Visible contamination on animals and carcasses and the microbiological condition of meat

It is generally assumed that preventing visible contamination of or removing visible contamination from carcasses will enhance the microbiological safety of meat. Visible contamination of carcasses can be reduced by washing or otherwise cleaning animals before slaughter, by dehairing hides before carcasses are skinned or dressed with the skin on, or by performing skinning and eviscerating operations in manners that avoid the transfer of filth from the hide to the meat or the spillage of gut contents. Visible contamination can be removed by washing, trimming, or vacuuming carcasses. The available data appear to indicate that, of the various actions that can be taken to obtain carcasses that are free of visible contamination, only minimizing the visible contamination of meat during skinning and eviscerating operations may also ensure a degree of control over the microbiological contamination of meat. It might be preferable for visible contamination to be controlled largely by superior skinning and eviscerating practices rather than by animal or carcass cleaning treatments, which may not prevent the depositing of bacteria on or the removal of substantial numbers of bacteria from carcasses.     

An investigation of Escherichia coli O157 contamination of cattle during slaughter at an abattoir

The extent of contamination with Escherichia coli O157 was determined for 100 cattle during slaughter. Samples from 25 consecutively slaughtered cattle from four unrelated groups were collected from the oral cavity, hide, rumen, feces after evisceration, and pre- and postchill carcass. Ten random fecal samples were collected from the pen where each group of animals was held at the abattoir. E. coli O157 was detected using automated immunomagnetic separation (AIMS), and cell counts were determined using a combination of most probable number (MPN) and AIMS. E. coli O157 was isolated from 87 (14%) of the 606 samples collected, including 24% of 99 oral cavity samples, 44% of 100 hides, 10% of 68 fecal samples collected postevisceration, 6% of 100 prechill carcass swabs, and 15% of 40 fecal samples collected from holding pens. E. coli O157 was not isolated from rumen or postchill carcass samples. E. coli O157 was isolated from at least one sample from each group of cattle tested, and the prevalence in different groups ranged from less than 1 to 41%. The numbers of E. coli O157 differed among the animals groups. The group which contained the highest fecal (7.5 x 10(5) MPN/g) and hide (22 MPN/cm2) counts in any individual animal was the only group in which E. coli O157 was isolated from carcasses, suggesting a link between the numbers of E. coli O157 present and the risk of carcass contamination. Processing practices at this abattoir were adequate for minimizing contamination of carcasses, even when animals were heavily contaminated with E. coli O157.     

Horizontal transmission of Escherichia coli O157:H7 during cattle housing

Ruminant livestock, particularly cattle, is considered the primary reservoir of Escherichia coli O157:H7. This study examines the transmission of E. coli O157:H7 within groups of cattle during winter housing. Holstein Friesian steers were grouped in six pens of five animals. An animal inoculated with and proven to be shedding a marked strain of E. coli O157: H7 was introduced into each pen. Fecal (rectal swabs) and hide samples (900 cm2 from the right rump) were taken from the 36 animals throughout the study. Water, feed, and gate or partition samples from each pen were also examined. Within 24 h of introducing the inoculated animals into the pens, samples collected from the drinking water, pen barriers, and animal hides were positive for the pathogen. Within 48 h, the hides of 20 (66%) of 30 cohort animals from the six pens were contaminated with E. coli O157:H7. The first positive fecal samples from the noninoculated cohort animals were detected 3 days after the introduction of the inoculated steers. During the 23 days of the study, 15 of 30 cohort animals shed the marked E. coli O157:H7 strain in their feces on at least one occasion. Animal behavior in the pens was monitored during a 12-h period using closed circuit television cameras. The camera footage showed an average of 13 instances of animal grooming in each pen per hour. The study suggests that transmission of E. coli O157:H7 between animals may occur following ingestion of the pathogen at low levels and that animal hide may be an important source of transmission.     

