Evaluation of motility enrichment on modified semi-solid Rappaport-Vassiladis medium (MSRV) for the detection of Salmonella in foods

The detection and identification of Salmonella spp. is still troublesome and time consuming to the food industry. Employing the modified semi-solid Rappaport-Vassiliadis medium (MSRV), presumptive results for Salmonella can be obtained in 48 h, representing an interesting alternative to the standard methods. The specificity and sensitivity of the MSRV method were evaluated in this research. The efficiency of this method was also compared with the methodology recommended by the US Food and Drug Administration (FDA) using bismuth sulfite agar, XLT4 agar and Rambach agar. A total of 146 food samples comprised of 41 chicken thighs, 35 Brazilian fresh pork sausages, 35 samples of cocoa powder and/or granulated cocoa and 35 samples of grated fresh coconut, were examined. Overall, the rapid method (direct + indirect) and the standard culture detected 96.1% and 84.6% of the positive samples, respectively. No Salmonella was detected in the coconut or cocoa samples by any of the methods. Eighteen (43.9%) chicken thigh samples were contaminated with the microorganism. The rapid method (direct + indirect) and the standard culture detected 94.4% and 88.9% of these, respectively. Salmonella was detected in eight (22.8%) fresh pork sausage samples. The MSRV method detected Salmonella in all eight samples, while the standard gave positive results in six (75%). When compared with the standard method, the indirect method showed 86.4% sensitivity and 96.8% specificity, while the direct MSRV showed a sensitivity of 71.4% and specificity of 99.2%. Combined, both MSRV methods showed 95.5% sensitivity and 96.8% specificity. The MSRV medium also reduces the time necessary for the isolation of Salmonella from foods.

Genetic mapping of resistance factors to Phytophthora palmivora in cocoa

Phytophthora palmivora causes pod rot, a serious disease on cocoa widespread throughout the producing regions. In order to ascertain the genetic determination of cocoa resistance to P. palmivora, a study was carried out on two progenies derived from crosses between a heterozygous, moderately resistant Forastero clone, T60/887, and two closely related and highly susceptible Forastero clones, one completely homozygous, IFC2, and one partially heterozygous, IFC5. The cumulative size of both progenies was 112 individuals. Plants were subjected to natural and artificial inoculation of P. palmivora in C te d'Ivoire. The genetic maps of T60/887 and of IFC5 were constructed using amplified fragment length polymorphism (AFLP) markers and microsatellites. The map of T60/887 comprised 198 markers assembled in 11 linkage groups and representing a total length of 793 cM. The map of IFC5 comprised 55 AFLP markers that were assembled into six linkage groups for a total length of 244 cM. Ratio of rotten over total number of fruit under natural infection was measured for each tree over two harvests. Artificial inoculations were performed on leaves and pods. These tests were weakly correlated with the pod rot rate in the field. Five quantitative trait loci (QTLs) of resistance were detected for T60/887 but none were common between the three traits measured. Stability and reliability of the experimental procedures are discussed and revealed the difficult use of these artificial tests on adult trees for a good prediction of field resistance.

Characterization of an amylase produced by a Trichoderma harzianum isolate with antagonistic activity against Crinipellis perniciosa, the causal agent of witches' broom of cocoa

An isolate of Trichoderma harzianum showing antagonistic activity against Crinipellis perniciosa, the causal agent of the witches' broom disease of cocoa, produces substantial amounts of hydrolytic enzymes. An amylase purified from isolate 1051 had a molecular mass of about 68.7 kDa. Maximal activity against soluble starch was determined at pH 4.0 and 60 degrees C. The K(m) and V(max) values were 3.5 mg ml(-1) and 1.67 mg min(-1) of reducing sugar. The end products were mostly malto-oligosaccharides. The enzyme also hydrolyzed glycogen, amylopectin, maltotriose, and maltotetraose, but not pullulan or cellobiose. Maltose was only barely hydrolyzed. The purified amylase exerted a discrete hydrolytic effect on the C. perniciosa cell wall in vitro as observed by scanning electron microscopic analysis. While Fe(3+), Al(3+), Zn(2+), and Cu(2+) were effective in inhibiting the purified amylase, Mn(2+) considerably enhanced the activity. Ca(2+), Mg(2+), and Co(2+) showed no substantial effect on enzyme activity.

