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.

Raw hamburger: an interstate common source of human salmonellosis.

An interstate common-source outbreak of salmonellosis was first detected in the United States in September and October, 1975, when a tenfold increase in Salmonella newport isolates was noted through routine salmonella surveillance by the Colorado Department of Health. Eighteen primary cases with a distinctive antibiotic resistance pattern (tetracycline, streptomycin, and sulfonamides) were evaluated in a case-control study, and illness was found to be associated with eating raw hamburger (p less than .001) from any store of one grocery chain (p less than .001). A Dallas, Texas, processing plant that supplied the Colorado markets also supplied other states, and these other states were alerted. Maryland discovered nine S. newport isolates with the same antibiogram and, as in the Colorado outbreak, illness was associated with eating raw or very rare ground beef from the same grocery chain (p less than .03). A third outbreak of S. newport with the same antibiogram occurred on a Florida military base. S. newport with the same antibiogram and a phage lysis pattern identical to those of the human epidemic isolates was cultured from frozen hamburger recovered in Colorado and Florida. The associated hamburger originated at the same Dallas, Texas, processing plant. A source of the epidemic strain was not identified, but the organism probably originated before delivery to the plant.

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.

Preservation of refrigerated meats with controlled atmospheres: Treatment and post-treatment effects of carbon dioxide on pork and beef.

Whole pork loins were divided into roasts and subjected to air control and carbon dioxide enriched atmospheres at 1°C for up to 21 days. Quintuplicate samples of both control and carbon dioxide treated loins were transferred to air storage at 0,4,7, 14 and 21 days and further held for 0, 3(4), 7 and 10 days at 4°C. Microbiological counts were taken at all time permutations. The results indicated a strong inhibiting effect of the carbon dioxide atmosphere on microbial growth as well as a marked residual effect during post-treatment storage in air. Satisfactory colour and odour were maintained on the loins for extended storage times, with visual and olfactory deterioration preceding microbial spoilage. Beef round wedges were treated in a similar manner. Although bacterial spoilage inhibition was comparable, colour degeneration was rapid and severe, making the method unsuitable for treatment of finished beef cuts.

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.