Temperature effects on pathogenic microorganisms

Temperature is a key parameter in bio-control of vegetable foods, since it has a direct influence in microbial growth.

When considering the relationship of temperature to microbial life, two things must be considered: the holding temperature of the micro-organism and the length of time for which microorganisms are exposed to that temperature.

Most pathogenic microorganisms prefer temperature below 42 °C because they normally live at the body temperatures of man and animal or the air temperature experienced by plants. Some types of micro-organisms prefer either extremely cold or hot environments.

Cold temperatures often significantly slow the growth of microorganisms, which is the reason refrigeration is used to control bacterial growth.

In natural environments where micro-organisms are commonly subject to rapid changes in temperature, it is perks not surprising that they have evolved protection mechanisms.

E. coli, for example, synthesize cold shock proteins in response to a temperature down shift.

Researchers reported that, under certain conditions moderately cold storage temperature (-2 to -4 °C) resulted greatly in greater destruction of bacteria than storage at -20 C.

When cells are frozen rapidly, both intra- and extracellular fluid are freezes. Slow freezing, however, causes an intra and extracellular osmotic gradient, which can result in cellular disruption.

High temperatures usually kill most microorganisms. Steam sterilization and boiling water are two common techniques used to kill pathogenic microorganisms.
Temperature effects on pathogenic microorganisms

Foodborne Pathogens

A pathogen is an organism that is able to cause cellular damage by establishing in tissue, which results in clinical signs with an outcome of either morbidity or mortality.

Many foodborne bacterial pathogens can cause invasive disease in addition to acute gastrointestinal symptoms, such as diarrhea and vomiting.

Infection with some foodborne pathogens can be followed by chronic sequelae or disability. Yersinia enterocolitica infection can cause reactive arthritis.

Common foodborne pathogens include:
Bacillus cereus
Campylobacter jejuni
Clostridium botulinum
Clostridium perfringens
Cryptosporidium parvum
Escherichia coli 0157:H7
Giardia lamblia
Hepatitis A
Listeria monocytogenes
Norwalk, Norwalk like or norovirus
Salmonellosis
Staphylococcus
Shigella
Toxoplasma gondii
Vibrio Yersiniosis

Poverty, competition for food, crowding, war, famine and natural disaster help pathogens to survive and spread in the environment.

Domestication of animals also allowed pathogens to come into contact with humans and thus, acquires a new host.

The complexity of the global food market means that the control of foodborne disease is a joint responsibility and requires action at all levels from the individual to international groups, and at all parts of the supply chain from the farm to the fast food restaurants.

Careful quality control in the food industry is essential for preventing outbreaks of foodborne disease and for controlling food spoilage.

Many foods are routinely examined for the presence-causing and food spoilage microorganism.

There are key principles developed by the WHO:
*Keep clean
*Separate raw and cooked
*Cook thoroughly
*Keep food at safe temperatures
*Use safe water and raw materials
Foodborne Pathogens

What is cross contamination of food?

Food-borne illnesses are often caused by cross –contamination. Cross contamination is the transfer of harmful bacteria from one food to another. It takes space when pathogens are transferred between food, surfaces or equipment.

Contaminants that are of primary concern to food manufacturers are pathogen bacteria, viruses and food allergens.

While most cross-contamination cases occur in the back-of-the-house, servers can cause this situation as well.

An example of this is using the same cutting board to cut salad tomatoes and to slice raw chicken. Other example: food containing allergens is not cleaned off equipment properly and the allergens then contaminate a product that is supposed to be allergen free.

Cross contamination is most likely to happen when:
*raw food touches or direct contact a high risk food – this is direct contamination
*Liquid or juices from a raw food drip on to a high risk food - this is indirect contamination or drip contamination
*Bacteria are carried by hands or utensils form a raw food to a high risk food – this is indirect contamination.

Illness will result of the newly contaminated food item is not cooked thoroughly before service. 

Cross-contamination can occur in manufacturing plants, grocery stores, restaurants and in the home.

How to avoid cross-contamination?
*Properly store raw food below ready-to-eat food
*Never mix food products when restocking
*Have separate preparation areas for raw and cooked items
*Properly clean and sanitize utensil, equipment and surfaces
*Clean and sanitize work areas when changing from food preparation
*Ensuring food is properly covered during storage
What is cross contamination of food?

Pathogenic microorganisms

In the food industry, bacteria colonizing the processing equipments are a potential source of food contamination by spoilage or pathogenic microorganisms.

Foods may considered to be microbiologically unsafe owing to the presence of microorganisms which may invade the body (such as Salmonella,. Listeria, E. coli) or those which produce a toxin ingested with food (e.g. Clostridium botulinum, Staphylococcus aureus and Bacillus cereus).

There are six types of microorganism that can contaminate food bacteria, viruses, parasites, toxins, yeasts and molds.

The first four are considered pathogenic microorganisms meaning they can cause illness when ingested.

These can be present in food simply because they are part of the natural environment.

The two main features of pathogenic microorganisms that elicit their disease causing mechanism are:
*ability to invade tissues
*ability to produce toxins.

In the former cases, invasiveness encompass mechanism for colonization, for bypassing of host defense and for production of extracellular compounds which facilitates invasion.

The food contains a rich medium for bacterial growth; protein, fat, carbohydrates, minerals vitamins and a high percentage of water it an excellent substrate for growing of bacteria including pathogenic bacteria that can be in the environment and prosperous medium for enzymatic activity.

Pathogenic microorganisms