Relative effectiveness of selenite cystine broth, tetrathionate broth, and Rappaport-Vassiliadis medium for the recovery of Salmonella spp. from foods with a low microbial load.

The relative effectiveness of Rappaport-Vassiliadis (RV) medium, selenite cystine (SC) broth, and tetrathionate (TT) broth for the recovery of Salmonella spp. from foods with a low microbial load was determined. RV medium made from its individual ingredients and incubated at 42 degrees C was compared with a commercial preparation of SC broth, incubated at 35 degrees C, and TT broth incubated at 35 and 43 degrees C, for the recovery of Salmonella spp. Twenty-one artificially contaminated food types that included dairy foods, spices, and egg products, as well as other low-microbial-load foods, were analyzed. The foods were inoculated with single Salmonella serovars at target levels ranging from 0.04 to 0.4 CFU/g. No significant differences (P< or =0.05) among the selective enrichment broths for the recovery of Salmonella spp. from 18 of the foods were observed. Significantly fewer Salmonella-positive test portions of gelatin, guar gum, and nonfat dry milk were recovered with RV medium than with SC broth incubated at 35 degrees C and TT broth incubated at 35 and 43 degrees C. TT broth incubated at 35 degrees C recovered the greatest number of Salmonella-positive test portions. For the recovery of Salmonella spp. from foods with a low microbial load, it is recommended that TT broth incubated at 35 degrees C and RV medium incubated at 42 degrees C be used.

Comparison of sorbitol MacConkey and hemorrhagic coli agars for recovery of Escherichia coli O157:H7 from brie, ice cream, and whole milk.

The relative efficacies of hemorrhagic coli (HC) agar and several formulations of sorbitol MacConkey (SorMac) agar, with and without 0.1% (w/v) 4-methyllumbelliferyl-beta-D-glucuronide (MUG), in recovering unstressed and heat-stressed Escherichia coli O157:H7 from Brie cheese, ice cream, and whole milk were determined. Recovery of unstressed E. coli O157:H7 was determined quantitatively by spread-plating diluted samples onto different agars and performing plate counts. Recovery of stressed E. coli O157:H7 was determined qualitatively by enriching samples in modified trypticase soy broth, streaking the incubated enrichments, and isolating E. coli O157:H7 colonies from the agars. HC agar and the SorMac agar formulations did not differ significantly in their ability to recover unstressed E. coli O157:H7 from ice cream and whole milk; however, HC agar recovered significantly more unstressed E. coli O157:H7 from Brie cheese than did the SorMac agar formulations. Bacteriological Analytical Manual and Oxoid SorMac agar formulations made from individual ingredients, did not differ significantly in recovering unstressed E. coli O157:H7 from Brie cheese. The efficiency of the commercially available Oxoid SorMac agar could not be determined because of overgrowth by indigenous microflora. HC and SorMac agars did not differ significantly in recovering stressed E. coli O157:H7 from Brie cheese, ice cream, and whole milk. MUG had no apparent effect on recovery of either stressed or unstressed E. coli O157:H7 from the dairy foods examined.

Relative effectiveness of selenite cystine broth, tetrathionate broth, and rappaport-vassiliadis medium for recovery of Salmonella spp. from raw flesh, highly contaminated foods, and poultry feed: collaborative study.

