Environmental microbiology

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ENVIRONMENTAL
MICROBIOLOGY
Julia Hartati, dr

Microbiology of Food
 Transmission of gastrointestinal
infections is usually a result of ingestion
of contaminated food or water
 Under usual conditions, the gut flora
maintains a harmless relationship with
the host
 Gastrointestinal infections result from
organisms that are able to survive the
harsh conditions of the stomach and
competition with the microbial flora and
to produce damage to the tissues of the
gastrointestinal tract
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Food bacteriology is focused on :
 spoilage
 diseases transmission
 Food and dairy products may be contaminated
in a variety of ways and from a variety of
sources:
 Soil and water: Alcaligenes, Bacillus,
Citrobacter, Clostridium, Pseudomonas,
Serratia, Proteus, Enterobacter, and
Micrococcus
 Food utensils: depends on the type of food and
the manner in which the utensils were handled

Enteric microorganisms of humans and
animals: Bacteroides, Lactobacillus,
Clostridium, Escherichia, Salmonella,
Proteus, Shigella, Staphylococcus, and
Streptococcus
Food handlers: Staphylococcus, which is
generally found on hands and skin, and
in the upper respiratory tract
Animal hides and feeds: Microorganisms
found in water, soil, feed, dust, and fecal
debris can be found on animal hides

Food poisoning :
 is restricted to infection by enteric pathogen
contaminating food, or
 Ingestion of food containing exotoxins produced by
bacteria
Mycotoxins :
 many fungi produce poisonous substances (mycotoxins)
 cause serious or fatal diseases if ingested
 The mycotoxins of important to human :
• toxin of the poisonous mushroom
• aflatoxin
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Aflatoxins:
 are produced by Aspergillus flavus
 They are highly toxic and carcinogenic
 May cause cirrhosis & cancer of the liver
Control bacteria in food–prevention of
spoilage :heating, sugar, drying, acids,
Salting, low temperature, Smoking,
irradiation, Chemical preservation
Control of bacteria in food–prevention of
diseases transmission :
 Preventable only by rigid sanitation control and improve
personal hygiene
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Organisms that can cause disease by
means of a preformed toxin include
Clostridium botulinum, Bacillus cereus,
and S. aureus. The severity of disease
ranges from a mild diarrhea to a rapidly
fatal intoxication.
Food poisoning by B.cereus and S.
aureus is relatively common and is self-
limiting. Botulism, caused by C.
botulinum, although rare, can be life-
threatening

A commonly seen cause of the diarrhea and
intestinal infection is E. coli. This organism
is a member of the intestinal flora;
however, some strains of E. coli produce
cytotoxins that cause alterations in the
biochemical activity of the intestinal
epithelial cells, resulting in problems with
fluid and electrolyte control by the
intestinal cells.
Three strains of E. coli, referred to as
enterotoxigenic, are a common cause of
“traveler diarrhea” and other intestinal
problems

the classic intestinal pathogen is Vibrio
cholerae, the cause of cholera. This
organism produces an enterotoxin that
causes the outpouring of fluid from the
cells into the lumen of the intestine.
Massive amounts (up to 20 L per day)
can be lost.
Other intestinal pathogens are
Clostridium difficile, Shigella spp.,
Aeromonas hydrophila, Campylobacter
jejuni, and Salmonella spp

A number of viruses also cause diarrheal
disease
Viral agents in this category include
hepatitis, rotavirus, adenovirus,
coxsackievirus, and Norwalk-like agents
Numerous parasites, such as
Fasciolopsis buski, Giardia lamblia,
Entamoeba histoyitica, and Balantidium
coli, also infect the gastrointestinal

By enumerating microorganisms in
milk and foods, the quality of a
particular sample can be determined.
Although the microorganisms cannot
be identified, the presence of a high
number suggests a good possibility
that pathogens may be present. Even
if a sample contains a low microbial
count, it can still transmit infection.