Equivalence of assurance Gold Enzyme Immunoassay for visual or instrumental detection of motile and nonmotile Salmonella in all foods to AOAC culture method: collaborative study

Six foods representative of a wide variety of processed, dried powder processed, and raw food types were analyzed by the Assurance Gold Salmonella Enzyme Immunoassay (EIA) and AOAC INTERNATIONAL culture method. Paired samples of each food type were simultaneously analyzed; one sample by the Assurance method and one by the AOAC culture method. The results for Assurance method were read visually and instrumentally with a microplate reader. A total of 24 laboratories representing federal government agencies and private industry, in the United States and Canada, participated in this collaborative study. Food types were inoculated with species of Salmonella with the exception of raw ground chicken, which was naturally contaminated. No statistical differences (p < 0.05) were observed between Assurance Gold Salmonella EIA with either visual or instrumental interpretation and the AOAC culture method for any inoculation level of any food type or naturally contaminated food. The Assurance visual and instrumental options of reading sample reactions produced the same results for 1277 of the 1296 sample and controls analyzed.

Equivalence of Visual Immunoprecipitate Assay (VIP) for Salmonella for the detection of motile and nonmotile Salmonella in all foods to AOAC culture method: collaborative study

Six foods representative of a wide variety of processed, dried powder processed, and raw food types were analyzed by the Visual Immunoprecipitate Assay (VIP) for Salmonella and AOAC INTERNATIONAL culture method. Paired samples of each food type were simultaneously analyzed; one sample by the VIP method and one by the AOAC culture method. A total of 24 laboratories representing federal government agencies and private industry, in the United States and Canada, participated in this collaborative study. Food types were inoculated with species of Salmonella with the exception of raw ground chicken, which was naturally contaminated. No statistical differences (p < 0.05) were observed between VIP for Salmonella interpretation and the AOAC culture method for any inoculation level of any food type or naturally contaminated food. The method was adopted Official First Action status by AOAC INTERNATIONAL.

Salmonella in foods--a new enrichment procedure for use with the TECRA Salmonella visual immunoassay: collaborative study

A collaborative study was conducted to compare a new enrichment procedure for the TECRA Salmonella Visual Immunoassay with the reference method given in the U.S. Food and Drug Administration's Bacteriological Analytical Manual (BAM 7th Ed.). Three food types (milk powder, black pepper, and soy flour) were analyzed in Australia, and 3 food types (milk chocolate, dried egg, and raw turkey) were analyzed in the United States. Thirty-eight collaborators participated in the study. No significant differences (p > 0.05) were observed for the pairwise comparison of the proportion of positive samples for the TECRA method with that for the reference method. The new enrichment procedure for the TECRA method has been adopted First Action by AOAC INTERNATIONAL.

Cocoa fermentations conducted with a defined microbial cocktail inoculum

Cocoa fermentations were performed in wooden boxes under the following four experimental regimens: beans naturally fermented with wild microflora; aseptically prepared beans with no inoculum; and beans inoculated with a defined cocktail containing microorganisms at a suitable concentration either at zero time or by using phased additions at appropriate times. The cocktail used consisted of a yeast, Saccharomyces cerevisiae var. chevalieri, two lactic acid bacterial species, Lactobacillus lactis and Lactobacillus plantarum, and two acetic acid bacterial species, Acetobacter aceti and Gluconobacter oxydans subsp. suboxydans. The parameters measured were cell counts (for yeasts, filamentous fungi, lactic acid bacteria, acetic acid bacteria, and spore formers, including reisolation and identification of all residual cell types), sugar, ethanol, acetic acid, and lactic acid contents (and contents of other organic acids), pH, and temperature. A cut test for bean quality and a sensorial analysis of chocolate made from the beans were also performed. The natural fermentation mimicked exactly the conditions in 800-kg boxes on farms. The aseptic box remained largely free of microflora throughout the study, and no significant biochemical changes occurred. With the zero-time inoculum the fermentation was almost identical to the natural fermentation. The fermentation with the phased-addition inoculum was similar, but many changes in parameters were slower and less pronounced, which led to a slightly poorer end product. The data show that the nearly 50 common species of microorganisms found in natural fermentations can be replaced by a judicious selection and concentration of members of each physiological group. This is the first report of successful use of a defined, mixed starter culture in such a complex fermentation, and it should lead to chocolate of more reliable and better quality.

LOCATE enzyme-linked immunosorbent assay for detection of Salmonella in food: collaborative study

A collaborative study was performed in 27 laboratories to validate the enzyme-linked immunosorbent procedure LOCATE for rapid detection of Salmonella in foods. Results were read visually and with a microtiter plate reader. The LOCATE method was compared with the Bacteriological Analytical Manual (BAM)/AOAC INTERNATIONAL culture method for detecting Salmonella in 6 foods: milk chocolate, nonfat dry milk, dried whole egg, soy flour, ground black pepper, and ground raw turkey. Two foods--dried whole egg and black pepper--required repeat rounds because insufficient data sets were produced initially (AOAC INTERNATIONAL stipulates a minimum of 15 sets per food type). Each laboratory tested one or more of the 6 foods. A total of 1 439 samples were analyzed, and no significant differences (P < 0.05) were observed between LOCATE with either visual or reader detection and BAM/AOAC INTERNATIONAL results. The LOCATE screening method with visual or reader detection is recommended for Official First Action Approval.