A collaborative study was performed in 18 laboratories to validate use of Rappaport-Vassiliadis (RV) medium in the standard culture method for recovery of Salmonella spp. from raw, highly contaminated foods and poultry feed. RV medium made from its individual ingredients and incubated at 42 degrees C was compared with selenite cystine (SC) broth incubated at 35 degrees C and tetrathionate (TT) broth incubated at 35 degrees and 43 degrees C for effectiveness in recovery of Salmonella spp. Four artificially contaminated foods (oysters, frog legs, mushrooms, and shrimp) and poultry feed and one naturally contaminated food (chicken) were analyzed. The artificially contaminated foods were inoculated with single serovars of Salmonella at target levels of 0.04 colony-forming units (CFU)/g for the low level and 0.4 CFU/g for the high level. For analysis of 1125 test portions, RV medium (42 degrees C) recovered Salmonella from 409 test portions; TT (43 degrees C), from 368 test portions; TT (35 degrees C), from 310 test portions; and SC (35 degrees C), from 334 test portions. Overall, RV medium was comparable with or better than other selective enrichments for recovery of Salmonella from the foods in this study, except mushrooms. From mushrooms, SC broth (35 degrees C) recovered more positive test portions than did RV medium (42 degrees C) and TT broth (43 degrees C). The method for detection of Salmonella in raw, highly contaminated foods and poultry feed using RV medium has been adopted by AOAC INTERNATIONAL. AOAC Official Method 967.25, Salmonella in Foods, Preparation of Culture Media and Reagents, has been revised to include RV medium, and the applicability of AOAC Official Method 967.26, Salmonella in Foods, Detection, has been restricted to processed foods.

Usefulness of cellulase in recovery of Salmonella spp. from guar gum.

Most foods examined for Salmonella spp. by the procedure described in the U.S. Food and Drug Administration's Bacteriological Analytical Manual are preenriched at a 1:9 sample/broth ratio. However, 25 g guar gum (an emulsifying agent) is not wetted completely in 225 mL of preenrichment broth, and after a 24 h incubation at 35 degrees C, the product is transformed into a viscous, nonpipettable mass. The effects of 4 factors (inorganic salts, pH, temperature, and various enzymes) on the viscosity of the sample/preenrichment mixture during incubation were determined. Addition of various inorganic salts or adjustment of pH from 4.0 to 9.0 had no significant effect on the viscosity of the incubated mixture. Elevated incubation temperatures of 42 degrees, 44 degrees, and 46 degrees C reduced viscosity but were well above the optimal growth temperature for Salmonella, 35 degrees C. Addition of cellulose to lactose broth at a final concentration of 0.01% reduced viscosity of the mixture, making it readily pipettable. At least one Salmonella cell was consistently recovered from 25 g samples of guar gum, which represents a most probable number value of 0.04 cell per g.

Relative effectiveness of selective plating agars for recovery of Salmonella species from selected high-moisture foods.

The relative effectiveness of 6 selective plating media were compared for effectiveness in recovery of Salmonella spp. from selected high-moisture foods. Three new plating agars (EF-18, Rambach, and xylose lysine Tergitol-4) and 3 selective plating agars (bismuth sulfite, Hektoen enteric, and xylose lysine desoxycholate) recommended by AOAC INTERNATIONAL and the Bacteriological Analytical Manual (BAM) were compared. The agars were streaked from cultures selectively enriched in selenite cystine broth, tetrathionate broth, and Rappaport-Vassiliadis medium. The high-moisture foods studied were naturally contaminated pork sausage, chicken parts, turkey parts, and frog legs and artificially contaminated shrimp, oysters, egg yolks, and lettuce. The relative effectiveness of each selective plating agar was determined by recovery of Salmonella spp. and enumeration of false-positive and false-negative reactions. Although the new selective plating agars compared favorably with the AOAC/BAM-recommended agars, they offered no advantage. Incubation of selective enrichment broths at elevated temperatures decreased the numbers of false-positive and false-negative reactions for all 6 selective plating agars.

Relative effectiveness of selenite cystine broth, tetrathionate broth, and Rappaport-Vassiliadis medium for the recovery of Salmonella from raw flesh and other highly contaminated foods: precollaborative study.

