Dairy pathogen surviving conditions

the common pathogen concern with dairy is the listeria. read the following info about the conditions that it can survive.

source: http://www.scientistlive.com/news/daily-news/13826/microbial-contaminants-dead-or-deadly.thtml

Listeria monocytogenes are abundant in the natural environment. Unpasteurised milk has a natural microbial flora containing up to 10cfu/ml of the bacteria. Listerias show a regular rod form (0.5µm-2µm length/0.4µm-0.5µm diameter), with a lag phase of 24-48 hours and a regeneration time of 20 hours.In a dairy plant, controlling Listeria bacteria is challenging because of their ubiquity and unique characteristics: * The ability to grow at refrigeration temperature (down to 0-1°C). * A higher thermal resistance than other pathogens. * A tolerance towards low pH (down to 4.4). * Sodium chloride levels (up to 12 per cent).When final dairy product becomes contaminated, the production process is usually to blame. Bacteria are easily spread by contact with wet surfaces and with process fluids, such as water that is used for curd and butter washing, lactose removal, and pasta filata cheese (mozzarella) stretching. Contamination can result from poor plant or equipment design, improper identification of contamination sources, lack of appropriate process controls, and inefficient sanitation.

Spoilage Microorganisms in Milk

The microbial quality of raw milk is crucial for the production of quality dairy foods. Spoilage is a term used to describe the deterioration of a foods' texture, colour, odour or flavour to the point where it is unappetizing or unsuitable for human consumption. Microbial spoilage of food often involves the degradation of protein, carbohydrates, and fats by the microorganisms or their enzymes.

In milk, the microorganisms that are principally involved in spoilage are psychrotrophic organisms. Most psychrotrophs are destroyed by pasteurization temperatures, however, some like Pseudomonas fluorescens, Pseudomonas fragi can produce proteolytic and lipolytic extracellular enzymes which are heat stable and capable of causing spoilage.
Some species and strains of Bacillus, Clostridium, Cornebacterium, Arthrobacter, Lactobacillus, Microbacterium, Micrococcus , and Streptococcus can survive pasteurization and grow at refrigeration temperatures which can cause spoilage problems.

Pathogenic Microorganisms in Milk

Hygienic milk production practices, proper handling and storage of milk, and mandatory pasteurization has decreased the threat of milkborne diseases such as tuberculosis, brucellosis, and typhoid fever. There have been a number of foodborne illnesses resulting from the ingestion of raw milk, or dairy products made with milk that was not properly pasteurized or was poorly handled causing post-processing contamination. The following bacterial pathogens are still of concern today in raw milk and other dairy products:
Bacillus cereus
Listeria monocytogenes
Yersinia enterocolitica
Salmonella spp.
Escherichia coli O157:H7
Campylobacter jejuni

It should also be noted that moulds, mainly of species of Aspergillus , Fusarium , and Penicillium can grow in milk and dairy products. If the conditions permit, these moulds may produce mycotoxins which can be a health hazard.

source: http://www.foodsci.uoguelph.ca/dairyedu/micro.html