Inactivation of Escherichia coli O157:H7 in Beef Roasts Cooked in Conventional or Convection Ovens or in a Slow Cooker under Selected Conditions.

Inactivation of Escherichia coli O157:H7 in beef roasts cooked under selected cooking conditions was evaluated. Eye of round roasts were each inoculated at five sites in the central plane with a five-strain cocktail of E. coli O157:H7 at ca. 6.3 log CFU per site and cooked to center temperatures of 56 to 71°C in a convection oven set at 120, 140, 180, or 200°C, in a conventional oven set at 120 or 210°C, and in a slow cooker set on high or low. Prime rib roasts were each inoculated at 10 sites throughout the roast with the same E. coli O157:H7 cocktail at ca. 6.6 log CFU per site and cooked in the conventional oven set at 140 or 180°C to center temperatures of 58 to 71°C. The number of sites yielding E. coli O157:H7 after cooking decreased with increasing roast center temperature for the eye of round roasts cooked in the convection oven or in the slow cooker at a given setting, but this trend was not apparent for roasts of either type cooked in the conventional oven. Reductions of E. coli O157 in both types of roasts were generally less at the center than at other locations, particularly locations closer to the surface of the meat. When eye of round roasts were cooked to the same center temperature in the convection oven, the reduction of E. coli O157:H7 increased with increasing oven temperature up to 180°C and decreased after that. The reduction of E. coli O157:H7 in replicate roasts cooked under conditions in which the organism was not eliminated during cooking mostly differed by >1 log CFU per site. However, E. coli O157:H7 was not recovered from any of the inoculation sites when eye of round roasts were cooked to 65, 60, 60, or 63°C in the convection oven set at 120, 140, 180, and 200°C, respectively; cooked to 63 or 71°C in the conventional oven set at 120 and 210°C, respectively; or cooked to 63°C in the slow cooker set at high or low. For prime rib roasts, E. coli O157:H7 was not recovered from any of the inoculation sites in roasts cooked to 71 or 58°C in the conventional oven set at 140 and 180°C, respectively.

Unusual compositions of microflora of vacuum-packaged beef primal cuts of very long storage life.

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.

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.

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.

Relationship between the numbers of Escherichia coli and the prevalence of Escherichia coli O157:H7 on hides of carcasses at a large beef packing plant.

Due to the expense of monitoring multiple serotypes of Escherichia coli at slaughter, a study was conducted at a beef abattoir in southern Alberta to determine relationships between E. coli and E. coli O157:H7 on hides. Swab samples were collected from carcasses immediately prior to hide removal over 8 weeks in summer (n = 591) and winter (n = 686). Detection of E. coli was highest in summer (P < 0.05), although detection of E. coli O157:H7 did not differ by season. Numbers of E. coli did not vary by season, but were affected by slaughter plant hygiene schedules. E. coli O157:H7 was more likely (P < 0.001) to be detected on hides of carcasses with the most E. coli (>3.5 log CFU/50 cm²). For E. coli < 3.5 log CFU/50 cm², the likelihood of detecting E. coli O157:H7 did not differ. Consequently, for 83% of carcasses, there was no relationship between numbers of E. coli and detection of E. coli O157:H7 on hides.

Enhanced control of microbiological contamination of product at a large beef packing plant.

