Visvalingam, J., H. Wang, M. K. Youssef, J. Devos, C. O. Gill, and X. Yang, "Spatial and Temporal Distribution of Escherichia coli on Beef Trimmings Obtained from a Beef Packing Plant", Journal of Food Protection, vol. 79, issue 8, pp. 1325-1331, 2016. Abstract

The objective of this study was to determine the immediate source of Escherichia coli on beef trimmings produced at a large
packing plant by analyzing the E. coli on trimmings at various locations of a combo bin filled on the same day and of bins filled
on different days. Ten 2,000-lb (907-kg) combo bins (B1 through B10) of trimmings were obtained from a large plant on 6 days
over a period of 5 weeks. Thin slices of beef with a total area of approximately 100 cm2 were excised from five locations (four
corners and the center) at each of four levels of the bins: the top surface and 30, 60, and 90 cm below the top. The samples were
enriched for E. coli in modified tryptone soya broth supplemented with 20 mg/liter novobiocin. The positive enrichment cultures,
as determined by PCR, were plated on E. coli/coliform count plates for recovery of E. coli. Selected E. coli isolates were
genotyped using multiple-locus variable-number tandem repeat analysis (MLVA). Of the 200 enrichment cultures, 43 were
positive by PCR for E. coli, and 32 of these cultures yielded E. coli isolates. Two bins did not yield any positive enrichment
cultures, and three PCR-positive bins did not yield any E. coli isolates. MLVA of 165 E. coli isolates (30, 62, 56, 5, and 12 from
B6 through B10, respectively) revealed nine distinct genotypes. MLVA types 263 and 89 were most prevalent overall and on
individual days, accounting for 49.1 and 37.6% of the total isolates, respectively. These two genotypes were also found at
multiple locations within a bin. All nine genotypes belonged to the phylogenetic group A0 of E. coli, suggesting an animal origin.
The finding that the trimmings carried very few E. coli indicates an overall effective control over contamination of beef with E.
coli at this processing plant. The lack of strain diversity of the E. coli on trimmings suggests that most E. coli isolates may have
come from common sources, most likely equipment used in the fabrication process.

Liu, Y., M. K. Youssef, and X. Yang, "Effects of Dry Chilling on the Microflora on Beef Carcasses at a Canadian Beef Packing Plant", Journal of Food Protection, vol. 79, issue 4, pp. 538-543, 2016. Abstract

The aim of this study was to determine the course of effects on the microflora on beef carcasses of a commercial dry chilling process in which carcasses were dry chilled for 3 days. Groups of 25 carcasses selected at random were sampled when the chilling process commenced and after the carcasses were chilled for 1, 2, 4, 6, 8, 24, and 67 h for determination of the numbers of aerobes, coliforms, and Escherichia coli. The temperatures of the surfaces and the thickest part of the hip (deep leg) of carcasses, as well as the ambient air conditions, including air temperature, velocity, and relative humidity (RH), were monitored throughout the chilling process. The chiller was operated at 0°C with an off-coil RH of 88%. The air velocity was 1.65 m/s when the chiller was loaded. The initial RH levels of the air in the vicinity of carcasses varied with the locations of carcasses in the chiller and decreased rapidly during the first hour of chilling. The average times for shoulder surfaces, rump surfaces, and the deep leg of carcasses to reach 7°C were 13.6 ± 3.1, 16.0 ± 2.4 and 32.4 ± 3.2 h, respectively. The numbers of aerobes, coliforms, and E. coli on carcasses before chilling were 5.33 ± 0.42, 1.95 ± 0.77, 1.42 ± 0.78 log CFU/4,000 cm(2), respectively. The number of aerobes on carcasses was reduced by 1 log unit each in the first hour of chilling and in the subsequent 23 h of chilling. There was no significant difference (P > 0.05) between the numbers of aerobes recovered from carcasses after 24 and 67 h of chilling. The total numbers (log CFU/100,000 cm(2)) on carcasses before chilling and after the first hour of chilling were 3.86 and 2.24 for coliforms and 3.30 and 2.04 for E. coli. The subsequent 23 h of chilling reduced the numbers of both groups of organisms by a further log unit. No coliforms or E. coli were recovered after 67 h of chilling. The findings show that the chilling regime investigated in this study resulted in significant reductions of all three groups of indicator organism

Yang, X., F. Tran, M. K. Youssef, and C. O. Gill, "Determination of Sources of Escherichia coli on Beef by Multiple-Locus Variable-Number Tandem Repeat Analysis", Journal of Food Protection, vol. 78, issue 7, pp. 1296-1302, 2015. Abstract

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.

Gill, C. O., and M. K. Youssef, "Emerging pathogens.", Encyclopedia of Meat Sciences, London, Elsevier, 2014.
Gill, C. O., J. Devos, M. K. Youssef, and X. Yang, "Effects of selected cooking procedures on the survival of Escherichia coli O157: H7 in inoculated steaks cooked on a hot plate or gas barbecue grill", Journal of Food Protection, vol. 77, issue 6, pp. 919-926, 2014. Abstract

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.