Microbial assessment of an upward and downward dehiding technique in a commercial beef processing plant

Preventing microbial contamination during dehiding is challenging, and skinning methods are of critical importance for the hygienic status of beef carcasses. Two skinning methods are usually employed: upward hide pulling (UHP) and downward hide pulling (DHP). This study has compared the microbiological contamination of carcasses using both systems in a beef processing plant in the process of changing its dehiding method from UHP to DHP. 100 cm² areas from eight carcass sites (ham, chuck, rump, bung, flank, brisket, shin and neck) were sampled on 36 skinned carcasses dehided by each technique. Total viable counts (TVCs) and Enterobacteriaceae counts for each site were determined. No significant differences were observed in total (pooled-samples) carcass contamination regardless of the method used. However, significant differences (p < 0.05) in TVCs were observed at the flank, shin, brisket and neck. These differences can be attributed to possible deficiencies in the implementation of the HACCP pre-requisite programmes, and are not necessarily associated with the skinning method per se.     

SOURCES OF CONTAMINATION DURING SLAUGHTER AND MEASURES FOR CONTROL

This paper is concerned with processes and procedures involved in the contamination of beef, lamb and pork carcasses during slaughter. The hides of beef and the fleece of sheep are major sources of carcass contamination. The spread of pathogens from beef hides to the carcass, operatives and surfaces in the abattoir is demonstrated. Efforts to clean the hide of cattle and the fleece of sheep are outlined, with reference to the success of these treatments in reducing carcass contamination. The effect of bringing very dirty or dungy animals to slaughter is considered in terms of the effect on carcass contamination after slaughter. The influence of tying the bung (or rectum) in reducing carcass contamination is discussed, as is the use of plastic bags as an additional control in preventing pathogen spread on pig carcasses. The relationship of this revised procedure in reducing the occurrence of yersiniosis in Norway is shown. The use of a commercially automated system to tie beef bungs is discussed in relation to reducing carcass contamination. A comparison between the removal of faecal contamination on carcasses by trimming or using a new steam-vacuumized system is presented. The effect of preevisceration washing of beef carcasses is described and the rationale relating to bacterial removal using this treatment is discussed. The influence of evisceration as a source of carcass contamination is demonstrated in relation to sheep slaughter. The processes of carcass decontamination using washing with water at different temperatures, steam pasteurization and hot lactic acid are compared in relation to their ability to remove bacteria from beef carcass surfaces. Finally, the effect of line speed and the impact of technology advances on beef and sheep carcass contamination is reviewed.     

Incidence of coagulase positive Staphylococcus on beef carcasses in three Australian abattoirs.

The contamination of beef carcasses with coagulase-positive staphylococci (CPS) was studied at three beef abattoirs (A, B and C). The incidence and the number of CPS were determined on cattle hides immediately after slaughter and on three carcass sites (brisket, flank and round) at different points during processing along the slaughter line. The incidence of CPS on cattle hides ranged from 20 to 68.6%. At abattoir A, 6.5% of the carcasses sampled before evisceration were contaminated with CPS, compared to 40% of the carcasses after evisceration. The incidence on carcasses changed little during further processing; however, after chilling for 72 h, the incidence increased to 83%. After evisceration, the brisket and flank areas were more often contaminated than the round. A similar pattern of contamination was observed at abattoir B. At abattoir C, 26.7% of the samples collected before evisceration were contaminated and this fell to 16.7% after evisceration. After chilling for 72 h, the incidence of carcass contamination with CPS increased to 46.7%. The average number of CPS on contaminated carcasses prior to and after overnight chilling was less than 50 colony-forming units (cfu)/cm2 and, after weekend chilling, increased to 64 and 112 cfu/cm2 in abattoirs A and B, respectively. Of the isolates tested, 71.4% produced staphylococcal enterotoxin and 21% could not be classified phenotypically. The hands of workers and environmental sites associated with the evisceration process were examined for CPS at abattoir A. Hands were heavily contaminated and were the likely source of CPS contamination at this abattoir.     

