They report their findings in the September 2008 issue of the journal Applied and Environmental Microbiology.
Protozoa are unicellular microorganisms that feed on bacteria, and sometimes the bacteria survive and replicate within the protozoa, the study claims.
Bacteria such as Campylobacter, E. coli 0157:H7, Listeria and Salmonella that survive within protozoa may be able to resist desiccation and disinfectants, claims the team, which may explain how Salmonella food poisoning still occurs even after the processor takes the required safety measures.
They added that an increase in antimicrobial resistance and virulence of bacterial pathogens after passage through protozoa has been previously demonstrated.
In this study, the researchers used a series of methods to screen for protozoa in meat-cutting plants.
Five plants were inspected, one plant produced beef (A), two plants processed pork (B and C) and the two other plants produced beef, pork and poultry (D and E).
They were visited during February to May 2007 and samples were taken after a waiting period of two hours after cleaning and disinfection.
The team found communities of amoebae, ciliates, and flagellates to be present in all the plants.
Protozoa were detected in floor drains, standing water on the floor, soiled bars of cutting tables, plastic pallets and out-of-use hot water knife sanitizers. In addition, protozoa were identified on surfaces which come into direct contact with meat.
“Only the plant E fulfilled the legal requirement of a viable bacteria count of 0 to 10 CFU/cm2 for all surface samples tested.
“For plants A to C, the limit was exceeded in only a minority of the samples, In plant D, seven of the samples were unacceptable, including samples from the balance, board meat tenderizer, cutting tables, and saws which were heavily contaminated,” said the group.
Cultures were then refrigerated for seven days, after which protozoa were still detected in half of the samples. Through microscopic observations researchers identified up to 61 morphospecies.
“This survey showed that there is high protozoan species richness in meat-cutting plants and that the species included species related to known hosts of food-borne pathogens,” say the researchers.
They added that in most of the samples that yielded a protozoan-positive enrichment culture, residual organic material and/or water was present and said their results suggest that a good hygiene score does not necessarily correlate with an absence of protozoa in the food processing environment.
“Protozoa are known to be common inhabitants of drinking water. The possibility that protozoa are spread by means of droplets formed by the aerosolization of water that is sprayed or splashed during cleaning and disinfection processes cannot be excluded.
“Locations which were inadequately cleaned and disinfected because of ignorance or inaccessibility (holes in plastic pallets, undersides of cutting boards and conveyor belts, and upper sides of rails) harbored protozoa,” concluded the scientists.
They said that further research is required to determine the survival of protozoa and their internalized bacteria in food processing environments under stress conditions such as heat, extreme pH values and disinfection.
Source: Applied and Environmental Microbiology 74. 18:5741-5749Published online ahead of printMicroscopic and molecular studies of the diversity of free-living protozoa in meat-cutting plantsAuthors: M.J.M. Vaerewijck, K. Sabbe, J. Bare, K. Houf