Methods for the Recovery of Clostridia from Foods

Detection and Enumeration of Spore-Forming Bacteria in Powdered Dairy Products

With the abolition of milk quotas in the European Union in 2015, several member states including Ireland, Luxembourg, and Belgium have seen year on year bi-monthly milk deliveries to dairies increase by up to 35%. Milk production has also increased outside of Europe in the past number of years. Unsurprisingly, there has been a corresponding increased focus on the production of dried milk products for improved shelf life. These powders are used in a wide variety of products, including confectionery, infant formula, sports dietary supplements and supplements for health recovery. To ensure quality and safety standards in the dairy sector, strict controls are in place with respect to the acceptable quantity and species of microorganisms present in these products. A particular emphasis on spore-forming bacteria is necessary due to their inherent ability to survive extreme processing conditions. Traditional microbiological detection methods used in industry have limitations in terms of time, efficiency, accuracy, and sensitivity. The following review will explore the common spore-forming bacterial contaminants of milk powders, will review the guidelines with respect to the acceptable limits of these microorganisms and will provide an insight into recent advances in methods for detecting these microbes. The various advantages and limitations with respect to the application of these diagnostics approaches for dairy food will be provided. It is anticipated that the optimization and application of these methods in appropriate ways can ensure that the enhanced pressures associated with increased production will not result in any lessening of safety and quality standards.

Quantitative risk assessment of human salmonellosis in Canadian broiler chicken breast from retail to consumption

The current quantitative risk assessment model followed the framework proposed by the Codex Alimentarius to provide an estimate of the risk of human salmonellosis due to consumption of chicken breasts which were bought from Canadian retail stores and prepared in Canadian domestic kitchens. The model simulated the level of Salmonella contamination on chicken breasts throughout the retail-to-table pathway. The model used Canadian input parameter values, where available, to represent risk of salmonellosis. From retail until consumption, changes in the concentration of Salmonella on each chicken breast were modeled using equations for growth and inactivation. The model predicted an average of 318 cases of salmonellosis per 100,000 consumers per year. Potential reasons for this overestimation were discussed. A sensitivity analysis showed that concentration of Salmonella on chicken breasts at retail and food hygienic practices in private kitchens such as cross-contamination due to not washing cutting boards (or utensils) and hands after handling raw meat along with inadequate cooking contributed most significantly to the risk of human salmonellosis. The outcome from this model emphasizes that responsibility for protection from Salmonella hazard on chicken breasts is a shared responsibility. Data needed for a comprehensive Canadian Salmonella risk assessment were identified for future research.

Selective enumeration of spores of Clostridium species in dried foods

The suitability of a variety of media and procedures for the enumeration of sulphite-reducing clostridia in food was investigated. The most suitable procedure was pasteurization of the 1/10 macerate for at least 1 min at 80 degrees C; followed by culture at 30 degrees C for up to 3 d in a sulphite-based, differential reinforced clostridium medium, without bicarbonate or lactate but with an increased iron concentration, and sulphite and iron added after sterilization. Black sulphite-reducing colonies were finally tested for sensitivity to metronidazole and confirmation of their failure to grow on agar slopes under aerobic conditions.

Simplified methods for the microbiological evaluation of bottled natural mineral waters

The conventional methods for the microbiological examination of natural mineral water were compared with a simplified procedure. The results indicate that when indicator micro-organisms are present in water, they may not be detected in the simplified method. An alternative procedure, including the determination of Pseudomonas aeruginosa, is suggested.

Growth and formation of toxin by Clostridium botulinum in peeled, inoculated, vacuum-packed potatoes after a double pasteurization and storage at 25 degrees C

A process that claims to use a double pasteurization to produce vacuum-packed potatoes for storage at ambient temperature has been evaluated. After the first pasteurization, potatoes are vacuum-packed and stored at 25 degrees-35 degrees C for up to 24 h, which is intended to allow germination of bacterial spores, and are then pasteurized again. When potatoes were inoculated with spores of Clostridium botulinum and subjected to this double-pasteurization process a high proportion of spores remained viable and resulted in growth and formation of toxin within 5-9 d at 25 degrees C. To provide an appropriate reduction in the risk o survival and growth of Cl. botulinum, peeled, vacuum-packed potatoes for storage at ambient temperature should be given a heat treatment equivalent to an F(0)3 process. If they are not given such a heat treatment they should be stored at a temperature below 4 degrees C.

Comparison of media and methods for counting Clostridium perfringens in poultry meat and further-processed products

A Most Probable Number (MPN) method involving Differential Reinforced Clostridial Medium followed by streaking on Willis & Hobbs medium was compared with direct plating of samples on Tryptose-Sulphite-Cycloserine agar without egg yolk, and two forms of Oleandomycin-Polymyxin-Sulphadiazine-Perfringens agar, one being prepared from a commercial, dehydrated product. With skin samples taken from chicken carcasses at different stages of processing, the three direct plating media gave similar counts of Cl. perfringens whereas results obtained with the MPN method were consistently lower. Although counts of Cl. perfringens from various further processed products were usually less than 10/g, the three plating media showed similar specificity for this organism. All media supported good growth of reference strains of Clostridium perfringens but it was found that physiologically similar species, including Cl. absonum, Cl. paraperfringens and Cl. perenne also grew uninhibited in these media and produced colonies identical with those of Cl. perfringens, thus indicating the need for confirmatory tests for Cl. perfringens when examining natural samples.

Characteristics of bacteria isolated by the anaerobic roll-tube method from cheeses and ground beef

In this study the methods of Hungate were used to quantitate the anaerobic bacteria present in commercially available ground beef, cheddar cheese, and German hand cheese. Of 235 anaerobic roll-tube isolates from ground beef and German hand cheese, all were facultative anaerobes. Of 213 anaerobic roll-tube isolates from cheddar cheese, 91% were facultative anaerobes and 9% were obligate anaerobes. Using results of biochemical tests, 14 or the 17 obligately anaerobic isolates from cheddar cheese were Propionibacterium acnes, two were strains of Propionibacterium that could not be speciated, and one was tentatively identified as a strain of Streptococcus evolutus. Obligate anaerobes were estimated to be present in the cheddar cheese at a level of about 10(6)/g. The possible significance of these levels of P. acnes in nonsterile foods is discussed.