Reducing Salmonella in the food chain

Food scandals, like the dioxin case, the BSE-crisis and several Salmonella incidents are still fresh in the memories of not only European farmers, but food processors, governments, retailers and, indeed, consumers. Yet, despite regulations across Europe being tightened in order to provide a greater degree of safety assurance, problems still arise, further eroding consumer confidence. Finally, for the control of residues of antibiotics in products of animal origin and for a rapid decrease of the Salmonella contamination in the food chain, there is light at the end of the tunnel.

Improved analytical tests to detect antimicrobial residues and pathogens in food products are becoming increasingly available. A test for the rapid detection of antimicrobial residues (e.g. Premi®Test from DSM Nutritional Products) is already available and easy-to-use detection methods including those for pathogens are being added. These improved test methods will offer novel and rapid solutions for all industries involved in the food chain, from animal feed to food of animal origin.

Salmonella breakthrough

In the case of Salmonella, one of the most stubborn and regularly occurring problems in the food chain, there has been a real breakthrough. Despite it being easy to analyze through classical microbiology, testing for Salmonella wasn’t even required in some European countries up to a few years ago. Yet the problem is widespread and affects a broad range of foodstuffs, from meat and fish, poultry and eggs, to fruit and vegetables, and even chocolate. Salmonella contamination may cause intestinal discomfort, fever, and, only in extreme cases, it may cause death (e.g. in the weak and elderly), but indeed, it is still responsible for countless millions of stomach upsets around the world each year.

The Salmonella contamination can occur anywhere in the food chain; on farms and in rearing units, in factories where agricultural products are processed into feed ingredients, or complete animal feed, or anywhere bacteria have a chance to grow. In feed production, the process of pelletizing, which uses heat and pressure, offers one of the few barriers to transmission. But the recent introduction of Salmonella serotyping with the Premi®Test Salmonella of DSM and Check-Points, is particularly significant in solving the problem because it not only offers a speedy detection method, it also enables an exact tab to be put on the bacteria. And more significant still, it enables the source of the problem to be traced back to the hatchery, breeder flock, feed mill, grow-out farm or processing plant where the problem arose. This is mainly due to the availability of Salmonella serotyping.

Tracing the problem

In addition to processing, there are two basic transmission routes for Salmonella: vertical and horizontal. In the case of poultry, which worldwide has traditionally been the biggest source of Salmonella poisoning, vertical transmission is from the grandparent stock through the parent hatchery, rearing breeders, breeders and broiler hatchery, to the processors, retailers and kitchen. Horizontal transmission, which is more complex and sometimes is more difficult to trace, can take place via the feed, equipment or environment at any of the stages mentioned for vertical transmission.

Measures to trace the source of contamination along the vertical route involve sampling procedures such as protective overshoes, feed dust, pallet coolers, hatchery down, chicken-box liners, transportation boxes, box washers, chicken faeces, caeca and skin, as well as breast meat. Monitoring and prevention involves sampling at all stages of the production chain, like chicken houses, hatcheries, feed and feed mills, tracing the source of contamination and cleaning and disinfecting chicken houses, slaughterhouses and equipment, environment and staff.

Dutch success

In addition to strict monitoring, cleaning and disinfection regimes, preventative measures aimed at eliminating or reducing the problem in flocks in The Netherlands include vaccination (up to now only possible for 2 serotypes, S.enteritidis and S.typhimurium), probiotic and antibiotic treatments, and acidified or pelletized feeds. The successful monitoring of breeder houses has owed much to the regular analysis and rapid serotyping of Salmonella positive samples. To avoid contamination of separate lots from other breeder houses, a special regime involving meticulous segregation (separation or canalization) has been introduced targeting the minimization of cross-contamination. Similar strict monitoring measures were introduced in grow-out houses and on farms, while processing plants were subjected to strict canalization and cleaning regimes.

A similar regime is carried out at breeders and hatcheries with daily sampling of each new hatch. At grow-out houses, protective overshoes are sampled 10 days before stock is slaughtered. Finally, in the processing phase, 30 caecal or feather, skin and meat samples are taken at every house. Over a sustained period of several years (1997 – 2006) this anti-Salmonella action programme in The Netherlands, in which serotyping has played a key role, has resulted in less than 1% occurrence of both the Salmonella enteritidis and typhimurium bacteria, and a fall in overall contamination from 35% to 6%. Conclusive evidence of a successful anti-Salmonella strategy.

In the meantime, EU regulations and guidelines require a regular monitoring in the production chain for food of animal origin. In this regulation, serotyping is required for 5 strains mostly involved in illnesses related to Salmonella contamination. In the coming years more, and finally all, strains will be added to this list.

Monitoring for Salmonella and serotyping the positive samples will be an integral part of the control for this aspect of food safety of products of animal origin.

Serotyping key

There are 2000 Salmonella subtypes or serovars. Different Salmonella contaminations are often caused by different serovars. Classical serological methods require well trained and experienced staff and full serovar identification can take up to 3 weeks or more. But routine serovar identification is important for two main reasons: first, recent EU and national requirements demand more detailed serovar identification when positive salmonella contamination is found. Second, routine serovar identification enables each specific cause of salmonella contamination in the food chain to be pinpointed, thus reducing salmonella contamination by taking appropriate sanitary measures in the specific part of the production chain, such as, broiler house, feed mill or hatchery. As has been demonstrated in The Netherlands, excellent results have been achieved with this approach.

Peter Platteschor, General Manager of Nutrilab B.V., a Dutch lab accredited by the national regulatory body, the RVA, and with many years of experience in the field, said, “We have carried out many tests with Premi®Test Salmonella since its introduction in January 2007 and both we and our customers have every confidence in this method. Not only is it reliable, it is also fast and produces results much quicker than alternative methods.”

To meet the challenges presented by salmonella contamination and to meet the tighter governmental regulations, DSM Nutritional Products and its partner Check-Points, introduced a Salmonella serotyping method that enables the source of contamination in the supply chain to be indicated faster and with greater precision. The routine is extremely fast and can be carried out in the lab, enabling appropriate action to be taken to prevent further contamination. Called Premi®Test Salmonella, it goes beyond the primary-screening stage and identifies a large number of serovars in a single test.