Bacteriophage – A potential processing aid to control pathogens

Bacteriophages (or phages) are viruses that infect bacteria. They are labelled intracellular obligate parasites that function by binding to the surface of a target bacterium, inserting their DNA or RNA, then taking over the genetic machinery of the organism. One effect of this insertion is the rapid production of millions of phage particles, which are released when the host cell disintegrates, and infect other target bacteria.

Historically, phages have been of interest to the dairy industry as they can infect cheese starter cultures, killing the starter, and causing dead vats. So the dairy industry goes to great lengths to prevent phage attacks by practising good hygiene and the rotation of mixed-strain starter cultures.

Currently there is considerable interest in the potential use of phages to control animal and human illnesses, and to control pathogens in food or on food contact surfaces. For example, phages have been used to reduce Escherichia coli and Salmonella spp. on fresh horticultural produce and meats. Interest is also growing as phages are perceived to be natural antimicrobial compounds.

As natural antimicrobial agents, phages offer several advantages for the food industry. They are:        
(i) highly specific to a target bacterium
(ii) self-replicating and self-limiting
(iii) cheap and simple to propagate
(iv) of low toxicity  
(v) able to withstand food processing stresses
(vi) have a long shelf life.

However, phages may be immobilized by the food matrix and lose their ability to infect the target organism.

In August 2012, Food Standards Australia New Zealand approved the use of a bacteriophage preparation as a processing aid for certain ready-to-eat (RTE) foods at risk of contamination by Listeria monocytogenes. The FSANZ assessment found the preparation effective in reducing numbers of L. monocytogenes on foods including sliced ham, hot dogs, salmon and smoked salmon, various cheeses, lettuce, and cabbage. This preparation is GRAS (Generally recognised as safe) in the United States by the Food and Drug Administration and the United States Department of Agriculture and can be used as a processing aid in all food products susceptible to Listeria. The European Food Safety Agency (EFSA) has determined that bacteriophages may be very effective in the elimination of specific pathogens from foods.

Whatever the future is for phage preparations, they should not be seen as an alternative to good hygiene practices, effective cleaning and sanitation, and the use of other pathogen control strategies in the food industry. They represent an additional hurdle that food manufacturers may wish to utilise to enhance the safety of RTE foods – but only under conditions that are validated and verified, and documented in their food safety program.

Importantly, manufacturers need to undertake monitoring to identify the potential development of resistance (or reduced susceptibility) to a phage preparation, or the selection of resistant strains. So if a dairy manufacturer was exploring the use of a bacteriophage preparation, they would need to consider where along the dairy production-processing chain it would be used, whether it is effective against a resident strain of L. monocytogenes, and evaluate the potential for the selection and ascendency of phage resistant strains of L. monocytogenes.

Reading

Soni, K.A. and Nannapaneni, R. (2010). Removal of listeria monocytogenes biofilms with bacteriophage P100. Journal of Food Protection, 73, (8), 1519-1524.

EFSA Panel on Biological Hazards (2012). Scientific Opinion on the evaluation of the safety and efficacy of ListexTM P100 for the removal of Listeria monocytogenes surface
contamination of raw fish. EFSA Journal, 10, (3): 2615

FSANZ Application A1045 (2012). Bacteriophage Preparation as a Processing Aid

S.M. Sillankorva et al. (2012). Bacteriophages and Their Role in Food Safety. International Journal of Microbiology. Vol. 2012,
Article ID 863945, doi:10.1155/2012/863945

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