Effects of shearing and fleece cleanliness on microbiological contamination of lamb carcasses

The meat industry in Norway has developed national guidelines for Good Hygiene Practices for slaughtering and skinning, based on categorisation of animals. These include shearing sheep and lambs in the abattoirs immediately before slaughter. The aim of this study was to investigate microbiological carcass contamination associated with: (i) different shearing regimes; (ii) fleece cleanliness; and (iii) the slaughter process. In addition, the efficacy of the national guidelines in reducing microbial contamination was evaluated. A total of 280 swab samples were collected from the brisket areas (100 cm(2)) of 140 naturally contaminated lamb carcasses in a commercial abattoir. Half the samples were collected at skinning of brisket areas at the start of the slaughter-line and half of them were collected at the end of slaughter-line, just before chilling. The lambs were divided into four groups (n=35) according to the duration of the period between shearing and slaughter: (i) 0 days (shorn at the abattoir immediately before slaughter); (ii) three days; (iii) seven days; and (iv) not shorn. Mean log colony forming units (CFU) per 100 cm(2) at skinning were 5.78 and 6.95 for aerobic plate count (APC) (P<0.05), 1.65 and 2.78 for Escherichia coli (P<0.05) for shorn and unshorn lambs, respectively. For shorn lambs, divided according to the period between shearing and slaughter, the mean log CFU per 100 cm(2) were 5.45, 5.75, 6.12 (APC) and 1.77, 1.46, 1.71 (E. coli) for the 0-days, 3-days and 7-days groups, respectively (P<0.05 for the difference between 0- and 7-days groups in APC results). A four-category scale (0-3) was used for assessing fleece cleanliness before skinning. Visually clean lambs (score '0') had lower levels of APC on the carcass surfaces than those categorised as dirty (score '2-3') (P<0.05). The carcasses at the end of the slaughter-line had lower levels of APC than they had at skinning. However, the statistical significant reduction of E. coli on carcass surfaces at skinning point for shorn lambs, were impaired and no longer significantly different from the unshorn group at the end of the slaughter-line. The increased E. coli level at the end of the slaughter-line might be explained by weaknesses related to slaughter hygiene in particular suboptimal evisceration in the abattoir which was used as a basis for our trial, and thus the national guidelines concerning shearing had not the fully intended effect on reducing microbial carcass contamination.     

Prevalence of Salmonella and Campylobacter in beef cattle from transport to slaughter

The objective of this study was to evaluate the effect of typical production practices during the transport of cattle on the resulting incidence of Salmonella and Campylobacter in the feces, on the hides, and on the carcasses of these cattle and in the environment (trucks, holding pens, and knock boxes). Various factors were evaluated, including the type of animal (feedlot cattle vs. adult pasture cattle), the breed of cattle, the body condition of the animal, the age of the animal, the time of feed and water withdrawal, the contamination level of the transport vehicle at the feedlot or farm, the transport time, the time cattle were held in the holding pen at the plant, and the contamination level of the holding pen. Four groups of each type of animal were sampled on different days. Samples were collected from cattle prior to transport and after transport (rectal and hide swabs) as well as from the carcasses of these cattle. Pre- and posttransit samples were also taken from the transport vehicle and from the holding pen and knock box at the slaughter facility. For feedlot cattle, fecal shedding stayed fairly constant for both organisms before and after transport (3 to 5% for Salmonella and 64 to 68% for Campylobacter). However, the shedding rate for adult cattle increased from 1 to 21% for Salmonella but stayed constant for Campylobacter (6 to 7%). Contamination of hides with Salmonella increased for both animal types from a level of 18 to 20% to a level 50 to 56%. For Campylobacter, the contamination level decreased from 25 to 13% for feedlot cattle but remained unchanged for adult animals (1 to 2%). Nineteen percent of feedlot cattle carcasses and 54% of adult cattle carcasses tested positive for Salmonella, while only2% of feedlot cattle carcasses and none of the adult cattle carcasses tested positive for Campylobacter. Thus, for feedlot cattle, the factors considered in this study did not affect the shedding of either organism but did affect the contamination of hides with both. For adult animals, the factors increased both shedding of and hide contamination with Salmonella only, not Campylobacter.     