Chrysosporium species, potential spoilage organisms of chocolate

Standard methods of analysing foods for the presence of moulds are inadequate for the detection of genera such as Chrysosporium which do not grow at the high water activities of most mycological media. The use of malt, yeast, 50% glucose agar (MY50G) in sealed containers as an enrichment medium allowed time for germination and growth of heat-stressed spores. Three Chrysosporium spp., C. xerophilum Pitt, C. inops (Carmichael) and C. farinicola (Burnside) Skou, were isolated from commercial chocolate bars with a water activity (aw) of approximately 0.28. Chrysosporium inops was isolated from commercial milk crumb and a new Chrysosporium sp. was isolated from Ghanaian cocoa beans. In chocolates made by coating MY50G agar (aw = 0.89) with chocolate (aw = 0.27) containing C. inops arthroconidia, two types of deterioration were seen after storage. The first was fat bloom due to recrystallization of the cocoa butter on the outer and inner chocolate surface. The second was growth of C. inops which occurred on the inside chocolate surface adjacent to the MY50G agar filling and on the outside surface after holding at 92% equilibrium relative humidity (erh) for 12 d. There was some evidence that C. inops could grow on the outside of chocolates held at 5.7% erh after 4 months' storage at 25 degrees C. The appearance of the white fungal growth was not unlike fat bloom to the naked eye but was clearly different with the electron microscope.

Evidence for natural transformation of Bacillus subtilis in foodstuffs

The effect of foodstuffs on the natural transformation of Bacillus subtilis was investigated. As examples of complex food matrices milk with various fat contents as well as chocolate milk were used. The frequencies of transformation varied with the fat content and ranged between 3.8 X 10(-4) and 1.4 X 10(-3). Highest frequencies of about 3 X 10(-3) were observed in chocolate milk with 1.5% fat. Development of competence was observed in chocolate milk, resulting in maximal transformation frequencies upon incubation for 10-12 h at 37 degrees C.

VIDAS enzyme-linked fluorescent immunoassay for detection of Salmonella in foods: collaborative study

The VIDAS SLM method for detection of Salmonella was compared with the Bacteriological Analytical Manual (BAM)/AOAC culture method in a collaborative study. Twenty laboratories participated in the evaluation. Each laboratory tested one or more of 6 test products: milk chocolate, nonfat dry milk, dried whole egg, soy flour, ground black pepper, and ground raw turkey. No significant differences (P < 0.05) were observed between the 2 methods. The 2 methods were in agreement for 99% of 1544 samples analyzed. Of the 20 samples out of agreement, 8 were VIDAS SLM positive and BAM/AOAC negative, and 12 were VIDAS SLM negative and BAM/AOAC positive. The VIDAS SLM method for detection of Salmonella in foods has been adopted first action by AOAC INTERNATIONAL.

Time to B. cereus about hot chocolate

OBJECTIVE

To determine the cause of illnesses experienced by employees of a Minneapolis manufacturing plant after drinking hot chocolate bought from a vending machine and to explore the prevalence of similar vending machine-related illnesses.

METHODS

The authors inspected the vending machines at the manufacturing plant where employees reported illnesses and at other locations in the city where hot chocolate beverages were sold in machines. Tests were performed on dry mix, water, and beverage samples and on machine parts.

RESULTS

Laboratory analyses confirmed the presence of B. cereus in dispensed beverages at a concentration capable of causing illness (170,000 count/gm). In citywide testing of vending machines dispensing hot chocolate, 7 of the 39 licensed machines were found to be contaminated, with two contaminated machines having B. cereus levels capable of causing illness.

CONCLUSIONS

Hot chocolate sold in vending machines may contain organisms capable of producing toxins that under favorable conditions, can induce illness. Such illnesses are likely to be underreported. Even low concentrations of B. cereus may be dangerous for vulnerable populations such as the aged or immunosuppressed. Periodic testing of vending machines is thus warranted. The relationship between cleaning practices and B. cereus contamination is an issue for further study.

Salmonella detection in cocoa and chocolate by motility enrichment on modified semi-solic Rappaport-Vassiliadis medium: collaborative study

A collaborative study was performed in 13 laboratories (including the authors' laboratories) to validate motility enrichment on modified semi-solid Rappaport-Vassiliadis (MSRV) medium for rapid detection of motile Salmonella in cocoa powder and chocolate. The MSRV method was compared with the AOAC standard culture method for detection of Salmonella in cocoa powder, milk chocolate, sweet chocolate, and dark chocolate. Chocolate samples were artificially inoculated with Salmonella at 2 levels of contamination. Cocoa powder was inoculated at 2 levels with naturally contaminated dust from cocoa beans. Uninoculated control samples were also included for each type of product. The sensitivity rate was 98.1% for the MSRV method and 94.9% for the AOAC culture method. The specificity rate was 100.0% for both methods. There was no significant difference in the proportion of samples positive by MSRV and the AOAC culture methods for any of the food types. The MSRV method has been adopted first action by AOAC INTERNATIONAL.

