Clean, sanitize equipment to prevent transfer of E. coli during grinding of raw beef.

Discerning the transfer rate of pathogens from processing equipment to meat products is challenging due to the difficulty in culturing these pathogens on selective media.

So, scientists at the University of Missouri used the green fluorescent protein (GFP) gene as a marker to monitor how E. coli O157:H7 can move to beef from contaminated equipment. Their research shows how important cleaning and sanitizing beef processing equipment is, and confirms the importance of disassembling, cleaning and sanitizing the machinery before, during and after processing products. The use of the gene as a marker for monitoring pathogen cross-contamination patterns demonstrates its usefulness in these studies.

The researchers sprayed E. coli O157:H7, at [10.sup.9]CFU per ml, onto the surface of a stainless table. The pathogen was recovered from the surface of the table after 0.5 hour, 4 hours, 8 hours and 24 hours. There were significant decreases found in the number of colony-forming units at each time point.

Then a commercial meat grinder was sprayed with about [10.sup.9] CFU per ml of E. coli O157:H7 that had been labeled with the GFP gene. Pieces of raw boneless chuck roast beef, 375 g each, were separately ground, and 25 g from each piece were stomached and plated onto plate count agar supplemented with 50 mg per ml of ampicillin and 60 mg per ml of L(+)-arabinose.

The number of E. coli O157:H7 decreased logarithmically to [10.sup.3] CFU per g after a total of 7.5 kg beef was ground. The levels of E. coli O157:H7 in the ground beef decreased significantly at the start of grinding, but the decreases were not significant in subsequent samples. Researchers applied a 24-hour enrichment in peptone water at 35 C when the pathogen was not detected by direct plating. Enriched samples were positive for E. coli O157:H7 after another 1.5 kg of beef was ground. This indicated that the pathogen still remained in the ground beef even though it was undetectable by the direct plating method.

Further information. Azlin Mustapha, Food Science Program, University of Missouri, 256 William Stringer Wing, Eckles Hall, Columbia, MO 65211; phone: 573-882-2649; fax: 573-882-0596; email: mustaphaa@missouri.edu.

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