Development of an experimental model to assess the ability of Escherichia coli O157:H7-inoculated fecal pats to mimic a super shedder within a feedlot environment

This study was conducted to develop an experimental model that could assess the ability of Escherichia coli O157:H7-inoculated fecal pats to mimic a super shedder (>10(4) CFU/g of feces) within a feedlot environment. The day before the study began, 48 steers that had been negative for E. coli O157:H7 in feces for three consecutive weeks were sorted into three treatment groups, with two replicate pens per treatment and 8 steers per pen. Steers within the pens (20.50 by 10.75 m) were exposed to control feces or feces inoculated with two levels of a mixture of five strains of nalidixic acid-resistant E. coli O157:H7 (low level, 10(2) CFU/g; high level, 10(5) CFU/g). Five 300-g fecal pats were introduced into the pens twice daily (10:00 a.m. and 2:30 p.m.) on days 0 through 6 and days 14 through 20. Pats were placed in the pen at random locations to mimic defecation of a steer within the pen. Fecal grab samples, hide swab samples (500-cm2 area of the rump), natural fecal pat samples (freshly voided), and rope samples (1.22-m-long manila rope) where obtained at multiple times during the 49-day trial to evaluate the spread of nalidixic acid-resistant E. coli O157:H7 throughout the feedlot environment and among penmates. Immunomagnetic separation and selective media were used to detect E. coli O157:H7. Nalidixic acid-resistant E. coli O157:H7 was detected in 13 high-level treatment fecal grab samples, 7 high-level treatment hide swab samples, 1 low-level hide swab sample, and 2 high-level rope samples. For both fecal grab and hide swab samples, the overall prevalence of E. coli O157:H7 in the high-level group was greater (P < 0.01) than that for the pooled low-level and control groups. Addition of inoculated fecal pats to pens increased transmission of E. coli O157:H7 among penmates, but cattle that acquired E. coli O157:H7 shed the bacterium for only a short time at low levels. Transmission of E. coli O157:H7 from the feces of super shedders to naive penmates may contribute to the observed transient nature of shedding of E. coli O157:H7 among feedlot cattle.     

Efficacy of hypobromous acid as a hide-on carcass antimicrobial intervention

Escherichia coli O157:H7 and Salmonella on cattle hides at slaughter are the main source of beef carcass contamination by these foodborne pathogens during processing. Hypobromous acid (HOBr) has been approved for various applications in meat processing, but the efficacy of HOBr as a hide antimicrobial has not been determined. In this study, the antimicrobial properties of HOBr were determined by spraying cattle hides at either of two concentrations, 220 or 500 ppm. Treatment of hides with 220 ppm of HOBr reduced the prevalence of E. coli O157:H7 on hides from 25.3 to 10.1% (P < 0.05) and reduced the prevalence of Salmonella from 28.3 to 7.1% (P < 0.05). Treatment of hides with 500 ppm of HOBr reduced (P < 0.05) the prevalence of E. coli O157:H7 on hides from 21.2 to 10.1% and the prevalence of Salmonella from 33.3 to 8.1%. The application of 220 ppm of HOBr reduced (P < 0.05) aerobic plate counts, total coliform counts, and E. coli counts on hides by 2.2 log CFU/ 100 cm(2). The use of 500 ppm of HOBr resulted in reductions (P < 0.05) of aerobic plate counts, total coliform counts, and E. coli counts by 3.3, 3.7, and 3.8 log CFU/100 cm(2), respectively, demonstrating that the use of higher concentrations of HOBr on hides resulted in additional antimicrobial activity. These results indicate that the adoption of a HOBr hide wash will reduce hide concentrations of spoilage bacteria and pathogen prevalence, resulting in a lower risk of carcass contamination.     

