Possible solution of capturing viable Enterohemorrhagic Escherichia coli (EHEC) in clinical patient stool.

For clinical diagnosis of enterohemorrhagic Escherichia coli (EHEC）, it needs to capture viable EHEC cells from stool sample in the view of medical fee points. However, there is no comprehensive solution for the detection of viable EHEC cells since there are wide variety of serotype and susceptibility against potassium tellurite which is commonly used for selective agent in selective medium for EHEC. In these background, EHEC Clear-HT System (EHEC-CHT）, a novel effective chromogenic medium system for screening comprehensive viable EHEC, was developed. When EHEC-CHT was assessed using 128 microbes including 49 clinical isolated EHEC strains, EHEC-CHT detected all 49 EHEC strains as typical blue-colored colony regardless of both serotype and susceptibility to potassium tellurite. EHEC-CHT was compared with Japanese commercially available tellurite-based EHEC selective media using 107 clinical patient stool samples. EHEC-CHT showed higher detection ratio than conventional tellurite-based selective media compared, and 7% improvement at least in detection ratio in this study.

Impact of Spreading Time to Recovery Rate in Suitability Test of Solid Agar Media.

In these days, all agar media used for both pharmaceutical and industrial territories were required to meet performance criteria. There were recovery rates of assigned microorganisms as performance criteria in both pharmacopeia and ISO standards. However, in spreading plate method, there is no concrete spreading time even though it is shown only "as quickly as possible" in ISO standards. In this study, we verified the impact of spreading time in spreading plate method for the quality control of SCD (Soybean Casein Digest) agar plate. When 30s, 60s, and 120s of spreading time were compared using Bacillus subtilis ATCC 6633, Escherichia coli ATCC 8739, Pseudomonas aeruginosa ATCC 9027, Staphylococcus aureus ATCC 6538, Candida albicans ATCC 10231, and Aspergillus brasiliensis ATCC 16404, respectively, there is no significant difference in recovery rates of all strains tested between 30s and 60s. However, recovery rates of E. coli and P. aeruginosa were decreased in 120s of spreading time. Our results demonstrated that spreading using plastic rod would be better to complete within 60s in spreading plate method since long spreading time had the impact to recovery rate of certain bacteria.

Comparative Evaluation of Selective Media for the Detection of Bacillus cereus.

The commercially available 3 types of selective media in Japan were compared for the detection of Bacillus cereus. When assessed inclusivity using 25 B. cereus strains, MYP agar, NGKG agar, and chromogenic X-BC agar demonstrated excellent inclusivity. For exclusivity study using 50 non-B. cereus strains, MYP, NGKG, and X-BC allowed to grow 11, 7, and 3 strains, respectively. Of the grown bacteria on each strains tested, only 2 strains of B. thuringiensis formed typical B. cereus colonies on all selective media tested. The NGKG and X-BC were compared with MYP as a reference using artificially contaminated food (fried rice, plain rice, fried noodle, and potato salad ), since MYP is recommended in ISO 7932: 2004. The both correlation coefficients between NGKG and MYP, and X-BC and MYP were 0.999. Therefore, we demonstrated that NGKG and X-BC can be adapted to ISO 7932: 2004 method for selected food as well as MYP.

MC-Media Pad CC for Enumeration of Total Coliforms in a Variety of Foods.

