A comparison of the efficiency of two forms of Rappaport-Vassiliadis enrichment medium

The efficiencies of Rappaport-Vassiliadis medium made with tryptone (RV-tryptone) or soya peptone (RV-soya) incubated for 48 h, were compared for the recovery of salmonellae from 575 naturally contaminated samples of five different types. The two forms of RV medium were found almost equally efficient. In RV-tryptone 161 positive samples and 36 serotypes were recovered while in RV-soya 157 positive samples and 33 serotypes were detected. The differences are slight. After a short incubation for only 6 h at 43°C, 57.0% of the positive samples were detected in RV-tryptone while 54.1% were positive in RV-soya. These results show that the onset of growth of salmonellae from naturally contaminated samples is similar in both forms of RV medium. RV-soya is slightly more inhibitory to competing organisms than RV-tryptone. It is concluded that the Rappaport-Vassiliadis medium is equally effective for the isolation of Salmonella from naturally contaminated samples whether made with tryptone (Difco) or with soya peptone (Oxoid).     

Recovery of Salmonella from refrigerated preenrichment and refrigerated enrichment media

The productivity of the standard cultural procedure for the isolation of Salmonella using preenrichment in buffered peptone water (BPW) followed by inoculation into Rappaport-Vassiliadis (RV), tetrathionate (TBG) (Difco) and selenite-cystine (SC) (Difco) enrichment broths, was compared with that using preenrichment and enrichment cultures which had been held under refrigeration (72 h at 5–10°C). Seventy-seven of 251 samples of food products were found to contain Salmonella. Refrigerated preenrichment cultures inoculated into RV medium (43°C), TBG broth (43°C) and SC broth (37°C) yielded salmonellae from 93.5, 85.7 and 54.5% contaminated samples, respectively. Refrigerated cultures in RV, TBG and SC broths, inoculated onto three selective plating media, identified 100, 87.0 and 41.6% of the contaminated samples, respectively.The selective plating medium brilliant green deoxycholate agar was at least as productive as brilliant green sulpha agar and bismuth sulphite agar, when streaked from RV and TBG broths, but was less effective when streaked from SC broth.     

Salmonella isolation using RVS broth and MLCB agar

Experiments were carried out to determine sources of variation which might influence the reliability of Rappaport Vassiliadis (RV) broth and Mannitol lysine crystal violet brilliant green agar (MLCB). The amount of MgCl₂.6H₂O in the RV broth formula is critical and should be approximately 29 gl⁻¹ of the ready to use medium. When soya peptone is used instead of tryptone, the medium should be buffered when stored for longer periods of time before use. This buffered soya peptone medium is called RVS broth in order to prevent confusion with the ‘classical’ RV broth.MLCB agar proved in our hands to be an excellent medium for the isolation of H₂S positive Salmonella when used after enrichment in RVS broth. Care should be taken however that when ‘home-made’ the agar should contain sufficient Mg.     

Improvement of Salmonella recovery from frozen ground meat by transfer of small volumes of pre-enriched samples

Two hundred and eighty 100-g samples of ground beef free of salmonellae were purchased from a meat plant. High levels of Salmonella typhimurium or Salmonella enteritidis were added to each of 80 samples, and Salmonella anatum or Salmonella dublin to each of 60 samples. After storage at −30°C for 2–3 months the samples were defrosted and blended with 900 ml of buffered peptone water. The suspensions were pre-enriched at 37°C for 20 h, and from each culture 1 ml and in parallel 1 loop (4 mm diameter) were transferred to selective enrichment media, and subsequently streaked onto selective agar plates. Taking into consideration all single combinations of the selective enrichment media and agar plates, salmonellae were isolated 968 times and 1038 times with 1-ml and 1 loop trasfer volumes, respectively. The loop method gave a statistically significant (P < 0.001) increase in recoveries of salmonellae over the 1-ml volume. Colonies orginating from the loop transfers more frequently represented pure or almost pure cultures of salmonellae.     

