The continuing expansion of interest in probiotic bacteria has led to an increase in manufactured Functional Foods and medicines containing these bacteria. Given the intestinal origin of these microorganisms, the challenges these sensitive bacteria face in order to be in a highly viable state throughout processing, storage and gastrointestinal transit to the site of action in the human gut are enormous. These bacteria encounter stresses including temperature, acid, bile, exposure and osmotic and oxidative stress in both product matrices and during gastrointestinal transit. However, like all bacteria, probiotic bacteria retain a broad arsenal of molecular mechanisms to combat the often lethal environmental stresses encountered during processing and following ingestion. A comprehensive appreciation of these mechanisms should inevitably lead to the design and manufacture of probiotic cultures, which retain greater viability through to the target site in the intestine. This review attempts to catalogue the cellular processes available to probiotic bacteria to facilitate survival in stressful conditions, and to speculate on how manipulation of these cellular systems can lead to production of designer strains with enhanced viability in food systems and efficacy following ingestion.

Aims:  To determine the relationships between the major organisms from the cheese‐making personnel and environment and the surface of a smear cheese. Methods and Results:  360 yeast and 593 bacteria from the cheese surface, the dairy environment and the hands and arms of personnel were collected. Pulsed‐field gel electrophoresis, repetitive sequence‐based polymerase chain reaction and 16S rDNA sequencing were used for typing and identifying the bacteria, and mitochondrial DNA restriction fragment length polymorphism and Fourier‐transform infrared spectroscopy for typing and identifying the yeast. The three most dominant bacteria were Corynebacterium casei, Corynebacterium variabile and Staphylococcus saprophyticus, which were divided into three, five and seven clusters, respectively, by macrorestriction analysis. The same clones from these organisms were isolated on the cheese surface, the dairy environment and the skin of the cheese personnel. Debaryomyces hansenii was the most dominant yeast. Conclusions:  A ‘house’ microflora exists in the cheese plant. Although the original source of the micro‐organisms was not identified, the brines were an important source of S. saprophyticus and D. hansenii and, additionally, the arms and hands of the workers the sources of C. casei and C. variabile. Significance and Impact of the Study:  This is the first time that the major contribution of the house microflora to the ripening of a smear‐ripened cheese has been demonstrated.

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Aims:  In this study, we compare seven different methods which have been designed or modified to extract total DNA from raw milk and raw milk cheese with a view to its subsequent use for the PCR of bacterial DNA. Materials and Results:  Seven extraction methods were employed to extract total DNA from these foods, and their relative success with respect to the yield and purity of the DNA isolated, and its quality as a template for downstream PCR, was compared. Although all of the methods were successful with respect to the extraction of DNA naturally present in cheese, they varied in their relative ability to extract DNA from milk. However, when milk was spiked with a representative Gram‐positive (Listeria monocytogenes EGDe) or Gram‐negative (Salmonella enterica serovar Typhimurium LT2) bacterium, it was established that all methods successfully extracted DNA which was suitable for subsequent detection by PCR. Conclusions:  Of the seven approaches, the PowerFood™ Microbial DNA Isolation kit (MoBio Laboratories Inc.) was found to most consistently extract highly concentrated and pure DNA with a view to its subsequent use for PCR‐based amplification and also facilitated accurate detection by real‐time quantitative PCR. Significance and Impact of the Study:  Accurately assessing the bacterial composition of milk and cheese is of great importance to the dairy industry. Increasingly, DNA‐based technologies are being employed to provide an accurate assessment of this microbiota. However, these approaches are dependent on our ability to extract DNA of sufficient yield and purity. This study compares a number of different options and highlights the relative success of these approaches. We also highlight the success of one method to extract DNA from different microbial populations as well as DNA which is suitable for real‐time PCR of microbes of interest, a challenge often encountered by the food industry.