CHAPTER 2

UNDERSTANDING MICROORGANISMS

Definition of terms:
1. Pathogens - are disease causing microorganisms (bacteria, viruses, parasite and fungi)
2. Bacteria - single celled living micro organisms responsible for the decay of many plant
and animal diseases.
3. Virus - The smallest of the microbial food contaminants, viruses rely on a living host
to reproduce.
4. Parasite - An organism that needs a living host to survive.
5. Fungi - can be single celled or multi cellular microorganisms can that can cause food
spoilage and lives by absorbing nutrients from organic matter
6. pH - – potential of Hydrogen. A measure of the acidity or alkalinity of a
solution, numerically equal to 7 for neutral solutions, with increasing alkalinity and
decreasing with increasing acidity. The pH scale commonly in use ranges from 0 to 14.

7. Spore - The spore is formed by some bacteria, thickens walls to protect from adverse
condition such as extreme acidity and temperature.
8. Vegetative Stage - is a condition favorable for bacteria to grow and multiply rapidly.
9. Budding Reproduction - – a form of asexual reproduction where in new bud or bump is
formed from the mother cell.
10. Water Activity – The amount of moisture available in food for
microorganisms to grow.

BACTERIA
-Bacteria consist of only a single cell (unicellular)
-Bacteria reproduce through “binary fission” when one cell divides to form two new cells
-All bacteria exist in a vegetative stage
-Some bacteria has the ability to form a spore where they can survive in an adverse or extreme
conditions “spore forming bacteria”
-Bacteria are “photosynthetic”, they have the ability to make their own food through the use of the
sunlight, thus bacteria also gives off oxygen.
- An average bacterium measures 1 micrometer

Classification of Bacteria:
1. Spoilage Bacteria – where they breakdown foods so they look, taste and
smell bad. Thus, food is undesirable to eat and unacceptable.
2. Pathogenic Bacteria – are disease causing bacteria that can make people ill if
they or their toxins are consumed with foods.

Shapes of bacteria:
1. Coccus or Cocci – spherical shaped bacteria
2. Bacillus or bacilli – rod shaped bacteria
3. Spirilla - spiral shaped bacteria
 How they move?
• Bacteria use it’s “flagella”, a hair like appendages use to swim around.
• Some stick out thin, rigid spikes called “fimbriae” to help hold them
to surfaces.

4 Phases of Growth of Bacteria:

1. Lag Phase –bacteria adapt themselves to growth conditions. It is the period where
the individual bacteria are maturing and not yet able to divide.
2. Log Phase or Logarithmic Phase –“exponential phase” growth is
very rapid, doubling in numbers in every few minutes
3. Stationary Phase - the growth rate slows as a result of nutrient depletion
and accumulation of toxic products. This phase is reached as the
bacteria begin to exhaust the resources that are available to them.
4. Death or Decline Phase - bacteria run out of nutrients and die

6 Conditions Bacteria Needs to Grow and Multiply

1. Food
2. Acidity
3. Temperature
4. Time
5. Oxygen
6. Moisture

Food:
 Bacteria feed on Protein and Carbohydrates. Foods that contain these items
can support the growth of microorganisms
 Potentially Hazardous Foods have the potential for contamination, they have
the characteristics to allow microorganisms to grow and multiply.

Acidity:
 Bacteria grows best at a slightly acidic and slightly neutral environment (pH
4.6 to 7.5)
 Some bacteria can develop a “spore” such as acidophilic
bacteria, where it could grow
And multiply in an acidic environment
Time:
• Under ideal conditions, bacterial cells can double in number every 25 minutes
to 30 minutes.
• Pathogens starts to multiply in four hours at the Temp. Danger Zone
Temperature
• Temperature Danger Zone - temp. range 41F-140F (5C-60C). Food borne
bacteria grow and reproduce.
• Temperature Abuse –foods that have not been to a safe temperature or kept
at the proper temperature
• Psychrophilic bacteria – grow within the temperature range
of 32⁰F(0⁰C) – 70⁰F (21⁰C) (spoilage organisms)
• Mesophilic bacteria – grow at temp. 70⁰F(21⁰C) – 110⁰F(43⁰C)
• Thermophilic bacteria – grows best above 110⁰F (43⁰ C)

Oxygen
Bacteria differ in their oxygen requirement.

Anaerobic bacteria – cannot survive when oxygen is present bec. it is toxic to them.
Anaerobic bacteria grow well in vacuum packaged foods or canned foods where
oxygen is not available.
Aerobic bacteria – need oxygen to grow
Facultative anaerobic bacteria – can grow with or without free oxygen but have a preference
Microaerophilic organisms – can survive in a very little amount oxygen

Moisture
Moisture is important factor in bacterial growth. The amount of water available for bacterial
activity.
• Water Activity level – is the measure of the amount of water that is not
available for bacterial to grow. ( 0- 10)
• Potentially hazardous foods (PHF) – foods that have a water activity level of .85
or higher

**Bacteria remain alive and become potentially hazardous when moisture is added**
VIRUSES  Except viruses.
 Microbes are single-celled organisms • Viruses can’t metabolize nutrients,
that can perform the basic functions of produce and excrete wastes, move around on
life — metabolism, reproduction, and their own, or even reproduce unless they
adaptation. are inside another organism’s cells.
• They aren’t even cells.

• Viruses are the simplest and tiniest of microbes; they can be as much as 10,000
times smaller than bacteria.
• Viruses comes in many sizes and shapes
• Viruses consist of a small collection of genetic material (DNA or RNA)
encased in a protective protein coat called a capsid.
• Some may survive in freezing and cookin

PARASITE
• A parasite is an organism that lives by feeding upon another organism. Parasites
living in the human body feed on our cells, our energy, our blood, the food we eat and
even the supplements we take.
• There are several types of parasites: protozoa are single celled organisms that are
only visible under a microscope, while worms come in all sizes from threadworms,
that measure less than one centimeter, to tapeworms that grow up to 12 meters in
length.
• They grow naturally in many animals such as pigs, cats and rodents
• They can be killed by proper cooking or freezing
FUNGI
 Fungi are a group of organisms and micro-organisms that are classified
within their own kingdom, the fungal kingdom, as they are neither
plant nor animal.
 Fungi draw their nutrition from decaying organic matter, living plants and
even animals.
 Many play an important role in the natural cycle as decomposers and
return nutrients to the soil, they are not all destructive.
 Fungi usually reproduce without sex. Single-celled yeasts reproduce
asexually by budding.

Examples of Fungi are:

1) Mold
 Mold cause spoilage in food and could cause illnesses
 They grow under almost any conditions, but grow well in sweet, acidic
food with low water activity.
 Freezing temperatures prevent or reduce the growth of molds, but not
destroyed
 Some molds produce called “aflatoxins”
2) Yeasts
 Yeast also cause food spoilage
 Yeast spoilage produce a smell or taste of alcohol. They appear in pink
color discoloration
 They also grown well in sweet, acidic foods with low water activity level
such as jellies, honey and fruit juices.