Methodology for Salmonella in Feed Compared

SWEDEN - Researchers in Uppsala compared cultural methods for the detection of Salmonella in feed and feed ingredients, and found their methods to be equally sensitive and specific, although the detection levels in different materials varied considerably.

10 February 2009

3 minute read

Europe

Animal feed as a source of infection to food producing animals is much debated. In order to increase our present knowledge about possible feed transmission it is important to know that the present isolation methods for Salmonella are reliable also for feed materials.

Salmonella control of food-producing animals was started in Sweden in the late 1950s. The present control programme for feed, based on hazard analysis of critical control point (HACCP) principles was initiated by the feed industry in 1991.

Sevinc Koyuncu and Per Haggblom from the National Veterinary Institute at Uppsala in Sweden compared the ability of the standard method used for isolation of Salmonella in feed in the Nordic countries, the NMKL71 method (Nordic Committee on Food Analysis) was compared to the Modified Semisolid Rappaport Vassiliadis method (MSRV) and the international standard method (EN ISO 6579:2002).

Five different feed materials were investigated, namely wheat grain, soybean meal, rape seed meal, palm kernel meal, pellets of pig feed and also scrapings from a feed mill elevator.

Four different levels of the Salmonella serotypes S. Typhimurium, S. Cubana and S. Yoruba were added to each feed material.

For all methods, pre-enrichment in Buffered Peptone Water (BPW) were carried out followed by enrichments in the different selective media and finally plating on selective agar media.

The results obtained with all three methods showed no differences in detection levels, with an accuracy and sensitivity of 65 per cent and 56 per cent, respectively.

However, Muller-Kauffmann tetrathionate-novobiocin broth (MKTTn), performed less well due to many false-negative results on Brilliant Green agar (BGA) plates.

Compared to other feed materials, palm kernel meal showed a higher detection level with all serotypes and methods tested.

Conclusions

The authors were surprised that the results showed that the accuracy, sensitivity and specificity of the investigated cultural methods were equivalent. However, the detection levels for different feed and feed ingredients varied considerably.

Reference

Koyuncu S. and P. Haggblom. 2009. A comparative study of cultural methods for the detection of Salmonella in feed and feed ingredients. BMC Veterinary Research 2009, 5:6doi:10.1186/1746-6148-5-6.