Mayonnaise - a crucial test for salmonella vaccine? - UK - One of the most virulent sources of salmonella poisoning can be home-made mayonnaise, which normally contains the yolk of raw, unpasteurised eggs.

The finished product can be left for long periods of time at room temperature. If the eggs are infected with any salmonella 'bugs' this provides them with an ideal environment in which to multiply rapidly.

To help protect consumers against salmonella infection, the majority of laying hens in the UK are now vaccinated against Salmonella enteritidis - one of the most common sources of food poisoning in humans. The most popular vaccine with egg producers, accounting for around 70 per cent of the market, is TAD Salmonella vac E, a welfare friendly, live, oral vaccine developed by Lohmann Animal Health.

To put their product to a critical consumer test Lohmann organised an experiment in which a traditional mayonnaise recipe was made up by an independent UK accredited laboratory and 'spiked' with salmonella.

The mayonnaise was divided into eight samples and two of each were inoculated with a culture of the wild (Leipzig) strain of salmonella bacteria, with TAD Salmonella Vac E vaccine and another commercially-available vaccine, while two were left untreated.

The samples were then incubated for 24 and 48 hours respectively at 30ºC. While Salmonella enteritidis was isolated from the samples inoculated with the wild strain and the other commercially-available vaccine, there was no growth in either the samples inoculated with TAD Salmonella vac E or the uninoculated samples.

"This test at the consumer end of the food chain confirms our confidence in this product. We know that our vaccine strain is not transmitted from the hen into the egg, but the fact that salmonella couldn't be detected in the mayonnaise even when directly inoculated into the sample is remarkable," commented Dr Ilka Schröeder, of Lohmann Animal Health's research and development department.

Source: Lohmann Animal Health - 31st May 2005