Youssef, M. K., C. O. Gill, and X. Yang, "Storage life at 2 °C or −1.5 °C of vacuum-packaged boneless and bone-in cuts from decontaminated beef carcasses", Journal of the Science of Food and Agriculture, vol. 94, issue 15, pp. 3118-3124, 2014. Abstract

BACKGROUND: The microbiological condition of beef produced at North American plants has been improved as a result of the use of effective carcass-decontaminating treatments. The effect of these treatments on the storage life of beef has not been established. In this study, beef primal cuts in vacuum packs stored at −1.5 or 2 ∘C for up to 160 days were assessed for their microbiological and organoleptic properties.
RESULTS: The odours of boneless cuts were acceptable after storage at either temperature for ≤160 days; and the flavours of steaks from boneless cuts stored at 2 or −1.5 ∘C for ≤70 or ≤120 days, respectively, were acceptable. The storage life of bone-in cuts stored at 2 or −1.5 ∘C was, respectively, shorter or the same as that of boneless cuts stored at the same temperature. More than 20 microbial species thatwere mostly obligate aerobeswere present on both types of cuts before storage. After storage for ≥30 days, the microflora was dominated by carnobacteria and Enterobacteriaceae were present in the flora from early storage times.
CONCLUSIONS: A storage life of 120–140 days was attained by vacuum-packaged beef primals from decontaminated carcasses stored at −1.5 ∘C. The bone-in cuts stored at 2 ∘C were spoiled at earlier times, probably by Enterobacteriaceae.

Youssef, M. K., X. Yang, and C. O. Gill, "The relationship between numbers of bacteria on surfaces and in deep tissues of mechanically tenderized beef", Food Control, vol. 46, pp. 502-507, 2014. Abstract

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.

Youssef, M. K., C. O. Gill, F. Tran, and X. Yang, "Unusual compositions of microflora of vacuum-packaged beef primal cuts of very long storage life", Journal of Food Protection , vol. 77, issue 12, pp. 2161-2167, 2014. Abstract

Vacuum-packaged top butt cuts from a beef packing plant that does not use any carcass decontaminating interventions were assessed for their organoleptic and microbiological properties during storage at 2 or -1.5°C. Cuts stored at 2°C were acceptable after storage for 140 days but were unacceptable after 160 days because of persistent sour, acid odors. Odors of cuts stored at -1.5°C for 160 days were acceptable. The numbers of aerobes on cuts increased from <1 log CFU/cm(2) to 7 or 6 log CFU/cm(2) for cuts stored at 2 or -1.5°C, respectively. The numbers of Enterobacteriaceae increased from <-1 log CFU/cm(2) to 5 or 3 log CFU/cm(2) for cuts stored at 2 or -1.5°C, respectively. Bacteria recovered from initial microflora were, mainly, strictly aerobic organisms. Bacteria recovered from cuts stored for 160 days were mainly Carnobacterium spp. that grew on an acetate-containing agar generally selective for lactic acid bacteria other than Carnobacterium. C. divergens and C. maltaromaticum were recovered from cuts stored at 2°C, but C. maltaromaticum was the only species of Carnobacterium recovered from cuts stored at -1.5°C. No lactic acid bacteria of genera that usually predominate in the spoilage microflora of vacuum-packaged beef at late storage times were recovered from the spoilage microflora. The findings indicate that carnobacteria, initially present at very small numbers, grew exponentially to persistently dominate the spoilage microflora of vacuum-packaged beef cuts of unusually long storage life.

Youssef, M. K., M. D. Klassen, and C. O. Gill, "The microbiological effects of procedures used in commercial practice for cleaning mechanical tenderizing equipment used with beef", Journal of Food Rsearch, vol. 3, issue 1, pp. 105-1116, 2014.
Youssef, M. K., M. Badoni, X. Yang, and C. O. Gill, "Sources of Escherichia coli deposited on beef during breaking of carcasses carrying few E. coli at two packing plants", Food Control, vol. 31, issue 1: Elsevier, pp. 166-171, 2013. Abstract

Microbiological samples were obtained from the hands of workers, personal equipment and conveyor belts, in the carcass breaking facility of a beef packing plant where chilled carcasses carry coliforms and Escherichia coli at numbers < 1 cfu/10,000 cm2. Before work started, steel mesh gloves carried coliform and E. coli at numbers of 4 and 3 log cfu/25 items, respectively, while their numbers on conveyor belts were >2 and <2 log cfu/2500 cm2, respectively. After a period of work the numbers of both coliforms and E. coli on steel mesh gloves and conveyor belts were reduced by about 1 log unit, but the numbers on cotton gloves worn under steel mesh gloves were 5 and >4 log cfu/25 items, respectively. The findings indicate that the proximate source of most coliforms and E. coli that contaminate cuts and trimmings are, respectively, cotton gloves and conveyors. Microbiological samples were similarly obtained at a second plant where drying of carcass surfaces during chilling gave carcasses with coliforms and E. coli at numbers about 1 cfu/1000 cm2. Before work started, steel mesh gloves were free of coliforms and E. coli; and the uniform wearing of rubber gloves over cotton ones precluded contamination of cotton gloves. The conveyor belt carried coliforms and E. coli at numbers about 1 cfu/cm2 and >1 cfu/100 cm2, respectively, before work started; and at numbers < 1 cfu/cm2 and about 1 cfu/100 cm2, respectively, after a period of work. The findings indicate that at the second plant both cuts and trimmings are contaminated with coliforms and E. coli from the conveyor.