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Friday, 16 November 2018

November 16, 2018

Micro organisms in Food






Food is an idea medium in which many micro organisms readily grow and multiply. The characteristics of a given food such as nutrient content, water content, pH and osmotic pressure determine the type of micro organisms that grow and multiply in it. Food readily becomes contaminated by

• animals like flies , cockroaches and rats;

• dirty utensils and equipment; and

• unhygienic habits of the people who handle.

Micro organisms in contaminated food multiply rapidly if the food is

•kept at temperatures between 20 to 35°C, 

• not cooked long enough to kill micro organisms and their spores, and to break down their toxins.

    When we eat contaminated food, we tend to get diseases that affect the alimentary canal. Food poisoning is a very common illness associated with eating contaminated food. This gives the common pathogenic micro organisms that contaminate food.
November 16, 2018

Pathogenic Micro organisms in the Body






Pathogenic micro organisms usually establish themselves in our bodies and cause diseases

• when the body resistance is low;

• when the normal microflora in the body is disrupted by antibiotic therapy; and

• in infants where the normal microflora is not established yet.

    The following conditions lower the body's ability to twist or fight against pathogens:

• malnutrition;

• stress and overwork;

• harmful habits like smoking and drinking; and

• environmental pollution.


How micro organisms enter the body 

      The various ways In which and places through which pathogenic micro organisms enter the body are as follows:

• Through cuts, wounds and abrasions on the skin, e.g Clostridium tetani (found in soul) which causes tetanus

• Through the nose and mouth, e.g. influenza virus

• Through the mouth and oesophagus, e.g. entamoeba histolytica which causes amoebic dysentery

• Through direct contact, e.g. ringworm fungi and the spirochaete which causes syphilis


How pathogens harm the body:

Pathogenic micro organisms harm the body

• by using the Host's nutrients for their own growth and reproduction and thus starving the host tissue's;

• by destroying or damaging the tissues of the affected part of the body;

• by producing toxins or poisons which affect the functioning of a particular organ or system in the body. (Toxins are produced as waste products by micro organisms)


November 16, 2018

Carriers of Micro organisms





Air , water and food are non living agents that carry micro organisms from one place to another. Animals are the living agents that carry micro organisms from place to place. The animals that carry pathogenic micro organisms are known as vectors. Important vector include

• insects like house flies , cockroaches, fleas, mosquitoes and tsetse flies, and 

• other animals like rats , dogs and cats.

    Anal vectors may carry micro organisms from place to place or from person to person mechanically or biologically.

Mechanical Method:

In this method, the animals vector carry pathogens on their bodies. The pathogens are merely carried passively, they do not grow or multiply on the body of the vector. These animal vectors usually breed and live in filthy places like rubbish heaps, faeces and drains. They like to feed on our food and so contaminate it. The housefly with its hairy sticky body and filthy habit is an idea vector that carries pathogens mechanically. Pathogens carried in this way include shigella sp. , salmonella enteriditis, salmonella typhi  vibrio cholerae and entamoeba histolytica.


Biological method:

In this method, the vector becomes infected by feeding on the body fluid (e.g blood) of an infected person or animal. The pathogens develops and multiplies in the body of the vector. Latter  , the vector infects a healthy person while feeding on his/her body fluids.

    In the biological method, a part of the life cycle of the pathogen takes place In  the  body of the vector. Many viruses and pathogenic protozoa are carried biologically by insect  vectors e.g.

• Aedes mosquito carried the virus that causes fever , and • tsetse fly carried the protozoan, trypanosoma, which causes sleeping sickness in humans.

November 16, 2018

Micro organisms in Our Body and Food





Normal microflora in the body

Micro organisms start to colonize the body of a human infant just a few hours after birth. By the time the infant becomes an adult, numerous bacteria, yeasts and protozoa are established on and in the body. These are known as the normal microflora of the human body.

     Examples of the normal microflora on and in the body of a healthy adult. These play the following Important roles:

• they prevent or interfere with the invasion of the body by pathogens. They do this by physically occupying the  surfaces on and in the body. They produce substances which interfere with the survival or multiplication of certain pathogens.

• they become pathogenic when the Host's resistance becomes low. For example , the spirilliae commonly found in the mouth becomes pathogenic and causes throat infection in women with anaemia.

