Bacteria are microscopic single-celled organisms found everywhere. They can be beneficial, like in fermentation, or dangerous if they cause infection. Bacteria are identified microscopically by their shape, size, structure, and staining reactions. Encapsulation and endospore formation allow some bacteria to resist adverse conditions. As bacteria grow in food, they can discolor or slimify surfaces, and change textures through reactions like hydrolysis. Many important food-spoiling or fermenting bacterial genera are discussed, including Lactobacillus, Clostridium, Salmonella, and Staphylococcus. Groups of bacteria that form lactic, butyric, or propionic acid are important in food

1. BACTERIA

2. BACTERIA
Definition of bacteria:
Bacteria are microscopic living organisms usually one-celled,
that can be found every where
. They can be dangerous such as when they cause infection
or beneficial , as in the process, fermentation and that of
decomposition.

3. General characteristics
of bacteria
1. Morophological characteristics : one of the
first steps in the identification of bacteria in a
food is microscopic examination to as certain
the shape , size ,structure and staining
reactions of the bacteria present
Encapsulation
The presence of capsules or slime may a/c for
ropiness of a food .
In addition capsules severe, to increase the
resistance of bacteria to adverse conditions
such as heat or chemicals .
Most capsules are polysaccharides of dextirin

4. Formation of endospores
• It is characteristics of some bacteria to form long chains and other to clump under certain
conditions .It is more difficult to kill all bacteria in intervined chains or sizable clumps than
to destroy seperate cells .

5. • 2) Cultural characteristics ;
• Bacterial growth in and on foods often is extensive to make the food unattractive
in appearance and objectable .
• pigmented bacteria cause dicolourations on the surfaces of foods ;films may
cover the surfaces of liquids ; growth can make surface sllimy ;or growth
throughout the liquids may result in undesirable cloudiness orsediment
• 3) Physiological characteristics;
The growth and activity of bacteria in foods cause changes include hydrolysis of
complex carobohydrates to simple ones;hydrolysis of protiens
polypeptides,aminoacids,and ammonia or amines ;and hydrolysis of fats to
glycerol and fatty acids .
O-R reactions,which are utilized by the bacteria to obtain energy from foods such as
organic acids ,alcohols and gases

6. Genera of bacteria important in food bacteriology
• Genus acetobacter ; These bacteria oxidize ethyl alcohol to acetic . They are
definite spoilage problem in alcoholic beverages.

7. Genus Aeromanas ; They are frequently
isolated from aquatic environments .A
hydrophilia can be human pathogen

8. • Genus Alcaligens ; As the name suggest, an
alkaline reactions usually is produced in the
medium growth . A viscolactis cause ropiness
in milk , and A metalcaligenes gives slimy
growth on cottage chesse

9. Genus Alteromonas : They are marine organisms that are
important in sea foods

10. • Genus Arthrobacter :A predominant soil
organisms , it inert in most foods.

11. • Genus brevi bacterium :B .linens may be imp
in the surface smear of certain cheese.
• Where culture produce an orange red
pigmentation and helps ripening

12. Genus Brochotrix ; They spoil meat when they are stored
aerobically.

13. • Genus Campylobacter : several strains of C
FETUS subsp . Jejuni have been associated
with gastroenteritis in humans.

14. • Genus clostridium ; many species
actively ferment carbohydrates with the
production of acids.

15. Genus corynebacterium ; The diphtheria organisms may be
transported foods . Present on the cow udder cause of bovine
mastitis .

16. • Genus Dessulfotomaculum ; spoil canned
foods.

17. • Genus enterobacter ; widely distributed in
nature.

18. Genus Erwinia : The species of this genus are plant
pathogens that necrosis or soft rots in plants and there fore
damage plants and vegetables and fruit products from them .

19. • Genus escherichia ; found in feces , a pre
dominant gram negative rod isolated from the
intestinal tract of warm blooded animals and
widely distributed in nature.

20. • Genus flavobacterium ; The yellow to
orange pigmented species of this genus may
cause discolorations on the surface meats and
be involved in the spoilage of shellfish.

21. Genus gluconobacter; They form ropiness in beer
.

22. Genus halobacterium ; They grow and cause
discolarations on foods high in salt , such as
salted fish

23. genus klebsiella : k pneumoniae is the causitive
organism for a bacterial pneumonia in humans

24. Family Lactobacillaceae
Genus Lactobacillus; They ferment sugars to yield lactic acid
as the main product

25. • Genus Microbacterium; Bacteria of this genus
are important because of their resistance to
adverse conditions and their use in
production of vitamins.

26. • Genus Propionibacterium ; They ferment
lactic acid carbohydrates and poly phenols to
propionic acetic acid and carbon dioxide . In
swiss cheese certain species ferment the
lactates to produce the gas that helps form
the holes or eyes and also contribute to the
flavour.

27. Genus proteus; Bacteria of this genus have been involved in
the spoilage of meats seafood and eggs.

28. • Genus Shigella; Species of shigella ,
causing bacillary dysenteries , may be
transported by foods

29. Groups of bacteria important in food
Bacteriology
Lactic acid – forming bacteria or lactics; These bacteria
ferment sugars to lactic acid . This may be desirable in
making products such as sauerkraut and cheese . But
undesirable in terms of spoilage of wines because they
usually form acid rapidly .
EX. Leuconostoc , Lacto bacillus , Streptococcus and Pediococcus
.
.

30. • Butyric acid forming bacteria or
butyrics; Most bacteria of this group are
spore forming anaerobes of the genus
clostridium.

31. • Propionic acid – Bacteria that produce propionic acid
and are used in dairy fermentation .

32. Pectinolytic Bacteria: Pectin are complex carbohydrates that
are responsible for cell wall rigidity in vegetables and fruits
pectin substances derived from citrus fruits can be used in
commercial products as gelling agents. Ex : bacillus , Erwinia
.

33. • Pigmented Bacteria: Colours produced by
pigmented bacteria growing on or in foods.
Flavobacterium – yellow to orange; Serratia-
Red; Halobacterium- pink

34. Gasforming Bacteria : Many kinds of bacteria produce small
amounts of gas and yield it slowly
. Ex : Leuconostoc, Proteus , Enterobacter, Lactobacillus, Bacillus
and Clostridium.
Leuconostoc,Lactobacillus,Propionibacterium, produces only
CO2. Other genera prodce both CO2 and H2