A study of the prevalence and enumeration of Salmonella enterica in cattle and on carcasses during processing

Salmonella prevalence and counts were estimated for samples from the oral cavity, hide, rumen, and feces of 100 cattle at slaughter and from the pre- and postchill carcasses of these cattle. Samples were collected from 25 consecutively slaughtered cattle from each of four unrelated groups slaughtered at a single abattoir on different days. Ten additional fecal samples from each group were collected from their respective abattoir holding pens prior to slaughter. The prevalence of Salmonella was estimated using automated immunomagnetic separation, and the counts were estimated using a combination of most probable number (MPN) and automated immunomagnetic separation. A total of 606 samples were collected with Salmonella isolated from 157 (26%), including 29% of oral cavities, 68% of hides, 16% of feces collected after evisceration, 25% of rumen samples, 2% of prechill carcasses, 3% of postchill carcasses, and 48% of feces collected from holding pens. The prevalence and count of Salmonella varied between the different groups of animals tested. The highest count obtained was from a rumen sample (1.1 x 10(4) MPN/g). Other counts were generally low, with a maximum count in feces collected after evisceration and in the abattoir holding pens of 93 and 23 MPN/g, respectively. The highest count on hides, in oral cavities, and on carcasses was 4.8 MPN/cm2, 23 MPN/g, and 0.31 MPN/cm2, respectively. Even though Salmonella was present on the hides and in the rumen and feces of at least one animal from each group of cattle, the processing of animals at this abattoir resulted in few contaminated carcasses, and when contamination occurred, Salmonella was detected at low numbers.     

Transportation and lairage environment effects on prevalence, numbers, and diversity of Escherichia coli O157:H7 on hides and carcasses of beef cattle at processing

Hide has been established as the main source of carcass contamination during cattle processing; therefore, it is crucial to minimize the amount of Escherichia coli O157:H7 on cattle hides before slaughter. Several potential sources of E. coli O157: H7 are encountered during transportation and in the lairage environment at beef-processing facilities that could increase the prevalence and numbers of E. coli O157:H7 on the hides of cattle. On three separate occasions, samples were obtained from cattle at the feedlot and again after cattle were stunned and exsanguinated at the processing plant (286 total animals). The prevalence of E. coli O157:H7 on hides increased from 50.3 to 94.4% between the time cattle were loaded onto tractor-trailers at the feedlot and the time hides were removed in the processing plant. Before transport, nine animals had E. coli O157:H7 in high numbers (> 0.4 CFU/cm2) on their hides. When sampled at the slaughter facility, the number of animals with high hide numbers had increased to 70. Overall, only 29% of the E. coli O157:H7 isolates collected postharvest (221 of 764) matched pulsed-field gel electrophoresis types collected before transport. The results of this study indicate that transport to and lairage at processing plants can lead to increases in the prevalence and degree of E. coli O157:H7 contamination on hides and the number of E. coli O157:H7 pulsed-field gel electrophoresis types associated with the animals. More study is needed to confirm the mechanism by which additional E. coli O157:H7 strains contaminate cattle hides during transport and lairage and to design interventions to prevent this contamination.     

Effects of a minimal hide wash cabinet on the levels and prevalence of Escherichia coli O157:H7 and Salmonella on the hides of beef cattle at slaughter