BACKGROUND: Standard coliform count methods require the preparation of agar, the use of the pour-plate technique, the overlay of agar, and in some cases, the transfer of suspect colonies to broth medium for confirmation. The MC-Media Pad CC for the enumeration of coliforms is a ready-to-use dehydrated sheet medium with no agar preparation, no spreader, and no confirmation step required. OBJECTIVE: Using a paired study design, the MC-Media Pad CC was compared to standard method ISO 4832:2006 for 10 matrixes including raw ground pork, raw chicken, cream, cream cheese, ready-to-cook vegetable mix, vegetable juice, cooked prawns, crab pâté, ham sandwiches, and cooked rice. METHODS: Each matrix was tested at three levels of coliform contamination (approximately 102, 104, and 106 CFU/g). Five replicate 10 g test portions per level were tested in a paired comparison by the MC-Media Pad CC and ISO 4832:2006 methods. In addition, inclusivity/exclusivity, robustness, and product consistency and stability were evaluated. RESULTS: The candidate and reference methods demonstrated SDs ranging from 0.027 to 0.264 and 0.025 to 0.157, respectively. The difference of means ranged from -0.015 to 0.381, showing no practical difference between the methods. The MC-Media Pad CC detected 58/62 inclusivity strains and correctly excluded 26/31 exclusivity organisms, similar to the reference method. Robustness testing demonstrated no significant change in results when small changes were made to sample volume, incubation temperature, and incubation time. The product consistency study demonstrated no significant difference between lots of product and supported the 1.5 year shelf life. CONCLUSIONS: The results support the conclusions that the MC-Media Pad CC is a suitable alternative to the ISO 4832:2006 reference method for the matrixes examined and the data support AOAC Performance Tested MethodSM certification.

MC-Media Pad EC for Enumeration of Escherichia coli and Coliforms in a Variety of Foods.

BACKGROUND: Standard coliform count methods require preparation of agar, the use of pour-plate technique, the overlay of agar, and in some cases, the transfer of suspect colonies to broth medium for confirmation. The MC-Media Pad EC for enumeration of Escherichia coli and coliforms is a ready-to-use dehydrated sheet medium with no agar preparation, no spreader, and no confirmation step required. OBJECTIVE: Using a paired study design, the MC-Media Pad EC was compared with standard method ISO 4832:2006. Ten matrixes including raw ground pork, raw chicken, cream, cream cheese, ready-to-cook vegetable mix, vegetable juice, cooked prawns, crab pâté, ham sandwiches, and cooked rice were evaluated in the study. METHODS: Each matrix was tested at three levels of contamination (approximately 102, 104, and 106 CFU/g). Five replicate 10 g test portions per level were tested in a paired comparison by the MC-Media Pad EC, ISO 4832:2006, and ISO 16649-2:2001 (Part 2) methods. In addition, inclusivity/exclusivity, robustness, and product consistency and stability were evaluated. RESULTS: The candidate and reference methods demonstrated standard deviations ranging from 0.034 to 0.188 and 0.028 to 0.181, respectively, for E. coli counts and 0.047-0.188 and 0.025-0.157, respectively, for total coliforms. The difference of means ranged from -0.025 to 0.331 for E. coli and from -0.037 to 0.372 for total coliforms, showing no practical difference between the methods. The MC-Media Pad EC detected 49/50 E. coli and 60/63 coliform inclusivity strains and correctly excluded 30/32 exclusivity organisms for E. coli and 24/31 exclusivity organisms for total coliforms, which was similar to the reference method. Robustness testing demonstrated no significant change in results when small changes were made to sample volume, incubation temperature, and incubation time. The product consistency study demonstrated no significant difference between lots of product and supported the 1.5 year shelf life. CONCLUSIONS: The results support the conclusions that the MC-Media Pad EC is a suitable alternative to the ISO 4832:2006 and ISO 16649-2:2001 reference methods for the matrixes examined and the data support AOAC Performance Tested MethodSM certification. HIGHLIGHTS: The MC-Media Pad EC was approved for Performance Tested Method certification No. 011901.

Evaluation of a Novel Chromogenic Selective Medium for the Improved Detection of Campylobacter from Stool Samples.