Comparison of culture media for enrichment and isolation of Salmonella spp. from frozen Channel catfish and Vietnamese basa fillets

Frozen fillets of Channel catfish and Vietnamese basa fish were used to compare Salmonella spp. recovery effectiveness of selective enrichment in Rappaport–Vassiliadis (RV) broth and tetrathionate broth (TT) and selective isolation on Hekteon enteric (HE) agar, xylose lysine deoxycholate (XLD) agar, and bismuth sulfite (BS) agar. Isolate confirmation was through fatty acid methyl ester analysis. Of 60 samples analyzed, 25 were found contaminated with Salmonella (42% incidence). Salmonella spp. recovery after enrichment in RV medium was 35% on HE agar, 30% on XLD agar, and 42% on BS agar. Similarly, after enrichment in TT broth, HE and XLD agars recovered 22% each and BS agar recovered 37%. No performance difference (p > 0.05) was observed in the recovery of Salmonella using the combinations of BS, HE, and XLD agars with RV broth and BS agar with TT broth. The combination of selective enrichment in RV and selective isolation on BS gave numerically greatest isolation of Salmonella from Channel catfish and Vietnamese basa fish compared to other isolation combinations.     

Collaborative study on the use of motility enrichment on modified semisolid Rappaport-Vassiliadis medium for the detection of Salmonella from foods.

A collaborative study was performed in 15 laboratories to evaluate the use of motility enrichment on modified semisolid Rappaport-Vassiliadis (MSRV) medium for rapid Salmonella detection in a variety of food products. The results of this procedure were compared with those obtained by the cultural procedure using Rappaport-Vassiliadis (RV) broth as selective enrichment and modified brilliant green agar for selective plating. The tests were performed with Salmonella reference samples (SRS) as well as with naturally contaminated food products. When SRS were used without added food the productivity of both MSRV and RV was 96%. When SRS were combined with reference samples containing competitive bacteria the productivity was 98% for MSRV and 95% for RV. In the tests with food samples the productivity of MSRV was 92% with SRS added to food and 96% with naturally contaminated samples, while the productivity of RV was 88% and 90%, respectively. Statistical analysis showed that there was no significant difference between the procedures.     

Comparison of four methods for isolation of Yersinia enterocolitica from raw and pasteurized milk from northern Iran

Four methods for isolation of Yersinia enterocolitica from raw and pasteurized milk from northern Iran were compared. Three hundred and ten raw milk samples were collected from tanks on their arrival at various central dairies, and 40 pasteurized milk samples were collected from tanks on their arrival at a manufacturing plant. Each sample was examined for the presence of Y. enterocolitica by (1) direct culture; (2) enrichment in double-strength buffered peptone water at 4 degrees C for 1 month; (3) enrichment in modified Rappaport medium at room temperature for 72 h after a preenrichment in double-strength peptone water at 4 degrees C for 1 month; and (4) enrichment in a medium containing sucrose, tris (hydroxymethyl) aminomethane, sodium azide, and ampicillin at 28 degrees C for 48 h after a preenrichment in double-strength peptone water at 4 degrees C for 1 month. All samples and enrichments were spread on MacConkey agar plus calcium chloride and Tween 80, Yersinia selective agar, and Hektoen medium plus ampicillin. Five samples (1.6%) of raw milk but no pasteurized milk samples were positive for Y. enterocolitica. No Y. enterocolitica were recovered by methods 1 or 2. Y. enterocolitica were recovered from 2 samples by method 3 followed by culture on Yersinia selective agar, and from 5 samples by method 4 followed by culture on Hektoen medium plus ampicillin. The isolates were biotype 1A or 1B, serotype O:7-13 or O:9 and phage type Xo or Xz. All isolates were resistant to ampicillin and amoxicillin, and sensitive to tetracycline, streptomycin, chloramphenicol, and trimethoprim-sulfamethoxazole.     

Sampling Methods for Detection of Salmonella in Raw Chicken Carcasses

Detection of Salmonella in thaw water, pericloacal skin and whole carcass rinse samples from naturally contaminated broiler chickens was compared. Of 100 birds tested, 70 were found to contain salmonellae by the three sampling techniques combined; the median level of contamination was 0.27 salmonellae/100g eviscerated carcass weight. Recovery with the whole carcass rinse technique (93%) was significantly greater than that obtained with thaw water (63%) and skin (74%) methods; performance of the latter two methods was not statistically different. Thaw water does not provide a reliable index of Salmonella contamination and therefore is not a suitable method for the nondestructive analysis of poultry carcasses. Selective enrichment in tetrathionate brilliant green broth and plating on bismuth sulfite agar identified the greatest number of contaminated carcasses under all sampling conditions.     

