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

In this work a procedure was optimized to recover Salmonella typhimurium fr om a vegetable compost after its artificial contamination. A combination of a bacteriological method, immunomagnetic separation (IMS) and polymerase c hain reaction (PCR) techniques allowed a reduction in the detection time to 30 h while maintaining high specificity. The lower threshold of direct amp lification from extracts of contaminated compost was 10(8) salmonellae g(-1 ). To improve the sensitivity, a combination of shortened pre enrichment an d enrichment procedures was optimized and the growth of S. typhimurium eval uated. Immunomagnetic separation using anti-Salmonella Dynabeads(TM) permit ted the recovery of 30 salmonellae per 50 g of compost, the same value obta ined with the traditional microbial method, which takes two days longer. Al ternative purification methods to reduce organic compound inhibition of the PCR reaction mixture did not improve Salmonella detection under a threshol d of 10(5) salmonellae g(-1).