BD mCCDA Clear-HT (CCHT; Nippon Becton Dickinson Company, Ltd.) , a novel chromogenic selective medium was evaluated for its superior capacity to isolate Campylobacter jejuni/ coli. When CCHT was assessed using 142 microbes including 42 Campylobacter jejuni/ coli strains, all Campylobacter strains were found to form purple-colored colonies on CCHT whereas all the other microbes failed to grow. CCTH was then compared with commercially available selective media using 100 stool samples including 40 Campylobacter positive samples. CCHT detected Campylobacter jejuni/ coli from 39 of 40 (97.5%) stool samples whereas it allowed competitive bacteria to grow as false positive colonies from 1 (1.0%) of 100 stool samples. The values of relative sensitivity (%) and specificity (%) for CCHT were 97.5 and 98.3 in this study. Our results demonstrated that CCHT had the highest detection ratio for Campylobacter jejuni/ coli and the highest inhibition ratio against competitive bacteria among all selective media compared.

Evaluation of the Novel Dry Sheet Culture Method for the Enumeration of Enterobacteriaceae.

MC-Media PadTM EB (MMP-EB) , a novel sheet culture method for the enumeration of Enterobacteriaceae, has been evaluated. When both inclusivity and exclusivity of MMP-EB were assessed using 104 microbes including 51 Enterobacteriaceae strains, all tested Enterobacteriaceae strains grew and formed obvious red-colored colonies and all tested non-Enterobacteriaceae strains were shown different appearance from Enterobacteriaceae strains. For the comparison study of the method, MMP-EB was compared with violet red bile glucose agar (VRBG) according to ISO 21528-2:2017 and PetrifilmTM Enterobacteriaceae Count Plate (Petrifilm EB) method using 100 naturally contaminated food samples. The correlation coefficients between MMP-EB and VRBG, and MMP-EB and Petrifilm EB were 0.940 and 0.972, respectively. Furthermore, there were no statistically significant difference between MMP-EB and both reference methods. Our results demonstrated that MMP-EB was a suitable alternative method for the enumeration of Enterobacteriaceae in food samples.

Comparison of Chromogenic Selective Media for the Detection of Cronobacter spp. (Enterobacter sakazakii).

　The four types of chromogenic selective media that are commercially available in Japan were compared for establishing a Japanese standard method for detecting Cronobacter spp. based on ISO/TS 22964:2006. When assessed using 9 standard Cronobacter spp. strains and 29 non-Cronobacter strains, Enterobacter sakazakii isolation agar, ChromocultTM Enterobacter sakazakii agar, CHROMagarTM E. sakazakii, and XM-sakazakii agar demonstrated excellent inclusivity and exclusivity. Using the ISO/TS 22964:2006 method, the recovered numbers of 38 Cronobacter spp. strains, including 29 C. sakazakii isolates obtained from each medium, were equivalent, indicating that there was no significant difference (p > 0.05) among the four types of chromogenic selective media. Thus, we demonstrated that these four chromogenic selective media are suitable alternatives when using the standard method for detecting Cronobacter spp. in Japan, based on the ISO/TS 22964:2006.

MC-Media Pad SA (Sanita-kun SA) for the Enumeration of Staphylococcus aureus in a Variety of Foods.

MC-Media Pad SA (formerly known as Sanita-kun SA) is a dry rehydratable film medium for the enumeration of Staphylococcus aureus. The performance of the method in a variety of foods was compared with that of ISO 6888-1:1999, Microbiology of Food and Animal Feeding Stuffs - Horizontal Method for the Enumeration of Coagulase-Positive Staphylococci (Staphylococcus aureus and Other Species) - Part 1: Technique Using Baird-Parker Agar Medium. The validated matrixes included pastrami, a sliced cooked chicken roll, cooked prawns, cold-smoked salmon, pasta salad, sandwich spread, fresh uncooked pasta, infant cereal, custard, and raw-milk Brie cheese. In the matrix study, five replicates at each of three contamination levels were tested as paired test portions. Across all matrixes, the difference in mean log10 values ranged from -0.32 to 0.10, which was within the acceptable range of -0.50 to 0.50. Thus, all 10 matrixes met the acceptance criterion at all concentration levels. Further, only two matrixes, cooked prawns and raw-milk Brie cheese, had 95% confidence limits outside the -0.50 to 0.50 criterion, and these were at the lowest concentration level for each matrix. The candidate method sr varied from 0.03 to 0.22 log10 CFU/g. This compares favorably with the reference method SD, which ranged from 0.06 to 0.30 log10 CFU/g. The candidate and reference methods detected 51 of 53 inclusivity strains, with both methods not detecting the same two strains. The candidate method did not detect any of the 32 exclusivity strains, whereas the reference method did not detect 30 of the 32 exclusivity strains; the 2 strains detected by the reference method were S. delphini and S. hyicus, both developing atypical colonies on Baird-Parker plates. The product consistency study demonstrated no significant difference between lots of product and supported the 1 year shelf life. Robustness testing yielded no significant differences when small variations were made in sample volume, incubation temperature, and incubation time. Thus, the data show equivalent or better performance of the Sanita-kun SA/MC-Media Pad SA method compared with the International Organization for Standardization reference method, in support of AOAC Performance Tested MethodSM certification.

