J.M. Cox

The growth, properties and interactions of yeasts and bacteria associated with the maturation of Camembert and blue-veined cheeses

The growth of yeasts and bacteria were monitored during the maturation of Camembert and blue-veined cheese produced in Australia. Yeasts were prominent throughout maturation, growing to 10(5)-10(9)/g, depending on the manufacturer. Debaryomyces hansenii predominated, but there were lesser, inconsistent contributions from Yarrowia lipolytica. Of the non-lactic acid bacteria, Acinetobacter species were significant during the maturation of Camembert but not blue-veined cheeses, and grew to 10(6)-10(8) cfu/g. Staphylococcus and Micrococcus species were consistently isolated from the cheeses with Staphylococcus xylosus growing to 10(5)-10(9) cfu/g, depending on the product. Lactic acid bacteria (10(7)-10(9) cfu/g) were present throughout maturation but were not identified. Interactions between the various yeasts and bacterial isolates were examined. Several strains of D. hansenii exhibited killer activity but not against Y. lipolytica. None of the yeasts were antagonistic towards the bacteria but some strains of D. hansenii enhanced the growth of Y. lipolytica and S. xylosus. The yeast and bacterial isolates exhibited various degrees of extracellular proteolytic and lipolytic activities.

Isolates of Salmonella enterica Enteritidis PT4 with enhanced heat and acid tolerance are more virulent in mice and more invasive in chickens.

Two Enteritidis PT4 isolates which differed in inherent tolerance to heat, acid, H2O2 and the ability to survive on surfaces were used to infect mice, day-old chicks or laying hens. The acid-, heat-, H2O2- and surface-tolerant isolate was more virulent in mice and more invasive in laying hens, particularly in reproductive tissue. However, no significant differences were observed in behaviour in chicks. Both PT4 isolates were able to infect chicks housed in the same room as infected birds, although the heat-tolerant isolate survived significantly better than the heat-sensitive one in aerosols.

Advances in enteropathogen control in poultry production.

Poultry meat has been associated frequently and consistently with the transmission of enteric pathogens, including Salmonella and Campylobacter. This association has resulted in the development of HACCP‐based intervention strategies. These strategies (hurdles) begin with elite breeder flocks and filter down the production pyramid. These hurdles include those already established, such as biosecurity, vaccination, competitive exclusion, pre‐ and probiotics, feed and water control, and those more experimental, such as bacteriophage or immunoglobulin therapy. The reduction in enteropathogens entering the processing plant, which employs critical control points, further reduce the exposure of consumers to these organisms. The synergistic application of hurdles will result in an environment that is restrictive and detrimental to enteropathogen colonization and contamination.

Cereulide, the emetic toxin of Bacillus cereus, is putatively a product of nonribosomal peptide synthesis

Aims:  To determine if cereulide, the emetic toxin produced by Bacillus cereus, is produced by a nonribosomal peptide synthetase (NRPS).

Cronobacter (‘Enterobacter sakazakii’): current status and future prospects

The genus Cronobacter accommodates the 16 biogroups of the emerging opportunistic pathogen known formerly as Enterobacter sakazakii. Cronobacter spp. are occasional contaminants of milk powder and, consequently, powdered infant formula and represent a significant health risk to neonates. This review presents current knowledge of the food safety aspects of Cronobacter, particularly in infant formula milk powder. Sources of contamination, ecology, disease characteristics and risk management strategies are discussed. Future directions for research are indicated, with a particular focus on the management of this increasingly important bacterium in the production environment.

The interplay between Campylobacter and Helicobacter species and other gastrointestinal microbiota of commercial broiler chickens

BackgroundPoultry represent an important source of foodborne enteropathogens, in particular thermophilic Campylobacter species. Many of these organisms colonize the intestinal tract of broiler chickens as harmless commensals, and therefore, often remain undetected prior to slaughter. The exact reasons for the lack of clinical disease are unknown, but analysis of the gastrointestinal microbiota of broiler chickens may improve our understanding of the microbial interactions with the host.MethodsIn this study, the fecal microbiota of 31 market-age (56-day old) broiler chickens, from two different farms, was analyzed using high throughput sequencing. The samples were then screened for two emerging human pathogens, Campylobacter concisus and Helicobacter pullorum, using species-specific PCR.ResultsThe gastrointestinal microbiota of chickens was classified into four potential enterotypes, similar to that of humans, where three enterotypes have been identified. The results indicated that variations between farms may have contributed to differences in the microbiota, though each of the four enterotypes were found in both farms suggesting that these groupings did not occur by chance. In addition to the identification of Campylobacter jejuni subspecies doylei and the emerging species, C. concisus, C. upsaliensis and H. pullorum, several differences in the prevalence of human pathogens within these enterotypes were observed. Further analysis revealed microbial taxa with the potential to increase the likelihood of colonization by a number of these pathogens, including C. jejuni.ConclusionDepletion of these taxa and the addition of taxa that compete with these pathogens, may form the basis of competitive exclusion strategies to eliminate them from the gastrointestinal tract of chickens.