Swab samples were obtained from groups of 25 carcasses at various stages of processing at a large beef packing plant. The log mean number of aerobes recovered from carcasses after skinning was 2.2 log CFU/cm(2). Spraying the uneviscerated carcasses with 5% lactic acid reduced the numbers of aerobes by about 1 log unit; but subsequent carcass dressing operations, a second treatment with 5% lactic acid, pasteurizing, and carcass cooling had no substantial effect upon the number of aerobes on carcasses. The total numbers of coliforms or Escherichia coli cells recovered from skinned carcasses were <2 log CFU/2,500 cm(2). The numbers were reduced by the washing of uneviscerated carcasses but increased after evisceration operations. The numbers were reduced by spraying with lactic acid and pasteurizing, with no coliforms or E. coli being recovered from pasteurized carcass sides. No coliforms or E. coli cells were recovered from the forequarters of cooled carcass sides, but E. coli cells were recovered from the hindquarters of 1 of 50 cooled carcass sides, at 1.4 log CFU/1,000 cm(2). The numbers of aerobes on conveyor belts in the carcass breaking facility were similar to the numbers on cooled carcass, but the numbers of aerobes on cuts and trimmings and the number of coliforms and E. coli cells on the products and belts were higher than the numbers on carcasses. The findings indicate that most cooled carcasses produced at the plant carry E. coli at numbers <1 CFU/10,000 cm(2) but that product can be contaminated with small numbers of E. coli (<1 CFU/100 cm(2)) during carcass breaking.

Mycobacterium avium subsp. paratuberculosis in dairy products, meat, and drinking water.

Mycobacterium avium subsp. paratuberculosis (Map) is the cause of Johne's disease, a chronic infection of the gut, in ruminant animals that provide milk and/or meat for human consumption. Map also may be involved in Crohn's disease and type 1 diabetes in humans. Although the role of Map in human diseases has not been established, minimizing the exposure of humans to the organism is considered desirable as a precautionary measure. Infected animals can shed Map in feces and milk, and the organism can become disseminated in tissues remote from the gut and its associated lymph nodes. The presence of at least some Map in raw milk and meat and in natural waters is likely, but the numbers of Map in those foods and waters should be reduced through cooking or purification. The available information relating to Map in milk and dairy products, meats, and drinking water is reviewed here for assessment of the risks of exposure to Map from consumption of such foods and water.

Effects on the development of blown pack spoilage of the initial numbers of Clostridium estertheticum spores and Leuconostoc mesenteroides on vacuum packed beef.

Beef steaks were inoculated with Clostridium estertheticum spores and Leuconostoc mesenteroides cells at all combinations of numbers of 0, 10, 100 or 1000/cm(2) for each organism. After vacuum packaging the steaks were stored at 4, 1, or -1.5°C. Pack volumes were determined by water displacement at suitable intervals. Irrespective of L. mesenteroides numbers, for packs containing meat inoculated with 0, 10, 100 or 1000 spores/cm(2), 60, 16, 3 and 1 of 60 packs did not swell. The times of onset of swelling were twice as long at -1.5 as at 4°C, but they were not affected by the inoculated numbers of L. mesenteroides. Rates of pack swelling increased with increasing storage temperature and number of spores, but decreased with increasing numbers of inoculated L. mesenteroides. Lactic acid bacteria can apparently prevent development of blown pack spoilage of vacuum packs containing meat contaminated with low numbers of C. estertheticum.

Effects of experience with swabbing procedures on the numbers of bacteria recovered from carcasses by swabbing with sponges.

Each carcass in groups of 25 pig, cattle, or bison carcasses was sampled by five people: two or three people experienced with carcass sampling and two or three without previous experience. Each person sampled a different randomly selected site on a dressed carcass side by swabbing an undelimited area of approximately 100 cm(2) with a moistened synthetic sponge. The numbers of aerobic bacteria, coliform bacteria, and Escherichia coli recovered from each sample were determined. The mean log and log mean values were calculated for each set of 25 counts for each group of bacteria from pig carcasses and each set of 25 aerobic counts from cattle and bison carcasses from the samples obtained by each person. Values for the log of the total number recovered were calculated for all the sets of counts from samples obtained by each person. Most of the corresponding statistics for each set of counts of the same type for samples obtained by five people from the same group of carcasses differed by less than 0.5 log unit. These findings indicate that the numbers of bacteria recovered from carcasses by swabbing with sponges are unlikely to differ substantially as a result of samples being collected by different people using the same procedure.

