Simultaneous recovery of bacteria and viruses from contaminated water and spinach by a filtration method.

Water and leafy vegetables eaten fresh are increasingly reported as being involved in food-borne illness cases. The pathogenic agents responsible for these infections are mainly bacteria and viruses and are present in very small quantities on the contaminated food matrices. Laboratory techniques used to isolate or detect the contaminating agent differ enormously according to the type of microorganisms, generating time and economical losses. The purpose of this study was to optimize a single method which allows at the same time the recovery and concentration of these two main types of pathogenic organisms. Water and spinach samples were artificially contaminated with the feline calicivirus (FCV), rotavirus, hepatitis A virus (HAV), Escherichia coli, Listeria monocytogenes, Campylobacter jejuni and Salmonella Typhimurium. The principle behind the recovery technique is based on the use of a positively charged membrane which adsorbs both viruses and bacteria present in the water or in the rinse from the vegetables. Using conventional microbiology, PCR and RT-PCR, this filtration technique allowed a detection level superior to 10² CFU/g for S. Typhimurium, E. coli, L. monocytogenes and C. jejuni and to 10¹ PFU/g for FCV, HAV and rotavirus. This combined method can also be applied to other bacterial and viral species for the identification of the responsible agent for food-borne illnesses.