Changes in the Carriage of Campylobacter Strains by Poultry Carcasses during Processing in Abattoirs

The recent development of simple, rapid genotyping techniques for Campylobacter species has enabled investigation of the determinative epidemiology of these organisms in a variety of situations. In this study we have used the technique of fla typing (PCR-restriction fragment length polymorphism analysis of the flaA and flaB genes) to identify the sources of strains contaminating the carcasses of five campylobacter-positive and two campylobacter-negative broiler flocks during abattoir processing. The results confirmed that, in the United Kingdom, individual broiler flocks are colonized by a limited number of subtypes of Campylobacter jejuni or C. coli. In some but not all cases, the same subtypes, isolated from the ceca, contaminated the end product as observed in carcass washes. However, the culture methodology, i.e, use of direct plating or enrichment, affected this subtype distribution. Moreover, the number of isolates analyzed per sample was limited. fla typing also indicated that some campylobacter subtypes survive poultry processing better than others. The extent of resistance to the environmental stresses during processing varied between strains. The more robust subtypes appeared to contaminate the abattoir environment, surviving through carcass chilling, and even carrying over onto subsequent flocks. From these studies it is confirmed that some campylobacter-negative flocks reach the abattoir but the carcasses from such flocks are rapidly contaminated by various campylobacter subtypes during processing. However, only some of these contaminating subtypes appeared to survive processing. The sources of this contamination are not clear, but in both negative flocks, campylobacters of the same subtypes as those recovered from the carcasses were isolated from the crates used to transport the birds. In one case, this crate contamination was shown to be present before the birds were loaded.     

Changes in the carriage of Campylobacter strains by poultry carcasses during processing in abattoirs

The recent development of simple, rapid genotyping techniques for Campylobacter species has enabled investigation of the determinative epidemiology of these organisms in a variety of situations. In this study we have used the technique of fla typing (PCR-restriction fragment length polymorphism analysis of the flaA and flaB genes) to identify the sources of strains contaminating the carcasses of five campylobacter-positive and two campylobacter-negative broiler flocks during abattoir processing. The results confirmed that, in the United Kingdom, individual broiler flocks are colonized by a limited number of subtypes of Campylobacter jejuni or C. coli. In some but not all cases, the same subtypes, isolated from the ceca, contaminated the end product as observed in carcass washes. However, the culture methodology, i.e, use of direct plating or enrichment, affected this subtype distribution. Moreover, the number of isolates analyzed per sample was limited. fla typing also indicated that some campylobacter subtypes survive poultry processing better than others. The extent of resistance to the environmental stresses during processing varied between strains. The more robust subtypes appeared to contaminate the abattoir environment, surviving through carcass chilling, and even carrying over onto subsequent flocks. From these studies it is confirmed that some campylobacter-negative flocks reach the abattoir but the carcasses from such flocks are rapidly contaminated by various campylobacter subtypes during processing. However, only some of these contaminating subtypes appeared to survive processing. The sources of this contamination are not clear, but in both negative flocks, campylobacters of the same subtypes as those recovered from the carcasses were isolated from the crates used to transport the birds. In one case, this crate contamination was shown to be present before the birds were loaded.     

The prevalence of campylobacters and arcobacters in broiler chickens

Chicken carcasses from a supermarket and from a poultry abattoir were examined using methods designed to isolate as many strains of campylobacters and related organisms as possible. Strains of arcobacter, but no campylobacters, were isolated from every carcass after enrichment. Campylobacter jejuni subsp. jejuni was isolated from all carcasses examined by direct plating and other Campylobacter -like strains were isolated from nine out of 15 abattoir carcasses by direct plating but not after enrichment. Only the Camp. jejuni subsp. jejuni strains could be identified to species level using a readily available identification scheme and/or a commercial identification kit. Examination of caecal contents from the 15 abattoir poultry yielded Camp. jejuni subsp. jejuni and Campylobacter -like strains from 15 and eight by direct plating, and from six and nine after enrichment, respectively. Four sites in the intestine of the abattoir birds (60 samples) were examined for arcobacters and only one strain was isolated. This indicates that arcobacters are probably not normal inhabitants of the poultry intestine. Poultry is a rich source of other campylobacteria besides the thermophilic Campylobacter spp.     