Isolation of Salmonella typhimurium from outbreak-associated cake mix

During May and June of 2005, 26 persons in several states were infected by a single strain (isolates indistinguishable by pulsed-field gel electrophoresis) of Salmonella enterica serotype Typhimurium after eating cake batter ice cream. The cake mix used to prepare the cake batter in the ice cream was implicated by epidemiologic investigation as the source of Salmonella contamination. Initial tests did not detect Salmonella in cake mix collected during the outbreak investigation. The objective of this study was to evaluate different procedures to isolate Salmonella from the implicated cake mix, cake, and ice cream. All outbreak-associated food samples (14 samples) were collected during the outbreak investigation by health departments of several of the states involved. Different combinations of Salmonella isolation procedures, including sample size, preenrichment broth, enrichment broth, enrichment temperature, and isolation medium, were used. Salmonella Typhimurium was isolated from two cake mix samples; the food isolates were indistinguishable from the outbreak pattern by pulsed-field gel electrophoresis subtyping. Universal preenrichment broth was substantially better than was lactose broth for preenrichment, and tetrathionate broth was better than was Rappaport-Vassiliadis broth for isolating Salmonella from the two positive cake mix samples. Although more typical Salmonella colonies were observed on plates from enrichment cultures grown at 35 degrees C, more confirmed Salmonella isolates were obtained from plates of enrichment cultures grown at 42 degrees C. Brilliant green agar, xylose lysine tergitol 4 agar, xylose lysine desoxycholate agar, Hektoen enteric agar, and bismuth sulfite agar plates were equally effective in isolating Salmonella from cake mix. The best combination of preenrichment-enrichment conditions for isolating the outbreak strain of Salmonella was preenrichment of cake mix samples in universal preenrichment broth at 35 degrees C for 24 h, followed by enrichment in tetrathionate broth at 42 degrees C for 24 h.     

Detection of group D salmonellae including Salmonella Enteritidis in eggs by polymyxin-based enzyme-linked immunosorbent assay

A high-throughput, rapid method was devised for the detection of Salmonella Enteritidis in egg products. For each target organism, preenrichment in nutrient broth was followed by selective enrichment in Rappaport-Vassiliadis soya peptone and tetrathionate brilliant green broths or by plating on modified semisolid Rappaport Vassiliadis (MSRV) agar medium. The presence of Salmonella Enteritidis was determined by subjecting portions of the selective broth cultures or swarming growth on MSRV medium to an enzyme-linked immunosorbent assay (ELISA) procedure using polymyxin immobilized in the wells of a microtiter plate as a high-affinity adsorbent for lipopolysaccharide (LPS) antigens. Sample extracts were reacted with polymyxin-coated microwells, and captured LPS antigens were detected immunoenzymatically with a commercially available Salmonella factor O9-specific antibody. The polymyxin-ELISA was 100% sensitive and 100% specific for Salmonella strains bearing the O9 antigen. When the ELISA was combined with enrichment using either the selective broths or plating on MSRV medium, the system was an effective means for detection of Salmonella Enteritidis in artificially inoculated egg products. The polymyxin-ELISA is a simple and inexpensive assay for group D salmonellae (including Salmonella Enteritidis) in a convenient 96-well microtiter plate format, making this system ideally suited for processing large numbers of samples.     

Factors affecting survival, growth, and retrieval of Salmonella Poona on intact and wounded cantaloupe rind and in stem scar tissue

Studies were done to determine the survival and recovery of Salmonella enterica serotype Poona from cantaloupe rind as affected by environmental conditions between the time of contamination and analysis. Detection and enumeration of the pathogen as influenced by analytical methods were also investigated. Combinations of preenrichment broth (lactose broth or universal preenrichment broth), enrichment broth (Rappaport–Vassiliadis broth or tetrathionate broth), and selective agar medium (bismuth sulfite agar or xylose lysine desoxycholate agar) for detecting S. Poona on inoculated cantaloupes stored at 4°C for 7 days or 21°C for 3 days were equivalent in performance. The use of nalidixic acid resistance as a marker in S. Poona and nalidixic acid in media used to enhance detection or enumeration of the pathogen by inhibiting background micro-flora in sanitizer efficacy studies, for example, would not adversely affect its survival on or recovery from cantaloupes. Overall, the composition of the carrier (water or 5% horse serum, a high organic matrix) used to prepare inocula did not influence the number of S. Poona recovered from the intact rind surface, wounds in the surface, or the stem scar tissue. Regardless of inoculation site or composition of the carrier, populations on spot inoculated melons stored at 4°C remained constant between 2 and 24 h after inoculation. The pathogen grew within 24 h in wounds of spot- and dip-inoculated cantaloupes stored at 21°C and 37°C. The addition of up to 1.0% Tween 80 to 0.1% peptone used to remove S. Poona from the rind surface did not adversely affect viability and may have enhanced detachment. Consideration of these observations is recommended when developing a method to test the efficacy of sanitizers in killing salmonellae on the rind surface of inoculated cantaloupes and to detect or enumerate salmonellae that may be natural contaminants.     