The effectiveness of selenite cystine (SC) broth, tetrathionate (TT) broth, and Rappaport-Vassiliadis (RV) medium for recovery of Salmonella spp. from 8 highly contaminated foods was determined. RV medium prepared from individual ingredients and incubated at 42 degrees and 43 degrees C was compared with 2 commercial (Difco and Oxoid) media incubated at 42 degrees C. Naturally and artificially contaminated foods were tested under 2 protocols. For Protocol 1, each food was preenriched in the appropriate medium. After incubation, serial 10 fold dilutions of the preenriched foods were inoculated into selective enrichment media and incubated at 35 degrees, 42 degrees, or 43 degrees C. Effectiveness of these conditions was evaluated by most probable number determination of Salmonella spp. recovered. Productivity of selective enrichments did not differ significantly with this protocol, except that with Oxoid RV medium the number of Salmonella cells recovered from most of the foods was significantly reduced. For Protocol 2, twenty 25 g test portions from artificially inoculated foods were examined qualitatively for Salmonella spp. The effectiveness of the broth/temperature combinations was determined by the number of positive tests under each condition. RV medium prepared from individual ingredients and TT broth incubated at 43 degrees C yielded significantly more Salmonella-positive tests from frog legs and lettuce than did SC and TT broths incubated at 35 degrees C or commercial RV medium incubated at 42 degrees C. With pork sausage and ground beef, significantly fewer Salmonella-positive tests were found with Oxoid RV medium incubated at 42 degrees C and SC incubated at 35 degrees C than from other selective enrichments.(ABSTRACT TRUNCATED AT 250 WORDS)

Effectiveness of a one-day procedure for recovery of Salmonella from milk powders.

A rapid procedure for enumerating Salmonella in milk powders was evaluated. Dry whole milk and instant nonfat dry milk were rehydrated, artificially inoculated with various numbers of Salmonella cells, and stomached. Test portions were then treated with Tween 80 and pancreatic trypsin, and incubated for 1 h at 30 degrees C. The incubated test portions were centrifuged at 10,000 x g for 15 min at 5 degrees C, and the resuspended pellets were plated on xylose lysine desoxycholate agar. The effectiveness of the procedure was expressed in terms of percentage recovery of the inoculum. The procedure, which was evaluated in 76 trials using 7 Salmonella serovars, recovered < or = 73% of the inoculum for half of the trials conducted. Its effectiveness was dependent on the serovar, level of inoculation, and type of milk powder used.

Effectiveness of the Bacteriological Analytical Manual culture method for the recovery of Shigella sonnei from selected foods.

The relative retention of the indigenous morphological, biochemical, and serological characteristics by Shigella sonnei was tested under various storage conditions (room temperature, refrigeration, freezing at -20 degrees C and at -70 degrees C, and lyophilization). The use of a selective (desoxycholate citrate) agar rather than a nonselective (brain heart infusion) agar gave a lower conversion rate of smooth to rough colonies, and the percentage of rough colonies derived from cultures stored for prolonged periods increased under all conditions. With respect to biochemical characteristics, there were no major differences in the reactions of smooth vs rough variants. For serological characteristics, smooth variants agglutinated more readily in homologous antisera than did rough variants. S. sonnei populations maintained at -70 degrees C with glycerol remained reasonably stable and were used in recovery studies. Up to six foods (potato salad, chicken salad, cooked salad shrimp, lettuce, raw ground beef, and raw oysters) were inoculated with unstressed, chill-stressed, or freeze-stressed S. sonnei cells. Test portions (25 g) were inoculated with serial 10-fold dilutions of culture and subsequently analyzed by the culture method described in the U.S. Food and Drug Administration's Bacteriological Analytical Manual. It was found that the method was relatively ineffective for the recovery of S. sonnei from raw ground beef and raw oysters.

Research note: growth of Salmonella enteritidis in Grade A eggs during prolonged storage.

Migration of Salmonella enteritidis through egg albumen to the yolk and its subsequent growth in the yolk were examined. Submersion of eggs in .1% mercuric chloride solution for 1 h followed by submersion in 70% ethanol for 30 min resulted in an eggshell surface from which no Salmonella organisms were recovered. The eggs were then inoculated with S. enteritidis under the shell membrane. Although growth of S. enteritidis was negligible in eggs refrigerated up to 16 days, the population level of the organism increased by more than 8 log10 units in unrefrigerated eggs stored for the same amount of time.

Warfarin embryopathy in siblings.

Two siblings were noted to have the physical stigmata of the fetal warfarin syndrome. Their mother had received warfarin sodium for thrombophlebitis during both pregnancies but not during that of an unaffected sibling. Teratogens may produce syndromes that mimic genetic disease in both phenotype and familial aggregation.