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Study Shows Detection of Salmonella in Feed Needs Two Tests

20 June 2013

ARGENTINA - Based on a recently published paper, researchers recommended using at least two methods to increase the chances of detecting Salmonella gallinarum or S. pullorum in poultry feed.

M. Cecilia Soria of the Instituto Nacional de Tecnología Agropecuaria (INTA) in Entre Ríos - with co-authors there and from Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) have compared three culture methods and PCR assays for Salmonella gallinarum and Salmonella pullorum detection in poultry feed.

To detect S. gallinarum or S. pullorum in artificially contaminated poultry feed, they compared nine culture combinations, including three pre-enrichment/enrichment methods (tryptic soy broth plus ferrous sulphate/tetrathionate Hajna, tryptic soy broth plus ferrous sulphate/selenite cystine broth, and Salmosyst) in combination with three selective agars (xylose lysine desoxicholate agar added with tergitol 4, EF-18, and Önöz), respectively. Additionally, a single PCR technique was applied combined with two different pre-enrichment media (tryptic soy broth plus ferrous sulphate and Salmosyst).

The specificity and positive predictive value were 1 for all methods. There were some differences among Salmonella strains for sensitivity and accuracy in the culture and Salmosyst-PCR methods.

The sensitivity and accuracy values were less than 0.60 and 0.64, respectively, whereas the negative predictive values were between 0.12 and 0.23.

Two PCR methods did not show any difference in the parameters of performance evaluated. Kappa coefficients showed good agreement between both methods.

None of the culture combinations was able to detect S. gallinarum or S. pullorum when the inoculum was less than 3 × 102 colony-forming units (cfu) per 25g, except the Salmosyst broth method, which could recover S. gallinarum from 3 × 101cfu per 25 g onward.

Overall, there were differences in the detection limits among the strains and methods used, the researchers reported in their paper published in Poultry Science.

In general, the three selective plating media did not show any significant difference in the parameters of performance studied for each strain.

On the other hand, the agreements were slight to fair when culture methods were compared among them and with both PCR methods.

The differences in the detection levels that were obtained using these methods and the difficulty in detecting S. gallinarum or S. pullorum in feed represent a potential problem when a poultry feed sample is considered to be negative.

As a result, the reserchers recommend using at least two methods to increase the chances of detecting S. gallinarum or S. pullorum in poultry feed.

Reference

Soria M.C., M.A. Soria, D.J. Bueno and H.R. Terzolo. 2013. Comparison of 3 culture methods and PCR assays for Salmonella gallinarum and Salmonella pullorum detection in poultry feed. Poult. Sci.  92(6):1505-1515. doi: 10.3382/ps.2012-02926

Further Reading

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