May 12, 2008

Viruses to fight salmonella and campylobacter

As antibiotics are banned in Europe, virus is touted to be the best weapon against dreaded salmonella and campylobacter that are the major cause of food poisoning throughout Europe.

In a study done financed by the European Commission which is participated by some universities from United Kingdom, Portugal and Spain, some viruses are found to be good alternatives to antibiotics in poultry production to ward off harmful bacteria.

One such virus is phages as they only infect bacteria and are the most abundant organisms on earth. They are highly specific affecting only the target bacterium, are non-toxic to animals and plants, and are able to self-reproduce as long as the corresponding host bacteria are present.

Bacteriological studies have indicated that phages are able to multiply in host bacteria within animals, and new phages to attack resistant host strains are readily selected.

Finally, production of phages to very high numbers is simple, rapid and relatively inexpensive. The research shows that phages have been used successfully as therapeutic agents in Eastern Europe and the former Soviet Union for many years. Their clinical use was not widespread in western countries because of the advent of antibiotics, but the increasing occurrence of bacterial antibiotic resistance has renewed interest in this approach.

This EC project (Phagevet) seeks to isolate, characterise, produce and apply phages highly active against salmonella and campylobacter, to young birds and assess their efficacy in minimising or eliminating these two pathogens.

To date, the project's Russian partner, NIIgenet in Moscow has isolated and selected phages against salmonella and the activity have been determined on many strains of these food poisoning bacteria, in particular S enteritidis, the major species associated with poultry.

Similar research at the Universidade do Minho in Portugal has produced several active campylobacter phages, and researchers at the University of Bristol have tested both these on chicks.

Day-old chicks were infected with S enteritidis and seven days later were orally administered different doses (high, medium and low, to optimise the number of phages) of a salmonella-specific phage. Gut contents were analysed post mortem for both surviving salmonellae and phages.

A similar method was followed for campylobacter, although a different method of administering the phage was used.

Treatment of the two bacterial infections with phages gave different results. Treatment of the salmonella infection with phage resulted in an immediate and large reduction in salmonellae (99.9 percent) but this effect did not persist for the seven days of the experiment. In contrast, numbers of campylobacter were reduced by a smaller amount (99.0 percent) at Day 2, and the effect persisted for seven days.

Since these food-poisoning bacteria were not entirely eliminated, only reduced, by phage application, there appears to be a balance established between "predator" (phage) and "prey" (host bacteria).

This suggests that application of phages for control of numbers of these two bacteria entering the food chain might best be made 24 to 48hours before slaughter, so that the dramatic reductions in salmonella and campylobacter coincide with the birds entering the processing plants.

These encouraging results prove the principle of using phages to control food-poisoning bacteria in live birds, and suggest that a commercial product could soon be available following further development and trials, perhaps within 2-3 years.