Methods for Detecting Viruses in Foods: Background and General Principles

Viruses are sometimes transmitted through foods. Hepatitis A (HA) and some viral gastroenteritides are the diseases now known to be spread most frequently in this way, but any virus from the human intestines probably could be. Bacterial indicators of fecal contamination show limited correlation with the incidence of viruses in foods, so tests to detect the viruses themselves are needed. The epidemiologic record has led to selection of shellfish (bivalve molluscs) and vegetables and fruits as foods for which test methods should be described, and ground beef and raw milk are also considered here because of the great interest they have attracted among research workers. Viruses in foods are presently detected on the basis of the infections they cause in cultured primate cells, but these cell culture methods do not permit detection of the HA virus nor the most important of the foodborne gastroenteritis viruses. Current methods of virus detection entail liquefaction of the food sample, clarification of the sample suspension, possibly concentration of the clarified food extract, and inoculation of cell cultures; a certain amount of specialized equipment is required for some of these procedures. The inclusion of the proper controls is critical to interpretation of results that are obtained

Methods to Detect Viruses in Foods: Testing and Interpretation of Results

Viruses that may be detected in foods should be considered pathogenic and treated with appropriate caution. In this discussion, specific procedures for extracting viruses from shellfish are presented for each of the major commercial species of bivalve molluscs. Other foods for which specific extraction methods are detailed include lettuce, frozen strawberries, ground beef and raw milk. Viruses that may be detected by the methods described are those which are capable of producing a perceptible effect while replicating in cultured primate cells. Both results that are apparently positive and those that are apparently negative require careful interpretation; one must be extremely skeptical if large numbers of food samples obtained at the market appear to yield viruses. The procedures that are now available have some important limitations, including inability to detect the viruses that cause most of the reported foodborne disease. Approaches to surmounting these limitations include use of serologic methods to detect viruses that do not cause perceptible effects in cell cultures and improvement of procedures for extracting all viruses from food samples

Produção de enterotoxinas e da toxina da síndrome do choque tóxico por cepas de Staphylococcus aureus isoladas na mastite bovina Production of enterotoxins and toxic shock syndrome toxin by Staphylococcus aureus strains isolated from bovine mastitis

<abstract language="eng">A total of 72 strains of Staphylococcus aureus were examined for the production of staphylococcal enterotoxins (SE) A, B, C, D and toxic shock syndrome toxin (TSST-1). The strains were isolated from milk samples from cows with mastitis in dairy herds of São Paulo State, Brazil. Off 72 isolates, 38 (52.8%) produced SEA, 38 (52.8%) SEB, 32 (44.4%) SED, 28 (38.9%) SEC and 27 (37.5%) TSST-1. From the 72 strains, 66 (91.7%) produced, at least, one or more toxin, including TSST-1