Genotypic Analysis of Escherichia coli Strains from Poultry Carcasses and Their Susceptibilities to Antimicrobial Agents

Plasmid profiling and amplified fragment length polymorphism (AFLP) analysis were used to genotype 50 Escherichia coli strains from poultry carcasses. Thirty different plasmid profiles were evident, and clustering of the AFLP data showed that they were a distinctly heterogeneous group of strains. Susceptibility testing against five antimicrobial agents used in the South African poultry industry showed all strains to be susceptible to danofloxacin and colistin, while the majority (96%) were resistant to two tetracyclines.     

Molecular tracking, through processing, of Campylobacter strains colonizing broiler flocks

Many of the poultry flocks produced in the United Kingdom are colonized with Campylobacter, and the intensive nature of poultry processing usually results in contaminated carcasses. In this study, a previously reported molecular oligonucleotide probe method was used to track a specific flock-colonizing strain(s) on broiler carcasses during processing in two United Kingdom commercial poultry processing plants. Five Campylobacter-positive flocks were sampled at four points along the processing line, postbleed, postpluck, prechill, and postchill, and two Campylobacter-negative flocks processed immediately after positive flocks were sampled prechill. flaA was sequenced from Campylobacter strains isolated from these flocks, and strain-specific probes were synthesized. Skin and cecal samples were plated onto selective agar to give individual colonies, which were transferred onto membranes. These were then hybridized with the strain- and genus-specific probes. For all the 5 positive flocks, there was a significant reduction in campylobacters postbleed compared to postpluck but no subsequent fall on sampling pre- and postchill, and the strain(s) predominating on the carcasses throughout processing came from the flock being processed. This indicates that strains from the abattoir environment were not a significant cause of carcass contamination in flocks with well-established campylobacter colonization. However, negative flocks that were preceded by positive flocks were contaminated by strains that did not generally originate from the predominating strains recovered from the ceca of the previous positive flocks. This suggests that the abattoir environment has a significant role in the contamination of carcasses from negative but not fully colonized flocks.     

Genotypic Analyses of Escherichia coli O157:H7 and O157 Nonmotile Isolates Recovered from Beef Cattle and Carcasses at Processing Plants in the Midwestern States of the United States

Escherichia coli O157:H7 and O157 nonmotile isolates (E. coli O157) previously were recovered from feces, hides, and carcasses at four large Midwestern beef processing plants (R. O. Elder, J. E. Keen, G. R. Siragusa, G. A. Barkocy-Gallagher, M. Koohmaraie, and W. W. Laegreid, Proc. Natl. Acad. Sci. USA 97:2999–3003, 2000). The study implied relationships between cattle infection and carcass contamination within single-source lots as well as between preevisceration and postprocessing carcass contamination, based on prevalence. These relationships now have been verified based on identification of isolates by genomic fingerprinting. E. coli O157 isolates from all positive samples were analyzed by pulsed-field gel electrophoresis of genomic DNA after digestion with XbaI. Seventy-seven individual subtypes (fingerprint patterns) grouping into 47 types were discerned among 343 isolates. Comparison of the fingerprint patterns revealed three clusters of isolates, two of which were closely related to each other. Remarkably, isolates carrying both Shiga toxin genes and nonmotile isolates largely fell into specific clusters. Within lots analyzed, 68.2% of the postharvest (carcass) isolates matched preharvest (animal) isolates. For individual carcasses, 65.3 and 66.7% of the isolates recovered postevisceration and in the cooler, respectively, matched those recovered preevisceration. Multiple isolates were analyzed from some carcass samples and were found to include strains with different genotypes. This study suggests that most E. coli O157 carcass contamination originates from animals within the same lot and not from cross-contamination between lots. In addition, the data demonstrate that most carcass contamination occurs very early during processing.     

High-Resolution Genotyping of Campylobacter Strains Isolated from Poultry and Humans with Amplified Fragment Length Polymorphism Fingerprinting

