Various aspects such as food processing, food preservation, canning, Pasteurization of milk, study of food borne microbial diseases and their control is studied

Food microbiology is the study of the microorganisms that inhabit, create, or contaminate food, including the study of microorganisms causing food spoilage. "Good" bacteria, however, such as probiotics, are becoming increasingly important in food science.

In addition, microorganisms are essential for the production of foods such as cheese, yogurt, bread, beer, wine and, other fermented foods.

Explore food microbiology, from pathogenic organisms to the processes that beneficial microorganisms contribute to, such as fermentation and spoilage. You’ll learn about the detection and quantification of pathogenic organisms, how they survive in food and processing environments, and how to characterize those that are emerging. You’ll also discover the microbiology of health and wellness foods, learn about quality control issues, and much more.

Food safety

Food safety is a major focus of food microbiology. Pathogenic bacteria, viruses and toxins produced by microorganisms are all possible contaminants of food. However, microorganisms and their products can also be used to combat these pathogenic microbes. Probiotic bacteria, including those that produce bacteriocins, can kill and inhibit pathogens. Alternatively, purified bacteriocins such as nisin can be added directly to food products. Finally, bacteriophages, viruses that only infect bacteria, can be used to kill bacterial pathogens. Thorough preparation of food, including proper cooking, eliminates most bacteria and viruses. However, toxins produced by contaminants may not be liable to change to non-toxic forms by heating or cooking the contaminated food.


Fermentation is one of the methods to preserve food and alter its quality. Yeast, especially Saccharomyces cerevisiae, is used to leaven bread, brew beer and make wine. Certain bacteria, including lactic acid bacteria, are used to make yogurt, cheese, hot sauce, pickles, fermented sausages and dishes such as kimchi. A common effect of these fermentations is that the food product is less hospitable to other microorganisms, including pathogens and spoilage-causing microorganisms, thus extending the food's shelf-life. Some cheese varieties also require molds to ripen and develop their characteristic flavors.

Food testing

To ensure safety of food products, microbiological tests such as testing for pathogens and spoilage organisms are required. This way the risk of contamination under normal use conditions can be examined and food poisoning outbreaks can be prevented. Testing of food products and ingredients is important along the whole supply chain as possible flaws of products can occur at every stage of production.Apart from detecting spoilage, microbiological tests can also determine germ content, identify yeasts and molds, and salmonella. For salmonella, scientists are also developing rapid and portable technologies capable of identifying unique variants of Salmonella .

Food safety is a major focus of food microbiology involving the handling, preparation, and storage of food in ways that prevent foodborne illness.

Foodborne pathogens are the leading causes of illness and death in less developed countries killing approximately 1.8 million people developed countries foodborne pathogens are responsible for millions of cases of infectious gastrointestinal diseases each year, costing billions of dollars in medical care and lost productivity.

Polymerase Chain Reaction (PCR) is a quick and inexpensive method to generate numbers of copies of a DNA fragment at a specific band ("PCR (Polymerase Chain Reaction)," 2008). For that reason, scientists are using PCR to detect different kinds of viruses or bacteria, such as HIV and anthrax based on their unique DNA patterns. Various kits are commercially available to help in food pathogen nucleic acids extraction PCR detection, and differentiation. The detection of bacterial strands in food products is very important to everyone in the world, for it helps prevent the occurrence of food borne illness. Therefore, PCR is recognized as a DNA detector in order to amplify and trace the presence of pathogenic strands in different processed food

Factors Affecting Growth of Microorganisms

The food processor reduces potential problems from microorganisms in several ways:

·        Removing or destroying them by trimming, washing, heating, pickling, by adding chemicals, or by encouraging competition by acid- or alcohol-forming organisms.

·        Minimizing contamination from equipment, people, the environment, and from unprocessed food.

·        Minimizing microbial growth on equipment, by cleaning and sanitizing, and in the product itself by adjusting storage temperature, pH, and other environmental factors.

·        Although each factor affecting growth is considered separately in the following discussion, these factors occur simultaneously in nature. When more than one condition is somewhat adverse to microbial growth, their inhibitory effects are cumulative.


Temperature is the most efficient means to control microbial growth. Based on their tolerance of broad temperature ranges, microorganisms are roughly classified as follows:

Psychrophies grow only at refrigeration temperatures.

