A complete knowledge of food contamination for B.Sc and M.Sc microbiology student

1. Dr. Priyanka Ghosh (PhD)
Contamination of food

2. Green Plants and Fruits
 Natural surface flora of plants varies with plants, like
Pseudomonas, Alcaligens, Flavobacterium,
Micrococcus, coliform and Lactic acid bacteria.
 The no. of bacteria will depend on the plant and its
environment and may ranges from few 100/1000 per
square centimeter of surface to million.
 Unwashed tomato contain 1000 microorganisms where
washed tomato show 400-700/2cm.
 Exposed surfaces of plants become contaminated by
soil, water, sewage, air and animals.
 Some fruits have been found to contain viable
microorganisms in their interior. Yeasts have been found
inside undamaged fruits, also found in healthy roots and
tuber vegetables.

3. Animals:
 Microbes are present in animals as - surface flora,
flora of respiratory tract, flora of gastrointestinal
tract.
 Feather and foot of poultry carry heavy
contamination from soil, manure, feed and water
 Staphylococci present in respiratory tract.
 Micrococci, beta-hemolytic streptococci present in
skin of many meat animals.
 Feces and fecal contaminated products of animals
contain enteric organisms including Salmonella
and cause Salmonellosis.

4. Pig and beef contaminated by Salmonella. As further it is
processed and handling aseptic way so these organisms may less
causes salmonellosis in human.
Egg and egg products also may cause Salmonellosis but now
pasteurization of egg product controlled these issues.
Animal Human
Food
List of organisms:
Brucella, Mycobacterium tuberculosis, Coxiella, Listeria, Campylobacter,
Beta-hemolytic streptococci, Salmonella, Enteropathogenis Escherichia
coli, parasites, viruses.
Insects and birds cause mechanical damage to fruits and
vegetables, introduce microorganisms and open the way of microbial
spoilage.
When infected animals died and finally mixed with soil by
decomposing manner and plants collected food from that source may
added coliform bacteria or enterococci.

5. Sewage:
 Untreated domestic sewage when used for domestic
fertilize plant crops then plant foods contaminated with
human pathogen especially by those causing
gastrointestinal disease.
 Natural water contaminated with sewage contribute
their microorganisms to shellfish, fish and other
seafood.
 Treated sewage also add some organisms to water and
soil but the no. of pathogens decreases than raw
sewage.

6. Soil:
 When microbiologist try to search a new kind of
microorganisms they turn to soil. Soil is a huge
source of microorganisms (mainly heat resistant
spore forming organisms).
 Fertile soil contain large no and kind of
microorganisms and ready to contaminate the
surface of plants. Surfaces of animals roaming over
the land.
 Soil dust whipped up by air, soil particle carried by
water and touched the food.
 Modern methods of food handling mainly washing
the surfaces of foods and removal of much of soil
from the surfaces to avoid soil dust contamination.

7. Water:
 Surface water(streams/ pools), stored water(lake/large
ponds), ground water(springs/well).
 Different source may range from a few to several
hundred bacteria/ml.
 Natural water contains chiefly Pseudomonas,
Chromobacterium, Proteus, Micrococcus, Bacillus,
Streptococcus, Enterobacter and Escherichia.
 They are mainly present in water surrounding fish,
other sea life, intestinal tract of sea fauna.

8. Cont…..
Food microbiologist shown interest in two aspect of water:
1. Economic aspects
2. Public health aspects
To assure coliform tests is done but some nonfermenting
bacteria like Pseudomonas grown in water lines but not
detected by coliform test so, total plate count also must
process
Chlorination of water is done to maintain sanitary quality of
water. Amount of chlorine 0.025-2 more parts of
available chlorine per million parts of water, this is
completely depends on composition and contamination of
water.

9. Cont…..
From economic view:
 Water should have an acceptable taste, odor, color, clarity,
chemical composition, bacterial content and should be
available in sufficient volume at a desired temperature.
 Contamination comes from: as an ingredient, for washing
foods, for cooling heated food, manufactured ice for
preserving foods e.g. coliform bacteria enter milk from
cooling tank water and made trouble during cheese making.
 Treatment of water has been takes place to avoid these
problems: filtration, sedimentation, chlorination, ultraviolet
ray irradiation etc. soft drink water treated with uv-ray.
 Sometime filters behave as a source of water
contamination with certain bacteria.

10. Air:
 Food contamination by air, important for sanitary
as well as economic reasons.
 Respiratory tract infection caused by air.
 Air used for aeration of food and that increase the
total no of organisms in food.
 Yeast, mold spores from air give trouble in cheese,
meat, sweetened condensed milk and sliced bread,
bacon.

11. Source:
Microorganisms
get into air or
dust or lint;
spray from
streams, lakes,
ocean, droplet
of moisture
from coughing,
sneezing,
talking. Growth
of sporulating
molds on walls,
ceilings, floors,
foods and
ingredients.
Kinds: Molds spore
for their small size,
resistance to drying,
large no. of molds
plant. Many mold
spore are not water-
wet readily so not
sediment from humid
air. Cocci more
numerous than rod
shaped bacteria. Dust
free air not contain
any organisms. Soil
organisms from
soil/dust, water
organisms from water
spray, plant
organisms from feed/
fodder dust.
Numbers: total no of
organisms at a certain
period of an area depend
on some factors, like
amount of movement,
sunshine, humidity,
location, amount of
suspended dust or spray.
Moving air brings
organisms in it. Number
increased by air currents
caused by movement of
people, ventilation,
breezes. Dry air contain
more than moist air. A
hard/ steady rainfall
removes organisms from
soil.

12. Treatmentsof air:
Microorganisms reduced from air by some natural
conditions:
1. Sedimentation
2. Sunshine
3. Washing by rain/snow
Microbes removal from air by artificial processes:
1. Filtration (cotton, fiber glass, activated carbon)
2. Chemical treatment (ultra-violet tunnels or room with
uv-ray)
3. Heat/ electrostatic precipitation (successful but
expensive)

13. Handling and processing:
Equipments comes contact
during packaging.
Personnel during packaging
Workers shed from 103 to 104
viable organisms per minute.