Sources Of Microorganisms
In Foods
Prof. Mohammad Shubair
Microorganisms get into food from both
natural sources and from external sources to
which a food comes into contact from the time
of production until the time of consumption.
 Natural sources for foods of animal origin
include skin, hairs, feathers, gastrointestinal
tract, urogenital tract, respiratory tract, milk
ducts(teat canal) in udders of milk animals.
Natural micro-flora exist in ecological balance
with their hosts, and their types and levels vary
greatly with the types of plants and animals as
well as their geographical locations and
environmental conditions.
Besides natural microorganisms, foods can be
contaminated with different types of
microorganisms coming from outside sources
such as: air- soil- sewage- water- feedshuman- food ingredients- equipmentpackages- insects
Microbial types and their levels from
these sources getting into foods vary
widely and depend on the degree of
sanitation used during the handling of
foods.
Predominant Microorganisms In
Different Sources
 Plants( Fruits and Vegetables)
• The inside tissue of foods from plant sources are
essentially sterile except for few porous vegetables(
radishes, onion, cabbage).
• Some plants produce natural antimicrobial metabolites
that can limit the presence of microorganisms.
• Fruits and vegetables harbor microorganisms on the
surface ; their types and level vary with:
soil condition, type of fertilizer, water used,
air quality.
Examples of Microorganisms In Plants
 Molds, Yeasts, lactic acid bacteria,Pseudomonas,
Alcaligenes, Micrococcus, Erwinia, Bacillus,
Clostridium, Enterobacter.
 Pathogens like enteric types can be present if the
soil is contaminated with untreated sewage.
Factors increasing the number of
microorganisms in plants:
- Diseases of the plant, damage of the surface, long
delay between harvesting and washing,
unfavorable storage and transport before
processing and improper storage after processing
Reduction of Microbial Load In Foods Of
Plant Origin
• Use of treated sewage for fertilizers
• Damage reduction during harvesting
• Quick washing with good quality water to
remove soil and dirt.
• Storage at low temperature before and
after processing.
Animals, Birds, Fish and Shellfish
• Food animals and birds normally carry many
types of indigenous microorganisms in
gastrointestinal tract, respiratory tract, urogenital
tract and teat canal in the udder as well as in
skin, hooves, hair and feathers.
• The number of these microorganisms depends on
the specific organ e.g. in large intestine >1010/g.
• Many animals act as carriers, they can harbor
pathogens like S. aureus, E. coli, Campylobacter,
and Listeria without showing symptoms.
• Laying birds may carry S. enteritidis in the ovaries.
• Fish and shellfish carry normal flora in the scales,
skin and digestive tracts. They can also carry
pathogenic bacteria e.g. V. parahaemolyticus .
• Many spoilage and pathogenic microorganisms
can get into foods of animal origin (milk, egg,
meat, fishery products) during production and
processing.
• Milk can be contaminated with fecal materials on
the udder surface.
• Meat can be contaminated with intestinal
contents during slaughtering.
• Meat from food animals and birds can be
contaminated with several spoilage and
pathogenic microorganisms from skin, hair
and feathers e.g. S. aureus, Micrococcus,
Propionibacterium, Corynebacterium, Molds
and Yeasts.
Prevention Of Food Contamination
From Animal Sources
 Good housing and supply of uncontaminated feed
and water.
 Testing animals and birds for pathogens and
culling the carriers.
 Using good quality water for washing the carcases.
 Hair removal.
 Removal of Contaminated parts
 Proper cleaning of the udder before milking
Cooling milk immediately after milking and
processing .
Collection of eggs quickely after laying.
Fish and marine products should be harvested
from unpolluted water, and stored properly.
AIR
Microorganisms are present in dust and
moisture droplets in the air.
Microorganisms do not grow in dust.
Microorganisms in air are transient and variable
depending on the environment.
 Level of Microorganisms in air is controlled by:
• The degree of humidity, Size, Level of dust
particles, Temperature, Air velocity and
Resistance to drying .
• Dry air with low dust content and higher
temperature has a low microbial level.
Examples Of Microorganisms Present In
Air
•
•
•
•
Spores of Bacillus Spp.
Clostridium Spp.
Molds and Yeasts
Cells of Gram Positive Bacteria e.g. Micrococcus and
Sarcina
 If the surroundings contain a source of pathogens e.g.
animal and poultry farms or a sewage treatment
plant, different types of bacteria including pathogens
and viruses can be transmitted via air.
 Control Measures:
• Removing potential sources, Air filtration, Reducing
humidity, Installing ultra violet lamps.
Soil
• Soil used to grow agricultural produce and raise animals
and birds contains several varieties of microorganisms.
• Microorganisms can multiply in soil and their numbers
can be very high(billions/g).
 Microorganisms Found In Soil:
• Molds and Yeasts, Enterococcus, Bacillus, Clostridium,
Enterobacter, pseudomonas, Proteus, Micrococcus and
Parasites.
• Soil contaminated with fecal materials can be the in
foods. source of enteric pathogens and viruses
Sewage
Sewage can contaminate crops with
microorganisms when it is used as fertilizer
e.g. enteropathogenic bacteria, viruses and
parasites.
Sewage should be treated before using as
fertilizer to kill pathogens.
Effective washing of foods following
harvesting is important.
Water
• Contamination of foods with pathogenic bacteria ,
viruses and parasites has been recorded.
• Waste water can be recycled for irrigation.
• Potable water may contain bacteria capable of
causing food spoilage such as Pseudomonas,
Alcaligenes, flavobacterium.
• Improperly treated water can contain pathogenic and
spoilage microorganisms.
• Water used in food processing should be of higher
microbial quality than that of potable water.
Humans
Between production and consumption, foods
come in contact with different people handling
the foods, they include:
• People working in farms
• People working in processing plants.
• People handling food in restaurants
• People in retail stores and at home.
• Human carriers have been a source of
pathogenic microorganisms in food.
Major Sources Of Microbial Contamination
Of Foods By Humans
• Improperly cleaned hands.
• Lack of aesthetic sense and personal
hygiene.
• Dirty clothes and hair.
• Presence of minor cuts and infection in
hands and face.
• Diseases(Influenza, Throat infection,
Hepatitis A and others).
• Pathogens such as S. aureus, Salmonella,
Shigella, Pathogenic E. coli, Hepatitis A can be
introduced into food from human sources.
Control Measures:
• Proper training of personnel in personal
hygiene.
• Regular checking of health
• Maintaining efficient sanitary and aesthetic
standards.
Food Ingredients
 Many ingredients can be the source of
spoilage and pathogenic microorganisms
• e.g. Spices have very high populations of
mold and bacterial spores
The ingredients should be produced under
sanitary conditions.
Setting up acceptable microbial
specifications for the ingredients.
Equipment
Equipment can be a source of contamination
• Many microorganisms can get in food from
equipment e.g Salmonella, Listeria, Enteric
bacteria, Micrococcus, Escherichia,
Pseudomonas, Lactobacillus, Leuconostoc,
Clostridia, Bacillus, Yeast and Molds.
• Proper cleaning and sanitation of equipment
should be emphasized.
Miscellaneous
•
•
•
•
•
•
•
•
•
Food might be contaminated from other sources;
Packaging and Wrapping materials
Containers
Flies
Vermins
Birds
House pets
Rodents
Proper care should be taken not to contaminate
food from these sources.