Introduction to
Food Microbiology
 This course is intended to provide Medical Laboratory Science
students with basic techniques for food microbiology laboratory
in accordance with standard methods for qualitative and
quantitative detection of microorganisms in food and water.
 Those microorganisms important in the food industry include the
bacteria, viruses, yeasts, molds, and protozoans.
 Isolation of and identification of microbial food contaminants
help to understand how infectious agents enter and spread
through the food chain and therefore come up to with
procedures to prevent or minimize exposure of the consumer to
such agents.
 Many are helpful and serve useful functions such as causing
breads to rise, fermenting sugars to alcohol, assisting in the
production of cheese from milk, and decaying organic matter to
replenish nutrients in the soil. Microorganisms can also cause
foods to spoil and make them inedible.
Reasons for microbial food analysis

To meet certain set of standards.

To estimate the shelf-life of the product.

To determine quality of the food.

For public health purposes.
What are the organisms that you look
for ?

Indicator organism(s)

An indicator organism or group of organisms is one whose numbers in a
product reflect the success or failure of GMP "Good Manufacturing
Practices".

Coliform group of microorganisms and Escherichia coli are commonly used
as indicator organisms.

Index organism

An index organism is one whose presence implies the possible
occurrence of a similar but pathogenic organism.

E. coli is used an index organism and its presence indicates
possible presence of pathogenic Enterobacteriacea
e.g. Salmonella sp.

Food borne pathogens
There are two types of food borne pathogens:
1.
Those which cause infection; must grow in food in large numbers and cause
infection when consumed together with food.
 The most common microorganisms in this category includes Salmonella
typhimurium, enteropathogenic E. coli, Vibrio parahaemolyticus, Yersinia
enterocolytica.
2.
Those which cause intoxication must grow in food in large
numbers and produce enough toxin and when consumed
together with food cause intoxication.
The most common microorganisms in this category includes,
Clostridium botulinum, Staphylococcus aureus and toxigenic
fungi e.g. Aspergillus flavus.

Infectious organisms

Spoilage organisms
Organisms whose presence in small numbers in food or water and when consumed
can cause infection.
In this case, the food acts as a vector but not necessarily as a growth medium.
Infectious organisms can be transmitted by various ways including man to man
and are said to be contagious.
• Organisms in this group includes: Vibrio cholerae O1, Salmonella typhi, Shigella
sonnei, Bacillus anthracis, Hepatitis B virus etc
 Spoilage organisms are the organisms whose growth in the food creates
undesirable characteristics in that food.
Any microorganism which is not intentionally added into food or intentionally
allowed to grow in food so as to impart certain qualities in that food is considered
a contaminant.
Growth of the contaminant in that food will spoil the food making it unfit for
human consumption.
• Some useful microorganisms e.g. lactic acid bacteria are considered as spoilage
organisms when in beer, wine and fruit juices but not in milk.
How to analyze ?

Quantitative analysis

Serial decimal dilution, Aerobic plate count, Pour plate count.

Total viable count.

Most Probable Number (MPN) method.

Yeast and Molds count.
 Qualitative analysis
Presence or absence of a specified microorganism e.g.:

Salmonella spp.

E. coli O157:H7

V. cholerae O1
Culture methods

Pre-enrichment, broth enrichment, broth selective, enrichment
selective agar, Differential agar.

Biochemical tests: Sugar fermentation, Amino acid decarboxylation,
gelatin liquefaction lecithinase production.

Serology: Agglutination precipitin coagulation.

Colony morphology: shape, color, texture, size.

Cell shape by microscope: Bacillus coccus streptococcus.

Gram stain characteristics: Gram positive, gram negative.

Motility: Motile; Number of flagella arrangement, non-motile.
Laboratory Safety Rules

In the food microbiology laboratory infectious materials are processed
as many of the microorganisms used in this course may be pathogenic for
humans .

Equipment, biological agents and chemicals can pose safety hazards to you
if you do not follow laboratory protocols.

As a result, certain rules are necessary to prevent the spread of
infectious agents, the possibility of infecting yourself or other people and
to prevent contamination of specimen with environmental microorganisms.
Safety in a microbiology laboratory starts with
protecting yourself:
Cover long hair or keep it tied up and out of way.
Always wearing closed shoes.
Wearing personal protective equipment (coat, gloves, eye protection; glasses
arepreferred).
Never applying cosmetics, or placing objects (fingers, pencils) in the mouth
or touching the face.
Never eating, drinking or chewing gum in the laboratory.
Washing hands prior and after lab working with water and soap.
Keep the lab bench free of unnecessary materials.
Disinfecting lab benches prior to and at the conclusion of each lab session.
Good lab practice, including methods for aseptic transfer, returning
materials to proper locations,
proper care and handling of equipment, and Keeping the bench top clear of
extraneous materials.
Dispose all contaminated materials in autoclave bags and proper disposal of other
different types of waste.
The coats should be kept separately from other things in your bag.
Reporting all injuries, accidents, spills and broken glassware to the instructor and
receiving instructions for cleanup.
Always using appropriate pipetting devices and understanding that mouth pipetting
is forbidden.
Using universal precautions posted in the lab and see inside front cover of this
laboratory manual.
Read all assigned materials before the lab session.
Never lick your fingers, or put your fingers in your mouth. No mouth pipetting.
Pick up any sharps, including broken glass with forceps and place in sharps
container.
Remove gloves and shoes cover before removing area of the spill, put on biohazard
bag.
Laboratory requirments

Lab coat

Matches or lighter

Soap

Waterproof permanent marker

Small or medium size towel

Sealable plastic bag

Rubber band

General Food Microbiology Manual