MC-Media Pad ACplus™ for Enumeration of Aerobic Counts in a Variety of Foods.

The MC-Media Pad ACplus™ is a dry, rehydratable film medium for the enumeration of aerobic bacterial colonies. The performance of the method in a variety of foods was compared to that of U.S. reference methods: U.S. Department of Agriculture (USDA) Food Safety and Inspection Service (FSIS) Microbiology Laboratory Guidebook (MLG) Chapter 3.02 "Quantitative Analysis of Bacteria in Foods as Sanitary Indicators" (USDA/FSIS MLG 3.02); Standard Methods for the Examination of Dairy Products (SMEDP) Chapter 6 "Microbiological Count Methods, Standard Plate Count Method" (SMEDP 6); AOAC Official MethodSM 966.23 Microbiological Methods; and ISO 4833-1:2013 "Microbiology of the food chain-Horizontal method for the enumeration of microorganisms-Part 1: Colony count at 30 degrees C by the pour plate technique." The validated matrixes included raw chicken breast and raw ground pork for USDA/FSIS MLG 3.02; cream cheese and yogurt drink for SMEDP 6; parsley, vegetable juice, prawns, tuna pate, sandwiches, and pasta salad for AOAC Method 966.23, and raw chicken breast, raw ground pork, cream cheese, yogurt drink, parsley, vegetable juice, prawns, tuna pate, sandwiches, and pasta salad for ISO 4833-1:2013. In each matrix study, five replicates at each of three contamination levels were tested as paired test portions. All 10 matrixes were compared to the appropriate U.S. reference methods under MC-Media Pad ACplus standard-usage conditions (35 ± 1°C for 48 ± 2 h). Across all matrixes, the difference of mean log10 values ranged from -0.43 to 0.44, within the acceptable range of -0.50 to 0.50. The candidate method repeatability SD (sr) varied from 0.03 to 0.23 log10 CFU/g, comparing favorably to the reference method SD, which ranged from 0.06 to 0.30 log10 CFU/g. Seven matrixes were compared to the appropriate U.S. reference methods under MC-Media Pad ACplus rapid-usage conditions (35 ± 1°C for 24 ± 2 h). Of the 21 matrix/concentration combinations, only three instances of difference of mean >0.5 log were observed. The ranges of sr values of the rapid-usage candidate method (0.023-0.324) and the reference method (0.013-0.236) were similar for the seven matrixes tested. All 10 matrixes were compared to the International Organization for Standardization (ISO) reference method under MC-Media Pad ACplus alternate-method conditions (30 ± 1°C for 72 ± 3 h). All 10 matrixes yielded a mean difference between methods of <0.5 log, and the ranges of sr values were similar between the candidate alternate method (0.037-0.378) and the ISO reference method (0.037-0.437). The product consistency study demonstrated no significant difference between lots of product and supported the 2-year shelf life. Robustness testing yielded no significant differences when small variations were made in sample volume, incubation temperature, and incubation time. Thus, the data show equivalent or better performance of the MC-Media Pad ACplus method compared to the relevant reference methods in support of AOAC Performance Tested MethodSM certification.

