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

Changes in microbial contamination levels of porcine carcasses and fresh pork in slaughterhouses, processing lines, retail outlets, and local markets by commercial distribution

The objective of this study was to evaluate the changes in microbial contamination levels of each porcine carcass and fresh pork in a general distribution process. A total of 100 commercial pigs were sampled (six sampling sites per individual, total 600 samples) at four sequential stages: slaughterhouse (after carcass grading and boning), processing line, retail outlet, and local market. No significant differences were observed in the contaminant percentages among sampling sites and sample collection years (P>0.05) with the exception of Bacillus cereus. The contaminant percentage of B. cereus at 1st collection year was higher than these of 2nd collection year (28.31% vs. 12.26%, P<0.05). B. cereus and Listeria monocytogenes were the most frequently detected pathogenic bacteria in the slaughterhouse and markets, respectively. On the other hand, Escherichia coli O157:H7 and Yersinia enterocolitica were not detected in carcasses or pork collected from any carcass sites and pork samples. However, the frequency of pathogenic bacteria in end-products at local markets was not highly related to the initial contamination of porcine carcasses in the slaughterhouse. Thus, the improvement of microbial safety for pork end-products requires hygienic control of porcine carcasses and meat cutting during all operations in the slaughterhouse, processing line, retail outlet, and local market.

Evaluation of control over the microbiological contamination of carcasses in a lamb carcass dressing process operated with or without pasteurizing treatment

The aim of this study was to quantify the hygienic status of a lamb slaughterhouse by means of multivariate statistical analysis, to demonstrate how the microbiological data could be exploited to improve the lamb slaughter process by constructing control charts and to evaluate the potential effect of an intervention step such as steam application on the microbiological quality of lamb carcasses. Results showed that pelt removal and evisceration were hygienically uncontrolled. TVC and Enterobacteriaceae progressively increased from the stage 'after pelt removal of hind and forelegs/before final pulling' to the stage 'after evisceration/before pluck removal' thus indicating possible deposition of microorganisms during these operations. It seems that the processing stages of freshly produced carcasses were better distinguished by Enterobacteriaceae, with evisceration contributing mostly to the final Enterobacteriaceae counts. Application of steam during the lamb slaughter process reduced microbial counts without adverse effects on the organoleptic characteristics of the carcasses. Moreover, the construction of control charts showed that decontamination with steam contributed to the maintenance of an in control process compared to that before the application of steam, suggesting the potential use of steam as an intervention step during the lamb slaughter process.

Count data distributions and their zero-modified equivalents as a framework for modelling microbial data with a relatively high occurrence of zero counts

In many cases, microbial data are characterised by a relatively high proportion of zero counts, as occurs with some hygiene indicators and pathogens, which complicates the statistical treatment under the assumption of log normality. The objective of this work was to introduce an alternative Poisson-based distribution framework capable of representing this kind of data without incurring loss of information. The negative binomial, and two zero-modified parameterizations of the Poisson and negative binomial distributions (zero-inflated and hurdle) were fitted to actual zero-inflated bacterial data consisting of total coliforms (n=590) and Escherichia coli (n=677) present on beef carcasses sampled from nine Irish abattoirs. Improvement over the simple Poisson was shown by the simple negative binomial (p=0.426 for chi(2) test for the coliforms data) due to the added heterogeneity parameter, although it slightly overestimated the zero counts and underestimated the first few positive counts for both data sets. Whereas, the zero-modified Poisson could not cope with the data over-dispersion in any of its parameterizations (p<0.001 for chi(2) tests), the parameterizations of the zero-modified negative binomial presented differences in fit due to approximation errors. While the zero-inflated negative binomial parameterization was apparently reduced to a negative binomial due to a non-convergence of the logit parameter estimate, the goodness of fit of the hurdle negative binomial parameterization indicated that for the data sets under evaluation (coliforms data with approximately 13% zero counts and E.coli data with approximately 42% zero counts), the zero-modified negative binomial distribution was comparable to the simpler negative binomial distribution. Thus, bacterial data consisting of a considerable number of zero counts can be appropriately represented by using such count distributions, and this work serves as the starting point for an alternative statistical treatment of this kind of data and stochastic risk assessment modelling.

