Tetrathionate Broth Research Articles

Isolation of Salmonella organisms from the mesenteric lymph nodes of horses at necropsy

Objectives To determine the prevalence of Salmonella infections in horses at necropsy. Design Cross-sectional prevalence survey. Animals 102 horses. Procedure Mesenteric lymph nodes were collected from horses that were necropsied. Horses had died or were euthanatized because of severe disease or at the request of the owner. Twenty-eight of the horses were racehorses euthanatized following acute catastrophic injuries on the racetrack. Mesenteric lymph nodes were submitted for Salmonella culture via direct plating of tissue specimens on MacConkey agar and by use of 4 enrichment culture techniques that used tetrathionate and selenite enrichment broth and brilliant green and Salmonella-Shigella selective plating media. Results Salmonella typhimurium was isolated from the mesenteric lymph nodes of 2 foals (2/102, 1.96% of the horses). Salmonella organisms were not isolated from the mesenteric lymph nodes of adult horses. Conclusions and Clinical Relevance Prevalence of Salmonella infections in horses of our study (1.96%) suggests that the results of cross-sectional surveys, using bacteriologic culture to determine prevalence of Salmonella infection, should be interpreted with caution. Prevalence of Salmonella infections determined in a single facility may not reflect the prevalence of Salmonella-infected horses in the general population; furthermore, obtaining a Salmonella isolate from a horse does not establish that the horse is a chronic Salmonella carrier. (J Am Vet Med Assoc 1999;215:507–510)

Safety and quality evaluation of street foods sold in Zaria, Nigeria

Ready-to-eat foods and beverages were purchased from street food sellers in Zaria, Nigeria for microbiological analysis. Total aerobic organisms were cultured on plate count agar, Staphylococcus aureus was isolated on Baird Parker agar, Bacillus cereus on mannitol-egg yolk-polymyxin agar and Salmonella on Salmonella-Shigella agar after enrichment in tetrathionate broth. The mean aerobic counts for the food from mobile food sellers (MS), stationary food sellers without shelter (SWS) and stationary food sellers with shelter (SS) were not significantly different from one another except for ‘kunu’ and ‘moin-moin’ with counts ranging from 3.67 ± 0.4 log 10/g to 4.29 ± 1.14 log 10/g for ‘kunu’ and 2.84 ± 0.55 log 10/g to 4.7 ± 0.84 log 10/g for ‘moin-moin’. However, all the counts were lower than the permissible level of count (5.0 log 10/g) for cooked foods. Out of 160 food samples tested, 42 (26.3%) were contaminated with B. cereus, 24 (15.9%) with S. aureus. Six (18.3%) of the 32 coagulase positive S. aureus isolates tested produced enterotoxin A (SEA). More than 50% of the coagulase positive S. aureus were resistant to the common antimicrobial drugs used in the treatment of staphylococcal and wound infections. None of the samples from MS were contaminated with S. aureus and no Salmonella was isolated from all the samples. Samples from SWS had the highest frequency of contamination with B. cereus and S. aureus. Education of the street food handlers and the public on environmental sanitation and safe food handling practices is recommended.

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°C was compared with a commercial preparation of SC broth, incubated at 35°C, and TT broth incubated at 35 and 43°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 ≤ 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°C and TT broth incubated at 35 and 43°C. TT broth incubated at 35°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°C and RV medium incubated at 42°C be used.

Presence of Salmonella in the crop and ceca of broiler chickens before and after preslaughter feed withdrawal

