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General Microbiology


Lecture One


What is Microbiology?
In the broadest sense, microbiology is the study of all organisms that are invisible to the naked eye such as bacteria and viruses
However in practice microbiologists in the food industry are often examining larger small organisms such as nematodes and fungi and insect parts.
How Large are Microbes?
Most bacteria are around 1 micrometer (µm) also called a micron (µ) in diameter.
There are however larger microbes such as Yeast, Mold, Algae and Protozoa have an average width of 10 µ
Smaller microbes can be much smaller: from larger pox viruses at about 0.1 µ to small foot and mouth viruses at 0.01µ diameter.
Even smaller microbes exist than this with Viroids being less than 0.001 µ in fact single molecules of RNA
Much smaller again are the Prions that are simply single protein molecules
There are 1 million micron (µ) in a meter,
1000 nanometres (nm) in a micrometer
and therefore there are 1 billion nm in a meter.
The major groups of microbes:

The major groups of microbes are the Bacteria, Archaea, Viruses, Viroids, Prions, Fungi, Algae, Protozoa, and small animals such as Helminths (worms) and Mites

One of the first things to realise about the microbial world is that microorganisms are everywhere. Almost every natural surface is colonised by microbes (including your skin). Some microorganisms can live quite happily in boiling hot springs, whereas others form complex microbial communities in frozen sea ice.

Most microorganisms are harmless to humans. You swallow millions of bacteria every day with no ill effects. In fact, we are dependent on microbes to help us digest our food and to protect our bodies from pathogens. Microbes also are essential to keep the biosphere running by carrying out essential functions that recycle the elements needed for our survival such as decomposition of dead animals and plants to release CO2 and the fixing of Nitrogen and Sulfur.

Microbes are the most abundant form of life on Earth. More than half the biomass on this planet consists of microorganisms; animals on the other hand constitute only 15% of the mass of living organisms on Earth.
Note that microbes come in many shapes and sizes; some of them can even form large visible structures such as mushrooms. Learn more about microbial diversity by visiting the Microbe Zoo on the MSU web page.

Microbes are important in regard to food for both positive and negative effects:

Good: Bacteria are important in supplying nutrients to plants and helping digestion in animals Intestinal bacteria assist protection from food borne disease

Intestinal bacteria provide us with vitamins and other essential nutrients

Bacteria are used in food fermentations to process food

Microbes can be used as a form of food as biomass

Bad: Microbes are a significant cause of food borne disease Microbial Food spoilage wastes about a third of the wolds food production

Food spoilage is a constant problem in food preservation.


 Useful Links:

William Angliss Institute
Nutrition Australia
American Society for Microbiology 
Barry Brazier 
The Institute of Food Technologists 
About Melbourne