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.

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.

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.

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.

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.

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.

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.

Effects of peroxyacetic acid, acidified sodium chlorite or lactic acid solutions on the microflora of chilled beef carcasses.

The effects of solutions of 0.02% peroxyacetic acid, acidified 0.16% sodium chlorite, 2% lactic acid and 4% lactic acid on the natural flora of the distal surfaces of pieces of brisket, from chilled beef carcass quarters delivered from two slaughtering plants to a processing plant, were investigated. Peroxyacetic acid and acidified sodium chlorite solutions had little effect on the numbers of aerobes, coliforms or Escherichia coli on meat from one plant, and were less effective than 4% lactic acid for reducing the numbers of bacteria on meat from the other plant. With meat from both plants, treatment of meat with 4% lactic acid and holding for 5 or 60 min at 7+/-1 degrees C before sampling resulted in reductions of all three groups of bacteria by >/=1.5 log unit. Treatment with 2% lactic acid resulted in similar reductions when meat was sampled 5 min after the treatment, but reductions were about 1 log unit when meat was sampled 60 min after the treatment. Treatment of carcass quarters with 4% lactic acid resulted in reductions of bacterial numbers of >/=2 log units at distal surfaces, but

Microbiological and organoleptic qualities of vacuum-packaged ground beef prepared from pasteurized manufacturing beef.

Manufacturing beef was pasteurized by immersion in water of 85 degrees C for 60 s, or was not pasteurized before being coarsely ground. The coarsely ground beef was vacuum-packaged and stored at 2 degrees C for up to 6 weeks. Before storage and at weekly intervals, three packs of pasteurized and three of unpasteurized beef were opened. The meat from each pack was finely ground and displayed in two overwrapped packs at 4 degrees C for 3 days after storage for up to 3 weeks, or for 2 days after longer storage times. Samples for microbiological analysis were obtained at the times of preparation of display packs and at the end of display. Displayed meat was assessed daily for colour, discolouration and retail acceptability, and for odour intensity and acceptability at the end of display. Before storage, the numbers of total aerobic bacteria, presumptive pseudomonads and presumptive Brochothrix thermosphacta recovered from pasteurized meat were >1 log unit less than the corresponding numbers recovered from unpasteurized meat, but the numbers of presumptive lactic acid bacteria and presumptive enterobacteria were <1 log unit less from pasteurized than from unpasteurized meat. After all periods of storage and display, the numbers of bacteria recovered from pasteurized and unpasteurized meat at each time were mostly similar. The colour of pasteurized meat was perceived as being paler than that of unpasteurized meat, but discolouration and retail acceptability of pasteurized and unpasteurized meat were perceived as similar at most times. The odours of displayed, pasteurized and unpasteurized meat were perceived to be similar at all times that odours were assessed. The findings indicate that pasteurizing of manufacturing beef to improve the microbiological safety of ground beef would not unacceptability degrade the appearance of the ground product, but that the storage life of ground beef would not be greatly extended by the treatment.

The microbiological effects of trimming sticking wounds in pasteurized pig carcasses.

Neither pasteurizing of uneviscerated carcasses nor trimming reduced the numbers of total aerobic bacteria recovered from sticking wounds in pig carcasses. However, trimming after pasteurizing increased the numbers of coliforms and Escherichia coli recovered from sticking wounds, whereas pasteurizing without trimming reduced these counts.

Microbiological sampling of meat cuts and manufacturing beef by excision or swabbing.

Groups of 25 beef or pork loin primal cuts or of pieces of stored or not stored manufacturing beef were sampled by excision and by swabbing with cotton wool, sponge, and gauze. Total aerobic counts, coliforms, and Escherichia coli from each sample were enumerated. Values for the mean log10, log10 mean, and/or the log10 total numbers recovered were calculated for each set of 25 bacterial counts. Those statistics indicated that, for product sampled without storage, swabbing with cotton wool or sponge recovered about 30%, and swabbing with gauze recovered about 10% of the bacteria recovered by excision sampling; but that for product sampled after storage, swabbing with cotton wool or sponge recovered about 50% and swabbing with gauze recovered about 15% of the bacteria recovered by excision sampling. However, the incidences of samples positive for coliforms and E. coli were less for stored than for nonstored product with all methods of sampling. The findings indicate that the conditions of meat surfaces, the handling of product, and the state of the microflora might all affect the numbers of bacteria recovered by any sampling technique. Thus, the relationship between the numbers recovered by excision or any selected swabbing technique may differ for different types of noncomminuted, raw meat product.

Effects of hot water pasteurizing treatments on the microbiological condition of manufacturing beef used for hamburger patty manufacture.