Recent studies have suggested that crop contents may serve as an important source of Salmonella carcass contamination within processing plants. During the present study, we evaluated the effect of preslaughter feed withdrawal on the presence of Salmonella in the crops of broilers from nine commercial broiler flocks reared in individual growout houses. Crops were collected aseptically from 40 randomly selected broilers in each flock before feed removal and at the end of the feed withdrawal period, immediately before capture and transport to the processing plant. Similarly, the ceca were collected before and after feed withdrawal in six of the nine broiler flocks. The presence of Salmonella in the crops and ceca was determined by enrichment culture in tetrathionate broth followed by culture on brilliant green agar. The incidence of Salmonella in crop contents increased significantly (P < 0.05) in five of the nine flocks during feed withdrawal. The total number of Salmonella contaminated crops from all nine flocks increased significantly (P < 0.005) from 7/360 (1.9%) before feed removal to 36/359 (10.0%) at the end of feed withdrawal. The increased incidence of Salmonella in the crop contents was associated with an increased tendency of the broilers to consume contaminated rearing house litter during feed withdrawal. The incidence of Salmonella in the ceca increased nonsignificantly from 14/240 (5.8%) before feed removal to 19/240 (7.9%) at the end of feed withdrawal. The results indicate that the incidence of Salmonella crop contamination may increase as much as fivefold during preslaughter feed withdrawal and represent a critical preharvest control point in reducing Salmonella entry into the processing plant.

Selective Isolation of Pseudomonas stutzeri from vertebrate faeces on Rambach agar

Faecal samples collected from 308 wild birds of 25 species and 19 rodents of 3 species in South Moravia (Czechland) were pre-incubated in Müller-Kauffmann tetrathionate broth at 42 degrees C for 24 h and then streaked onto Rambach agar plates which were incubated at 37 degrees C for 48 h. Seventeen out of 22 isolates forming orange-red colonies on Rambach agar were identified as Pseudomonas stutzeri, the rest as Pseudomonas sp. and Alcaligenes sp. The colonies of P. stutzeri were either dry, wrinkled and adherent to the agar (resembling Bacillus) or smooth, less adherent (mimicking Salmonella). P. stutzeri was recovered from five species of vertebrates caught in farmland habitats: the house sparrow (Passer domesticus), the tree sparrow (P. montanus), the great warbler (Acrocephalus arundinaceus), the wood mouse (Apodemus sylvaticus) and the common vole (Microtus arvalis). The overall isolation rate was 4.5% in birds (12.6% in house sparrows) and 15.8% in rodents. The procedure can be useful for the isolation of P. stutzeri in clinical and environmental studies.

Prevalence of fecal shedding of Salmonella organisms among captive green iguanas and potential public health implications

Objective To determine prevalence of fecal shedding of Salmonella organisms among captive green iguanas (Iguana iguana). Design Cohort study. Animals 12 captive green iguanas. Procedure Iguanas were isolated in an environmental chamber, and fecal samples were collected weekly for 10 consecutive weeks. Samples were incubated aerobically in tetrathionate broth for 18 to 24 hours. Aliquots were then transferred to Hektoen and Salmonella-Shigella agar plates and incubated for an additional 18 to 24 hours. Isolated colonies were subcultured on nutrient agar slants, and Salmonella isolates were serogrouped and serotyped. Results All 12 iguanas were found to be shedding Salmonella organisms at least once during the study, and multiple serotypes were isolated from 7 of the 12. Salmonella organisms were isolated from 88 of 106 (83%) fecal samples; 21 samples contained multiple Salmonella serotypes. Overall, 11 Salmonella serotypes were identified. In 74 of 100 instances, when a particular Salmonella serotype was isolated from an individual Iguana, the same serotype was also isolated from a subsequent fecal sample from that iguana. Clinical Implications Results suggested that most iguanas have a stable mixture of Salmonella serotypes in their intestinal tracts and intermittently or continuously shed Salmonella organisms in their feces. Veterinarians should advise their clients on precautions for reducing the risk of acquiring these organisms from their pets. Public health officials trying to determine whether an iguana is the source of a specific Salmonella serotype that caused infection in human patients should submit at least 3 fecal samples collected from the iguana 1 week apart for bacterial culture. (J Am Vet Med Assoc 1998;213:48-50)