Mycobacterium avium subsp. paratuberculosis in muscle, lymphatic and organ tissues from cows with advanced Johne's disease.

Blood, liver, kidney, lymph nodes and muscle tissue were obtained from the carcasses of five cows with advanced Johne's disease. Samples from the raw tissues, from cooked muscle tissues and from cooked hamburger patties that contained chopped mesenteric lymph nodes were collected aseptically. Each sample was divided into two portions, one of which was decontaminated. Both portions were homogenized. Homogenates were spread on selective agar for the recovery of Mycobacterium avium subsp. paratuberculosis (Map) and inoculated into a Map growth medium with the organism being detected in the cultures by PCR procedures and Ziehl-Neelsen staining. Map were recovered at numbers > 10(3) cfu/g from 7 of 15 liver and mesenteric and ileocaecal lymph node samples; and at lesser numbers from 5 of 15 kidney and superficial inguinal and prescapular lymph node samples. The numbers recovered from decontaminated and not decontaminated portions of each sample were generally similar. Map was recovered from 1 and detected in 6 of 50 not decontaminated portions of samples of raw, chilled or frozen meat; and detected in 1 of 15 not decontaminated samples of meat cooked to 61 degrees C, and in 1 of 40 samples of meat cooked to >/=70 degrees C. Map was detected in 2 of 4 samples of mesenteric lymph nodes cooked to 61 degrees C, but not in samples cooked to > or =70 degrees C. The findings indicate that Map may be present in meat from infected animals at low numbers, but that any such organisms are likely to be inactivated when meat is cooked to a well done condition.

Effects on the microbiological condition of product of decontaminating treatments routinely applied to carcasses at beef packing plants.

Reports on the microbiological effects of decontaminating treatments routinely applied to carcasses at beef packing plants indicate that washing before skinning may reduce the numbers of enteric bacteria transferred from the hide to meat. Washing skinned carcasses and/or dressed sides can reduce the numbers of aerobes and Escherichia coli by about 1 log unit, and pasteurizing sides with steam or hot water can reduce their numbers by > 1 or > 2 log units, respectively. Spraying with 2% lactic acid, 2% acetic acid, or 200 ppm of peroxyacetic acid can reduce the numbers of aerobes and E. coli by about 1 log, but such treatments can be ineffective if solutions are applied in inadequate quantities or to meat surfaces that are wet after washing. Trimming and vacuum cleaning with or without spraying with hot water may be largely ineffective for improving the microbiological conditions of carcasses. When contamination of meat during carcass dressing is well controlled and carcasses are subjected to effective decontaminating treatments, the numbers of E. coli on dressed carcasses can be < 1 CFU/ 1,000 cm2. However, meat can be recontaminated during carcass breaking with E. coli from detritus that persists in fixed and personal equipment. The adoption at all packing plants of the carcass-dressing procedures and decontaminating treatments used at some plants to obtain carcasses that meet a very high microbiological standard should be encouraged, and means for limiting recontamination of product during carcass breaking and for decontaminating trimmings and other beef products should be considered.

Prevalence on beef carcasses of Mycobacterium avium subsp. paratuberculosis DNA.

Fifty samples were collected from each of skinned and dressed carcasses, from each of culled beef breeding cows and fed beef cattle <18 months old at two beef packing plants A and B, and from culled dairy cows at a packing plant C. The 450 samples were collected by swabbing an area of about 1000 cm2 in the anal region of each carcass. DNA extracted from each swab was tested for the IS900 and F57 sequences of the Mycobacterium avium subsp. paratuberculosis (MAP) genome by two stage, nested polymerase chain reaction (PCR) procedures. An internal amplification control (IAC) was detected in 45 or more of each group of 50 DNA preparations. IS900 and F57 were detected in some IAC-positive preparations from all and all but one of the groups of carcasses, respectively. Of the IAC-positive preparations in each group, between 6 and 54% were positive for IS900, and between 4 and 20% were positive for F57. When preparations were tested by single stage, quantitative PCR procedures, IS900 was detected in two samples but F57 was detected in none. The MAP DNA on carcasses was probably derived from small numbers of MAP from the environment that contaminated the animals' hides.