For epidemiological studies of Campylobacter infections, molecular typing methods that can differentiate campylobacters at the strain level are needed. In this study we used a recently developed genotyping method, amplified fragment length polymorphism (AFLP), which is based on selective amplification of restriction fragments of chromosomal DNA, for genetic typing of Campylobacter jejuni and Campylobacter coli strains derived from humans and poultry. We developed an automated AFLP fingerprinting method in which restriction endonucleases HindIII and HhaI were used in combination with one set of selective PCR primers. This method resulted in evenly distributed band patterns for amplified fragments ranging from 50 to 500 bp long. The discriminatory power of AFLP was assessed with a C. jejuni strain, an isogenic flagellin mutant, and distinct C. jejuni strains having known pulsed-field gel electrophoresis and fla PCR-restriction fragment length polymorphism genotypes. Unrelated C. jejuni strains produced heterogeneous patterns, whereas genetically related strains produced similar AFLP patterns. Twenty-five Campylobacter strains obtained from poultry farms in The Netherlands grouped in three C. jejuni clusters that were separate from a C. coli cluster. The band patterns of 10 C. jejuni strains isolated from humans were heterogeneous, and most of these strains grouped with poultry strains. Our results show that AFLP analysis can distinguish genetically unrelated strains from genetically related strains of Campylobacter species. However, desirable genetically related strains can be differentiated by using other genotyping methods. We concluded that automated AFLP analysis is an attractive tool which can be used as a primary method for subtyping large numbers of Campylobacter strains and is extremely useful for epidemiological investigations.     

Genetic diversity in Helicobacter pullorum from human and poultry sources identified by an amplified fragment length polymorphism technique and pulsed-field gel electrophoresis

Helicobacter pullorum was first isolated from the faeces and carcasses of poultry and has been associated with human gastroenteritis. The aim of this study was to examine interstrain genetic diversity within H. pullorum. Two fingerprinting techniques were used: amplified fragment length polymorphism (AFLP) and pulsed field gel electrophoretic (PFGE) analysis. The 20 strains examined were from four countries and comprised 13 human isolates and seven poultry isolates. Their identity was confirmed by a species-specific PCR assay. The human and poultry isolates had distinct genotypes and most strains showed a high degree of genetic diversity. Genotyping also indicated a clonal origin for two strains from the same poultry flock, and established a close relatedness between three chicken carcass isolates from a processing plant. It is concluded that these two genotyping techniques will provide a useful basis for future epidemiological investigations of H. pullorum in poultry, and may provide a link with its possible causal role in human gastrointestinal infections.     

Contamination of Pig Carcasses at Two Abattoirs by Escherichia coli with Special Reference to O-serotypes and Antibiotic Resistance

Evidence of the source of carcass contamination of pigs at slaughter was obtained by determining presumptive coliform counts on faeces and on carcass surfaces, and comparing the O-serotypes and antibiotic sensitivity patterns of Escherichia coli from both sites. All of the 16 pig carcasses from the slaughter line of a commercial abattoir were contaminated with presumptive coliform bacilli on most sites examined; the carcasses of six out of eight pigs slaughtered at the Meat Research Institute (MRI) abattoir were also contaminated, but only small numbers of coliforms could be detected on a few of the sites. The proportion of O-serotypes of E. coli present in faeces which were also detected on carcass surfaces, indicating faecal contamination, varied between 0 and 8.6% in MRI slaughtered pigs but reached 66.6% in one group of commercially slaughtered pigs. O-serotypes found on carcass surfaces but not in the faeces of the pigs, were used as an indication of environmental contamination and this was very evident in the commercially slaughtered pigs. A high proportion of E. coli O-serotypes in the gut were resistant to antibiotics and these were also often found on the carcass surface and, since the range of O-serotypes in the pig is similar to that reported in man, the pig must be considered to be a potential reservoir of antibiotic resistant E. coli for man.     

Sources of Psychrotrophic Bacteria on Meat at the Abattoir

An export abattoir was examined to determine the sources and types of psychrotrophic bacteria which gain access to meat. Gram negative psychrotrophs were recovered from the hides, from structural and work surfaces within the abattoir, and from carcasses and meat at all stages of processing. Microbacterium thermosphactum was recovered intermittently at all sampling sites. Psychrotrophic and total counts and the incidence of M. thermosphactum on carcasses and meat increased during processing through the abattoir. Structural and work surfaces may be as important as the hide as sources of bacterial contaminants on meat. Seasonal variation was observed in psychrotrophic counts which correlated positively with rainfall and negatively with temperature.     

High-resolution genotyping of Campylobacter strains isolated from poultry and humans with amplified fragment length polymorphism fingerprinting.