Flies and Their Bacterial Loads in Greyhound Dog Kennels in Kansas

Breeders of greyhound dogs traditionally feed racing animals and nursing bitches raw meat, and that meat generally is obtained frozen from commercial renderers. Previous studies have shown that the rendered meat is frequently contaminated with enteric bacteria, including Salmonella spp., and that during thawing the rendered meat is exposed to filth flies common in dog kennels. Nursing greyhound pups tend to experience a high morbidity and mortality from intestinal infections, and we attempted to determine in this study whether enterics could be spread to pups through contaminated flies. At intervals during 1995 and 1996, flies were trapped or were net-collected from 10 dog breeding kennels in the region around Abilene, KS. Trapped flies were identified and counted to determine population numbers, and netted flies were cultured in tetrathionate broth and streaked to medium selecting for Salmonella sp. and other lactose-negative Gram (-) bacteria. The relative numbers of different fly species varied with the sampling method, but traps and sweep nets produced similar proportions of the different fly species. Blow flies were twice as likely to be contaminated with enteric bacteria as any other fly. The most common enteric bacteria found were Proteus spp., followed by Providencia spp., Pseudomonas spp., and Salmonella spp. The incidence of Salmonella and Proteus spp. seemed to correlate more with accessibility of flies to dog excrement than to rendered meat. The apparent high incidence of enteric contamination of filth flies clearly implicates them as vectors of enteric diseases in kennels.

A comparison of procedures involving Single Step Salmonella, 1-2 Test, and Modified Semisolid Rappaport-Vassiliadis medium for detection of Salmonella in ground beef

Procedures involving Single Step Salmonella (SSS), 1-2 Test, and Modified Semisolid Rappaport-Vassiliadis Medium (MSRV) were compared for their speed and sensitivity in detection of Salmonella in ground beef contaminated with one isolate of each of five Salmonella serotypes. Inocula of 10, 10 2 and 10 3 CFU/g of ground beef were used. When pre-enrichment in buffered peptone water and selective enrichment in tetrathionate broth were used, SSS and MSRV detected all five species of Salmonella at all levels of contamination, whereas the 1-2 Test was positive in 0, 12, and 15 of 15 tests at 10, 10 2 and 10 3 CFU/g, respectively. When only pre-enrichment was used, the results with MSRV were unchanged but the SSS test failed to detect S. typhimurium. Thus, with pre-enrichment the MSRV and SSS procedures were equally sensitive and both produced a result on the third day. The 1-2 Test was less sensitive and slower, with results available on day 4. The MSRV protocol was best overall.

Media for the detection and recognition of the enteropathogen Providencia alcalifaciens in faeces.

A medium (PAM: Providencia alcalifaciens medium) is described that enables the presence of the enteropathogen P. alcalifaciens in faeces to be detected with ease and simplicity. This organism is probably the only oxidase-negative organism likely to be present in tetrathionate broth cultures of faeces that is unable to ferment the mannitol, xylose or galactose present in the medium. Thus the red colonies of P. alcalifaciens appeared quite distinct from the lemon-yellow acid-forming colonies of all the other bacteria that ferment one or more of these sugars. Extensive tests showed the medium to be both highly specific and sensitive in detecting P. alcalifaciens. Two additional media are described that enable the identity of presumptive P. alcalifaciens isolates to be confirmed unequivocally and with ease.

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.

Ferrioxamine E-supplemented pre-enrichment and enrichment media improve various isolation methods for Salmonella

Supplementation of pre-enrichment broth and enrichment broth media with ferrioxamine E (1 μg ml ) significantly improved the recovery of Salmonella from artificially or naturally contaminated foods. Based on the selectivity of ferrioxamine E, Salmonella enteritidis and S. typhimurium could be isolated also from various mixed cultures (one Salmonella cell in 10 3–10 4-fold concentration of cells of competitors) by shaking for 6 h in supplemented buffered peptone water followed by cultivation on XLD- or XLT-4 agars. Isolation of Salmonella from these pre-enrichment cultures by use of Dynabeads ®-Anti-Salmonella was highly effective. 27 S. typhimurium strains were isolated from 762 naturally infected chicken giblets by use of unsupplemented Tetrathionate broth. However, 33 S. typhimurium isolates were obtained with ferrioxamine E-supplemented Tetrathionate broth from the same samples. Three Salmonella isolates out of 50 evenly divided meat meal samples were obtained by use of ferrioxamine E-supplemented buffered peptone water followed by direct streaking onto XLD- and Rambach agars, no Salmonella isolates could be detected by the conventional method.