Changes in the proteome of Escherichia coli during growth at 15 degrees C after incubation at 2, 6 or 8 degrees C for 4 days.

For better understanding of the complex behaviour of Escherichia coli at chiller temperatures, log phase E. coli grown at 15 degrees C were incubated at 8, 6, or 2 degrees C for 4 days, and were then incubated at 15 degrees C for 12 h. Cultures were sampled after incubation at the lower temperatures, and during subsequent incubation at 15 degrees C. Proteins extracted from the samples were separated by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE). Spots of 45 previously identified proteins that were differentially expressed at 15 or < or =8 degrees C were quantified by image analysis. After incubation at 8 or 6 degrees C for 4 days cells were growing with or without formation of elongated cells (filaments), respectively, but growth did not occur at 2 degrees C. In cells incubated at 8 or 6 degrees C proteins associated with the stress response and energy generation were upregulated and proteins associated with protein synthesis were downregulated, while protein levels in cells incubated at 2 degrees C were little changed. When cells were then incubated at 15 degrees C, the levels of differentially expressed proteins in cells that had been incubated at 8 or 6 degrees C decreased or increased towards the levels found in cells growing at 15 degrees C, but some proteins were still under or over expressed after 12 h. In cells incubated at 15 degrees C after incubation at 2 degrees C, the levels of many of the proteins declined but the levels of proteins associated with protein synthesis increased. The findings indicate that the physiological states of log phase E. coli incubated at < or =2 degrees C or at higher chiller temperature are different, but that for both states incubation at an above chiller temperature for >3 generations is required before protein levels adjusted to those usual for the higher temperature. Cells in these different physiological states may respond differently to other stresses encountered during warming of chilled foods.

Distributions of brine and bacteria in beef primal cuts injected with brine without, or before or after mechanical tenderizing.

Eye of round primal cuts of beef were injected with brines containing a dye and Listeria innocua. The amounts of brine in portions of meat were determined from the concentrations of dye in the tissues, and the numbers of L. innocua in the tissues were determined from the numbers of colonies recovered on hydrophobic grid membrane filters incubated on a selective agar. Portions of meat from primals injected with brine after extensive mechanical tenderizing yielded L. innocua at numbers that would be expected from the amounts of brine in the meat. However, portions of meat from primals injected with brine without or before mechanical tenderizing yielded only about 10% of the expected numbers of L. innocua. The numbers of L. innocua recovered from injected meat that was not tenderized, relative to the amount of brine retained by the meat, declined with decreasing brine pressure and increasing strokes per minute of the needle head. When brine was injected at about 5% with low brine pressure and high head speed, the numbers of L. innocua retained in the meat were <1% of the expected numbers. When injected meat was examined microscopically, L. innocua were observed only between the muscle fibres in meat that was not tenderized before injection, but between fibres and in lacunae in tissue damaged by mechanical tenderizing before injection. The distributions of brine and bacteria in injected primals apparently did not alter substantially during storage in vacuum packs, at 2°C, for 2 weeks.

Behaviours of log phase cultures of eight strains of Escherichia coli incubated at temperatures of 2, 6, 8 and 10 degrees C.