For epidemiological studies of Campylobacter infections, molecular typing methods that can differentiate campylobacters at the strain level are needed. In this study we used a recently developed genotyping method, amplified fragment length polymorphism (AFLP), which is based on selective amplification of restriction fragments of chromosomal DNA, for genetic typing of Campylobacter jejuni and Campylobacter coli strains derived from humans and poultry. We developed an automated AFLP fingerprinting method in which restriction endonucleases HindIII and HhaI were used in combination with one set of selective PCR primers. This method resulted in evenly distributed band patterns for amplified fragments ranging from 50 to 500 bp long. The discriminatory power of AFLP was assessed with a C. jejuni strain, an isogenic flagellin mutant, and distinct C. jejuni strains having known pulsed-field gel electrophoresis and fla PCR-restriction fragment length polymorphism genotypes. Unrelated C. jejuni strains produced heterogeneous patterns, whereas genetically related strains produced similar AFLP patterns. Twenty-five Campylobacter strains obtained from poultry farms in The Netherlands grouped in three C. jejuni clusters that were separate from a C. coli cluster. The band patterns of 10 C. jejuni strains isolated from humans were heterogeneous, and most of these strains grouped with poultry strains. Our results show that AFLP analysis can distinguish genetically unrelated strains from genetically related strains of Campylobacter species. However, desirable genetically related strains can be differentiated by using other genotyping methods. We concluded that automated AFLP analysis is an attractive tool which can be used as a primary method for subtyping large numbers of Campylobacter strains and is extremely useful for epidemiological investigations.     

Diversity and prevalence of Arcobacter spp. in broiler chickens

Ninety-nine strains of Arcobacter spp., isolated from 10 chicken carcasses purchased from a supermarket and 15 chicken carcasses collected from a poultry abattoir, were speciated using a variety of phenotypic identification methods. All were tested using API Campy test strips and the 16-test (Preston) identification scheme developed for campylobacters. Fifty strains were selected for examination using a more comprehensive probabilistic identification scheme, and the identity of representative strains confirmed by protein profiling using SDS-PAGE. All 25 carcasses yielded Arcobacter butzleri . Three supermarket and 10 abattoir carcasses also carried A. cryaerophilus , and two abattoir carcasses carried A. skirrowii . The API Campy scheme proved unsatisfactory for identifying these strains: only 20 of 99 strains were accurately identified, all of which were A. cryaerophilus , the only Arcobacter sp. included in the database. Moreover, 76 of 99 strains were misidentified. The 16-test scheme identified all the arcobacter strains as A. cryaerophilus, since neither A. butzleri nor A. skirrowii had been described when the scheme was developed. The computer-assisted probabilistic scheme succeeded in identifying all but one strain, the identity of which was clarified by the use of SDS-PAGE. To our knowledge this is the first time that arcobacters other than A. butzleri have been reported in poultry meat or any other food of animal origin. Their high prevalence in poultry products may be of significance to public health.     

Salmonella and Escherichia coli O157:H7 Contamination on Hides and Carcasses of Cull Cattle Presented for Slaughter in the United States: an Evaluation of Prevalence and Bacterial Loads by Immunomagnetic Separation and Direct Plating Methods

The hide and carcass hygiene of cull cattle at slaughter in four geographically distant regions of the United States was examined from July 2005 to April 2006 by measuring the aerobic plate counts (APC) and the prevalences and loads of Salmonella and Escherichia coli O157:H7. The geometric mean log₁₀ APC CFU/100 cm² levels on hides and preevisceration and postintervention carcasses ranged from 6.17 to 8.19, 4.24 to 6.47, and 1.46 to 1.96, respectively, and were highest in the summer (P < 0.0001). The average prevalences of Salmonella on hides and preevisceration and postintervention carcasses were 89.6% (95% confidence interval [CI], 85.1 to 94.0), 50.2% (95% CI, 40.9 to 59.5), and 0.8% (95% CI, 0.18 to 1.42), respectively. The prevalences of E. coli O157:H7 were 46.9% (95% CI, 37.3 to 56.6) and 16.7% (95% CI, 9.8 to 23.6) on hides and preevisceration carcasses, respectively. Examination of the concomitant incidence of Salmonella and E. coli O157:H7 showed that, on average, 33.3% (95% CI, 15.9 to 69.8) of cattle hide and 4.1% (95% CI, 0.98 to 17.3) of preevisceration carcass samples were contaminated with both pathogens. The pathogen prevalence on hides and carcasses was not significantly affected by the season; however, significant differences were observed between plants with respect to the incoming pathogen load and the ability to mitigate hide-to-carcass transfer. In spite of these differences, postintervention carcass contamination was significantly reduced (P < 0.001), likely as a result of the use of one or more of the processing interventions employed at each of the four processing plants examined.     