Nucleotide sequence and genomic organization of cacao swollen shoot virus

Cacao swollen shoot virus is classified as a badnavirus based on its nonenveloped, bacilliform particle morphology and double-stranded DNA genome. A complete copy of the genome was cloned into a plasmid vector and the sequence was determined from 75 overlapping subclones covering both strands. The genome contains 7161 base pairs and possesses an intergenic region and five putative open reading frames (ORF) capable of coding for proteins > 10 kDa. All of the ORFs are present on the plus-strand. ORF 1 (17 kDa) and ORF 2 (14 kDa) encode proteins of unknown function. The large ORF 3 (211 kDa) encodes a polyprotein that can be divided into three regions. Based on distant homologies with viral movement proteins, region 1 may encode a protein involved in cell-to-cell spread, while region 2 encodes the viral capsid protein. Region 3 contains consensus sequences for viral aspartyl proteinase, reverse transcriptase, and ribonuclease H characteristic of pararetroviruses. The last two ORFs (13 and 14 kDa) overlap ORF 3 and are not present in the other badnaviruses described.

Collaborative study of the International Office of Cocoa, Chocolate and Sugar Confectionery on Salmonella detection from cocoa and chocolate processing environmental samples

A comparative collaborative study was performed in 13 laboratories to evaluate the use of motility enrichment on Modified Semisolid Rappaport-Vassiliadis medium for rapid Salmonella detection from food-processing environmental samples. Artificially contaminated chocolate scrapings and naturally contaminated cocoa bean dust samples were used in the study. Pre-enrichment was performed in buffered peptone water with added casein and malachite green oxalate. Motility enrichment was compared with a conventional cultural procedure using Rappaport-Vassiliadis broth and selenite cystine broth as selective enrichment. The productivity of motility enrichment was 93.5% compared to a productivity of the cultural procedure of 92%. Statistical analysis showed that there was no significant difference between the two procedures. Modified Semisolid Rappaport-Vassiliadis medium is a sensitive and simple diagnostic tool for the microbiological safety evaluation of food-processing environments.

Comparison of growth and cellulolytic enzyme production in Aspergillus chevalieri and Penicillium steckii from mouldy cacao beans

Aspergillus chevalieri and Penicillium steckii grew best at 30 degrees C and at pH of 6.5-7.5. Among the carbon sources employed, sucrose supported maximum growth of A. chevalieri while glucose was best for P. steckii. Growth of both organisms was optimal on ammonium tartrate as the sole source of nitrogen. A. chevalieri and P. steckii grew in synthetic media containing, respectively, soluble or insoluble cellulose as the sole carbon source, releasing a cellulolytic enzyme into the medium. The enzymes from each organism were separated and partially purified by molecular exclusion and ion-exchange chromatography into two components. There was synergism between the components of enzymes from each organism in that they together released more glucose units from insoluble cellulose than could be predicted from their activities alone. The molar mass of the enzymes estimated from the elution volume on Sephadex was approximately 110 kg/mol for A. chevalieri and 94 kg/mol for P. steckii.

Estimation of human dose of staphylococcal enterotoxin A from a large outbreak of staphylococcal food poisoning involving chocolate milk

An outbreak of gastroenteritis in a school district in the United States was determined to be staphylococcal food poisoning due to 2% chocolate milk containing staphylococcal enterotoxin A (SEA). Twelve one-half pint (approx 0.28 l) cartons of the 2% chocolate milk from this outbreak were analyzed for the quantity of SEA present in the milk. The amount of SEA in the cartons varied from 94 to 184 ng with the average being 144 ng (mean = 139 +/- 45). The attack rate for vomiting among those who consumed more than one carton was greater (38.3%) than among those who consumed only one carton (31.5%) with the highest attack rate among those who consumed three or more cartons (44.4%).

Frequency of the Aspergillus flavus in some sensoric unchanged foodstuffs

By aid of a direct inoculation method it was followed the frequency of Aspergillus flavus - colony forming units in 11,526.5 p (100%) of 55 samples of some basic sensoric unchanged foodstuffs (cereal instant gruels 21%, milk powder 49%, pudding powders 7%, meal 9% and tea, coffee, cacao 12%) and inner contamination by A. flavus in 22,017 pieces of nuts and grains. It was found, that A. flavus colony forming units falls in Czechoslovak Socialistic Republic on the average on 7.2 g of the sample of crisp consistency (the least 0 colony/3.24%) of the investigated grains and nuts.