tested positive for E. coli O157. After treatment with all three interventions (Lactobacillus acidophilus probiotic, neomycin sulfate and E. coli O157:H7 bacterin), only 6.7 percent of the hide samples tested positive for E. coli O157. The same percent (6.7) of samples tested positive following a combined treatment of neomycin sulfate and E. coli O157:H7 bacterin as well. When treated with neomycin sulfate and Lactobacillus acidophilus in combination, just 7.1 percent of the hide samples tested positive for E. coli O157.

Treatment and Status of Interventions:  Lactobacillus acidophilus probiotic (Bovamine) was fed for 90 days prior to slaughter. This product can be implemented immediately as an intervention strategy. Neomycin sulfate (NEOMIX® AG 325 Medicated Premix) was fed, according to label, in Type C medicated solid feed at slightly below the recommended dosage. It was fed for three days, and then removed from the ration at least 24 hours before harvest to meet withdrawl requirements. Neomix is currently approved for treatment and control of colibacillosis (bacterial enteritis). The Food and Drug Administration needs to give direction as to whether control of E. coli O157:H7 would be considered an “extralabel drug use” under a valid veterinarian/client/patient relationship.

E. coli O157:H7 bacterin was administered two times during the study, 30 days apart. Since the vaccine is still in the experimental stage, U.S. Department of Agriculture-Food Safety and Inspection Service granted slaughter permits for the cattle vaccinated in this study. The checkoff-funded research builds the case for a possible vaccine solution using E. coli O157:H7 bacterin.

Implications

The Centers for Disease Control (CDC) estimates that there are 76 million cases of food-borne illness United States annually, with 14 million cases attributed to known pathogens. E. coli alone is estimated to account for 76,000 cases of food-borne illness and 76 deaths annually. Multiple intervention strategies to inhibit or eliminate E. coli in the beef production process are extremely important to the industry. The results of this study show that three E. coli O157 interventions (a microbial feed additive, antimicrobial feed additive and vaccine) produced reductions in E. coli O157 prevalence on hides and in fecal materials. There was also an additive effect of combining multiple treatments; the usage of all three interventions produced some of the largest reductions in E. coli O157 prevalence on both hides and in fecal samples.