MICROBIOLOGY QUICK LEARNFood MicrobiologyBACTERIA- Cultural Characteristics of Bacteria 

1. MICROBIOLOGY QUICK LEARN
FOOD MICROBIOLOGY
BACTERIA- CULTURALCHARACTERISTICS OF BACTERIA
Saajida Sultaana Mahusook

2. BACTERIA
Morphology
• Bacteria are unicellular organisms ranging in size from 0.5- to 5.0 µm.
• They are also known as prokaryotes as they do not possess true nuclei.
Their chromosome is composed of a single closed double-stranded DNA
circle called nucleoid.
• Structurally, a prokaryotic cell has cell wall, plasma membrane,
appendages such as flagella and pili (or fimbriae), and a cytoplasmic
region that contains the cell genome, ribosomes and various sorts of
inclusions.

3. Bacteria in Food Microbiology
• Bacteria are the most abundant of all organisms and
reproduce asexually.
• Bacteria are important members in Food Microbiology.
• Some bacterial species are
• capable of causing illness and food spoilage,
• there are also beneficial species that are essential to good health
(examples: synthesize vitamins, antibiotics, act as probiotic etc.)
and the environment.
• Every bacterial species have specific nutritional
requirements, temperature, pH, humidity, etc. for energy
generation and cellular biosynthesis.
• The bacterial cells divide at a constant rate depending
upon the composition of the growth medium, incubation
conditions and under favorable conditions.

4. Cultural Characteristics of Bacteria
Morphological Characteristics
• One of the basic steps in the identification of bacteria in food is done by
observing the microscopic characters such as size, shape, aggregation,
structure and staining reactions.
• The following characters are also important:
Encapsulation:
The presence of capsules or slime may contribute to sliminess or
ropiness of food. Capsules are composed of mainly polysaccharides of dextrin,
dextran or levan. Capsule makes the bacteria resistant to adverse conditions,
such as heat and chemicals and also a source of reserved nutrients.
Capsulated bacteria
under microscopesliminess of milk

5. Endospores:
• Bacteria of the genera Bacillus, Clostridium,
Desulfotomaculum, Sporolacto-bacillus and Sporosarcina have
the ability to form endospores. Vegetative cells form spores
under adverse conditions as a means of survival. Endospores
preserve the bacteria from starvation, drying, freezing,
chemicals, and heat. When favorable conditions return, the
spores germinate, becoming a vegetative cell with the ability to
reproduce.
Cell aggregates:
• Some bacteria form cell aggregates such as long chains or
form clumps under certain conditions. It is difficult to kill all the
bacteria when they exist as aggregates of cells than to destroy
separate cells.

6. Cultural Characteristics
• Bacterial growth in or on food makes the food unattractive
or objectionable to consume.
• Pigmented bacteria cause discolorations on the surface of
food, form films that cover the surface of liquids; make the
surface slimy or extensive growth in liquid cause
undesirable cloudiness or sediments.

7. Physiological Characteristics
• The growth and activity of bacteria on food accompanies
certain chemical reactions.
• The chemical changes include hydrolysis of complex
carbohydrates to simple ones;
• hydrolysis of proteins to polypeptides, amino acids, and
ammonia or amines;
• hydrolysis of fats to glycerol and fatty acids.
• Oxidation-Reduction reactions, which are utilized by bacteria to
obtain energy from foods (carbohydrates, other carbon
compounds, simple nitrogen- carbon compounds, etc.), yield
products such as organic acids, alcohols, aldehydes, ketones
and gases.
• It is important to know the factors that favor or inhibit the
growth and activity of bacteria is essential for understanding
the basic principles of food preservation and spoilage.

8. Reference
• Food Microbiology by Martin R. Adams and Maurice O.
Moss, 3rd e.
• Food Microbiology by William C. Frazier and Dannis C.
Westhoff, 5th e.