Methods of Study
Coliform analysis is carried out on food
samples as well as on water and milk to
determine whether fecal contamination has
occurred.
Meat: The surface, becomes contaminated
from dust or from handling immediately
upon dismemberment of the animal
Ground Meat: The grinding process intro-
duces the surface contaminants into the
interior of the meat and may also warm the
meat enough to encourage considerable
bacterial multiplication

Methods of Study
Fish: bacterial population will include
many marine halophilic and
psychrophilic forms
Shellfish: gathered near a sewage outlet
will contain numbers of sewage
bacteria, including both pathogenic
enterobacteria and viruses.
Fruits and Vegetables: Most vegetables
have a considerable surface
contamination of soil organisms. Fruits
acquire a surface flora through dust
contamination and handling.

Methods of Study
Eggs :The surface becomes
contaminated immediately after laying,
but penetration of the egg by bacteria is
normally prevented by a dry,
mucilaginous coating on the surface
Bread : Baking kills most
microorganisms, but spores of bacilli,
clostridia, and fungi persist and will
germinate to produce a new flora unless
preservatives are added.

Microbiology of Water
With increasing industrialization, water
sources available for consumption and
recreation have been adulterated with
industrial as well as animal and human
wastes
Polluted waters contain vast amounts of
organic matter that serve as excellent
nutritional sources for the growth and
multiplication of microorganisms
The presence of pathogenic
microorganisms in water indicates
contamination

 These pathogens are responsible for intestinal
infections such as bacillary dysentery, typhoid
fever, cholera, and paratyphoid fever
 Analysis of water samples on a routine basis
would not be possible if each pathogen
required detection. Therefore water is
examined to detect Escherichia coli, the
bacterium that indicates fecal pollution
 Pathogenic microorganisms reach the water
from :
 Soil
 Human excrement
 Bodies/ animal who have died of infectious diseases

Waterborne diseases may be acquired
by:
 drinking contaminated water
 washing utensil
 eating shellfish
Control of bacteria in water:
 sanitation of drinking water
 sanitation of swimming pool
 purification of sewage

Sanitation of drinking water:
 drinking water supplies may become
contaminated
 Can cause an epidemic of enteric diseases
 Water supplies usually filtered & chlorinated
Filtration of water supplies:
 trough beds of sands
 chlorinated by chlorine : 0,5 ppm will rid the
water of enteric pathogen

Sanitation of swimming pools:
 by chlorination, 0,5 ppm of free chlorine
 Coliform bacteria are used as indicator of pollution
 Staphylococcus of human origin persist longer than
coliform in chlorine – treated water
Sewage Purification
 Screening-Bulky  nondecomposable material is
screened and removed (bottles, paper, boxes, etc).
 Sludge formation  The screened sewage is allowed to
settle in large tanks. The sediment, containing much of the
organic matter and microorganisms, is called sludge.

 Sludge digestion  The sludge obtained by either process
described above consists of organic matter rich in bacteria
and other microbes
 Disposal of supernatant  The supernatant, after
chlorination, may be pumped into a large body of water.

Methods of Study
A. Quantitative Analysis
the method employed is plate count
(viable count)
by a serial dilution of water
Each dilution tube is plated in nutrient
agar
The resulting colonies counted

Example of a viable count
Dilution Plate Count*
Undiluted Too crowded
10-1
To count
10-2
510
10-3
72
10-4
6
10-5
1
The 10The 10-3-3
dilution has a suitabledilution has a suitable
number of colonies, the others beingnumber of colonies, the others being
either too high or too low for accuracy.either too high or too low for accuracy.
The original water sample is calculatedThe original water sample is calculated
to have contained 72,000(72 x 10to have contained 72,000(72 x 1033
))
viable cells per mL.viable cells per mL.

Qualitative analysis :
 to obtain a picture of the aquatic bacterial
population
 The method are :
 tube method  Dilutions of a water sample are inoculated
into tubes of a medium which is selective for coliform
bacteria and in which all co-liform bacteria but few
noncoliform bacteria will form acid and gas.
 membrane filtration method  A large measured volume
of water is filtered through a sterilized membrane of a
type that retains bacteria on its surface while permitting
the rapid passage of smaller particles and water.
 Both qualitative and quantitative methods are
used to determine the sanitary condition of
water

Environmental microbiology

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