Ten 12-kg lots of manufacturing beef from a single packing plant were obtained from a hamburger patty manufacturing plant. Each lot was divided into two, 6-kg portions, one of which was not treated while the other was treated with water of 85 degrees C. A portion from one lot was treated for 15 s. A portion from each of three lots was treated for 30 s, three portions were treated for 45 s, and three were treated for 60 s. Twenty-five pieces of meat from each portion were swabbed over areas of 100 cm2. Subsequently, each portion was first coarsely ground then finely ground, with twenty-five 100-g samples being taken from each portion at each stage of grinding. Each swab and sample of ground meat was separately processed for the enumeration of total aerobic counts, coliforms and Escherichia coli at levels of detection of 1 cfu/cm2, 1 cfu/100 cm2 and 1 cfu/100 cm2, respectively, for swab samples; and at a level of detection of 1 cfu/g for all three types of bacteria in samples of ground beef. A 250-kg batch of manufacturing beef was treated with water of 85 degrees C for 60 s. The product was processed through commercial equipment for manufacturing frozen hamburger patties. The flavour of patties prepared from the pasteurized product was compared with the flavour of patties prepared during normal commercial operation of the equipment. The weight of the manufacturing beef was not affected by the treatments. Similar total numbers of coliforms or E. coli were recovered per 2500 cm2 from the 25 swab samples or per 25 g from the 25 ground beef samples from each untreated portion. As the ratio of the surface area in cm2 to the weight in g would likely be < or = 1, the similar numbers indicated that swab sampling was inefficient for recovering coliforms and E. coli from the meat. However, coliforms and E. coli were recovered more frequently from swab than from ground beef samples from treated portions. Thus, some swabs from all three portions of beef treated for 30 s yielded coliforms and E. coli, but samples from portions treated for 45 or 60 s yielded few coliforms and no E. coli. The numbers recovered from the treated and untreated portions indicated that treatments for 45 or 60 s reduced both coliform and E. coli numbers by two orders of magnitude. The flavours of cooked patties prepared from the meat pasteurized with water of 85 degrees C for 60 s were not distinguished from the normal commercial product. The data indicate that pasteurizing manufacturing beef with water of 85 degrees C for 45 s could be a practicable treatment for enhancing the microbiological safety of frozen hamburger patties.

Assessment of the adequacy of cleaning of equipment used for breaking beef carcasses.

Enumeration of bacteria on product entering or leaving a beef carcass breaking process showed that the meat was being contaminated with Escherichia coli during the process. The equipment used in the process appeared to be well cleaned, and few bacteria were recovered from meat-contacting surfaces of cleaned equipment. However, careful inspection of the cleaned equipment revealed obscured locations in the equipment which harboured detritus that carried large numbers of aerobic bacteria including E. coli. The findings indicated that when the equipment was operated with wetting of the meat-contacting surfaces, bacteria from the persisting detritus were transferred to the meat-contacting surfaces and the meat. Similar increases in the numbers of E. coli on product as a result of the carcass breaking processes were observed at two of three other plants where the processes were examined. It therefore appears that compliance with current regulatory agency recommendations for conducting and monitoring the cleaning of carcass breaking equipment will not assure the control of hazardous microbiological contamination from carcass breaking equipment. Consequently, it is suggested that the adequacy or otherwise of each cleaning process should be assessed by reference to the mean numbers of suitable indicator organisms on product entering and leaving the production process that employs the cleaned equipment.

The hygienic and organoleptic qualities of ground beef prepared from manufacturing beef pasteurized by immersion in hot water.

Groups of 24 lots of manufacturing beef were untreated or treated by immersion in water of 85 °C for 15 s or 1 min. Each lot was ground, and total counts, coliforms and Escherichia coli were enumerated in samples from each ground lot. Each ground lot was divided into two portions, and their appearances were assessed by a panel 2, 24 and 48 hr after the treatment of the beef. Treatment for 15 s reduced the numbers of non-thermotolerant bacteria, including coliforms and E. coli, by about one order of magnitude. Treatment for 1 min reduced the numbers of non-thermotolerant bacteria by about two orders of magnitude, with reduction of the numbers of coliforms and E. coli in all samples to below the detection level of 1 CFUg(-1). Ground beef prepared from treated product tended to appear lighter in colour and duller than ground beef from untreated product, and to be more discoloured after 24 hr. However, the changes in the appearances of ground beef resulting from the treatment of manufacturing beef were small, and seemingly would not render the ground meat unacceptable for retail display. In a triangle taste test, there was no significant difference (p > 0.05) in the flavour of hamburger patties prepared from untreated beef or from beef treated for 1 min at 85 °C. The findings suggest that pasteurization of manufacturing beef could be a commercially useful technique for reducing the risk of infection with enteric bacteria to consumers of mass produced hamburger patties.

The effects of hot water pasteurizing treatments on the appearances of pork and beef.

