Enhanced Recovery and Isolation of Salmonella and Listeria Using a Novel Culture-Transfer-Inoculation Device.

A novel culture-transfer-inoculation device (CTID), comprised of a fiber-foam matrix suspended in the enrichment medium and thereafter used in subsequent transfers and inoculations, was used in the analysis of foods for Salmonella using the Food and Drug Administration (FDA) method and for Listeria using the FDA and United States Department of Agriculture (USDA) procedures. In these studies, the food sample was introduced into the enrichment medium including the CTID. Following incubation, transfer from the primary enrichment culture and subsequent transfers were made by both conventional procedures and by the CTID. Four-hundred-and-twenty-five samples were analyzed for Salmonella of which 115 were positive. Using conventional transfer and inoculation techniques, 87 positive results were observed; whereas using the CTID-modified technique, 112 positive results were obtained. The false-negative rate for the conventional transfer method was 21.7%. A 2.6% false-negative rate was observed with the CTID. The difference between conventional and CTID results were statistically significant (p<0.0160). One-hundred samples were analyzed for Listeria using the FDA method with 32 positive results. Using the CTID 42 positives were detected from the FDA enrichments. One-hundred-and-ninety-eight samples were analyzed using the USDA method with 77 positive results. With the CTID, the same samples yielded 86 positives. No false-negatives resulted through the use of the CTID while a 10.5% to 23.8% rate was observed with the conventional transfer method. The difference between conventional USDA and CTID-modified USDA results were statistically significant (p<0.0086). These data indicate that the fiber-foam matrix of the CTID provides a micro-environment enhancing the sensitivity of the culture methods for the detection of Salmonella and Listeria .

Comparison of Salmonella Bio-EnzaBead™ Immunoassay Method and Conventional Culture Procedure for Detection of Salmonella in Crustaceans.

The sensitivity of the Bio-EnzaBead™ enzyme immunoassay (EIA) for recovery of Salmonella in crustaceans was compared to a standard cultural method. Presumptive positive samples by the EIA procedure were confirmed culturally by plating their respective selective enrichments and post-enrichment M-broth cultures on bismuth sulfite, xylose desoxycholate, and Hektoen enteric agars. Use of tetrathionate, selenite cystine, and M-broth cultures was necessary for reliable confirmation of positive EIA reactions. Of 287 samples tested, 129 were positive by culture, while 130 were EIA-positive and were confirmed from the M-broth and/or the selective enrichments. When M-broth alone was used for confirmation of positive EIA readings, only 112 samples were shown to be positive, while 127 were confirmed from tetrathionate and selenite cystine. The importance of using all three media to confirm positive EIA readings was clearly demonstrated. There was a large number (76) of positive EIA assays which could not be confirmed culturally. These uncon-firmed positives were probably due to a cross-reacting organism present in the lot of material tested.

Comparison of Salmonella Bio-EnzaBead Immunoassay Method and Conventional Culture Procedure for Detection of Salmonella in Foods.

A rapid enzyme immunoassay screening procedure (EIA) utilizing two monoclonal antibodies specific for salmonellac was compared to the standard culture method (BAM/AOAC) on 1,289 samples representing 26 food types. The samples consisted of 760 artificially inoculated, 150 naturally contaminated, and 379 uninoculated food samples. There were 594 samples positive by the EIA (optical densities greater than 0.2 at 405 nm), of which 568 were confirmed culturally from M-broth. A total of 570 samples was positive by the BAM/AOAC procedure. Of the foods tested, there was no significant difference between the two methods, with the exception of cake mix and raw shrimp. The EIA was significantly better for detecting Salmonella in cake mix, while the culture procedure was more productive for shrimp. The method employed a 24 ± 2-h preen-richment, an 18-h selective enrichment, and a 6-h M-broth post-enrichment. The EIA assay required an additional 2 h for a total of 48 h, compared to a minimum of 4 d by BAM/AOAC.

The Salmonella Problem: Current Status and Future Direction 1.

Human salmonellosis continues to be an important public health problem. Consumer mishandling of poultry, meat and dairy products is the most frequent cause of outbreaks. Attempts to educate consumers in proper food handling practices have had disappointing results. Denmark has an intensive program directed towards students in the 7, 8, 9 and 10th grades. Canada is contemplating a similar program for students at the high school level. Similar efforts do not exist in the U.S. Contaminated animal feed continues to be an important source of infection to livestock. The recent rise in the importance of Salmonella agona and Salmonella hadar illustrates again the important chain leading from feed contamination to livestock infection to human infection. Scandinavian countries have intensive programs directed toward control of Salmonella in domestic meat animals. Indications are that this has decreased the incidence of Salmonella in livestock and that concurrently there has been a decreased incidence of human salmonellosis in these countries. The Nurmi concept, involving oral administration of the gastrointestinal flora of adult birds into newly hatched chicks and poults, shows promise as a practical and economical approach to reducing the incidence of salmonellae in poultry.

Status of Salmonella - Ten Years Later.

The current status of the Salmonella problem, 10 years after publication of the report of the Committee on Salmonella of the National Research Council, was reviewed. The incidence of human salmonellosis has increased during this period. The major source of the Salmonella problem in man still derives from foods of animal origin, especially poultry, beef and pork. Contaminated products cause disease as the result of inadequate cooking or cross-contamination of working surfaces in the kitchen environment. The epidemiology of human salmonellosis has not changed during the past decade. Surveillance remains a powerful tool for protecting the consumer by discovering on-going epidemics, but it has done little to control the endemic problem from which epidemics emerge. Several outbreaks during the past decade indicate that the infecting dose, at least for certain Salmonella strains in certain foods, is considerably lower than that indicated on the basis of volunteer studies with adult male prisoners. The National Research Council report, as well as those from numerous other groups, emphasized the need for consumer education if the incidence of food-associated outbreaks is to be reduced. The rising incidence of human salmonellosis indicates that consumer education programs have not been successful. It was suggested that courses of study in proper food handling practices could profitably be directed toward students in secondary schools and that as a result, on a long term basis, the incidence of foodborne illness, including salmonellosis, would be reduced. Since a large percentage of outbreaks is traced to mishandling of foods in commercial establishments, it was suggested that inspectional activities in hotels, restaurant and catering facilities be increased at the expense of decreased activities in food processing facilities.