Estimation of most probable number of Salmonella in retail samples of minced pork

The number of salmonellae in 174 samples of minced pork was determined by the Most Probable Number (MPN) method in two separate laboratories. The material examined was taken from a collection of samples which were Salmonella positive in an earlier study. The MPN estimation was carried out using portions of original samples which had been divided (2 x 100 g) before the initial examination and which had been deep frozen and stored for 1 to 14 weeks at -18 degrees C until re-examination. Of the 174 samples initially positive for Salmonella, 131 (75.3%) were positive on re-examination using pre-enrichment in buffered peptone water (BPW) and selective enrichment in Rappaport-Vassiliadis medium (RV) and in tetrathionate medium according to Muller-Kauffmann (MK). The majority of the samples gave Salmonella counts below 1000/100 g (96.7% at lab. A and 97.3% at lab. B). Comparison of the results from both laboratories showed good agreement in the distribution pattern of the frequencies within the MPN classes, but agreement between the same sample pair was poor (r = 0.23). RV medium proved to be superior to the MK medium.     

SALMONELLA CONTAMINATION OF EQUIPMENT AND BEEF CARCASSES IN THE BERLIN (WEST) SLAUGHTERHOUSE EVALUATED BY VARIOUS ENRICHMENT PROCEDURES

The spread of salmonellae in the abattoir environment during the slaughtering of cattle in the Berlin (West) slaughterhouse was investigated. A total of 99 (3. 66%) out of 2704 swab samples were positive. Cutting off the hooves and preskinning gave the highest recovery of salmonellae. Less recoveries were obtained after opening the abdominal cavity. Removal of head, loosening the skin of head, removing the hide and splitting the breastbone and the carcass did not result in the isolation of the organism. Salmonella anatum was the most common isolate. The same serotypes were isolated from both carcasses and equipment. A comparison between Tetrathionate-enrichment (TTE) and Cystine-Seleniteenrichment (CSE) was made with 2 different pre-enrichment periods (6h and 24 h); this was done with swab samples from red meat carcasses and slaughterhouse equipment. Overall, TTE had a higher isolation rate at 24 h preenrichment. The variation between enrichment media may be partly attributable to the multiple swab sampling technique used in the study.     

Improvement of Karmali Agar by Addition of Polymyxin B for the Detection of Campylobacter jejuni and C. coli in Whole‐Chicken Carcass Rinse

The Karmali agar was modified by supplementation with a high concentration of polymyxin B. The goal of the study was to evaluate the effect of a high concentration of polymyxin B on the ability and selectivity of the modified Karmali agar to isolate Campylobacter jejuni and Campylobacter coli from whole chicken carcass rinse. A total of 80 whole chickens were rinsed with 400 mL of buffer peptone water. The rinsed samples were incubated with 2× blood‐free modified Bolton enrichment broth for 48 h, and then streaked onto unmodified Karmali agar and modified Karmali agar supplemented with 100000 IU/L polymixin B (P‐Karmali agar). The suspected colonies were finally confirmed by colony PCR. The P‐Karmali agar exhibited a significantly better (P < 0.05) isolation rate than the unmodified Karmali agar (P‐Karmali agar, 73.8%; unmodified Karmali agar, 33.8%). Moreover, the selectivity of the P‐Karmali agar was also better (P < 0.05) than that of the other selective agar when comparing the number of contaminated plates (P‐Karmali agar, 68.8%; unmodified Karmali agar, 87.5%) and growth index of competing flora (P‐Karmali agar, 1.4; unmodified Karmali agar, 2.7). The improved selective agar excluded competing flora resistant to antibiotic agents in unmodified Karmali agar, increasing isolation rate and selectivity for C. jejuni and C. coli.     