Harborage of Escherichia coli O157:H7 and Salmonella on animal hides at slaughter is the main source of beef carcass contamination during processing. Given this finding, interventions have been designed and implemented to target the hides of cattle following entry into beef processing plants. Previous interventions targeting hides have not been suitable for all beef processing plants because of cost and space restrictions. In this study, a hide wash cabinet was evaluated to determine whether it was more amenable to widespread use in the beef processing industry, especially for small and medium-size plants. Overall, 101 (35.1%) of 288 beef cattle hides sampled before entry into the hide wash cabinet harbored E. coli O157:H7 at or above the limit of detection (40 CFU/100 cm2). After passage through the hide wash cabinet, only 38 (13.2%) of 288 hides had E. coli O157:H7 levels > or =40 CFU/100 cm2. Before the hide wash cabinet, 50 (17%) of 288 hides harbored E. coli O157:H7 at levels above 100 CFU/100 cm2, with one sample as high as 20,000 CFU/100 cm2. In contrast, only 14 (5%) of 288 hides had E. coli O157:H7 levels above 100 CFU/100 cm2 after hide washing, with the highest being 2000 CFU/100 cm2. These same trends also were found for Salmonella before and after hide washing. These results indicate that the hide wash cabinet described in this study was effective and should provide small and medium-size processing plants with an affordable hide wash intervention strategy.     

Pulsed field gel electrophoresis of related Escherichia coli O157 isolates associated with beef cattle and comparison with unrelated isolates from animals, meats and humans

The pulsed field gel electrophoresis (PFGE) diversity of 51 related Escherichia coli O157 isolates, associated with beef cattle from a single-farm-to-single abattoir (SF-SA) chain of events was determined. The 51 related E. coli O157 isolates from hides, faeces or carcasses of SF-SA cattle produced 11 different PFGE profiles. Also, the PFGE diversity of 6 isolates, associated with a second cattle abattoir, was determined; only two PFGE profiles were found. On the other hand, the PFGE diversity of 136 unrelated E. coli O157 isolates (from healthy meat animals, retail meats and cases of human disease) was also determined. The 136 unrelated E. coli O157 isolates produced 78 different PFGE profiles, most of which (approximately 70%) comprised only one isolate. Overall, the results showed: (a) related E. coli O157 isolates (from both SF-SA events, and the second abattoir) had a markedly narrower clonal profile than the 136 unrelated E. coli O157 isolates; (b) the isolation of identical PFGE types from hide, lairage environment, and carcasses confirms the significance of cross-contamination (both pre-slaughter and during skinning) taking place at abattoirs; and (c) PFGE typing of isolates offers a good tool for tracking sources/routes of such cross-contamination. Such cross-contamination may lead to originally E. coli O157-free animals (and resultant carcasses) becoming contaminated during farm-slaughter-dressing chain of events, so development of efficient control strategies is required.     

Development and evaluation of an on-line hide decontamination procedure for use in a commercial beef processing plantt

The hides of cattle are the source of Escherichia coli O157:H7 that contaminates beef carcasses during commercial beef processing. Therefore, effective interventions that reduce hide contamination should reduce subsequent carcass contamination. The first objective of this study was to identify the most effective reagents for decontamination of beef hides. Cattle hides draped over barrels were used for in vitro experiments to compare the efficacy of washes using 1.6% sodium hydroxide, 4% trisodium phosphate, 4% chlorofoam, or 4% phosphoric acid, each followed by a rinse step using either water or acidified (pH 7.0) chlorine at 200 or 500 ppm. All treatments using a water rinse reduced hide coliform counts by 1.5 to 2.5 log CFU/ 100 cm2. Compared with water rinses, 200 and 500 ppm acidified chlorine rinses increased efficacy by approximately 1.0 and 2.0 log CFU/100 cm2, respectively. Vacuuming of the treated areas to remove excess liquid improved hide cleanliness by an average of an additional 1.0 log CFU/100 cm2. The second objective was to evaluate the use of an on-line hide-wash cabinet that used a sodium hydroxide wash and a chlorinated (1 ppm) water rinse. Hides sampled before entering and after exiting the cabinet had aerobic plate counts and Enterobacteriaceae counts that were reduced by 2.1 and 3.4 log CFU/100 cm2, respectively, and the prevalence of E. coli O157 on hides was reduced from 44 to 17% when the cabinet was in use. Preevisceration carcass aerobic plate counts and Enterobacteriaceae counts were both reduced by 0.8 log CFU/100 cm2, and the prevalence of E. coli O157 on preevisceration carcasses was reduced from 17 to 2% when the cabinet was in use. These results support decontamination of hides as an effective means to reduce pathogen contamination of cattle carcasses during processing.     

