Clyde R. Wilson

Potential Role of Refrigerated Milk Packaging in the Transmission of Listeriosis and Salmonellosis

Cultures of three Listeria monocytogenes serotypes and three Salmonella spp. were applied to the exterior surfaces of waxed cardboard or plastic milk containers. Contamination sites were sampled with premoistened cotton swabs during 14 d of refrigeration. Unstressed cells of Listeria survived up to 14 d on the surfaces of waxed (1 serotype) and plastic (3 serotypes) containers. Heat-stressed cells of all three serotypes of Listeria survived for 2 d on both types of containers. One serotype survived for 4 d, but only on plastic containers. Unstressed cells of all three Salmonella strains survived up to 14 d on both types of containers. Heat-stressed Salmonella strains survived up to 2 d (waxed containers) and 4 d (plastic containers).

Sulfite Compounds as Neutralizers of Spice Toxicity for Salmonella

The ability of five inorganic chemical salts (K2SO3, K2SO4, Na2SO3, Na2SO4, and CaCO3) to neutralize the toxicity of six spices (allspice, cinnamon, clove, garlic powder, onion powder, and oregano) for Salmonella was evaluated. Their effect on four spices non-toxic to Salmonella (black pepper, white pepper, rosemary, and thyme) was also determined. The inhibitory effects of onion and garlic powders were overcome by addition of 0.5% of K2SO3 or Na2SO3 to pre-enrichments of lactose broth, nutrient broth, or trypticase soy broth. Allspice, cinnamon, clove, and oregano remained toxic to Salmonella in all pre-enrichment broths tested, with or without chemical additives. None of the chemical additives had any effect upon isolation of Salmonella from the non-toxic spices. Until a more practical method for analysis of allspice, cinnamon, clove, and oregano is developed, dilution of these spices to non-toxic levels is recommended.

Evaluation of Cultural Methods to Isolate Salmonella from Pressed Yeast and Dried Inactive Yeast

An improved method recently developed to isolate Salmonella from dried active yeast was evaluated for use with pressed yeast and dried inactive yeast. The method for dried active yeast consists of pre-enriching a 25-g sample in trypticase soy (TS) broth at a sample-broth ratio of 1:10, incubating at 35 ± 0.5 C for 24 ± 2 h, and transferring to lauryl sulfate tryptose (LST) and tetrathionate (TT) broths. After 24 ± 2 h at 35 C, the broths are streaked to selective agars. When evaluated for use with pressed yeast, Salmonella attained higher most probable number levels/ml with this method (7.9 × 104 – 3.3 × 106), than with 1% tryptone broth and a sample-broth ratio of 1:5 (1.7 × 103 – 1.7 × 106), which is the current examination procedure for pressed yeast. Salmonella was consistently isolated from selective agars streaked from TT broth, but was seldom isolated from selective agars streaked from LST broth because of massive overgrowth by non-salmonellae. With dried inactive yeast, this modified method was eq...

Recovery of Salmonella from Fluid Milk

Methodology was developed for isolation of Salmonella from skim milk, 2% fat milk, whole milk and buttermilk. Lactose broth, lactose broth plus brilliant green dye, buffered peptone water and each milk type plus brilliant green dye were evaluated as preenrichment broths. Incubation temperatures of 35 and 43°C were compared for use at the preenrichment stage. The recovery of Salmonella was determined after selective enrichment in selenite cystine, tetrathionate and Rappaport-Vassiliadis broths. Results indicated that fluid milk should be examined for Salmonella by being preenriched in lactose broth, subcultured to selenite cystine and tetrathionate broths and streaked to selective agars, with 35°C as the incubation temperature throughout the analysis.

Influence of Sample Reconstitution on Recovery of Salmonella Species from Low-Moisture Dairy Foods

Recovery of Salmonella species from dry whole milk, lactic casein, non-instantized nonfat dry milk, rennet casein and sodium caseinate was compared under rapid and slow conditions of rehydration. For rapid rehydration, a 25-g portion of each product was blended or swirled with 225 ml of appropriate preenrichment medium. After 60 min, the flask contents were adjusted to pH 6.8 and incubated at 35°C. For slow rehydration, a 25-g portion of each product was gently added to 225 ml of appropriate preenrichment medium, allowed to soak undisturbed for 60 min at room temperature, and then incubated at 35°C without pH adjustment. Recovery of Salmonella by the slow rehydration (soak) method was equal or enhanced for all products tested except sodium caseinate. Use of a meter instead of test paper to adjust the pH of rapid rehydration (blend/swirl) preenrichments did not improve recovery of Salmonella . Examination of dry whole milk and non-instantized nonfat dry milk by the soak method should be limited to 25-g amounts since 100-g and 375-g composites were not completely wetted. Composites of lactic and rennet casein weighing ⩽375 g, however, may be examined by the soak method without loss of analytical sensitivity.