Evaluation of the Quantitative Dry Culture Method (Sanitakun(TM) SA) for the Enumeration of Staphylococcus aureus in Artificially Contaminated Food Samples.

Sanita-kun(TM) SA for Staphylococcus aureus (SkSA), a novel dry sheet quantitative culture system, was evaluated. When the inclusivity and exclusivity of SkSA were assessed using 121 microorganisms including 47 S. aureus strains, the tested S. aureus strains formed blue-colored colonies on the SkSA and all the other microbes failed to grow. The SkSA was then compared with Baird-Parker agar (BP) according to ISO 6888-1, Mannitol salt agar with egg yolk (MSEY), and 3M Petrifilm(TM) STX (3M-STX) in 100 artificially contami nated food samples. The correlation coefficients between SkSA and BP, SkSA and MSEY, and SkSA and 3M-STX were 0.971, 0.989 and 0.996, respectively. Our results demonstrated that SkSA is a suitable alternative for the enumeration of S. aureus in foods.

Evaluation of a Novel Dry Sheet Culture Method for Rapid Enumeration of Total Aerobic Count in Foods.

A novel dry sheet culture method (Sanita-kun ACplus; SkACp) for rapid enumeration of total viable count has been developed. This rehydrated plate system comprises an adhesive sheet, nonwoven fabric coated with nutrients, and two types of water absorption polymers. In addition, SkACp facilitates methods for both rapid count (rapid mode: 24-h incubation) and accurate enumeration (standard mode: 48-h incubation) because it not only contains conventional 2,3,5-triphenyltetrazolium chloride but also contains two kinds of new tetrazolium salts for rapid and accurate enumeration of total aerobic count. When SkACp was assessed with 91 microorganisms, 87 strains (95.6%), excluding lactic acid and psychrotrophic bacteria, formed red-colored colonies within 24 h, whereas all microorganisms tested formed colonies within 48 h. The SkACp method, with both 24 and 48 h of incubation, was compared with plate count agar (PCA) and 3M Petrifilm AC (PAC) by using 107 naturally contaminated foods. For all foods tested (n = 107), the linear correlation coefficients of 48-h counts on SkACp compared with PCA and PAC were 0.98 and 0.75, respectively, while the 24-h counts on SkACp compared with PCA and PAC were 0.77 and 0.96, respectively. For foods tested, excluding yogurt and lactic beverages ( n = 101), the linear correlation coefficients of 48-h counts on SkACp compared with PCA and PAC were 0.98 and 0.96, respectively, while the 24-h counts on SkACp compared with PCA and PAC were 0.96 and 0.95, respectively. These results demonstrated that SkACp (48 h) is a useful alternative for the enumeration of the total aerobic count for all foods, whereas SkACp (24 h) was also an effective method for rapid enumeration in foods, excluding yogurt and lactic beverages.

Development of a Novel Chromogenic Medium for Improved Campylobacter Detection from Poultry Samples.

The presence of expanded-spectrum ß-lactamase (ESBL)-producing Escherichia coli is a common problem in the isolation of Campylobacter from poultry samples using conventional cefoperazone-based selective media. A novel chromogenic medium (CM-HT), based on modified charcoal cefoperazone deoxycholate agar (mCCDA), has been developed as a solution for improved Campylobacter detection from poultry samples. Although the basic components of CM-HT are the same as mCCDA, CM-HT uses both granular charcoal and sodium cefoxitin to enhance viewability and inhibit ESBL-producing bacteria. All tested Campylobacter jejuni (n = 31) and Campylobacter coli (n = 6) strains grew and formed purple-colored colonies on CM-HT. In contrast, the growth of all other tested microorganisms, including ESBL-producing E. coli strains, was suppressed by this medium. Additionally, 84 poultry samples were examined for the presence of Campylobacter using the ISO 10272-1 method (enrichment with Bolton broth) and the NIHSJ-02 method (enrichment with Preston broth) with mCCDA and CM-HT media for the isolation. The numbers of samples from which Camplylobacter was detected on CM-HT using Preston and Bolton broth were 22 and 18, whereas the numbers on mCCDA were 22 and 13, respectively. Only Campylobacter was detected on CM-HT using both enrichment broths; however, there were 5 and 19 samples from which ESBL-producing E. coli was detected on mCCDA using Preston and Bolton broth, respectively. Thus, there was a significant difference between CM-HT and mCCDA in selectivity for ESBL-producing E. coli regardless of which enrichment broth was used. The results obtained demonstrated that CM-HT is a possible solution for the improved isolation of Campylobacter from poultry samples.

