Milk produced in udder cells is sterile but due to its high nutrient content, it can be a good growth substrate for contaminating bacteria. The quality of milk is monitored via somatic cell counts and total bacterial counts, with prescribed regulatory limits to ensure quality and safety. Bacterial contaminants can cause disease, or spoilage of milk and its secondary products. Aerobic spore-forming bacteria, such as those from the genera Sporosarcina, Paenisporosarcina, Brevibacillus, Paenibacillus, Geobacillus and Bacillus, are a particular concern in this regard as they are able to survive industrial pasteurisation and form biofilms within pipes and stainless steel equipment. These single or multiple-species biofilms become a reservoir of spoilage microorganisms and a cycle of contamination can be initiated. Indeed, previous studies have highlighted that these microorganisms are highly prevalent in dead ends, corners, cracks, crevices, gaskets, valves and the joints of stainless steel equipment used in the dairy manufacturing plants. Hence, adequate monitoring and control measures are essential to prevent spoilage and ensure consumer safety. Common controlling approaches include specific cleaning-in-place processes, chemical and biological biocides and other novel methods. In this review, we highlight the problems caused by these microorganisms, and discuss issues relating to their prevalence, monitoring thereof and control with respect to the dairy industry.

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The Prevalence and Control of Bacillus and Related Spore-Forming Bacteria in the Dairy Industry

Inactivation and removal of Bacillus cereus by sanitizer and detergent

Comparative analysis of the diversity of aerobic spore-forming bacteria in raw milk from organic and conventional dairy farms

Bacillus cereus, a dairy-associated toxigenic bacterium, readily forms biofilms on various surfaces and was used to gain a better understanding of biofilm development by gram-positive aerobic rods. B. cereus DL5 was shown to readily adapt to an attached mode of growth, with dense biofilm structures developing within 18 h after inoculation when glass wool was used as a surface. Two-dimensional gel electrophoresis (2DE) revealed distinct and reproducible phenotypic differences between 2- and 18-h-old biofilm and planktonic cells (grown both in the presence and in the absence of glass wool). Whereas the 2-h-old biofilm proteome indicated expression of 15 unique proteins, the 18-h-old biofilm proteome contained 7 uniquely expressed proteins. Differences between the microcolony (2-h) proteome and the more developed biofilm (18-h) proteome were largely due to up- and down-regulation of the expression of a multitude of proteins. Selected protein spots excised from 2DE gels were subjected to N-terminal sequencing and identified with high confidence. Among the proteins were catabolic ornithine carbamoyltransferase and l-lactate dehydrogenase. Interestingly, increased levels of YhbH, a member of the sigma 54 modulation protein family which is strongly induced in response to environmental stresses and energy depletion via both σB and σH, could be observed within 2 h in both attached cells and planktonic cultures growing in the presence of glass wool, indicating that this protein plays an important role in regulation of the biofilm phenotype. Distinct band differences were also found between the extracellular proteins of 18-h-old cultures grown in the presence and in the absence of glass wool.

A. Christiansson

Papers

Bacillus cereus Spores in Raw Milk: Factors Affecting the Contamination of Milk During the Grazing Period