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Salmonella Intervention Strategies and Testing Methods

by 5m Editor
4 April 2009, at 12:00am

Dr Scott M. Russell, extension poultry scientist with the University of Georgia, describes and explains the implications of the different Salmonella intervention strategies and testing methods used in the US and EU in the March 2009 issue of the University's <em>Poultry Tips</em>.

Countries that produce poultry on a large scale have evolved different methods of production, processing, and testing especially with regard to controlling and testing for Salmonella. The implications of these differences will be discussed.

Production Differences

In the US, companies are limited as to the types of interventions they may use to control Salmonella in poultry during breeding, hatching and grow-out. These limitations are placed on the industry by economic factors, the US Food and Drug Administration and the sheer scale of production.

For example in Europe, some countries test all breeder flocks for Salmonella and destroy any breeder flock that is found to be positive. In this way, they have significantly reduced Salmonella to 3 to 6 per cent on birds coming into the processing facility. This approach is impossible in the US, as we produce twice as much poultry in Athens, Georgia than is produced in Sweden, where these practices are common.

Some countries in Europe use competitive exclusion to prevent Salmonella colonization of baby chicks. This approach is illegal in the US because the bacterial cultures used to inoculate chicks, which occupy the attachment sites in the intestine and produce by-products that kill Salmonella, are undefined – the particular species used are not specifically identified.

Salmonella vaccines are available in the US but are often cost-prohibitive.

Because of these limitations, the US poultry industry has placed much more emphasis on eliminating Salmonella in the processing plant, whereas in Europe, all of the effort to eliminate Salmonella is concentrated on the breeding and grow-out operations.

Processing Differences

In the US, over 99 per cent of companies use immersion chilling systems. In Europe, air chilling is most commonly used. This is important because immersion chilling is by far the most effective intervention tool available for poultry processors. In Europe, no chemicals are used to reduce Salmonella during processing, including chlorine. What happens when a flock that is contaminated with Salmonella enters the plant or what happens when the interventions used in the field break-down? In a word, nothing. The EU does not have any Salmonella regulations for poultry carcasses. The EU considers Salmonella on carcasses to be a sanitation indicator, not a food safety issue (Dr Nelson Cox, USDA-ARS).

Sampling Differences

In the US, the USDA-FSIS inspectors rinse a chicken with 400 mL of sterile buffered peptone water (whole carcass rinse). In the EU, they take a 25-gram neck skin composite sample from three carcasses and pool them.

Cox et al. (2008) conducted a study to the methods of the US and EU. These researchers found that both methods are fairly equivalent for detecting Salmonella but that neither is sensitive enough to be considered perfect. For example, on many carcasses, the neck skin method picked up the Salmonella, but none was found in the carcass rinse for that carcass and in other cases, the reverse occurred. Based on this study, both methods would need to be used together to really get a good idea of actual prevalence.

It is important to note that in some countries around the world, in particular for exported product, the test method is completely different. The chicken skin is sterilized using a blow-torch or iodine solution, then the skin is removed using sterile tweezers and a sample of deep breast muscle is taken and tested for Salmonella. It is interesting that Salmonella is never found using this technique, allowing the company/country to boldly state that they do not have any Salmonella on their poultry. This is misleading and causes great confusion. By this testing method, a company could say that their chicken is sterile, which is of course, impossible. Meanwhile, the USDA-FSIS is forcing companies in the US that are in Category 2 or 3 to post their Salmonella prevalence, names, addresses and USDA Plant Numbers (P-numbers) on the internet for the world to see.

Implications

Poultry companies in the US are placed in a very difficult situation. They are required to use chemicals in the plants to lower Salmonella to acceptable levels for the USDA. They do an excellent job in this regard. However, because they use chemicals, they cannot export to Europe. Moreover, they cannot use cost-effective measures such as competitive exclusion to control Salmonella during grow-out because they are too expensive or are against the law due to FDA regulations. Even though they effectively lower Salmonella to 7.5 per cent nationwide on post-chill carcasses, this is not acceptable to countries that have a 'zero tolerance' for Salmonella regulation for imported poultry, which is based on an inaccurate testing method. To add to the difficulty, now the companies that are in Category 2 or 3 of the Salmonella performance standard must have their Salmonella data posted on the internet, which eliminates their exportation to 'zero tolerance' countries.

Considerations

An extremely important question that must be answered is, what are the Europeans getting for the incredible expenditure of effort and money trying to eliminate Salmonella from the breeders, hatchery and grow-out operation? For example, what impact does this effort have on human salmonellosis? Cox et al. (2008) reported that the total number of people who have salmonellosis is far greater (42.8 per 100,000 people in Sweden versus the US where it is 14.9 per 100,000 people) in a country where extraordinarily expensive measures are used to eliminate Salmonella from the flocks prior to processing.

There should be an effort by leaders of these countries to use sound scientific principles to come together and agree on compatible methods for eliminating and testing for Salmonella. There is no logical reason why competitive exclusion, which has been used in the field for many years in Europe to eliminate Salmonella from the flock without any adverse effects, cannot be used in the US. This causes great confusion for companies that operate globally and for consumers who believe they are buying 'Salmonella-free chicken.

Reference

Cox, N.A., L.J. Richardson, J.A. Cason, R.J. Buhr, D.P. Smith, P.F. Cray and M.P. Doyle, 2008. Comparison of neck skin versus whole carcass rinse for prevalence of Salmonella and E. coli counts recovered from broiler carcasses. Presented at the US Poultry and Egg Association Exposition, Atlanta, Georgia.

March 2009