Research submenu topics are:

Microbiological methods, sampling plans and criteria for red meat abattoirs in the context of HACCP and quality assurance

Duration:

October 1st 2001 to July 31st 2005  

Background and Objectives:

Traditional visual inspection of carcases by trained personnel is not an effective strategy for protecting British consumers against meat-borne infections and physical and chemical hazards.  A Hazard Analyses and Critical Control Points (HACCP)-based approach to production and processing is better suited for the manufacture of hazard-free meat.  In keeping with decisions taken previously by regulatory authorities in the USA, Australia and New Zealand; EU Commission Directive EC/471/2001 became law for all red meat slaughterhouses in the EU in June 2003 (June 2002 for larger throughput plants).  An important change introduced by this new law was that all red meat slaughterhouses within the European Community were obliged to operate according to HACCP principles.  Microbiological sampling and testing of carcasses was also introduced to verify that HACCP schemes were effectively monitoring plant processing conditions.  These verification samples for carcasses are collected according to strictly defined sampling protocols and frequencies using an excision-based sampling method.  In the UK, excision sampling is not popular and is practiced by less than 4% of red meat plants because the physical damage caused is unsightly and reduces the value of the carcasses sampled.  In British slaughterhouses, one of the most widely practiced sampling methods for HACCP verification purposes is wet-dry swabbing using cotton-tipped stick swabs.  A survey of over 100 full throughput British meat plants revealed that method is used in >95% of premises for HACCP verification purposes. At the start of this study, the relationship between wet-dry swabbing and excision-based sampling was unclear.  A number of workers had previously concluded that excision recovered significantly higher numbers of bacteria from meat surfaces than wet-dry swabbing.  Although EU Directive EC/471/2001 stipulates that excision sampling should be used for HACCP verification purposes in red meat plants, it makes provision for alternative sampling methods to be used provided they have been demonstrated as fit for purpose.  The aims of this study were to assess the appropriateness of swab-based sampling; to examine potential reasons for the variability of microbial counts observed during carcass processing; and to determine the suitability of EU-specified indicator organisms as process control indicators for HACCP verification purposes in UK red meat plants.    

Approach and the results:

A comparison of wet-dry swabbing and surface tissue excision of bovine, ovine and porcine carcasses was undertaken to determine any influence of sampling method on carcass-derived microbiological counts.  Samples were collected from multiple visits to 23 commercial slaughterhouses operating under normal commercial processing conditions.  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.     

What it means and why it’s important: 

The implications of these findings for HACCP-style process control verification were investigated by weekly carcass sampling at three commercial slaughterhouses over a 13-week period.  In these plants, two sets of carcass samples were taken within a narrow time frame.  When the bacterial numbers from each of these sets of samples were compared, as much as 4 logs difference in the total aerobic counts were observed.  Thus it may not be appropriate to institute corrective actions based on a single week’s statutory microbiological test results in the context of slaughter process control and statutory hygiene enforcement.     

Project publications: (click here to request a paper from the authors by email)    

Hutchison, M. L., Walters, L. D., Reid, C.-A., Avery, S. M., Wilson, D., Howell, M., Johnston, A. and Buncic, S. 2005. A comparison of wet-dry swabbing and excision-sampling methods for microbiological testing of bovine, porcine and ovine carcasses at red meat slaughterhouses. J. Food Prot. 68:2155-2162.

Pepperell, R., Reid, C.-A., Nicolau, S., Hutchison, M. L., Walters, L. D., Johnston, A. and Buncic, S. 2005. Experimental comparison of excision and swabbing as microbiological sampling methods for carcasses. J. Food Prot. 68:2163-2168.