Comparison of modified Rappaport's medium (RV) and Muller-Kauffmann medium (MK-ISO) for the detection of Salmonella in meat products

Two Salmonella enrichment media, modified Rappaport's medium (RV) and Muller-Kauffmann medium according to the ISO formula (MK), as well as 4 inoculum ratios (0.1:10, 1:10, 0.1:100 and 10:100 ml pre-enrichment culture/selective enrichment medium) were compared. For this purpose 73 samples of filet américan (raw beef with a mayonnaise sauce) and minced meat, known to contain Salmonella, were analysed using the MPN procedure. Part of the filet américan samples were artificially contaminated with Salmonella and competing flora.After analysis of part of the samples the RV ratio 0.1:100 and MK 10:100 proved to be optimal. Comparison of results from these 2 combinations used for all samples showed a significant difference in favour of RV 0.1:100, except for the naturally contaminated filet américan samples for which no such difference was observed.For naturally contaminated samples the brillant green agar medium (Oxoid CM 329) used for isolation after selective enrichment showed smaller numbers of colonies of competing bacteria when inoculated from RV than from MK.It is concluded, that together with the standardized MK medium, the additional use of RV medium will increase Salmonella isolation from meat products.     

Detection and Isolation of Low Levels of E. coli O157:H7 in Cilantro by Real-Time PCR, Immunomagnetic Separation, and Cultural Methods with and without an Acid Treatment

Abstract: Leafy greens such as cilantro, contaminated with Escherichia coli O157:H7, have been implicated in cases of human illnesses. High levels of microflora in fresh cilantro make recovery of low numbers of E. coli O157:H7 difficult. To improve upon current methods, immunomagnetic separation (IMS) techniques in combination with real‐time PCR (RTiPCR) and selective enrichment protocols were examined. Rinsates were prepared from cilantro samples inoculated with low (～0.02 CFU/g) and slightly higher (～0.05 CFU/g) levels of E. coli O157:H7. Rinsate portions were enriched in modified buffered peptone water with pyruvate (mBPWp) for 5 h at 37 °C. After 5 h, selective agents were added to samples and further incubated at 42 °C overnight. Detection and recovery were attempted at 5 and 24 h with and without IMS. IMS beads were screened by RTiPCR for simultaneous detection of stx1, stx2, and uidA SNP. Additionally, broth cultures and IMS beads were streaked onto selective agar plates (Rainbow^®agar, R&F^®E. coli O157 Chromogenic medium, TC‐SMAC and CHROMagar? 0157) for isolation of E. coli O157:H7. Both broth cultures and IMS beads were also acid treated in Trypticase Soy Broth pH 2 prior to plating to selective media to improve upon cultural recovery. Although E. coli O157 strains were detected in most samples by PCR after 5 h enrichment, cultural recovery was poor. However, after 24 h enrichment, both PCR and cultural recovery were improved. Acidification of the broths and the IMS beads prior to plating greatly improved recovery from 24 h enrichment broths by suppressing the growth of competing microorganisms. Practical Application: Detection and recovery of Escherichia coli O157:H7 in fresh produce matrices (e.g., cilantro) can be complicated by high background microflora present in these foods. Rapid detection by molecular methods combined with effective enrichment and isolation procedures such as using immunomagnetic separation (IMS) techniques can quickly identify potential hazards to public health. Additional techniques such as acidification of enrichment broths can exploit acid resistance characteristics of pathogens such as E. coli O157:H7, facilitating their isolation in complex food matrices.     

Comparison of Methods for the Isolation of Salmonella Species from Lactic Casein

The efficiency of eight pre-enrichment media (lactose broth, two modifications of lactose broth (added NaHCO₃ or added NaHCO₃ and brilliant green dye), lauryl tryptose broth, nutrient broth, buffered peptone water, trypticase soy broth, and chemically defined M-9 medium) for recovering three Salmonella serotypes from casein was determined. Lowest Salmonella most probable numbers (MPNs) in artificially inoculated casein were found when samples were pre-enriched in either modification of lactose broth. None of the other media consistently gave the highest Salmonella MPNs. When 35 and 43°C incubation temperatures were compared during the pre-enrichment and selective enrichment stages of the isolation procedures, highest MPN values were obtained when 35°C was used throughout the analytical procedure. Blended casein homogenates required adjustment to pH 6.8 ± 0.2 for optimal recovery of Salmonella. Lactose broth used under these conditions of incubation temperature and pH adjustment generally resulted in methods sensitive enough to recover one Salmonella cell per gram of four types of casein (lactic, rennet, acid, and sodium caseinate).     