Contamination of food products with Mycobacterium avium paratuberculosis: a systematic review

Although a causal link between Mycobacterium avium subspecies paratuberculosis (MAP) and Crohn's disease has not been proved, previous studies suggest that the potential routes of human exposure to MAP should be investigated. We conducted a systematic review of literature concerning the likelihood of contamination of food products with MAP and the likely changes in the quantity of MAP in dairy and meat products along their respective production chains. Relevant data were extracted from 65 research papers and synthesized qualitatively. Although estimates of the prevalence of Johne's disease are scarce, particularly for non-dairy herds, the available data suggest that the likelihood of contamination of raw milk with MAP in most studied regions is substantial. The presence of MAP in raw and pasteurized milk has been the subject of several studies which show that pasteurized milk is not always MAP-free and that the effectiveness of pasteurization in inactivating MAP depends on the initial concentration of the agent in raw milk. The most recent studies indicated that beef can be contaminated with MAP via dissemination of the pathogen in the tissues of infected animals. Currently available data suggests that the likelihood of dairy and meat products being contaminated with MAP on retail sale should not be ignored.

The potential use of chilling to control the growth of Enterobacteriaceae on porcine carcasses and the incidence of E. coli O157:H7 in pigs

AIMS

To (i) monitor the presence of Enterobacteriaceae as indicators of faecal contamination on pig carcasses, (ii) examine the potential use of chilling as a critical control point (CCP) and establish its influence on pig carcass categorization by Decision 471/EC and (iii) determine the incidence of E. coli O157:H7 in pigs.

METHODS AND RESULTS

Porcine faecal samples and carcass swabs were collected before and after chilling at four Irish pig abattoirs and examined for Enterobacteriaceae and E. coli O157:H7. Chilling generally reduced Enterobacteriaceae counts on carcasses, but increases were also observed, particularly in one abattoir. E. coli O157:H7 was absent from carcasses before chilling, present on 0.21% after chilling and was recovered from 0.63% of faecal samples. All of the isolates were found to contain virulence genes associated with clinical illness in humans.

CONCLUSIONS

The data show that overall chilling had the capacity to reduce the numbers of carcasses positive for the presence of Enterobacteriaceae.

SIGNIFICANCE AND IMPACT OF STUDY

The influence of chilling on the categorization of pig carcasses suggests that it has the potential to improve the numbers of acceptable carcasses and the process could be used as a CCP within a HACCP plan.

Relationships between the density of different indicator organisms on sheep and beef carcasses and in frozen beef and sheep meat

AIM

To describe the relationship between the concentration of different indicator bacteria in red meat.

METHODS AND RESULTS

Enumeration data for aerobic plate count (APC), Enterobacteriaceae, coliforms and Escherichia coli biotype I were analysed from an Australia-wide survey of beef carcasses, sheep carcasses, frozen beef and frozen sheep meat. In all commodities, there was only low-to-moderate rank correlation (0.16-0.47) between concentration of APC and concentration of each Gram-negative indicator. Rank correlations between counts of Gram-negative indicators were much higher (0.47-0.92) especially when nondetections were excluded from analysis (0.78-0.94). Receiver-operator characteristics analysis showed that detection of coliforms can predict the presence of E. coli biotype I with almost 100% sensitivity but fails to predict absence in 2.7-8.5% of samples not containing E. coli biotype I.

CONCLUSIONS

Enumeration of coliforms is a useful adjunct to enumeration of E. coli biotype I or Enterobacteriaceae in red meat. The density of coliforms or Enterobacteriaceae can be used to predict the presence or absence of E. coli biotype I, although when the latter is at low prevalence errors in positive test prediction can be large.

SIGNIFICANCE AND IMPACT OF THE STUDY

A quantitative basis is provided for comparing the concentration of different indicator bacteria measured in the production, regulation and trade of red meat.

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.

Prevalence and characterisation of Cryptosporidium species in cattle faeces and on beef carcases at slaughter

Cattle are known reservoirs and asymptomatic excretors of Cryptosporidium, a protozoan parasite that causes severe and protracted diarrhoea in people. The incidence of Cryptosporidium was investigated in 288 matched samples taken from beef carcases of 1 g samples of faeces retrieved immediately after de-legging, 25 cm2 samples of beef excised from the rump of uneviscerated carcases, and 25 cm2 samples of beef excised from the brisket area of eviscerated carcases. Cryptosporidium species were detected in 21 of the faecal samples after salt flotation and immunofluorescent microscopy. The species isolated from the positive samples were identified by restriction fragment length polymorphism and PCR as Cryptosporidium andersoni (54.5 per cent) and Cryptosporidium parvum genotype 2 (45.5 per cent). In the faecal samples, there was a significantly higher prevalence of the parasite in samples taken in summer (May to July) and winter (November to January) than in spring or autumn. No Cryptosporidium species were recovered from any of the beef samples.

