summary.

1

This is module 2b, the Taxonomy, Role, and Significance of microorganisms in foods.

2

Raw food is not sterile. Here are a few close-up photos of some of the different microorganisms found in foods and water. At the top lieft is Escherichia coli, then moving clockwise is again e. coli, a Trichinella worm, Crytosporidium cyst, Hepatitis A, Teania worm, Trichinella worm mouth, Norovirus, and finally three mold colonies.

3

Most foods contain microorganisms. A few foods may have been processed in a manner that kills almost all microorganisms, such as commercial canning. But you may be surprised to know that even in commercially canned foods, some microorganisms are still present. We’ll discuss that in a later module. Basically, food microbiology deals with the two main concerns: Do the microorganisms cause illness and/or do the microorganisms cause spoilage? Naturally, a great deal of food microbiology is also PREVENTION of illness and spoilage.

4

Going one level deeper, food microbiologists would like to know what is total number of these organisms in food? What types of organisms are in the food? What organisms are in the environment around the food? And finally, how do we eliminate or minimize these organisms in foods or in food environments?

5

The microorganism’s role in nature is self-perpetuation. Their cellular machinery is built with that one goal in mind. On a larger scheme of things, microorganisms are an important symbiont with humans both internally and externally. Internally, we are outnumbered cell-for-cell by microorganisms. There are more microbial cells inside us than human cells. Humans are not exactly ruminants, but microbial biota play a vital role in human nutrition and digestion. Externally, microorganisms play a vital role in degrading materials back into their basic form. The old adage goes, imagine if microorganisms could not degrade trees back into carbon and nitrogen? Every tree that ever has grown would still be present on the planet.

6

There are five main groups of microorganisms: bacteria, yeasts, molds, protozoa, and viruses. These all contain DNA, with the exception of a few viruses that contain RNA. Prions are special organisms and it can be argued that they may not even be an organism. Prions contain no nucleic acids, but instead are made up of only protein. However, they still can infect, reproduce and cause illness.

7

Microorganisms are found in or on soil and water; plants & plant products; food utensils, animals, food handlers, and air or dust.

8

For the most part, soil is a harsh microbial environment. And, most microorganisms are growing very slowly or not at all. Living in the soil environment is very competitive by exclusion, inhibition, and nutrient limitation. Exclusion occurs when one microorganism outgrows another and overwhelms it. Inhibition occurs when one microorganism produces a byproduct that discourages growth of another. The classic example is mold produced antibiotics. However, it can be as simple as a fermentation microorganism producing excess lactic acid acidifying the environment. Nutrient limitation occurs when one microorganism consumes most or all of the available nutrient before others can use it to grow. An example is yeast can very quickly consume most sugars faster than most bacteria. They will grow quickly in a high sugar environment and be the dominant species.

9

Water is similar to soil in that it is nutritionally deficient. What carbon and nitrogen that makes it way into water is diluted by its shear volume. While soils throughout the planet have roughly the same temperature, water can vary from freezing to quite warm in tropical areas. Ocean water at its depths is quite cold even in the tropics. Therefore, we would expect to find many psychrotrophic (cold loving) microorganisms in water environments. Salt water in oceans also results in halotolerance or halophilia. Few gram positives can grow is salt water. Fresh water is the predominant habitat for the unicellular protozoan pathogens like Crytosporidium.

10

It might be assumed that all soil microorganisms colonize plants, but this is not the case. Only microorganisms that have an adhesion ability can survive on plants. Some of those can obtain nutrients from the plant tissue and can actually grow there. Fortunately, most foodborne illness bacteria do not colonize plants and are present only by chance. They also, for the most part, do not possess adherence properties or an ability to grow. Therefore, foodborne illness from plants is much smaller that it could be.

11

Animals are highly colonized by microorganisms. They have biota on their skins and hides, throughout their intestinal system, and in their environments. Occasionally animal tissue is parasitized by worms, but for the most part intact tissue is sterile. Most animals have warmer temperatures like humans. We find that many intestinal microorganisms have adapted to those warmer temperatures and grow best under those conditions. It is interesting to note that human intestinal tracts are also warm and we find the greatest number of foodborne illness pathogens are intestinal in origin. Living the way animals do, often intestinal biota and pathogens are spread throughout their environments via manure.

12

Humans are very similar to animals as a microbial environment. We have warm environment skin and intestinal biota. Our skin surface is made up of many species. One pathogen, Staphylococcus aureus can be found as a skin resident on as many as 30% of humans. The intestines can also harbor thousands of species including many of the potential foodborne illness microorganisms. Humans via feces can transfer these to food and then to others.

13

14

Bat Guano

15

Particulates in air can harbor and transport microorganisms. However, they are always in transit and relatively no growth occurs there. In most cases air or dust contains spores of molds and sometimes cysts of protozoans. As air contains more moisture, a few bacteria, mainly gram positives can be transported. Dust or accumulations of solids can harbor almost any microorganism that can survive the dry conditions.