The behaviours of cold-adapted, log-phase cultures of eight strains of Escherichia coli incubated at 2, 6, 8 and 10 degrees C for 10 days were examined by determining absorbance at 600 nm (A(600)), viable counts and cell size distribution as indicated by forward angle light scattering (FALS) values, obtained for samples collected each day from each culture. Cell lengths were determined from photomicrographs of samples for which the flow cytometry data indicated the mean cell lengths were maximal or minimal for each culture. At 2 degrees C, A(600) values for all strains and viable counts for some changed little, while viable counts for other strains declined progressively by >1 log unit. At 6 degrees C, A(600) values for most strains increased at progressively declining rates and then remained constant while viable counts increased to reach maximum values before maximum A(600) values were attained, and then declined. At 8 degrees C, the behaviours of most strains were similar to the behaviour at 6 degrees C. At 10 degrees C, seven of the strains grew exponentially, but for most of these the growth rate determined from A(600) values differed from that determined from viable count data. Mean FALS values for cultures incubated at 6, 8, or 10 degrees C showed various patterns of increase and decrease, indicating fluctuations in cell lengths. For all strains, the minimum cell length was <3 microm, but the maximum cell lengths ranged from <20 to >140 microm. The findings suggest that the formation of elongated cells or filaments is usual behaviour for E. coli growing at temperatures approaching or below the minimum for sustained growth.

Microbiological conditions of meats from large game animals and birds.

Large game animals and birds used for the commercial production of meat include deer of various species, wild boar and feral pigs, ostriches, emus and rheas, crocodiles and alligators, bison, and kangaroos. Meat from feral pigs and kangaroos is obtained from wild animals only, but much or most meat from the other game animals or birds is obtained from farmed animals. The microbiological conditions of meats from hunted animals can be compromised by poor placement of shots, the usual evisceration and sometimes further dressing of carcass in the field, and ageing of carcasses at ambient temperatures. However, the general microbiological conditions of carcasses from farmed game animals or birds slaughtered and dressed at suitable abattoirs can be comparable with or better than the microbiological conditions of carcasses from domestic animals or birds. The incidences of enteric pathogens on meat from wild or farmed game animals or birds can be less than those for meat from intensively reared domestic animals, but infection of some game meats with Trichinella or other foodborne parasites may occur.

Setting control limits for Escherichia coli counts in samples collected routinely from pig or beef carcasses.

Records of Escherichia coli counts in samples routinely collected from carcasses were obtained from one pork and three beef packing plants. The data obtained from each plant were divided into sets from consecutive 6-month periods. For each set of counts, log total counts were calculated for subsets of various sizes. For each set of log total counts, the mean (x), the standard deviation (SD), and an action limit of x + 3 SD were calculated, and the set was tested for a normal distribution. With the data from samples collected at the pork packing plant during 6 years, the proportion of samples with counts of zero in the 12 sets ranged from 15 to 45%. For that plant, appropriate action limits could be derived from log total counts for subsets of nine unit values. With the data from samples collected during 8 years at one beef packing plant, the proportion of samples with counts of zero in the 16 sets ranged from 88 to 99%. For that plant, appropriate action limits could be derived from log total counts for subsets of 15 unit values. With the data from samples collected during 2 or 2.5 years at each of the other beef packing plants, the proportion of samples with counts of zero in all sets was > 99%. For those data, action limits could not be derived from values for subsets of log total counts.

The effects on the microbiological condition of product of carcass dressing, cooling, and portioning processes at a poultry packing plant.

The log mean numbers of aerobes, coliforms, Escherichia coli and presumptive staphylococci plus listerias on chicken carcasses and carcass portions at various stages of processing at a poultry packing plant were estimated from the numbers of those bacteria recovered from groups of 25 randomly selected product units. The fractions of listerias in the presumptive staphylococci plus listerias groups of organisms were also estimated. Samples were obtained from carcasses by excising a strip of skin measuring approximately 5 x 2 cm(2) from a randomly selected site on each selected carcass, or by rinsing each selected carcass portion. The log mean numbers of aerobes, coliforms, E. coli and presumptive staphylococci plus listerias on carcasses after scalding at 58 degrees C and plucking were about 4.4, 2.5, 2.2 and 1.4 log cfu/cm(2), respectively. The numbers of bacteria on eviscerated carcasses were similar. After the series of operations for removing the crop, lungs, kidneys and neck, the numbers of aerobes were about 1 log unit less than on eviscerated carcasses, but the numbers of the other bacteria were not substantially reduced. After cooling in water, the numbers of coliforms and E. coli were about 1 log unit less and the numbers of presumptive staphylococci plus listerias were about 0.5 log unit less than the numbers on dressed carcasses, but the numbers of aerobes were not reduced. The numbers of aerobes were 1 log unit more on boneless breasts, and 0.5 log units more on skin-on thighs and breasts that had been tumbled with brine than on cooled carcasses; and presumptive staphylococci plus listerias were 0.5 log unit more on thighs than on cooled carcasses. Otherwise the numbers of bacteria on the product were not substantially affected by processing. Listerias were <20% of the presumptive staphylococci plus listerias group of organisms recovered from product at each point in the process except after breasts were tumbled with brine, when >40% of the organisms were listerias.

