Transcript FOOD MICROBIOLOGY MEDI 2371

FOOD MICROBIOLOGY
MEDI 2371
Prepared BY
PROF. MOHAMMAD EID SHUBAIR
Definition
 Food
Microbiology is the study of
microorganisms that inhabit, make or
contaminate food.
 Many microorganisms are used to make
food e.g the bacteria which converts liquid
milk into yogurt or cheese, yeast for
making bread, through fermentation.
 Other microorganisms or the toxins they
produce cause spoilage of food.

Foodborne diseases e.g gastroenteritis and
salmonellosis results from eating
contaminated food with various types of
microorganisms.
 Safety of food must be ensured to protect
human health.
 Food preservation is being used to avoid
health hazards.
 Preservation methods include drying,
cooking, smoking, salting, sugaring, low
temperature storage and radiation.
Following the discovery of microorganisms,
scientists associated the role of these
organisms with food spoilage, fermentation and
foodborne diseases.
Historical Development of
Food Microbiology
FOOD Fermentation
Louis Pasteur(1860) showed that fermentation
of lactic acid and alcohol from sugar was the
result of growth of specific bacteria and yeast.
 He
concluded that souring of milk was
caused by the growth of organisms in it.
 Theodor Schwan (1837) named the
organism involved in sugar fermentation
as Saccharomyces( sugar fungus).
 Emil Chirstian hansen (1883) used pure
culture of yeasts to ferment sugars.
FOOD Spoilage
Harry Russell (1895) showed that gaseous
swelling with bad odors in canned peas was
due to growth of heat-resistant bacteria(spores).
Tyndall(1876) observed that bacteria in
decomposing substances were always
traceable to air, substances or containers.
Bacillus coagulans was first isolated from
coagulated milk by B.W. Hammer(1915).
In 1902 the term psychrophile was first used by
Schmidt-Nielsen for organisms that grow at 0C.
Food Poisoning
 In
1857 milk was incriminated as a
transmitter of typhoid fever by W. Taylor
 In 1888 gaertner first isolated Salmonella
enteritidis from meat that had caused 57
cases of food poisoning.
 In 1894 T. Denys was the first to associate
Staphylococci in food poisoning.
 In 1896 Van Ermengen first discovered
Clostridium botulinum.

In 1906 Bacillus cereus food poisoning was
recognized.
 In 1937 paralytic shellfish poisoning was
recognized.
 In 1939 gastroenteritis caused by Yersinia
enterocolitica was first recognized by
Schleifstein and Coleman
 In 1951 Vibrio parahaemolyticus was shown to
be an agent of food poisoning.
 In 1960 the production of aflatoxin by
Aspergillus flavus was first reported.
 In 1986 Bovine spongiform encephalopathy was
first diagnosed in cattle in U.K.
Food Preservation

In 1810 preservation of food by canning was
developed by Appert in France.
 Fish and Fruits were first canned in 1840.
 In 1842 H- Benjamin in U.K. introduced
freezing foods by immersion in an ice and salt
brine.
 In 1878 the first successful cargo of frozen
meat went from Australia to England.
 In 1890 pasteurization of milk began in USA.
 In 1907, Metchnikoff isolated one of yogurt
bacteria (Lactobacillus bulgaricus).\
 In 1943, Procter in USA employed ionizing
radiation to preserve hamburger meat.
Groups of Microorganisms
In Food
 Enteric
Viruses
Hepatitis A and Hepatitis E Viruses
Rotavirus
Astrovirus
Enteric Adenovirus
Human Caliciviruses(Noroviruses and
Sapporo Viruses)
Parasites
– Ascaris
– Trichinella
– Taenia
– Giardia
– Entamoeba
– Cyclospora
– Toxoplasma
•MOLDS
 Produce
Mycotoxins
 Species of Aspergillus, Fusarium,
Penicillium, Claviceps
 Mycotoxins Include aflatoxin,
Ochratoxin, Ergot Alkaloids
 Bacteria
 Yersinia
 Vibrio
 Staphylococci
 Campylobacter
 Listeria
 Salmonells
 Shigella
 Escherichia coli
 Clostridia
 Bacillus cereus
Important Bacterial Groups
In Food

These bacteria have a rapid growth rate, ability
to grow under a wide range of temperature,
aerobiosis, pH, water activity, and utilization of
food nutrients
 They better survive adverse conditions such as
survival of spores at high temperatures.
1- Lactic Acid Bacteria