PESQUISA DE Salmonella spp. EM LEITE CRU, LEITE PASTEURIZADO TIPO C E QUEIJO "MINAS FRESCAL" COMERCIALIZADOS NO MUNICÍPIO DE PIRACICABA - SP

Este trabalho foi conduzido para detectar a ocorrência de Salmonella spp. em leite cru, leite pasteurizado tipo C e queijo "Minas Frescal". Analisaram-se 19 amostras de cada produto de diferentes marcas comerciais, adquiridas em diversos estabelecimentos comerciais em Piracicaba, SP. Segundo o padrão de amostragem e métodos adotados, não foi detectada a presença de Salmonella spp. nas amostras analisadas. Durante este trabalho, foi possível observar que os 3 meios de isolamento utilizados: agar verde brilhante, agar bismuto sulfito e agar Salmonella-Shigella, apresentaram baixa seletividade, uma vez que permitiram o crescimento de bactérias não pertencentes ao gênero Salmonella. O mesmo ocorreu com os caldos tetrationato e selenito-cistina utilizados no enriquecimento seletivo.

GROWTH RESPONSE OF SALMONELLA SPP. TO CYCLOHEXIMIDE AMENDMENT IN MEDIA

The present study was designed to evaluate cycloheximide as a potential media amendment to prevent fungal overgrowth on selective media for salmonellae enumeration. The objectives were to determine the effect of cycloheximide on Salmonella spp growth rates and to determine the effect of cycloheximide addition on Salmonella enumeration in selective media. The bacteria tested included two strains of Salmonella typhimurium (NO/NA and LT2) and one strain of Salmonella arizonae. All strains were grown in tryptic soy broth containing cycloheximide to determine the effect of cycloheximide on bacterial specific growth rates. The growth rate of all strains grown in tryptic soy broth were not significantly influenced by addition of cycloheximide at concentrations up to 1,000 mg/L. Growth rates of S. typhimurium NO/NA in minimal media were significantly decreased by addition of cycloheximide aerobically (300 mg/L) and anaerobically (600 mg/L). However, S. typhimurium NO/NA populations on brilliant green agar, MacConkey agar, and from selenite cysteine broth and tetrathionate broth were not affected by cycloheximide additions at concentrations up to 1,000 mg/L. Cycloheximide has potential as a fungistat additive for salmonellae selective media.

Evaluation of a Centrifugation Method for the Detection of Salmonella enteritidis in Experimentally Contaminated Chicken Eggs

Current recommendations for identification of Salmonella enteritidis (SE) contaminated eggs, as outlined by the USDA SE Task Force, require the combination of yolk and albumen from several eggs for room-temperature enrichment for 3 days prior to culture on solid medium. We describe the use of enzymatic digestion and chemical reduction to reduce viscosity and allow for concentration of Salmonella cells in egg albumen by centrifugation prior to enrichment and plating. In these studies, sanitized, intact, fresh shell eggs were inoculated with low numbers of viable SE. Albumen and yolk from six eggs in each group were separated; the albumen was pooled, treated with the proteolytic enzyme papain and the reducing agent N-acetyl-l-cysteine, and centrifuged, and the resulting pellet was incubated in tetrathionate broth (5 ml) at 37°C for 24 h prior to plating on brilliant green agar (BOA). For comparison, yolk and albumen from six eggs in each group were pooled, thoroughly mixed, and incubated at room temperature for 3 days prior to direct plating on BOA. Results from three trials indicated that the two culture techniques were equally sensitive for detection of Salmonella (range: 72 to 0.6 colony-forming units (CFU) of SE per pool). While as sensitive as the technique recommended by the SE Task Force, the centrifugation technique allowed more rapid (48 h) presumptive identification of Salmonella.