Microbiological Contamination and Primal Cut Yields of Skinned and Scalded Pork Carcasses

Microbiological contamination was determined in core samples from the surface of the ham, shoulder, belly and back of skinned and scalded pork carcasses. Aerobic plate counts of mesophilic organisms indicated that ham and shoulder areas of scalded carcasses had higher bacterial numbers than skinned carcasses. Contamination on the back of the carcass was similar for skinned and scalded carcasses, while skinned carcass bellies had slightly higher counts than did scalded bellies. Numbers of psychrotrophic bacteria were negligible in all cases. Weights of primal cuts were compared in skinned and scalded carcasses by alternately skinning one side of each of 23 pork carcasses, while the other side was left skin-on. Belly, picnic shoulder and ham yields were less for skinned sides, while the loin and Boston shoulder were not affected.     

Antimicrobial drug resistance of Salmonella and Escherichia coli isolates from cattle feces, hides, and carcasses

To determine patterns of cross-contamination and antibiotic susceptibility of microorganisms commonly associated with cattle, 60 cattle shipped to a commercial abattoir (20 in each of three separate trial periods) were followed through processing. Samples for bacterial isolation were collected from the feces and hides immediately before shipping, from the hides at the abattoir after exsanguination, and from the carcasses before evisceration and in the cooler. Samples were cultured for Salmonella and non-type-specific Escherichia coli. Salmonella was identified in 33.9% (n = 20) of the fecal samples and on 37.3% (n = 22) of the hides before shipment. At the abattoir, the proportion of hides from which Salmonella was isolated increased (P < 0.001) to 84.2% (48 hides). Nonspecific E. coli and Salmonella were recovered from 40.4 and 8.3% of preevisceration carcass samples, respectively. No Salmonella or nonspecific E. coli were recovered from hotbox carcass samples. Isolates were tested for antimicrobial drug susceptibility. For nonspecific E. coli, 80.3% (n = 270) of the isolates were resistant to at least one antimicrobial drug. For Salmonella, 97% (n = 101) of the isolates were resistant to at least one antimicrobial drug; however, only 4.0% were resistant to two or more. The most common resistance was to sulfamethoxazole. These results indicate that the presence of microorganisms resistant to antimicrobial drugs is common in cattle and beef. Further studies are needed to identify the sources and causes of this drug resistance.     

Effect of chemical dehairing on the prevalence of Escherichia coli O157:H7 and the levels of aerobic bacteria and enterobacteriaceae on carcasses in a commercial beef processing plant

The objective of this experiment was to test the hypothesis that cleaning cattle hides by removing hair and extraneous matter before hide removal would result in improved microbiological quality of carcasses in commercial beef processing plants. To test this hypothesis, we examined the effect of chemical dehairing of cattle hides on the prevalence of Escherichia coli O157:H7 and the levels of aerobic bacteria and Enterobacteriaceae on carcasses. Samples from 240 control (conventionally processed) and 240 treated (chemically dehaired before hide removal) hides (immediately after stunning but before treatment) and preevisceration carcasses (immediately after hide removal) were obtained from four visits to a commercial beef processing plant. Total aerobic plate counts (APC) and Enterobacteriaceae counts (EBC) were not (P > 0.05) different between cattle designated for chemical dehairing (8.1 and 5.9 log CFU/100 cm2 for APC and EBC, respectively) and cattle designated for conventional processing (8.0 and 5.7 log CFU/100 cm2 for APC and EBC, respectively). However, E. coli O157:H7 hide prevalence was higher (P < 0.05) for the control group than for the treated group (67% versus 88%). In contrast to hides, the bacterial levels were lower (P < 0.05) on the treated (3.5 and 1.4 log CFU/100 cm2 for APC and EBC) than the control (5.5 and 3.2 log CFU/100 cm2 for APC and EBC) preevisceration carcasses. Prevalence of E. coli O157:H7 was lower (P > 0.05) on treated than on control preevisceration carcasses (1% versus 50%). These data indicate that chemical dehairing of cattle hides is an effective intervention to reduce the incidence of hide-to-carcass contamination with pathogens. The data also imply that any effective hide intervention process incorporated into beef processing procedures would significantly reduce carcass contamination by E. coli O157:H7.     