Psychrotrophs grow well at refrigeration temperatures, but better at room temperature.

Mesophiles grow best at or near human body temperature, but grow well at room temperature.

Thermophiles grow only at temperatures about as hot as the human hand can endure, and usually not at all at or below body temperature.

Some psychrotrophic microorganisms grow very slowly in foods below freezing, but usually not below 19°F. There are a few reports of growth, usually of molds, at 14°F, but no reliable reports of growth below that temperature. This means that the standard storage temperature for frozen foods, O°F, does not permit microbial growth. However, many microorganisms survive freezing (Michener and Elliott, 1964).

Most psychrotrophs have difficulty growing above 90°F.

Most foodborne disease organisms are mesophiles. The food processor can feel safe in the knowledge that foods held above or below the limits and rotated properly will remain safe. A good rule of thumb is to store perishable foods below 40°F or above 140°F.

In the temperature range where both mesophilic and psychrotrophic organisms grow (about 41°F. to about 90°F), the psychrotrophs grow more rapidly, causing spoilage and at the same time frequently interfering with the growth of foodborne disease organisms (Elliott and Michener, 1965).

Food Poisoning

Human illnesses caused by foodborne microorganisms are popularly referred to as food poisoning. The common use of a single classification is due primarily to similarities of symptoms of various food-related diseases.Apart from illness due to food allergy or food sensitivity, foodborne illness may be divided into two major classes, food infection and food intoxication. Food infection results when foods contaminated with pathogenic, invasive, food poisoning bacteria are eaten. These bacteria then proliferate in the human body and eventually cause illness. Food intoxication follows the ingestion of preformed toxic substances which accumulate during the growth of certain bacterial types in foods.

The period of time between the consumption of contaminated foods and the appearance of illness is called the incubation period. The incubation period can range anywhere from less than one hour to more than three days, depending on the causative organisms or the toxic product.

Characteristics of the important bacterial food intoxications and foodborne infections. (NAS-NRC, 1975)*


Etiologic Agent

Incubation Period



Clostridium botulinum A.B.E.F toxin

Usually 1 to 2 days; range 12 hours to more than 1 week

Difficulty in swalling, double vision, difficulty in speech. Occasionally nausea, vomiting, and diarrhea in early stages. Constipation and subnormal temperature. Respiration becomes difficult, often followed by death from paralysis of muscles of respiration.

Staphylococcal food poisoning

Staphyloccal enterotoxin

1 to 6 hours; average 3 hours

Nausea, vomiting, abdominal cramps, diarrhea, and acute prostration. Temperature subnormal during acute attack, may be elevated later. Rapid recovery-usually within 1 day.


Specific infection by Salmonellaspp.

Average about 18 hours; range 7 to 72 hours

Abdominal pains, diarrhea, chills, fever, frequent vomiting, prostration. Duration of illness: 1 day to 1 week.

Shigellosis (bacillary dysentery)

Shigella sonnei, s. flexneri, s. dysenteriae, s. boydii

Usually 24 to 48 hours; range 7 to 48 hours

Abdominal cramps, fever, chills, diarrhea, watery stool (frequently containing blood, mucus, or pus), spasm, headache, nausea, dehydration, prostration. Duration: a few days.

EnteropathogenicEscherichia coliinfection

Escherichia coliserotypes associated with infant and adult infections

Usually 10 to 12 hours; range 5 to 48 hours

Headache, malaise, fever, chills, diarrhea, vomiting, abdominal pain. Duration: a few days.

Clostridium perfringens food poisoning

Clostridium perfringens

Usually 10 to 12 hours; range 8 to 22 hours

Abdominal cramps and diarrhea, nausea, and malaise, vomiting very rare. Meat and poultry products usually involved. Rapid Recovery.

Bacillus cereusfood poisoning

Bacillus cereus

Usually about 12 hours; range about 8 to 16 hours

Similar to Clostridium perfringenspoisoning

Vibrio Parahaemolyticusfood poisoning

Vibrio Parahaemolyticus

Usually 12 to 14 hours; range 2 to 48 hours

Abdominal pain, server watery diarrhea, usually nausea and vomiting, mild fever, chills and headache. Duration: 2 to 5 days.