Evaluation of a novel dry sheet culture method (Sanita-kun(R)) for rapid enumeration of yeasts and molds in foods.

Sanita-kun(R) Yeasts and Molds (SkYM), a novel dry sheet culture method for rapid enumeration of fungi, has been developed. This re-hydrated plate consists of a unique adhesive sheet, non-woven fabric coated with nutrients, antibiotic, water absorption polymer and uniquely synthesized 2-(2-methoxyphenyl)-3-(4-nitrophenyl)-5-phenyl-tetrazolium chloride for rapid enumeration of yeasts and molds. When SkYM was assessed using 37 microbes including 33 fungal strains, 29 fungal strains (87.9%) were formed red colored colonies within 48h whereas all yeasts and molds tested formed colonies within 72 h. All tested bacteria failed to grow. The SkYM method, with both 48 and 72 h of incubation, was compared with Dichloran Rose-Bengal Chloramphenicol Agar (DRBC; 5 days) according to ISO 21527-1, and with 3M Petrifilm YM (PYM; 5 days) and Nissui Compact Dry YM (CDYM; 5 days) commercially available dry culture methods using 100 naturally contaminated foods. The linear correlation coefficients of SkYM (48h) with DRBC, PYM and CDYM were 0.921, 0.929 and 0.947, respectively, whereas the linear correlation coefficients between SkYM (72 h) and DRBC, SkYM (72h) and PYM, SkYM (72h) and CDYM were 0.948, 0.877 and 0.911, respectively. These results demonstrated that SkYM was a useful alternative for rapid enumeration of yeasts and molds in foods.

Development of the novel chromogenic screening medium for methicillin-resistant Staphylococcus aureus.

MRSA-chrom, a novel chromogenic screening agar medium for methicillin-resistant Staphylococcus aureus (MRSA), was developed. There were all MRSA strains recovered in 24h as a specific blue-colored colony among 130 microbes including 42 MRSA strains. MRSA-chrom showed the highest detection ratio among 4 commercially available selective media using 50 clinical specimens.

Evaluation of a new chromogenic agar medium for Alicyclobacillus acidoterrestris.

Spoilage of fruit juices by a thermoacidophilic spore-forming bacterium, Alicyclobacillus acidoterrestris, is a big problem for fruit juice industries worldwide. We have developed a novel chromogenic selective agar medium (EAATSM) for the isolation and enumeration of A. acidoterrestris. A. acidoterrestris strains appeared as blue colonies on the EAATSM. Other Alicyclobacillus strains appeared as white colonies or were inhibited. A study comparing EAATSM and YSG agar was carried out using artificially contaminated samples of 50 fruit juice products. The correlation coefficient between EAATSM and YSG was 0.991.

A novel chromogenic screening medium for isolation of enterohemorrhagic Escherichia coli.