Comparison of Modified Immunodiffusion and Bacteriological Analytical Manual (BAM) Methods for Detection of Salmonella in Raw Flesh and Highly Contaminated Food Types

A wide variety of naturally contaminated and inoculated raw flesh and highly contaminated food types was analyzed by a modified immunodiffusion enrichment protocol and the Bacteriological Analytical Manual (BAM) method to determine the equivalence of these methods. This modification was developed by Agriculture Canada to allow addition of a high-temperature selective enrichment step in tetrathionate brilliant green broth at 42 degrees C while maintaining a 2-day total test time. Foods representing red meat, white meat, frog, and seafoods and one type of animal meal were evaluated. A total of 320 samples was tested, resulting in false negative rates of 5.2 and 3.5%, respectively, for the modified immunodiffusion and the BAM culture methods. The overall agreement rate was 96.9%.

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.

Development and evaluation of two novel oligonucleotide probes based on 16S rRNA sequence for the identification of Salmonella in foods.

DNA sequence in the V3 to V6 region of the 16S rRNA gene of Salmonella enteritidis was determined. By comparison of this sequence with those of Escherichia coli and Proteus vulgaris obtained from GenBank/EMBL database, three oligonucleotides termed as 16S I, 16S II and 16S III were synthesized. Hybridization of these oligonucleotides with 325 Salmonella isolates and some non-Salmonella isolates including the Salmonella closely related species of the family of Enterobacteriaceae showed that 16S II could not be used as a Salmonella specific-probe. 16S I and 16S III hybridized with all the Salmonella isolates tested, the former also hybridizing with Citrobacter spp. and the latter hybridizing with Klebsiella pneumoniae as well as Serratia marcescens. Since enrichment of the target cells in food samples was usually required prior to the DNA hybridization assay, the interference from those non-Salmonella isolates could be prevented by enrichment by culturing in lactose-combined tetrathionate (CTET) broth followed by Gram-negative (GN) broth at 37 degrees C and/or 43 degrees C. Such a culture step could inhibit the growth of Klebsiella spp., Ser. marcescens and/or Citrobacter spp. and allowed the specific detection of Salmonella.

Risk of Salmonellosis Associated with Consumption of Chocolate in Mexico

To assess the potential risk of salmonellosis associated with consumption of chocolate, the prevalence of Salmonella spp. was investigated in retail wrapped and nonwrapped solid chocolate in Guadalajara, Mexico. Previously, the efficiency of preenrichment and enrichment methods to isolate low numbers of Salmonella in chocolate was compared. Though not completely efficient, a preenrichment in nonfat milk without brilliant green, followed by enrichment in tetrathionate and selenite cystine broths gave better results than the other methods studied. Regarding the survey of retail chocolate, Salmonella was isolated from 2 (4.5%) of 44 samples of wrapped chocolate and from none of 56 samples of nonwrapped chocolate. The serovars identified were Salmonella agona and Salmonella derby. There were no significant differences between coliform counts or total bacterial counts obtained from wrapped and nonwrapped chocolate. The presence of Salmonella in chocolate is of concern due to the several low-infective-dose Salmonella outbreaks that have been linked to chocolate. On the other hand, a technique capable of detecting low numbers of Salmonella in chocolate is still needed.

Detection of Salmonella Enteritidis in Equine Feces using the Polymerase Chain Reaction and Genus-Specific Oligonucleotide Primers

Salmonella was identified in feces from horses, using the polymerase chain reaction (PCR) and genus-specific oligonucleotide primers. Feces from healthy horses were determined to be culture negative and PCR negative for Salmonella. Fecal samples were inoculated with known numbers of colony-forming units (CFU) of S. enteritidis. The fecal samples were enriched overnight in tetrathionate broth, and then DNA was extracted and amplified by PCR using genus-specific primers. Sensitivity of the assay extended to 10 degrees CFU Salmonella enteritidis/g feces; sensitivity of microbiologic culture with enrichment extended to 10 degrees CFU Salmonella enteritidis/g feces. Feces that were not inoculated with S. enteritidis were negative by the PCR. Detection of salmonellae in feces was possible using the PCR within 24 hours from the time of submission of samples. Because samples were enriched, isolates were available for determining antibiograms and serologic grouping or typing.

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)