   Many micro organisms which are non pathogenic in their nature environment in the human body becomes pathogenic when they move to a different environment in the body. For example, E. Coli normally found in the colon, causes urinary tract infections.
November 16, 2018

Micro Organisms in Water





Unlike the atmosphere, aquatic environment are rich in both organic and inorganic nutrients. The various aquatic environments like wells, ponds, lakes, streams, rivers and seas support a wide variety of bacteria, blue green algae, protists, algae and fungi. These micro organisms, commonly known as plankton, make up a large proportion of the total biomass of aquatic environments.

    Micro organisms found in water may be grouped into

• natural water micro organisms,

• soil micro organisms (washed into the surrounding water bodies during heavy rains) , and

• sewage micro organisms.

    Natural water micro organisms flourish in waters free from gross pollution. They include the following:

• Bacteria: These include aquatic species of coccus, bacillus, pseudomonas, azotobacter, thiobacillus, sarcina, micrococcus, vibrio, spurillum and epirochaeta. Most of these bacteria are heterotrophic, although there is also a significant number of Autotrophic and chemotrophic bacteria.

• blue green algae: these include oscillatoria, Nostoc and anabaena.

• protist: these include the autotrophic diatoms, dinoflagellates, chlamydomonas, chlorella and certain species of euglena, and the heterotrophic amoeba and paramecium.

• Algae: these include green algae, like Spirogyra and volvox, which often form a thick green floating scum near the shore of ponds. Together with the autotrophic protists, especially the diatoms, algae are the main primary producers in aquatic environments.

• fungi : aquatic fungi are primitive, belonging to the same class as moulds and mildews.

   Most soil and sewage micro organisms that find their way into water bodies die off eventually as they cannot reproduce  successfully in these habitats. Soil micro organisms include nitrifying and nitrogen fixing bacteria, streptomyces and certain fungi. Sewage micro organisms include

• Coliform micro organisms, I.e organisms found in intestines of vertebrates; and

• decomposers of organic matter of plant and animal origin.

Coliform micro organisms include viruses like enteroviruses and adenoviruses; non pathogenic bacteria like Escherichia coli, streptococcus faecalis and clostridium welchii; pathogenic bacteria like vibrio cholerae and salmonella typhi; and pathogenic protozoa like entamoeba histolytica.

Thursday, 15 November 2018

November 15, 2018

Identification of Micro Organisms


We use several techniques to identify micro organisms. These include the following:

• Observing the form and structure of micro organisms through a microscope. A light micro scope (magnification 1000x) may be used in the case of most micro organisms. The form and structure of viruses, however, can only be studied through an electron microscope (magnification 1000 000 X)

• Staining micro organisms with various types of stains and observing their reactions through the microscope. Simple stains like methylene blue and crystal violet bring out the size, shape and cell arrangements of the micro organisms. Differential stains bring out structures like flagella, capsules and spores. An important differential stain  is the Gram's stain. It divides bacteria into two groups: purple gram positive bacteria and red gram negative bacteria.

• Characteristics of colonies formed on various types of culture media.

• Oxygen requirement of of micro organisms, especially bacteria. Those that require oxygen are aerobes and those that can only grow and multiply in the absence of oxygen are known as obligate anaerobes. Many, however, can grow in the presence or absence of oxygen and are known ad facultative anaerobes. Anaerobes can form colonies within the nutrient agar medium, and not just on the surface.

• Biochemical tests to determine the activities of micro organisms, thus helping to identify those that look very similar. A common biochemical test is the fermentation of simple sugars to produce had and acids.

       The general properties of some virus groups that infect animals. It helps to identify the main groups of bacteria that are found in our environment. An example of a blue alga is Nostoc found in moist soil. Protists include

• plant like unicellular organisms like diatoms, chlorella and chlamydomonas, and 

• animal like ones like amoeba, paramecium, trypanosoma and plasmodium.

Common fungal micro organisms are the moulds and yeasts. Algae include Spirogyra and volvox.
November 15, 2018

Micro Organisms in Air






Micro organisms do not grow in air. However, dust and water droplets in air contain micro organisms. Spores produced by micro organisms are light and easily dispersed by air movements away from their sources of production. When these spores land on suitable substrates, they germinate, multiply and produce more spores. Nutrient agar exposed to air, shows the growth of various types of colonies of bacteria and fungi. Common micro organisms found in air are as follows:

• Virus : common cold virus, influenza virus, polio virus, poxvirus, measles Virus

• Bacteria : pneumococci, staphylococci , streptococci, bacillus anthracis (causes anthrax), mycobacterium tuberculosis (causes tuberculosis in humans) 

• Fungi : penicillium (blue green mould) , aspergilus, rhizopus nigricans (black or bread mould) , saccromyces (yeast).