Evidence for the Clustering of Antibacterial Resistance Phenotypes of Enterococci Within Integrated Poultry Companies

From July to December 2006, a panel of 401 enterococci was isolated from carcass rinse samples collected in five poultry processing plants in New Zealand. Agar diffusion assays for nine antibacterial drugs were used to obtain a resistance phenotype for each isolate. Hierarchical clustering techniques and diversity indices showed a high diversity of resistance phenotypes within each plant, with populations of Enterococcus faecalis showing greater heterogeneity than Enterococcus faecium. Bayesian modelling identified three clusters of phenotype patterns within the panel: the E. faecium isolates showed a high probability of containing two distinct clusters, whilst the E. faecalis isolates all grouped together to form the third cluster. The validity of these three clusters was examined using pairwise fixation indices and analysis of variance. Comparing the three clusters to the structure of the participating companies showed that resistance phenotypes for E. faecium isolated from processing plants that were geographically separated but were operated by the same integrated poultry company were more similar than E. faecium isolated from unconnected companies. Company-level management factors, such as the routine use of antibacterial drugs and the genetic line of birds reared, mirrored the structure of these clusters, thus indicating that company-level factors were the dominant selective pressures upon resistance phenotypes across all operating units within these integrated poultry companies.     

Enumeration of thermotolerant Campylobacter spp. from poultry carcasses at the end of the slaughter-line

AIM: To enumerate Campylobacter on poultry carcasses at the end of the slaughter-line, and investigate the extent to which Campylobacter from a positive flock were transmitted to other flocks during slaughter. METHODS AND RESULTS: The presence (in caeca) and the level (from carcasses) of Campylobacter were determined. The isolates were fingerprinted by amplified fragment length polymorphism (AFLP). A total of three of 13 broiler flocks and three of four-layer flocks harboured caecal Campylobacter. Carcasses from the caeca-positive broiler flocks were Campylobacter positive with numbers ranging from 2.6 x 10(4) to 2.6 x 10(6) CFU per carcass. Two caeca-negative broiler flocks, slaughtered directly after the positive broiler flocks, had the first carcasses contaminated with Campylobacter, with numbers below 2 x 10(4) CFU per carcass of the same AFLP haplotypes as the preceding flock. Campylobacter was detected on carcasses from only one of the caeca-positive layer flocks in numbers below 2 x 10(4) CFU per carcass. No Campylobacter was detected on carcasses from a flock succeeding the positive-layer flocks. CONCLUSION: Carcasses from Campylobacter-positive broiler flocks were heavily contaminated with Campylobacter, and transmitted low levels of Campylobacter to carcasses from negative flocks, slaughtered directly after. Campylobacter-positive layer flocks had low numbers of Campylobacter on the carcasses. SIGNIFICANCE AND IMPACT OF THE STUDY: The results indicate limited cross-contamination of Campylobacter between flocks at the slaughterhouse, reducing the advantage of logistic slaughter.     

Genotypic analysis of Escherichia coli strains from poultry carcasses and their susceptibilities to antimicrobial agents

Plasmid profiling and amplified fragment length polymorphism (AFLP) analysis were used to genotype 50 Escherichia coli strains from poultry carcasses. Thirty different plasmid profiles were evident, and clustering of the AFLP data showed that they were a distinctly heterogeneous group of strains. Susceptibility testing against five antimicrobial agents used in the South African poultry industry showed all strains to be susceptible to danofloxacin and colistin, while the majority (96%) were resistant to two tetracyclines.     

Enumeration of Salmonella from poultry carcass rinses via direct plating methods

Aim: To evaluate direct plating methods for the estimation of Salmonella load in poultry carcass rinses. Methods and Results: Two direct plating tools, the spiral plate count method (SPCM) and the hydrophobic grid membrane filtration (HGMF) method, were adapted to support quantification of Salmonella during poultry processing. Test samples consisted of 180 broiler carcasses from a commercial abattoir, 60 from each of three points in the processing line [pre‐inside–outside bird wash (pre‐IOBW), prechill and postchill]. The SPCM was used to estimate Salmonella load in pre‐IOBW rinses, while HGMF was used to estimate Salmonella levels in prechill and postchill rinses. Carcass rinses were also evaluated for Salmonella prevalence by enrichment methods. Mean prevalences of Salmonella were 95%, 100% and 41·7%, and the geometric mean loads were 3·7 × 10¹, 5·6 × 10⁰ and 5·0 × 10^?2 CFU ml^?1 for pre‐IOBW, prechill and postchill rinses, respectively. Conclusions: The methods described are useful for estimating the concentration of viable and typical Salmonella in poultry carcass rinses. Significance and Impact of the Study: Direct plating enumeration methods can facilitate the monitoring of Salmonella load on poultry carcasses throughout the production process, and the evaluation of new processing intervention strategies.     

