B01016: The evaluation and control of biofilm of significance to the food industry

Study Duration: December 1997 to July 1999

Contractor: University of Wales Institute, Cardiff

Bacteria are able to attach to surfaces and with the right conditions such as a suitable temperature, the presence of adequate moisture and nutrients, a population may increase forming a surface-attached structure that is termed a biofilm.

The bacteria in a biofilm often produce gums that bind and protect them. Biofilm develops in many environments and structures vary from thick, visible layers, as seen inside cooling towers, to dental plaque and the surface slime on pebbles in streams.

In industrial environments, biofilm can pose a problem as its development can affect the operational efficiency of processes and lead to detrimental fouling. In medical environments, biofilm can be a significant factor in hospital acquired infection, for example developing in the bore of catheter tubing and introducing potentially harmful bacteria to the tissues.

Once bacteria have attached to a surface or are growing within a biofilm population, they become more resistant to many of the control measures that are used against bacteria, including desiccation, temperature and action of chemical disinfectants.

In the food industry there is substantial evidence that biofilm readily forms on wet surfaces and that foodborne pathogens, including Listeria monocytogenes, Bacillus cereus and Staphylococcus aureus can grow in a biofilm population. It has also been suggested that other pathogens, including salmonella and campylobacter, may be harboured in biofilm, not necessarily growing but protected from the action of cleaning and disinfection.

Research has also shown that bacteria in biofilm populations can be dislodged during cleaning, forming aerosols that deposit bacteria onto clean surfaces, with the potential for cross-contamination to foods.

Much of the research on biofilm in the food industry has been conducted under laboratory conditions and so the survival and growth of pathogens in biofilm has not been unequivocally demonstrated in-situ. There is, however, much evidence of the detection of pathogens from surfaces in the food industry where the presence of biofilm is likely. Some studies have established that biofilm forms on both food contact and surrounding surfaces in the food industry.

The potential for biofilm formation in the food industry is well recognised and there are concerns that biofilm may provide refuge for food-poisoning bacteria. This study aims to examine the prevalence of biofilm in high risk food processing environments, and evaluate any pathogens associated with biofilm.

The approach taken to determine the significance of biofilm formation to the food industry will be to review work published on biofilm in the food industry. This will examine evidence of biofilm formation and its potential for pathogen survival and growth. Discussions will be held with other researchers in the field in an attempt to arrive at a definition of biofilm that would be relevant to the food industry.

A microbiological survey of high-risk food processing plants will be carried out, examining potential biofilm sites for a range of bacteria that might indicate the presence of biofilm and key foodborne pathogens. Sampling will be conducted before and after cleaning in an attempt to determine the effectiveness of cleaning on biofilm populations. Data will be evaluated with reference to the potential risks to food safety posed by biofilm.

Preliminary work will also be undertaken to evaluate a rapid method for assessing the microbial load on surfaces and to examine whether bacteria isolated from biofilm populations are more resistant to some chemicals used by the industry as disinfectants.

The results demonstrated that there is a potential for biofilm formation in the food industry. It is difficult to measure biofilm in situ, and so sites where high numbers of bacteria were found were identified as having biofilm present. Approximately 28% of food contact surfaces and 58% of environmental surfaces were deemed to have biofilm present, with floors being the most likely surfaces to harbour bacteria. Cleaning did not appear to have much effect on these populations. Very few food-poisoning bacteria were identified and these were in the main bacterial groups commonly associated with humans. No salmonella, E. coli O157 or campylobacter were isolated.

The use of a rapid method to assess the presence of bacteria on surfaces showed some potential with a good correlation between bacterial numbers and the rapid method results.

Preliminary work on biocide resistance suggests that some bacteria isolated from biofilm may be more difficult to control by the use of some chemical disinfectants, exhibiting increased resistance in laboratory tests.

This study shows that the food industry still does not fully understand the behaviour of bacteria in high risk processing areas or the cleaning methods used to control bacteria. The failure to identify food-poisoning bacteria suggests that biofilm is not a food safety risk but a food quality issue to which the industry must attend.

Final report is available from the Agency's Information centre.
To obtain a copy, please contact the Enquiry Desk, Information Services, Food Standards Agency (tel: 020 7276 8181/8182 or email: infocentre@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