A comparison of standard cultural methods for the detection of foodborne Salmonella.

The sensitivity of the standard cultural method of the International Organization for Standardization (ISO 6579 and ISO 3565 combined) was compared to that of the Health Protection Branch (HPB) procedure for the detection of foodborne Salmonella. Of 195 foods tested, 84 (43.1%) were found to contain salmonellae by one or more cultural conditions. Of these, 75 (89.3%) and 68 (81.0%) were identified by the ISO and HPB methods, respectively. The apparent lack of agreement between both methods likely stemmed from the low indigenous numbers of salmonellae in several food homogenates, and unequal transfer of the target microorganism into homologous ISO and HPB pre-enrichment broths. The sensitivities of the commercially available Muller-Kauffmann tetrathionate broth (MKTBG43, Oxoid CM343), and a closely-related medium prepared with Oxoid CM29 tetrathionate base varied from 86.9 to 89.3%, and were deemed equivalent to that obtained with the ISO formulation of MKTBG43 (89.3%). Comparatively fewer contaminated samples were identified from selenite cystine (SC35) and selenite brilliant green (SBG35) enrichment cultures (82.1-83.3%). The high selectivity and saccharide-independent response of the bismuth sulfite agar medium warrants its consideration as a mandatory plating medium in ISO methodologies for the effective detection of typical and atypical biotypes of foodborne Salmonella spp.     

Efficacy of prolonged (48 h) selective enrichment for the detection of foodborne Salmonella.

The effect of prolonged (48 h) incubation on the productivity of five enrichment-temperature conditions (tetrathionate brilliant green, 35 and 43 degrees C; Muller-Kauffman tetrathionate brilliant green, 43 degrees C; Rappaport-Vassiliadis, 43 degrees C; selenite cystine, 35 degrees C) was compared to homologous results obtained under standard (24 h) conditions of selective enrichment. Of 797 high moisture and 166 low moisture foods tested, 171 (21.5%) and 80 (48.2%), respectively, were found to contain salmonellae by one or more analytical condition. Combined results of the five enrichment conditions after 24 and 48 h of incubation identified 247 (98.4%) and 250 (99.6%) of the 251 contaminated samples identified in this study. Our results are at variance with earlier reports on the greater method sensitivity with extended (greater than or equal to 48 h) periods of selective enrichment. The productivities of individual enrichment conditions after each period of incubation varied markedly where recovery rates with TBG43 and MKTBG43 exceeded that obtained with SC35 and TBG35. Our findings also underline the determinant role of enrichment at an elevated temperature (43 degrees C), and use of multiple enrichment and plating media for the optimal recovery of foodborne Salmonella.     

Comparison of the reveal test, the U.S. Food and Drug Administration culture method, and selective media for recovery of Salmonella enteritidis from commercial egg layer flock environments

Salmonella is the leading cause of foodborne illnesses in the United States, and Salmonella Enteritidis (SE) is the second most frequently isolated Salmonella serovar. Egg products are most often associated with outbreaks of SE infection. To prevent SE contamination of eggs, many producers are implementing flock inspections for SE at their facilities. A rapid and simple method for detecting SE in poultry environmental samples is critical for effective control of SE. In this study, the Reveal test for SE was compared with the conventional U.S. Food and Drug Administration (FDA) culture method for detecting SE in naturally contaminated environmental samples. The efficacy of two enrichment media, tetrathionate broth (TT) and Rappaport-Vassiliadis medium (RV), and three selective plating media, brilliant green agar with novobiocin (BGN), xylose lysine tergitol 4 agar (XLT4), and bismuth sulfite agar (BS), also were compared for SE isolation. One hundred twenty-eight environmental drag swab samples were collected from two previously identified SE-positive chicken flocks in two U.S. states and analyzed in parallel using the Reveal test and the FDA culture method. Twenty-five samples (19.5%) yielded SE when the Reveal test was used, and 23 samples (18.0%) were positive for SE by the FDA culture method. No significant difference in efficacy (P = 0.527) was found between the two methods. The Reveal test had a sensitivity, specificity, and accuracy of 83, 94, and 92%, respectively. Overall, a significantly greater number of positive samples was obtained after enrichment in RV compared with TT. XLT4 and BGN were more efficient than BS for isolating SE. However, no single method or medium successfully recovered SE from all SE-positive environmental samples.