Incidence of aeromonads in samples from an abattoir processing lambs

Two hundred and thirty three samples of lamb carcasses, livers, kidneys and faeces, collected at a local abattoir, were examined to determine the incidence of motile Aeromonas spp. Wash water from the abattoir was also tested. Direct plating on starch ampicillin agar and enrichment in alkaline peptone water were used. The incidence of aeromonads was low. They were detected only after enrichment in 5/47 faecal samples and 11/50 carcass samples. The 41 strains of Aeromonas isolated were identified to species level and 93% of them were able to grow at 5 degrees C. The ability to produce both haemolysin and enterotoxin was species-related and was more common in Aeromonas hydrophila and A. sobria strains than in A. caviae strains.     

The aerobic psychotrophic populations on meat and meat contact surfaces in a meat production system and on meat stored at chill temperatures

At a city abattoir, a wholesaler and 10 different supermarkets, surface microbiological samples were taken of carcasses, hands and apron fronts of members of staff and equipment (mincers and saws). In addition, minced meat, packaged and displayed in chilled cabinets, was also sampled. Carcasses, personnel surfaces and equipment were monitored by a modified agar sausage technique. From each of the highest dilution psychotrophic plate counts, five colonies were selected randomly, isolated and identified (1265 in total). Microbes developing on chilled meat were also isolated from other surfaces in the production chain. On chilled meat (51%) and at the abattoir (36%) pseudomonads were the predominant organisms followed by the Gram-positive cocci on chilled meat and by Acinetobacter, Moraxella and Alcaligenes spp. at the abattoir. At the wholesaler Gram-positive cocci (32%) predominated, followed by Alcaligenes, Moraxella and Alcaligenes spp. Pseudomonas, Alcaligenes, Neisseriaceae and related genera, Gram-positive cocci, species from the coryneform groups of bacteria and yeasts were identified from all the surfaces monitored. Identification with the API NE20 was unsatisfactory. Enterbacteriaceae, lactobacilli and endospore-forming bacteria were identified occasionally, but their significance as contaminating organisms seems low. No Salmonella spp. were identified.     

Genotypic analysis of Escherichia coli recovered from product and equipment at a beef-packing plant

AIMS: To identify sources of Escherichia coli on beef by characterizing strains of the organism on animals, equipment and product at beef-packing plant. METHODS AND RESULTS: Generic E. coli were recovered from hides, carcasses, beef trimmings, conveyers and ground beef during the summer of 2001 (750 isolates) and winter of 2002 (500 isolates). The isolates were characterized by Random Amplification of Polymorphic DNA (RAPD). The numbers of E. coli recovered from dressed carcasses were less than the numbers recovered from hides. The numbers recovered from chilled carcasses were too few for meaningful analysis of the strains present on them but the numbers recovered from trimmings and ground beef were larger. The RAPD patterns showed that the majority of isolates from hides, carcasses, beef trimmings, conveyers and ground beef were of similar RAPD types, but a few unique RAPD types were recovered from only one of those sources. The E. coli populations present on the hides of incoming animals and in the beef-processing environment were highly diverse. Randomly selected E. coli isolates from each of the five sources were further characterized by pulsed-field gel electrophoresis (PFGE). Most genotypes of E. coli defined by PFGE corresponded to the E. coli types defined by RAPD. CONCLUSIONS: The hides of the incoming animals appeared to be only one of the sources of the E. coli on trimmings and in ground beef, as additional sources were apparently present in equipment used for carcass breaking. SIGNIFICANCE AND IMPACT OF THE STUDY: This study indicates that hazardous microbiological contamination of meat may occur after the dressing of carcasses at commercial beef-packing plants, which suggests that attention should be given to the control of the contamination of meat during carcass breaking as well as during the dressing of carcasses.