Differential expression of proteins in cold-adapted log-phase cultures of Escherichia coli incubated at 8, 6 or 2 degrees C.

Temperature is used to control the growth of microorganisms in foods. The minimum temperature for sustained growth of Escherichia coli is 7 degrees C. E. coli cells in the logarithmic phase of growth at 15 degrees C were incubated at 8, 6 or 2 degrees C. The cells grew with the formation of filaments at the two higher temperatures, but did not grow at 2 degrees C. In order to investigate more thoroughly the nature of filament formation in E. coli at temperatures near the minimum temperature for sustained growth, cells were harvested after 1 day at 2 degrees C or at times up to 4 or 8 days at 8 or 6 degrees C, respectively. Proteins extracted from the cells were separated by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), and spots containing differentially expressed proteins were identified by quadropole time-of-flight tandem (Q-ToF-2) mass spectrometry. For most of the identified proteins, the amounts were not substantially different in cells grown at 15 degrees C or incubated at 2 degrees C. In cells incubated at 8 or 6 degrees C, proteins associated with stress responses, the tricarboxylic acid cycle and electron transport were present in substantially greater amounts, and proteins associated with protein synthesis were present in substantially smaller amounts than in cells grown at 15 degrees C. These findings suggest that the stringent response is induced in E. coli incubated at temperatures near the minimum for growth, so the formation of filaments at those temperatures may be a result of the stringent response.

Microbiological sampling of poultry carcass portions by excision, rinsing, or swabbing.

Groups of 25 skin-on thighs or skin-on, skinned, or tumbled breast portions of broiler chicken carcasses were sampled by excision of skin or muscle tissue, rinsing, or swabbing. Counts of total aerobic bacteria, coliforms, and Escherichia coli were recorded for each sample. For all types of carcass portions, the mean log counts and the total log counts obtained for each group of bacteria by excision or rinsing mostly differed by <0.5 log unit. However, the counts obtained by swabbing were generally >0.5 log unit lower than the smaller of the values obtained by the other two sampling methods.

Factors affecting the microbiological condition of the deep tissues of mechanically tenderized beef.

Whole or halved top butt prime beef cuts were treated in two types of mechanical tenderizing machines that both pierced the meat with thin blades but that used blades of different forms. Aerobes on meat surfaces and in the deep tissues of cuts after treatments were counted. When cuts were treated at a laboratory using a Lumar machine, the contamination of deep tissues increased significantly (P < 0.01) with increasing numbers of aerobic bacteria on meat surfaces and decreased significantly (P < 0.001) with increasing distance from the incised surface. However, contamination did not increase significantly (P > 0.1) with repeated incising of the meat. When halved cuts were incised one or eight times using a commercially cleaned Ross machine at a retail store, the numbers of aerobes recovered from deep tissues were similar with both treatments. When halved cuts were treated in one or other machine, deep tissue contamination was greater with the Lumar machine than with the Ross machine. Contamination of deep tissues as a result of tenderizing by piercing with thin blades can be minimized if the blades are designed to limit the number of bacteria carried into the meat and the microbiological condition of incised surface is well controlled.