4.1. Microbiological monitoring

Until the late 1980s, microbiological testing was virtually the only practical hygiene monitoring method available. Using a swab, sponge or contact plate to sample the microbial population on a surface can provide valuable information about the level of contamination.

The sampling device is used to remove microorganisms from a known area (typically 100 cm2) of a surface such as a worktop or conveyor, or from equipment known to be a potential source of contamination, such as a valve or pump. The material collected is then suspended in a suitable diluent and transferred to a microbiological culture medium, usually in agar plates. After a period of incubation, the degree of contamination can be measured by counting any visible colonies. The main advantage of microbiological monitoring is that it provides a direct indication of microbial contamination, and it is also possible to test for the presence of specific organisms, such as foodborne pathogens.

Unfortunately, there are also a number of limitations, most notably the time taken to obtain results. The culture step normally requires at least 24 hours of incubation and must be carried out in a properly equipped laboratory, which is often off-site. This means that results are only ever available retrospectively and are of limited value for HACCP monitoring purposes, or for rapid cleaning assessment. Even if swabs are taken immediately after cleaning and disinfection, at least a full day of production is likely to have been completed before there is any information available on contamination levels. The results can also be badly affected by residual antimicrobial activity remaining on surfaces after sanitising, so that a special diluent containing inactivating compounds is required to prevent inhibition in the culture.

Nevertheless, microbiological sampling and testing remains a valuable technique, particularly for monitoring vulnerable equipment and fittings for pathogen contamination. Foodborne pathogens like L. monocytogenes, S. enterica, and E. coliare the target organisms in microbiological control according to regulation documents.