#5 Where microorganisms increase and decrease
Professor Emeritus at Hokkaido University
Advisor at Japan Food Research Laboratories
Even “harmful” food-poisoning microorganisms are trying hard to embrace their fragile lives in a definite place. Their genes might have ordered them to “bloom where God has planted you”.
Microorganisms start proliferating when the factors shown in Figure1 trun to be in proper condition. Bacteria that increase through cell division undergo explosive growth as shown in Table2. The period from a bacterium undergoes one cell division to another is called generation time. If conditions are right as in Table2, generation time of Vibrio parahaemolyticus is about 10 minutes, and that of salmonella and Escherichia coli is about 20 minutes.
Under the right conditions, one alive Vibrio parahaemolyticus multiplies to 4096 in 2 hours, and to an incredible number of 69 billion in 6 hours.
Prevention of microbial contamination as well as microbial control such as rinsing or microbiocide are addressed in each food-handling process (except for utilization of microbial proliferation such as fermentation or maturation) from farm to table as shown in Figure1. Decreasing microorganisms and preventing proliferation by refrigerating food are typical examples of such efforts.
It forms the basis of microbial control to understand at which process microorganisms increase or decrease by actually counting their numbers. If we take excessive or wrong countermeasures without sorting out the problems involved, waste of resources, deterioration of food quality, or rising cost might be invited.
Factors that influence proliferation of bacteria in Figure1 also serve as elements to be evaluated in microbial control. It is desirable to choose the most effective control method that hits the weak point of a targeted microorganism by investigating its proliferation factors. This will ensure food safety, and at the same time, prevent the deterioration of food quality such as color, taste and flavor
Microorganisms like bacterium, fermentum and fungus can adhere to food and proliferate at any point of the food chain in Figure1. Whether or not microorganisms proliferate depends on the proliferation factors. We need not only to conduct microbial control of finished food products but also to take a proper care of factors influencing their food chain. Especially, animate lives such as human beings, livestock and pet animals require attention because they can be hotbets for proliferation of food-poisoning bacteria like O157.
Microorganisms, yeasts and molds are equipped with a function for multiplication such as protein synthesis, but viruses not. Viruses are smaller than bacteria, and their genetic information such as DNA or RNA is compiled in their membranes. As viruses can not increase on their own, they parasitize other cells.
Every year, many people suffer from Norovirus in Japan too. Though survey results have not been released by developing countries, it is obvious that people around the world are bothered by this pathogen. Norovirus proliferates in human small-intestinal epithelial cells. They are not necessarily food-borne and can transmit from human to human. In order to prevent its infection, it is important to keep the virus from reaching the human small-intestinal epithelial cells. This requires a sanitized life of each individual through hand-washing, gargle and mask-wearing. It is recommended to prevent Norovirus from reaching small intestine rather than tackling it after its increase in that organ.
References (all in Japanese)
Miyamoto, T. Chapter 3, Shokuhin to Biseibutsu (Food and Microorganisms). Isshiki, K. ed. (2014). Shokuhin Eisei Gaku (Food Hygienics). Tokyo Kagaku Dozin
Ministry of Health, Labour and Welfare: Q&A on Norovirus (March 28, 2014)