These bacteria produce large quantities of lactic
acid from carbohydrates, species from genera
Lactococcus, Leuconostoc, Pediococcus,
Lactobacillus, and Streptococcus thermophilus.
2- Acetic Acid Bacteria
 They
are bacteria that produce acetic
acid , such as Acetobacter aceti
3- Propionic Acid Bacteria
 They
produce propionic acid and are
used in dairy fermentation e.g
Propionibacterium freudenreichii
4- Butyric Acid Bacteria
 They
are the bacteria that produce butyric
acid in relatively large amounts, Clostridium
butyricum is included in this group.
5- Proteolytic Bacteria
 They
are bacteria that can hydrolyze proteins
because they produce extracellular
proteinases, they include species in the
genera Micrococcus, Staphylococcus,
Bacillus, Clostridium, Pseudomonas,
Alteromonas, Flavobacterium, Alcaligenes,
some Enterobacteriaceae and
Brevibacterium.
6- Lipolytic Bacteria
They hydrolyze triglycerides as they produce
lipases. Species in genera Micrococcus,
Staphylococcus, Pseudomonas, Alteromonas
and Flavobacterium are included in this group.
7- Saccharolytic
bacteria
They hydrolyze complex carbohydrates, Species
in the genera Bacillus, Clostridium,
Pseudomonas, and Enterobacter are included
in this group.
8- Thermophilic Bacteria
They are the bacteria that are able to grow at 50C
and above. Species from genera Bacillus,
Clostridium, Pediococcus, Streptococcus and
Lactobacillus are included in this group.
9-Psychrotrophic Bacteria
They are the bacteria that are able to grow at
refrigerated temperature. Some species from
Pseudomonas, Alteromonas, listeria, Yersinia and
Aeromonas are included in this group.
10- Thermoduric Bacteria
 They
are the bacteria that are able to
survive Pasteurization temperature
treatment. Some species from
Micrococcus, enterococcus,
Lactobacillus, Bacillus(spores), and
Clostridium (spores) are included in this
group.
11- Halotolerant Bacteria
 Bacteria
that are able to survive high
salt concentration. Some species from
Bacillus, Stahylococcus, Vibrio are
included in this group.
12- Aciduric Bactria
 They
are the bacteria that can survive low pH.
Some species from Lactobacillus,
Lactococcus, Enterococcus, and
Streptococcus are included in this group.
13- Osmophilic Bacteria
 Bacteria
that can grow at a relatively higher
osmotic environment than that needed for
other bacteria. Some species from genera
Staphylococci, Leuconostic, and Lactobacillus
are included in this group. They are much less
osmotic than yeasts and molds.
14- Gas- Producing Bacteria
They are bacteria that produce gas(CO2, H2,
H2S) during metabolism of nutrients. Species
from genera Leuconostic, Lactobacillus,
Propionibacterium, Escherichia, Enterobacter,
Clostridium and Desulfotomaculum are
included in this group.
15- Slime Producers
They are the bacteria that produce slime
because they synthesise polysaccharides.
Examples include Xanthomonas, Leuconostic,
Alcaligenes, Enterobacterand lactobacillus.
16- Spore Formers
They are the bacteria that have the ability
to produce spores. Species from
Bacillus, Clostridium, and
Desulfotomaculum are included in this
group. They are further divided into:
Aerobic sporeformers
Anaerobic sporeformers
Flat sour sporeformers
Thermophilic sporeformers
Sulfide-producing sporeformers
17- Aerobes
They are the bacteria that require oxygen
for growth and multiplication. Examples
include Pseudomonas, Bacillus, and
Flavobacterium
18- Anaerobes
They are the bacteria that cannot grow in
the presence of oxygen. Species from
Clostridium are included in this group.
19- Facultative Anaerobes
They are bacteria that are able to grow in
both the presence and absence of
oxygen. Lactobacillus, Pediococcus,
Leuconostoc. Enteric pathogens, and
some species of Bacillus, Serratia and
Coliforms are included in this group.
20- Coliforms
Species from Escherichia, Enterobacter,
Cirtbacter and Klebsiella are included in
this group. They are used as index of
sanitation.
21- Fecal Coliforms
Mainly Escherichia coli is included in this
group. They are also used as an index
of sanitation.
22- Enteric Pathogens
Pathogenic Salmonella, Shigella,
Campylobacter, Yersinia, Escherichia,
Vibrio, Listeria, Hepatitis A, Rotavirus
and others that can cause
gastrointestinal infection are included in
this group
Descriptive Terms
Indicator organism(s)
An indicator organism or group of organisms is
one whose numbers in a product reflect the
success or failure of (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 as an index
organism and its presence indicates possible
presence of pathogenic enterobacteriacea e.g
Salmonella sp.
Food Poisoning Organisms
1- Those which cause the disease by
infection
2- Those which produce toxin in food
Those which cause infection must grow in
food in large numbers and cause infection
when consumed together with food.
Common organisms in this category
include Salmonella typhimurium,
enteropathogenic E. coli, Vibrio
parahaemolyticus and Yersinia
enterocolitica.
Toxin-Producing Organisms
These are microorganisms which cause
intoxication, they must grow in food in
large numbers and produce enough toxin
and when consumed together with food
cause intoxication.
Common microorganisms in this category
include Clostridium botulinum,
Staphylococcus aureus and toxigenic
fungi e.g. Aspergillus flavus.
Infectious Microorganisms
These are the 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 include; Vibrio cholerae O1,
Salmonella typhi, Shigella sonnei,
Hepatitis A etc.
Spoilage Organisms
Spoilage organisms are the organisms whose
growth in the food causes undesirable
characteristics in that food. Any organism
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 alcohol but not in milk.