Portions of post- and pre-rigor pork and beef were treated by immersion in water of 75 or 85 °C for 5, 10, 15 or 20 s. The appearances of untreated and treated cut muscle, fat, membrane covered and cut bone surfaces, and the overall appearances of treated and untreated meat pieces, were assessed by a 5-member panel 2 hr and 24 hr after each treatment. At those times, CIE L(∗)a(∗)b(∗) values were obtained for cut-muscle surfaces. The appearances of surfaces covered by membrane, of fat and cut bone surfaces of pre-rigor pork and beef, and of fat and cut bone surfaces of post-rigor pork, were not persistently degraded by any treatment. However, the appearances of fat and cut bone surfaces of post-rigor beef were persistently degraded by the harsher treatments, apparently because of pre-treatment staining of fat and changes in the bone marrow. Panel scores for the overall appearance and for the appearance of cut muscle surfaces were generally the same for each meat piece. All treatments caused patchy bleaching of cut muscle. The degraded appearances of pre- and post-rigor pork and post-rigor beef muscle persisted at 24 hr, but the appearances of beef muscle treated pre-rigor improved between 2 and 24 hr. Most treated muscle gave increased CIE L(∗) values and decreased a(∗) and b(∗) values as compared with untreated portions from the same primal cut. However, CIE b(∗) values for pre-rigor beef muscle were higher than for untreated muscle 2hr after treatment, but lower than for untreated muscle 24 hr after treatment. It appears that pasteurizing treatments cannot be applied to meat without some degradation of the appearances of cut muscle surfaces, which will persist in pork treated pre- or post-rigor and in beef treated post-rigor, but which will partially resolve during the storage of beef treated pre-rigor.

Use of total of Escherichia coli counts to assess the hygienic characteristics of a beef carcass dressing process.

Swab samples were obtained from 3 sites on the surfaces of beef carcasses passing through a high speed dressing process, with 24 samples from each site being obtained at each of 4 points in the process. The aerobic microflora recovered from each swab after incubation at 25 degrees C was enumerated and characterized, and numbers of coliforms and Escherichia coli were determined. The data on aerobic flora indicated that skinning results in similar contamination of all 3 sites, that further deposition of bacteria at the brisket site occurs after skinning, and that trimming and washing achieve modest decontamination of the neck and brisket site, and extensive decontamination of the rump site. Changes in flora compositions during processing were too limited to much affect the assessment based on the aerobic flora total counts alone. The E. coli data indicated that during skinning the rump site was more heavily contaminated with faecal organisms than the other sites, that contamination of the brisket site is little altered between skinning and carcass splitting, although there is an extensive redistribution of E. coli at the neck site and sporadic, limited decontamination of the rump site, and that trimming and washing do not decontaminate the neck or rump sites, but that the rump site is extensively decontaminated by trimming. There was good correlation between E. coli and coliform counts, but weak correlation between E. coli and aerobic, 25 degrees C, counts. The findings suggest that assessments of beef carcass dressing processes for Hazard Analysis: Critical Control Point (HACCP) purposes should be based on enumerations of E. coli, or perhaps coliforms, rather than of the aerobic flora, to avoid important misunderstandings of the hygienic effects of the various operations in a process.

Assessment of the Hygienic Characteristics of a Beef Carcass Dressing Process.

Swab samples were obtained from the surfaces of randomly selected beef carcasses passing through a high-speed dressing process. A single sample was obtained from each selected carcass from one of 10 sites. At each of 3 points in the process, 25 samples were obtained from each carcass site. The aerobic bacteria, coliforms, and Escherichia coli recovered from each sample were enumerated. Values for the means and standard deviations of each set of 25 values were calculated on the assumption that each set of values was log-normally distributed. The E. coli data indicated relatively heavy (mean log numbers > 2/100 cm2) contamination of carcasses with E. coli during the skinning of posterior sites; redistribution of E. coli , from relatively heavily to relatively lightly (mean log numbers about 0/100 cm2) contaminated sites during evisceration operations, and reduction of E. coli numbers at most sites as a result of trimming and washing operations. However, posterior sites remained the most heavily contaminated with E. coli . The findings for coliforms were similar to those for E. coli . In contrast, the total count data indicated heavy (mean log numbers > 3/cm2) contamination of anterior (brisket) sites as well as posterior sites and little redistribution of bacteria during evisceration operations. After trimming and washing operations, the mean log total numbers at most sites were about 2/cm2, but one brisket site remained heavily contaminated. It is suggested that E. coli or coliform data are appropriate for assessing carcass dressing processes for hazard analysis critical control point (HACCP) system purposes, while total count data are inappropriate for that purpose but may be appropriate, in relation to product storage stability, for quality management (QM) system purposes.

Hygienic Effects of Trimming and Washing Operations in a Beef-Carcass-Dressing Process †.

Swab samples were obtained from the surfaces of randomly selected beef carcasses passing through a high-speed dressing process. A single sample was obtained from a randomly selected site on the surface of each selected carcass. Fifty such samples were collected at each of four stages in the process. The aerobic bacteria, coliforms, and Escherichia coli recovered from each sample were enumerated. Values for the mean log units and standard deviations of each set of 50 log values were calculated on the assumption that the log values were normally distributed. The log of the arithmetic mean was estimated from the mean log and standard deviation values for each set. The results show that the average numbers of E. coli , coliforms, and aerobic bacteria which are deposited on carcasses during skinning and evisceration are not reduced by trimming, and that washing approximately halves the average numbers of those bacteria on carcasses. It is concluded that commercial trimming and washing operations are not effective means of decontaminating beef carcasses.