EHEC-chrom, a novel chromogenic screening agar medium for enterohemorrhagic Escherichia coli (EHEC) , was developed. A total of 52 EHEC strains, which were studied for the inclusivity study, grew and formed blue-green colored colonies on EHEC-chrom. When 43 gram-negative bacteria other than EHEC were inoculated for the exclusivity study, 10 strains grew and formed colorless colonies. A total of 28 gram-positive bacteria failed to grow and 1 yeast strain grew as colorless colonies. EHEC-chrom was compared with CHROMagar™ STEC, XM-EHEC agar and CT-MacConkey base agar with a specific sugar (CT-SorbitolMAC, CT-rhamnoseMAC and CT-sorboseMAC) as commercially available selective agar using 100 food samples artificially contaminated with low levels (<10 logCFU/25g) of EHEC. Numbers of samples from which EHEC was recovered by using EHEC-chrom, CHROMagar™ STEC, XM-EHEC agar and CT-MacConkey base agar with specific sugar were 62, 58, 59 and 60, respectively. Our results suggested EHEC-chrom was a useful alternative for EHEC screening in food.

Evaluation of the dry sheet medium (Compact Dry ETB(R)) for enumerating Enterobacteriaceae in meat samples.

Compact Dry ETB(R) (CD-ETB, ETB; Enterobacteriaceae) , a ready-to-use and self-diffusible dry medium sheet culture system for the detection and enumeration of Enterobacteriaceae, was evaluated. A total of 35 Enterobacteriaceae strains, which were studied for the inclusivity study, grew and formed red-purple colored colonies on the CD-ETB(R). When 17 gram-negative bacteria other than Enterobacteriaceae were inoculated for the exclusivity study, 2 strains grew and formed red-purple colonies, 9 strains formed colorless colonies, and 6 strains failed to grow. A total of 43 gram-positive bacteria and 3 yeasts failed to grow. The CD-ETB method was compared with the Violet Red Bile Glucose (VRBG) agar method according to ISO 21528-2 and the 3M Petrifilm(TM) EB (3M-EB(R)) method in 53 meat samples. The correlation coefficients between CD-ETB(R) and VRBG agar, CD-ETB(R) and 3M-EB(R), and 3M-EB(R) and VRBG agar were 0.962, 0.992 and 0.960, respectively.

Compact Dry(R) X-BC for the enumeration of Bacillus cereus in food samples.

We evaluated the effectiveness of using Compact Dry(R) X-BC (CD-XBC), a ready-to-use and self-diffusing dry medium sheet culture system based on a novel detection principle, for the detection and enumeration of Bacillus cereus. All 13 B. cereus strains, which were studied for the inclusivity study, grew as blue/green colonies on the CD-XBC. When 3 yeast strains and 103 bacterial strains other than B. cereus were tested for the exclusivity study, 5 strains formed white colonies, and 4 strains formed blue/green colonies, while 94 other strains failed to grow. The 4 strains that formed blue/green colonies were B. thuringiensis, which is known to have the same biochemical features as B. cereus. The CD-XBC method was compared with the MYP agar method (MYP) and the NGKG agar method (NGKG) in 130 artificially contaminated food samples. The correlation coefficients between CD-XBC and MYP, and CD-XBC and NGKG were 0.972 and 0.971, respectively.

Evaluation of the compact dry X-SA method for enumerating Staphylococcus aureus in artificially contaminated food samples.

Compact Dry X-SA (CD-XSA), a ready-to-use and self-diffusible dry medium sheet culture system for the detection and enumeration of Staphylococcus aureus, was evaluated. A total of 50 S. aureus strains, which were studied for the inclusivity study, grew as blue-colored colonies on the CD-XSA. When 114 bacteria other than S. aureus and 3 yeasts were inoculated for the exclusivity study, 37 strains produced white colonies, and 4 strains produced blue colonies, and 3 strains produced magenta colonies, while 73 other strains failed to grow. The CD-XSA method was compared with the mannitol salt agar with egg yolk (MSEY) method, the Baird-Parker agar (BP) method and the 3M Petrifilm(TM) STX (3M-STX) method in 105 artificially contaminated food samples. The correlation coefficients between CD-XSA and MSEY, CD-XSA and BP, and CD-XSA and 3M-STX were 0.945, 0.960 and 0.977, respectively.