Determination of the principal points of product contamination during beef carcass dressing processes in Northern Ireland

To determine the principal points of microbial contamination of carcasses during beef carcass dressing in Northern Ireland, 190 carcasses were sampled by swabbing 1,000 cm2 of the brisket. A detailed survey of one abattoir was initially conducted, with sampling of a total of 100 carcasses immediately after hide removal (H), after carcass splitting (S), and immediately after washing (W) before dispatch to the chiller. The total bacterial counts after incubation at both 22 and 37 degrees C indicated that there was no significant increase in the numbers of bacteria after the first sampling point, H (P > 0.05). To determine whether this was the case in the majority of Northern Ireland abattoirs, 15 carcasses were then sampled at each of an additional six abattoirs, at points H and W only. Total bacterial counts were significantly higher (P < 0.05) at H than at W, indicating that hide pulling was the major point of bacterial contamination of beef carcasses and hence a critical control point for the final microbiological quality of the carcasses. Mean counts of Enterobacteriaceae at both incubation temperatures were very low (< 10 CFU/cm2) but were higher at W than at H, probably indicating that washing was redistributing bacteria from the posterior to the anterior region.

Seasonal prevalence of Shiga toxin-producing Escherichia coli, including O157:H7 and non-O157 serotypes, and Salmonella in commercial beef processing plants

The seasonal prevalence of Escherichia coli O157:H7, Salmonella, non-O157 E. coli (STEC), and stx-harboring cells was monitored at three Midwestern fed-beef processing plants. Overall, E. coli O157:H7 was recovered from 5.9% of fecal samples, 60.6% of hide samples, and 26.7% of carcasses sampled before the preevisceration wash. This pathogen also was recovered from 1.2% (15 of 1,232) of carcasses sampled at chilling (postintervention) at approximate levels of <3.0 cells per 100 cm2. In one case, the E. coli O157:H7 concentration dropped from ca. 1,100 cells per 320 cm2 at the preevisceration stage to a level that was undetectable on ca. 2,500 cm2 at the postintervention stage. The prevalence of E. coli O157:H7 in feces peaked in the summer, whereas its prevalence on hide was high from the spring through the fall. Overall, Salmonella was recovered from 4.4, 71.0, and 12.7% of fecal, hide, and preevisceration carcass samples, respectively. Salmonella was recovered from one postintervention carcass (of 1,016 sampled). Salmonella prevalence peaked in feces in the summer and was highest on hide and preevisceration carcasses in the summer and the fall. Non-O157 STEC prevalence also appeared to vary by season, but the efficiency in the recovery of isolates from stx-positive samples ranged from 37.5 to 83.8% and could have influenced these results. Cells harboring stx genes were detected by PCR in 34.3, 92.0, 96.6, and 16.2% of fecal, hide, preevisceration carcass, and postintervention carcass samples, respectively. The approximate level of non-O157 STEC and stx-harboring cells on postintervention carcasses was > or = 3.0 cells per 100 cm2 for only 8 of 199 carcasses (4.0%). Overall, the prevalence of E. coli O157:H7, Salmonella, and non-O157 STEC varied by season, was higher on hides than in feces, and decreased dramatically, along with pathogen levels, during processing and during the application of antimicrobial interventions. These results demonstrate the effectiveness of the current interventions used by the industry and highlight the significance of hides as a major source of pathogens on beef carcasses.

Microbial quality of ostrich carcasses produced at an export-approved South African abattoir

The aim of this study was to evaluate the microbial quality of ostrich carcasses produced in a South African export-approved ostrich abattoir. Ninety surface samples were collected from 30 ostrich carcasses at three processing points in the abattoir: after skinning, after evisceration, and after chilling. Samples were evaluated for aerobic plate counts, for levels of Pseudomonas spp., Enterobacteriaceae, and Staphylococcus aureus, and for the presence of Escherichia coli. Surface counts (means +/- standard deviations) at postskinning, postevisceration, and postchilling processing points were, respectively, 4.32 +/- 0.62, 4.21 +/- 0.63, and 4.57 +/- 0.48 log CFU/cm2 for total aerobes; 2.82 +/- 1.65, 2.86 +/- 1.53, and 3.75 +/- 0.94 log CFU/ cm2 for Pseudomonas spp.; 2.89 +/- 0.78, 2.90 +/- 0.53, and 2.38 +/- 0.67 log CFU/cm2 for S. aureus; and 2.55 +/- 1.53, 2.78 +/- 1.31, and 2.73 +/- 1.46 log CFU/cm2 for Enterobacteriaceae. Statistically significant differences were detected between the counts for the postskinning and postchilling processing points and between the counts for the postevisceration and postchilling processing points for total aerobes, Pseudomonas spp., and S. aureus. Of practical significance was the increase in Pseudomonas spp. counts on samples collected after chilling. Seventeen of 90 samples (18.8%) tested positive for E. coli. Counts for E. coli-positive samples ranged from 1.0 to 3.79 log CFU/cm2, with a mean count of 2.15 +/- 0.94 log CFU/cm2. The majority of the samples testing positive for E. coli were collected after evisceration.

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.

