Mohamed Kamel

The possible origin of Escherichia coli found on cuts and trimmings in the breaking facility of a beef packing plant was examined using multiple-locus variable-number tandem repeat analysis. Coliforms and E. coli were enumerated in samples obtained from 160 carcasses that would enter the breaking facility when work commenced and after each of the three production breaks throughout the day, from the conveyor belt before work and after each break, and from cuts and trimmings when work commenced and after each break. Most samples yielded no E. coli, irrespective of the surface types. E. coli was recovered from 7 (<5%) carcasses, at numbers mostly ≤1.0 log CFU/160,000 cm(2). The log total numbers of E. coli recovered from the conveyor belt, cuts, and trimmings were mostly between 1 and 2 log CFU/80,000 cm(2). A total of 554 E. coli isolates were recovered. Multiple-locus variable-number tandem repeat analysis of 327 selected isolates identified 80 distinct genotypes, with 37 (46%) each containing one isolate. However, 28% of the isolates were of genotypes that were recovered from more than one sampling day. Of the 80 genotypes, 65 and 2% were found in one or all four sampling periods throughout the day. However, they represented 23 and 14% of the isolates, respectively. Of the genotypes identified for each surface type, at least one contained ≥9 isolates. No unique genotypes were associated with carcasses, but 10, 17, and 19 were uniquely associated with cuts, trimmings, and the belt, respectively. Of the isolates recovered from cuts, 49, 3, and 19% were of genotypes that were found among isolates recovered from the belt, carcasses, or both the belt and carcasses, respectively. A similar composition was found for isolates recovered from trimmings. These findings show that the E. coli found on cuts and trimmings at this beef packing plant mainly originated from the conveyor belt and that small number of E. coli strains survived the daily cleaning and sanitation process, thus persisting in the plant.

Beef steaks (2 cm thick) were each inoculated at three sites in the central plane with Escherichia coli O157:H7 at 5.9 ± 0.3 log CFU per site. Temperatures at steak centers were monitored during cooking on a hot plate or the grill of a gas barbeque. Steaks were cooked in groups of five using the same procedures and cooking each steak to the same temperature, and surviving E. coli O157:H7 at each site was enumerated. When steaks cooked on the hot plate were turned over every 2 or 4 min during cooking to between 56 and 62°C, no E. coli O157:H7 was recovered from steaks cooked to ≥58 or 62°C, respectively. When steaks were cooked to ≤71°C and turned over once during cooking, E. coli O157:H7 was recovered from steaks in groups turned over after ≤8 min but not from steaks turned over after 10 or 12 min. E. coli O157:H7 was recovered in similar numbers from steaks that were not held or were held for 3 min after cooking when steaks were turned over once after 4 or 6 min during cooking. When steaks were cooked on the grill with the barbeque lid open and turned over every 2 or 4 min during cooking to 63 or 56°C, E. coli O157:H7 was recovered from only those steaks turned over at 4-min intervals and cooked to 56°C. E. coli O157:H7 was recovered from some steaks turned over once during cooking on the grill and held or not held after cooking to 63°C. E. coli O157:H7 was not recovered from steaks turned over after 4 min during cooking to 60°C on the grill with the barbeque lid closed or when the lid was closed after 6 min. Apparently, the microbiological safety of mechanically tenderized steaks can be assured by turning steaks over at intervals of about 2 min during cooking to ≥60°C in an open skillet or on a barbecue grill. When steaks are turned over only once during cooking to ≥60°C, microbiological safety may be assured by covering the skillet or grill with a lid during at least the final minutes of cooking.

The objective of the study was to identify factors affecting the fractions of the bacteria naturally present on surfaces of beef cuts that are carried into deep tissues when the meat is mechanical tenderized by piercing with banks of thin blades. The surfaces and ten strips of meat from the deep tissues of beef primal cuts tenderized first and last on each of five days at a retail store meat fabrication facility were sampled for enumeration of total aerobic counts. Each strip was excised from the whole thickness of a cut after surfaces were sterilized. The mean log numbers of total aerobes recovered from the surfaces of cuts tenderized first or last each day were 2.18 and 1.57 log cfu cm−2, respectively. The mean log numbers recovered per strip from individual cuts tenderized first or last each day ranged from 0.30 to 1.45 and from 0.03 to 1.04 log cfu, respectively. These findings indicate that bacteria from the tenderizing equipment augmented the numbers of aerobes on the surfaces of cuts tenderized first each day, with some of the additional aerobes being carried into deep tissues. Subsequently, pieces of cuts stored in air at 2 °C were tenderized at a laboratory using commercial equipment. Each cut was divided into three pieces with one piece being not treated, one being sprayed with water and one being sprayed with 5% lactic acid. The mean log numbers of total aerobes recovered from the surfaces of not treated pieces of cut stored for 0, 2, 4, 6, 10 or 14 days were 0.6, 0.8, 2.6, 4.2, 8.5 and 8.9 log cfu cm−2, respectively. No aerobes were recovered from the deep tissues of any of the pieces of cuts tenderized on day 0. Mean log numbers recovered from the deep tissues of not treated tenderized pieces of cuts stored for 2, 4, 6, 10 or 14 days were 0.3, 0.3, 2.2, 7.8 and 8.1 log cfu per strip, respectively. Spraying with 5% lactic acid reduced the mean log numbers of aerobes on pieces of cuts stored for 2, 4, or 6 days by 1, 2 or 2 log units, respectively, but did not reduce the numbers on pieces of cuts stored for 10 or 14 days. Mean log numbers recovered from the deep tissues of tenderized pieces of cuts sprayed with 5% lactic acid were not significantly different (P > 0.05) from the mean log numbers recovered from the corresponding, tenderized not treated pieces of cuts. These findings showed that the fraction of the total aerobes on cut surfaces that are carried into deep tissues during mechanical tenderizing can vary with the stage of growth of the spoilage flora; and that reduction of numbers of aerobes on the surface by treatment with lactic acid before tenderizing does not necessarily reduce the numbers carried into deep tissues during tenderizing.