Effects of long- or short-haul transportation of slaughter heifers and cattle liner microclimate on hide contamination with Escherichia coli O157

Effects of cattle transportation on hide contamination with Escherichia coli O157 have been variable, and the present study was designed to clarify relationships among duration of transport, microclimate, and environment within the trailer and contamination of hides with E. coli O157. Crossbred Angus heifers from a feedlot in southern Alberta were sorted into 10 replicate loads containing 45 animals (short haul, 621.5 ± 2.1 kg of body weight) or 46 animals (long haul, 576.0 ± 1.7 kg of body weight). Long-haul trips (n = 5) were made in July and August to slaughter plant A, whereas short-haul trips (n = 5) were made in October to slaughter plant B. The same trailer unit and driver were used for all loads. Data loggers were located in the ceiling of each compartment of the trailers to record ambient temperature and relative humidity. Each heifer was swabbed on the perineum on-farm prior to loading and immediately after stunning at the slaughter plant (an average 12-h transport for long haul and 1-h transport for short haul). Swabs were transported on ice before immunomagnetic separation for detection of E. coli O157. Transportation did not affect prevalence of hide contamination with E. coli O157, although 80% of long-haul swabs were positive on-farm compared with 26% of short-haul swabs, due to seasonality of shedding E. coli O157. Cattle transported in the nose compartment had fewer positive hide swabs (P < 0.05) than cattle in the deck or belly compartments during long-haul trips, even though the nose had a higher (P < 0.05) temperature-humidity index than the other compartments. Prevalence of hide contamination varied widely among loads even when the organism was at seasonally low levels. This suggests that the feedlot pen has a greater effect on hide contamination at the slaughter plant than transportation factors including temperature-humidity index, loading density, and duration of transport.     

Molecular characterization of Escherichia coli O157:H7 hide contamination routes: feedlot to harvest

This study was conducted to identify the origin of Escherichia coli O157:H7 contamination on steer hides at the time of harvest. Samples were collected from the feedlot, transport trailers, and packing plant holding pens and from the colons and hides of feedlot steers. A total of 50 hide samples were positive for E. coli O157:H7 in two geographical locations: the Midwest (25 positive hides) and Southwest (25 positive hides). Hide samples were screened, and the presence of E. coli O157: H7 was confirmed. E. coli O157:H7 isolates were fingerprinted by pulsed-field gel electrophoresis and subjected to multiplex PCR procedures for amplification of E. coli O157:H7 genes stx1, stx2, eaeA, fliC, rfbEO157, and hlyA. Feedlot water trough, pen floor, feed bunk, loading chute, truck trailer side wall and floor, packing plant holding pen floor and side rail, and packing plant cattle drinking water samples were positive for E. coli O157:H7. Pulsed-field gel electrophoresis banding patterns were analyzed after classifying isolates according to the marker genes present and according to packing plant. In this study, hide samples positive for E. coli O157:H7 were traced to other E. coli O157:H7-positive hide, colon, feedlot pen floor fecal, packing plant holding pen drinking water, and transport trailer side wall samples. Links were found between packing plant side rails, feedlot loading chutes, and feedlot pens and between truck trailer, different feedlots, and colons of multiple cattle. This study is the first in which genotypic matches have been made between E. coli O157:H7 isolates obtained from transport trailer side walls and those from cattle hide samples within the packing plant.