Microbiological testing of raw, boxed beef in the context of hazard analysis critical control point at a high-line-speed abattoir

The efficacy of cold storage of raw, bagged, boxed beef was assessed microbiologically at a high-line-speed abattoir (270 carcasses per h). At the time of this study, plant management was in the process of creating a hazard analysis critical control point plan for all processes. Aerobic bacteria, coliforms, and type 1 Escherichia coli were enumerated (5 by 5-cm excision samples, hydrophobic grid membrane filter technology) before and after cold storage of this final product produced at six fabrication tables. In addition, the temperature-function integration technique (TFIT) was used to calculate the potential number of generations of E. coli during the first 24 or 48 h of storage of the boxed beef. Based on the temperature histories (total of 60 boxes, resulting from 12 product cuts, five boxes from each of two fabrication tables on each of 6 sampling days, and six types of fabrication tables), TFIT did not predict any growth of E. coli (with or without lag) for the test period. This was verified by E. coli mean log10 values of 0.65 to 0.42 cm2 (P > 0.05) determined by culture before and after the cooling process, respectively. Counts of aerobic bacteria and coliforms were significantly reduced (P < 0.001 and P < 0.05, respectively) during the initial period of the cooling process. There were significant microbiological differences (P < 0.05) between table-cut units.

The effects of preslaughter washing on the reduction of Escherichia coli O157:H7 transfer from cattle hides to carcasses during slaughter

Fresh bovine faeces were inoculated with a non-toxigenic, antibiotic resistant strain of Escherichia coli O157:H7, spread on the rump areas of 30 heifers and allowed to dry for 24 h. Ten of the cattle then entered the normal slaughter process without further treatment. The remaining cattle were washed with a powerhose for 1 min (10 animals) and 3 min (10 animals) before entering the normal slaughter process. Both washing treatments removed all visible faecal materials on the live animals although a significant reduction (P < 0.05) in E. coli O157:H7 levels on the hides was only observed on those animals which were powerhosed for 3 min. After slaughter, E. coli O157:H7 was detected on carcasses and on the knives and hands of operatives. Preslaughter washing for 3 min did not statistically reduce the numbers of E. coli O157:H7 transferred from the hide to the carcass during slaughter. However, the organism was not detected on three of the four areas of the carcass sampled, indicating that washing may be a suitable method of decontamination animal hides before slaughter and as such deserves further investigation.

A simulation model for studying the role of pre-slaughter factors on the exposure of beef carcasses to human microbial hazards

A Monte Carlo simulation model was constructed for assessing the quantity of microbial hazards deposited on cattle carcasses under different pre-slaughter management regimens. The model permits comparison of industry-wide and abattoir-based mitigation strategies and is suitable for studying pathogens such as Escherichia coli O157:H7 and Salmonella spp. Simulations are based on a hierarchical model structure that mimics important aspects of the cattle population prior to slaughter. Stochastic inputs were included so that uncertainty about important input assumptions (such as prevalence of a human pathogen in the live cattle-population) would be reflected in model output. Control options were built into the model to assess the benefit of having prior knowledge of animal or herd-of-origin pathogen status (obtained from the use of a diagnostic test). Similarly, a facility was included for assessing the benefit of re-ordering the slaughter sequence based on the extent of external faecal contamination. Model outputs were designed to evaluate the performance of an abattoir in a 1-day period and included outcomes such as the proportion of carcasses contaminated with a pathogen, the daily mean and selected percentiles of pathogen counts per carcass, and the position of the first infected animal in the slaughter run. A measure of the time rate of introduction of pathogen into the abattoir was provided by assessing the median, 5th percentile, and 95th percentile cumulative pathogen counts at 10 equidistant points within the slaughter run. Outputs can be graphically displayed as frequency distributions, probability densities, cumulative distributions or x-y plots. The model shows promise as an inexpensive method for evaluating pathogen control strategies such as those forming part of a Hazard Analysis and Critical Control Point (HACCP) system.

A comparison of Escherichia coli levels at four sampling sites on turkey carcasses

The objective of this study was to investigate the levels of Escherichia coli on different sites of turkey carcasses by sponge sampling using a 50 cm2 template. The breast, thigh, back, and cavity sites were sampled to determine which sites would be suitable for quantifying E. coli levels for the purpose of assessing control of the slaughtering and chilling processes. Results show that the breast and cavity sites have the lowest levels of E. coli (2.6 and 2.7 cfu/cm2, respectively), whereas thigh and back sites have the highest (6.7 and 7.6 cfu/cm2, respectively). Data analyses indicate that E. coli levels at the breast and cavity site are lower (P < 0.05) than the other sites. A composite sample consisting of thigh and back sites for E. coli testing is recommended for assessing process control in turkey slaughtering facilities.