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Microbiological Methods, Sampling Plans and Criteria for Red Meat Abattoirs in the context of HACCP

Project Code: M01020

30/06/2005

Division of Farm Animal Science, Department of Clinical Veterinary Science, University of Bristol,
Buncic, S ;
Direct Laboratories Ltd
Hutchison, M;
Division of Farm Animal Science, Department of Clinical Veterinary Science, University of Bristol,
Reid, C;
ADAS Consulting Ltd, Groesfaen
Wilson, D;
University of Bristol
Pepperell, R; Solano, S;
Direct Laboratories Ltd
Walters, L; Avery, S;
Department of Farm Animal and Equine Medicine and Surgery, University of London RVC
Johnston, A

In the first stage of the project i.e. before the start of the experimental and the field work could commence, it was necessary to obtain information from the UK meat industry on the current status of affairs with respect to sampling method(s) for microbiological testing of red meats of proven acceptability to the industry; sampling plans for high- and low-throughput red meat operators; and hygiene performance criteria in the context of HACCP/QA. A postal survey of slaughterhouses in England licensed under the Fresh Meat (Hygiene and Inspection) Regulations 1995 (As Amended) was conducted from 16 July to 16 August 2002. Quality Assurance department of red meat abattoirs were asked about their HACCP systems in place, staff hygiene training, details on sampling plans, sampling analysis, and laboratory methods and reporting. The total response rate for the survey was 10% (31/299). This relatively low response rate may not be unexpected for a postal survey of the red meat plant community given the sensitive nature of verification of HACCP and food hygiene as a subject matter. Among the red meat plants that responded, approximately two-thirds were full throughput plants (65#037;; 21/31), and 35#037; (11/31) were low throughput plants. The number of animals that full throughput plants processed per week ranged from 30 to 13,000 (mean = 4267 animals). The number of animals that low throughput plants processed per week ranged from 10 to 2,200 (mean = 331 animals). Over three-quarters of the meat plants processed cattle (77#037;; 24/31), 74#037; (23/31) processed sheep/lamb, a quarter (25#037;; 18/31) processed pigs, and 13#037; (4/31) processed other animals (goat, deer (venison), wild boar). The results of the survey indicated that: a) the data on current methods used by the meat industry to microbiologically verify HACCP in meat plants at the time, could be used as an aid to develop a suitable practice method for HACCP verification for the purposes of Decision 2001/471/EC; and b) it would also assist the overall project in having major importance in developing and recommending alternative EU-equivalent method(s) for microbiological testing of red meats of proven acceptability to the industry; sampling plans for high- and low throughput red meat operators; and hygiene performance criteria in the context of HACCP/QA. The results, however, also confirmed that at the time the information was not available, either in the scientific literature at that time, or from current practice in meat plants, to allow decisions to be made on criteria for the microbiological monitoring in meat plants. For that, both experimental- and field-investigation-based work had to be carried out so to advance the understanding of the problem and to obtain necessary data.

To compare the performance (microbial recoveries) of the two EU-legislation-described carcass sampling methods (wet-dry swabbing and excision), bovine, ovine and porcine carcasses were individually inoculated by dipping in various suspensions comprising a marker organism (Escherichia coli K12 or Ps. fluorescens) alone or in combination with two meat-derived bacterial strains, and sampled using two standard methods: cotton wet-dry swabbing and excision. The samples were examined for Total Viable Count (TVC) and Enterobacteriaceae numbers (EC) using standard ISO methods. Overall, when all three meat species were taken together, average bacterial recoveries obtained by the swabbing expressed as a percentage of the appropriate recoveries achieved by the excision were 21#037; (range 2-100#037;) and 25#037; (range 9-47#037;) for TVC and Enterobacteriaceae (EC), respectively. Several factors potentially contributing to these relatively low, and highly variable, bacterial recoveries by swabbing were investigated in separate experiments. Neither the difference in size of the swabbed area (10, 50 or 100 cm² on beef carcasses) nor the difference in time of swabbing (20 or 60 minutes after inoculation of pig carcasses) had a significant effect on the swabbing recoveries of the marker organism used. In an experiment with swabs preinoculated with the marker organism and then used for carcass swabbing, on average 12#037; of total bacterial load was transferred inversely i.e. from the swab to the carcass during standard swabbing procedure. In another experiment, on average 14#037; of total bacterial load was not released from the swab into the diluent during standard swab homogenisation. Use of custommade swabs with very abrasive buts, around which metal pieces of pan scourers were wound, markedly increased TVC recoveries from noninoculated lamb carcasses at commercial abattoirs compared to cotton swabs. In spite of the observed inferiority of the cotton wet-dry swabbing method, as compared with the excision with respect to bacterial recovery, the former is clearly preferred by the meat industry because it does not damage the carcass.

A large-scale evaluation of the two carcass sampling methods (wet-dry swabbing and excision) was undertaken in 23 commercial slaughterhouses with bovine, ovine and porcine carcasses to determine any influence of sampling method on carcass-derived counts of the natural microflora. Excision sampling produced significantly higher total aerobic and Enterobacteriaceae counts compared with those measured by wet-dry swabbing. Linear regression using transformed counts from near-adjacent carcases on processing lines for all three animal species revealed tenuous relationships between the swabbing- and excision-derived bacterial numbers. Thus it was not possible to calculate a factor, which allowed the inter-conversion of bacterial numbers for samples taken by each sampling method. Some factors, which confounded the identification of relationships between swabbing- and excision-based sampling, were investigated. Differences in bacterial populations were found on the surfaces of near-consecutive carcasses on the processing lines sampled. Uncertainty associated with laboratory analyses was also a contributing factor. The implications of these findings for HACCPstyle process control verification were investigated by weekly carcass sampling at three commercial slaughterhouses over a 13-week period. In these plants, two sets of seven carcass samples were taken within a narrow time frame (< 1 hour). When the bacterial numbers from each of these sets of samples were compared, as much as a 4 Log CFU cm^-2 difference in the total aerobic counts was observed. Thus it may not be appropriate to institute corrective actions based on a single week�s statutory microbiological test results. The results of these findings are discussed in the context of slaughter process control and statutory hygiene enforcement.

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