A validated miniaturized MPN method, based on ISO 6579:2002, for the enumeration of Salmonella from poultry matrices

Aims:  To validate the effectiveness of a miniaturized most probable number method (mMPN) in enumerating Salmonella from poultry matrices.

Diversity and toxigenicity among members of the Bacillus cereus group.

Members of the Bacillus cereus group were isolated from rice products by centrifugation-plating and conventional spread-plating methods. Random amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) results showed broad diversity among the strains and revealed some associations among isolates from raw and cooked rice samples, at the genotypic level. A comparatively greater diversity among strains was observed in isolates from raw rice than those from cooked rice and, generally, the RAPD profiles of isolates from raw and cooked rice were different, with only a few of them common to both types of rice. The toxigenic potential of the isolates was also determined by molecular and immunoassay analyses. The results revealed that most isolates from the B. cereus group were potentially or actually toxigenic, and some isolates could produce both diarrhoeal and emetic toxins. Generally, isolates belonging to the B. cereus group with the same RAPD pattern were shown to have a similar profile of enterotoxigenicity.

Application of a dense gas technique for sterilizing soft biomaterials

Sterilization of soft biomaterials such as hydrogels is challenging because existing methods such as gamma irradiation, steam sterilization, or ethylene oxide sterilization, while effective at achieving high sterility assurance levels (SAL), may compromise their physicochemical properties and biocompatibility. New methods that effectively sterilize soft biomaterials without compromising their properties are therefore required. In this report, a dense‐carbon dioxide (CO2)‐based technique was used to sterilize soft polyethylene glycol (PEG)‐based hydrogels while retaining their structure and physicochemical properties. Conventional sterilization methods such as gamma irradiation and steam sterilization severely compromised the structure of the hydrogels. PEG hydrogels with high water content and low elastic shear modulus (a measure of stiffness) were deliberately inoculated with bacteria and spores and then subjected to dense CO2. The dense CO2‐based methods effectively sterilized the hydrogels achieving a SAL of 10−7 without compromising the viscoelastic properties, pH, water‐content, and structure of the gels. Furthermore, dense CO2‐treated gels were biocompatible and non‐toxic when implanted subcutaneously in ferrets. The application of novel dense CO2‐based methods to sterilize soft biomaterials has implications in developing safe sterilization methods for soft biomedical implants such as dermal fillers and viscosupplements. Biotechnol. Bioeng. 2011; 108:1716–1725.

Evaluation of TECRA broth, Bolton broth, and direct plating for recovery of Campylobacter spp. from broiler carcass rinsates from commercial processing plants.

The purpose of this study was to compare a conventional culture broth method (Bolton enrichment), a newly developed proprietary broth method (TECRA Campylobacter enrichment), and direct plating for recovery of Campylobacter spp. from chicken carcass rinsates. Whole carcass rinses were taken from 140 carcasses at rehang (immediately after defeathering but before evisceration) and from 140 carcasses at postchill from eight different processing plants in the United States. The rinsate samples were packed in ice and shipped overnight to the laboratory. Aliquots of the rinsate were transferred into Bolton and TECRA enrichment broths and were direct plated. Standard laboratory procedures with Campy-cefex plates were followed for recovery of Campylobacter spp. For rehang carcasses, 94% were positive for Campylobacter spp. with the TECRA enrichment broth and 74% were positive with the Bolton enrichment broth. For postchill carcasses, 74% were positive for Campylobacter spp. with the TECRA enrichment broth and 71% were positive with the Bolton enrichment broth. Compared with the Bolton enrichment broth, TECRA enrichment broth significantly suppressed non-Campylobacter microflora (P < 0.05). Overall, TECRA enrichment broth yielded an 11% higher total number of Campylobacter-positive samples compared with the Bolton enrichment broth. Campylobacter spp. detection in postchill samples was significantly greater (P < 0.05) by enrichment (84%) than by direct plating (19%). The high number of Campylobacter-positive samples obtained with all procedures indicated that 99% of the carcass rinsates obtained at rehang and 84% obtained at postchill contained Campylobacter spp.