B09005: Review of microbiological methods in the food industry

Study Duration: June 1998 to March 2001

Contractor: Campden and Chorleywood Food Research Association (CCFRA)

Currently, there is no true objective understanding of the microbiological methods used routinely for the microbiological examination of foods. In addition, there is little understanding of the reasons for the choice of methods by particular laboratories or the current or future requirements for new methods. Whilst many methods are based upon traditional cultural techniques there are now a number of rapid methods available for the detection and the enumeration of micro-organisms. Between 1980 and 1981 a Delphi survey was conducted by Jarvis to predict future developments in rapid and automated methods. The survey of a small panel of experts in the field of food microbiology predicted that traditional enumeration methods would be superseded by automated colony counts and that by 1996 rapid methods for foodborne viruses and toxins would be commonplace.

However, despite advances in technology and the introduction over the past decade of a plethora of commercial assays and kits for the detection and enumeration of a wide range of micro-organisms, traditional culture based methods are still the most popular and widely used in food microbiology. The findings of the Delphi Forecast were discussed together with results from several preliminary information gathering surveys. These were conducted by the author at workshops and seminars relating to rapid and automated methods for the microbiological testing of foods and by a mail-in questionnaire. These surveys indicated that the majority of companies used or were requested to use standard methods, including ISO or other national and international organisation methods. Only a minority of companies had replaced conventional methods with rapid methods. There were some common reasons why food industry laboratories were reluctant to adopt new technology. These included methods not being approved or having official status and because certain tests, particularly those used for regulatory requirements, often stipulated the use of conventional methods. Furthermore, the high capital investment and cost of consumables associated with some new technologies, together with the need for well-trained technicians, made some new methods too expensive for many industry laboratories.

In the UK, there have been few or no comprehensive surveys of the Food Industry or laboratories carrying out microbiological testing of foods conducted to establish the type of testing, methods being used, or the reasons why laboratories choose certain methods over others. This survey was commissioned by the Ministry of Agriculture Fisheries and Food (MAFF), later transferring to the Food Standards Agency (FSA), in order to answer these and other questions relating to the microbiological testing of foods. This study surveyed, by means of a questionnaire, a comprehensive sample of over 300 companies involved, directly or indirectly with performing microbiological food analysis. A diverse range of laboratory types and sizes was chosen, including those from the food industry and private contract testing laboratories, as well as regional laboratories belonging to the Public Health Laboratory Service. This study will help to enable future research into method development to be focused in areas that will result in usable systems and highlight areas where knowledge and technical expertise is lacking. In addition, the findings of this study may stimulate interest by commercial companies to develop products for existing and alternative areas of microbiological testing in the future.

The first part of the survey involved the production of a single general questionnaire that was designed to gather general information on the status of testing in this country, the type and choice of methods being used and future method requirements and likely adoption of new technologies. This questionnaire was sent to companies with their own facilities to carry out testing in-house, as well as to those that sent samples to another company or laboratory for testing.

The second survey involved the production of eight separate questionnaires for specific bacteria, including the main pathogens associated with foods. These were designed to provide more detailed information on the types of methods, media and techniques used for their isolation, enumeration and identification. These questionnaires were sent only to those laboratories directly involved with testing foods for the particular bacteria in question.

Of the 308 laboratories in the survey, 208 belonged to food companies which had their own laboratory facilities. Private laboratories represented 13.5%, retailers 2%, Government and other laboratories 10% and sites with more than one function and those belonging to other categories not already mentioned made up the remaining 6.5%.

The majority (52%) of the laboratories were staffed by fewer than 5 people and the most common number of samples being tested in a typical week was 100-500 samples and 50-500 tests. The most common type of test sub-contracted to another laboratory was pathogen testing, followed closely by confirmation and identification of isolates obtained by the laboratory. The most popular reason for sending work to another laboratory was due to the lack of suitable containment facilities for the isolation of pathogens on site.

The types of foods examined varied although the most popular categories were milk and diary products and meat, poultry and their related products, which were being tested by over 40% of the companies in the survey. The most common plate count method was the aerobic mesophilic plate count (30°C) which was used by 84% of the laboratories with the majority carrying out 50-500 tests in an average week. This was also the common range for total coliforms with 78% of laboratories performing the test, followed by E. coli (73%) and total Enterobacteriaceae (64%). Testing for general yeasts and moulds was the most popular test for spoilage organisms (74%) followed by Pseudomonas (49%) and sulphite reducing clostridia (33%). The majority of laboratories performing tests in-house for specific bacteria (including pathogens), were testing for Staphylococcus aureus and other coagulase positive staphylococci. The next most popular test was for Salmonella spp. followed by testing for Listeria spp., Bacillus cereus and Listeria monocytogenes. Only 65 laboratories were testing for Campylobacter spp. in-house and 21 companies were having this test done by another laboratory. Testing for E. coli O157 was also low, with only 58 laboratories performing the testing in-house and 68 having testing done by another laboratory. Few laboratories (fewer than 40) were testing for Shigella spp., Brucella spp., Aeromonas spp., Vibrio spp. and Yersinia enterocolitica.

Whilst food industry laboratories represented the majority carrying out the tests, the highest number of laboratories carrying out 100+ tests monthly for campylobacter were private laboratories whereas high volume testing for E. coli O157 was being done by Government laboratories. Very few laboratories (typically 10 or fewer) were testing or having tests performed for protozoa and viruses. The majority (80%) of laboratories was not testing for bacterial toxins, although testing for staphylococcal enterotoxin was the most common test being done. This may be due, in part, to the greater availability of commercial kits to detect this range of toxins and also to the lack of demand for the other tests, which require specialist equipment and facilities.

Conventional culture methods were the most common category of methods being used by laboratories as they were universally applicable, regarded as cost effective, easy to use and there were historical reasons for their choice. Furthermore, they were often imposed by the customer. The main reasons for choosing rapid methods varied according to the type of method, although the most popular reasons were rapidity of results, reduced hands-on time, reliability and the methods being cost effective. Reasons for not choosing a particular method also varied but common reasons chosen included the cost of capital equipment, cost of consumables, insufficient validation data and the need to demonstrate the method's suitability in-house. In the case of molecular methods, lack of knowledge was another reason that reduced their uptake by laboratories, in addition to cost of equipment and running costs. A large majority (71%) of the laboratories stated that they were not planning to adopt new technologies. If methods were cheaper and simpler for toxins, protozoa and viruses, some laboratories indicated that they would consider testing for these, although the majority of laboratories indicated that tests for these were not applicable.

The results for this survey have confirmed many commonly held views that the vast majority of laboratories continue to use conventional culture methods and that factors that restrict the uptake of alternative methods and new technologies are largely based on cost, although this may be perceived cost, if the benefits of using rapid methods over conventional methods are taken into account. Conventional methods can be more labour intensive and take longer to obtain a result. The need for validation and in-house performance data as well as the demands by customers for conventional methods were other factors that reduced uptake of new technologies.

Final report is available from the FSA Library and Information centre.
To obtain a copy, please contact the Enquiry Desk, Dr Elsie Widdowson Library and Information Services, Food Standards Agency ( Tel: 020 7276 8181/8182 or Email: library&info@foodstandards.gsi.gov.uk ).

Contact: For any enquiries concerning this research project, please contact the relevant programme contact or email: science@foodstandards.gsi.gov.uk