Recovery of Salmonella typhimurium from compost with the IMS-PCR method

Abstract

In this work a procedure was optimized to recover Salmonella typhimurium from a vegetable compost after its artificial contamination. A combination of a bacteriological method, immunomagnetic separation (IMS) and polymerase chain reaction (PCR) techniques allowed a reduction in the detection time to 30 h while maintaining high specificity. The lower threshold of direct amplification from extracts of contaminated compost was 10⁸ salmonellae g^-1. To improve the sensitivity, a combination of shortened pre-enrichment and enrichment procedures was optimized and the growth of S. typhimurium evaluated. Immunomagnetic separation using anti-Salmonella Dynabeads™ permitted the recovery of 30 salmonellae per 50 g of compost, the same value obtained with the traditional microbial method, which takes two days longer. Alternative purification methods to reduce organic compound inhibition of the PCR reaction mixture did not improve Salmonella detection under a threshold of 10⁵ salmonellae g^-1.