A Survey of 18 Dry Dairy Product Processing Plant Environments for Salmonella , Listeria and Yersinia.

An environmental microbiological surveillance program was conducted throughout the dry milk industry in cooperation with the American Dairy Products Institute (ADPI). The purpose of the survey was to determine the frequency and location of certain pathogenic microorganisms in dry milk and whey processing plant environments. A total of 402 samples were collected from 18 plants by each respective plant's personnel. All plants participated on a voluntary basis in response to a request sent to all ADPI members. All 410 samples were tested for Listeria spp., 245 samples were tested for Salmonella , and 312 samples were tested for Yersinia . Of the total, five samples collected from five separate plants were positive for either Salmonella or Listeria . Two samples were positive for Listeria (one for L. monocytogenes ), and three samples were positive for Salmonella . None was positive for Yersinia . Four out of the five positive samples were taken from drains in receiving, dryer, and butter production areas of the plants. The fifth positive sample was collected from a prefilter to a dryer.

DNA hybridization assay for detection of Salmonella in foods: collaborative study.

A collaborative study was performed in 11 laboratories to validate a DNA hybridization (DNAH) procedure for detection of Salmonella in foods. The DNAH procedure was compared to the standard culture method for detection of Salmonella in 6 foods: ground pepper, soy flour, dry whole egg, milk chocolate, nonfat dry milk, and raw deboned turkey. With the exception of turkey which was naturally contaminated, uninoculated and inoculated samples of each food group were analyzed. Results for the DNAH method were significantly better than for the standard culture method at the 5% probability level for the detection of Salmonella in turkey. There was no significant difference between the methods for the other 5 foods. The method has been adopted official first action.

Enzyme immunoassay for detection of Salmonella in low-moisture foods: collaborative study.

A collaborative study was performed in 15 laboratories to evaluate a modification of the enzyme immunoassay (EIA) method for detection of Salmonella in foods (46.B21-46.B29). The modified EIA requires 18-24 h pre-enrichment, 6-8 h selective enrichment, and 14-18 h M-broth post-enrichment prior to performing the assay, which requires 1-2 h. Total assay time is 40-52 h. The modified method was compared with the standard culture method for detection of Salmonella in 5 low-moisture foods: nonfat dry milk, milk chocolate, meat and bone meal, dry whole egg, and ground pepper. The modified method has been adopted official first action for use with low-moisture foods.

Enzyme immunoassay for detection of Salmonella in foods: collaborative study.

A collaborative study was performed in 25 laboratories to validate an enzyme immunoassay (EIA) procedure utilizing 2 specific monoclonal antibodies for rapid detection of Salmonella in foods. The EIA was compared with the standard culture procedure for detection of Salmonella in 6 food types: ground black pepper, soy isolate, dried whole eggs, milk chocolate, nonfat dry milk, and raw deboned turkey. Uninoculated and inoculated samples were included in each food group analyzed, with the exception of poultry which was naturally contaminated. There was no significant difference in the productivity of the EIA and culture procedures at the 5% level for any of the 6 foods. The enzyme immunoassay screening method has been adopted official first action.

ICMSF Methods Studies. XI. Collaborative/Comparative Studies on Determination of Coliforms Using the Most Probable Number Procedure 1.

Results of two international collaborative studies on the MPN technique for determination of coliforms in foods are reported. Three methods involving use of different presumptive and confirmatory media were compared. Results of one collaborative study conducted among 15 laboratories using eight different types of inoculated foods showed differences among the laboratories as great as 3.3 log units. The greatest difference between confirmatory tests using different media was 0.5 log units. Results of the other collaborative study conducted among five laboratories using three types of naturally contaminated foods showed differences among the laboratories as great as 1.4 log units. The greatest difference between tests using different media was 0.2 log unit. Both studies showed that the 95% confidence limit for a single value reported by a given laboratory was ± 1 log unit or ± 0.45 log unit for a mean of five values. The second study showed that a major source of variation within laboratories was between replicate aliquots. The findings are discussed in terms of their significance with respect to the monitoring of microbiological specifications for food.

ICMSF methods studies. IX. The influence of selective enrichment broths, differential planting media, and incubation temperatues on the detection of Salmonella in dried foods and feed ingredients.

Ninety-eight dried foods and feed ingredients were analyzed for Salmonella using tetrathionate brilliant green (T) and selenite cystine (S) broths incubated at 35 and 43 degrees C. The four enrichment cultures for each sample were subcultured in duplicate onto brilliant green (BG) , Salmonella--Shigella (SS), and bismuth sulfite (BS) agars, one plate of each being incubated at 35 degrees C, the other at 43 degrees C. Salmonellae were isolated from 44 of the 98 samples. Differences in the Salmonella recovery rates from the four selective enrichment conditions were not significant. However, there was a trend toward a higher proportion of Salmonella colonies on the selective media when the enrichment broths were incubated at 43 degrees C, although the differences were significantly only with BG and SS subcultured from T. While the four enrichment systems were not significantly different, the trend toward a higher proportion of Salmonella colonies on the differential media subcultured from 43 degrees C enrichment broths indicates an advantage to incubation at the elevated temperature. Incubation of selective agars at 35 degrees C was best because at 43 degrees C Salmonella recovery was significantly reduced. Detection of salmonellae on BS was significantly better than on BG or SS.

ICMSF methods studies. VII. Indicator tests as substitutes for direct testing of dried foods and feeds for Salmonella.

The correlation between the occurrence of indicator organisms and salmonellae in the same sample homogenate of various classes of dried foods was studied. In the first phase of the work involving 5837 samples, 1943 contained fecal coliforms and 100 contained Salmonella. Fecal coliforms were not detected in 53 of the Salmonella-positive samples. In the second phase, an additional 637 samples were tested for the presence of Enterobacteriaceae, coliforms, fecal coliforms, and Salmonella. Enterobacteriaceae were detected in 538 samples, coliforms in 506, fecal coliforms in 343, and Salmonella in 49. All Salmonella-politive samples were also positive for Enterobacteriaceae and coliforms. However, 6 of 49 Salmonella-positive samples were negative for fecal coliforms. Therefore, the use of the fecal coliform test as an index of Salmonella contamination would result in the rejection of Salmonella-negative foods and the acceptance of Salmonella-positive foods. It is concluded that none of these indicator groups are reliable as an index of Salmonella contamination in dried foods.

Salmonella in natural animal casings.

Destruction of salmonellae in inoculated and naturally contaminated natural animal casings was studied. Salmonellae were effectively destroyed (99.999%) in inoculated hog casings after exposure for 24 h to saturated brine at pH 4.0 and 10.0 adjusted with acetic acid and sodium hydroxide, respectively. Treatment of inoculated hog and sheep casings in saturated brine or saturated brine with citric acid was not nearly as effective as brine containing acetic acid or sodium hydroxide. Salmonellae in naturally contaminated hog casings were virtually eliminated after 21 days of storage in crystalline sodium chloride. Salmonella in sheep and hog casings were eliminated after 7 days of storage in crystalline salt. Treatment of naturally contaminated hog casings with glycerin-salt or sorbitol-salt solutions was not as effective in destroying salmonellae as treatment with crystalline salt.

Microbiological examination of cocoa powder.

Total aerobic plate counts of 36 cocoa powders ranged from 100 to 27,000 per g, with 86% having counts of less than 9,300 per g. Bacillus and Micrococcus were the only genera identified.