Bacteria are microscopic single-celled prokaryotes that can be classified based on their shape, staining properties, and whether they require oxygen. They have a cell membrane and cell wall, and may possess structures like flagella, pili, and capsules. Bacteria contain a single circular chromosome as their genetic material within a nucleoid region of the cell but lack membrane-bound organelles. They can reproduce asexually through binary fission and be both helpful and harmful to humans.

3. Understand Bacteria
Know about the characteristics of
bacteria.
Know about the classification of
bacteria.
Know about the structure of bacteria.
Know about the disease cause by
bacteria.

4. The word bacteria is taken from the Latin and Greek
word Bakteria meaning “cane”
Bacteria is microorganism with few micro meter in
length and have a wide range of shapes (round, oval,
rod and spiral shapes)
First discovered by Antony Van Leeun Hook in 1796,
initially called Animacules.

5. The study of bacteria is known as Bacteriology,
while the study of the harmful effects of bacteria in the
body is known as Medical Bacteriology.
Bacteria is found everywhere in earth (e.g. soil, water,
deep earth crust, radio active waste, and acidic hot
spring.

6. A single gram contains 40 million bacteria while a
million bacteria found in a ml of water.
However, few of these are harmful to human body and
causes disease.
They produce more oxygen than plants.
Bacteria are the earlier life form on earth.
Their fossils found 2.5 millions years ago.

7. Size of bacteria is between 0.5 to 5 micrometer
They are prokaryotic microbes (has no membrane
bounded nucleus mitochondria)
Have single chromosome as a genetic material.
Enclosed in a rigid cell wall called
peptoglycane
Some bacteria along plasma membrane,
contain an additional membrane called
CAPSULE.

8. Reproduced by Amitosis (Asexual form of
reproduction)
Many bacteria form spores.
Some bacteria are autotropes while others are
heterotropes
Most grow best in pH 6.5 to 7.0
Many acts as decomposers recycling
nutrients.

10. feed on dead organic matter.
feed on host cell.
use sunlight to make food.
oxidize organic materials such as iron or sulfur to
make food

14. Those who appear in Round or Oval Shape
Those who appear ROD Shape
Those who appear in spring or spiral in shape

17. Those who require oxygen to live.
Those who don’t require oxygen to live.
Those who can adjust in either
presence or absence of oxygen.

18. A Gram stain is a test that checks for bacteria at the
site of a suspected infection such as the throat,
lungs, genitals, or in skin wounds. Gram stains may
also be used to check for bacteria in certain body
fluids, such as blood or urine.

19. In the late 1800’s, Christian
Gram observed that some
genera of bacteria retained a
dye-Iodine complex when
rinsed with alcohol, while
other genera were easily
decolorized with alcohol and
could be then visualized by a
contrasting counter stain.

20. This staining procedure defines two bacterial groups:
those which retain the primary dyes (“Positive by
Gram’s Method” or “Gram-Positive”) and those which
are easily decolorized (“Negative by Gram’s Method” or
“Gram-Negative”).This is the starting point for
bacterial identification procedures

21. can survive on extremely low temperature.
can survive on extremely low temperature.
can survive on extremely hot temperature.

22. Those who cause disease to humans
Those who do not cause disease to humans

24. Bacteria are classified as Prokaryotes
They are unicellular organisms that lack
nuclear membrane and true nucleus
They also lack some cell structures such as
mitochondria, endoplasmic reticulum and
Golgi bodies
The prokaryotic cell is simpler than
eukaryotic cell but has a more complex
cell envelope which protects against
hostile environment

25. ✓All bacteria, both pathogenic and saprophytic,
are unicellular organisms that reproduce by
binary fission

26. ✓ Most bacteria are capable of independent metabolic
existence and growth
Exceptions: Chlamydia and Rickettsia are obligate
intracellular organisms
✓Bacterial cells are extremely small and are most
conveniently measured in microns.

30. Flagella: organs of locomotion
✓Flagella occur on both Gram-positive and
Gram-negative bacteria, and their presence
can be useful in identification
✓They are found on many species of bacilli but
rarely on cocci

31. Pili : occur almost exclusively on Gram-negative
bacteria and are found on only a few Gram-
positive organisms (e.g., Corynebacterium
renale).

33. ❑ Flagella can be sheared from the cell surface
without affecting the viability of the cell
❑ The cell then becomes temporarily non-motile
❑ In time it synthesizes new flagella and regains
motility
❖The protein synthesis inhibitor chloramphenicol
blocks regeneration of flagella.

34. ➢Thin, hair-like appendages on the surface of many
Gram-negative bacteria
➢Proteins of pili are referred to as pilins
➢More rigid in appearance than flagella
➢Shigella species and E. coli- pili are distributed
profusely over the cell surface, with as many as 200 per
cell.

35. ➢Pili can come in two types: short, abundant
common pili, and a small number (one to six) of
very long pili known as sex pili

36. ❑Pili in many enteric bacteria confer adhesive
properties on the bacterial cells, enabling them to
adhere to various epithelial surfaces
❑To red blood cells (causing hemagglutination)
❑To surfaces of yeast and fungal cells
❑These adhesive properties of piliated cells play an
important role in bacterial colonization of epithelial
surfaces and are therefore referred to as
colonization factors

37. Some bacteria form capsules, which constitute
the outermost layer of the bacterial cell and
surround it with a relatively thick layer of
viscous gel
Capsules may be up to 10 µm thick, usually made of
polysaccharides and rarely polypeptides
Capsules of encapsulated pathogens are often important
determinants of virulence

38. Encapsulated species are found among both Gram-
positive and Gram-negative bacteria
Mutational loss of enzymes involved in the
biosynthesis of the capsular polysaccharides can result
in the smooth-to-rough variation seen in the
pneumococci
Confer resistance to phagocytosis and hence provide the
bacterial cell with protection against host defenses to
invasion

39. ❖ Consists of the membrane and the structures
surrounding the cytoplasm
1. Plasma/ Cell Membrane- phospholipid bilayer with
embedded proteins that envelop the cytoplasms
❖ Lacks sterols except Mycoplasma.
❖ Acts as osmotic barrier and site of electron
trasnsport chain for energy generation

40. ✓Are the site of active transport
✓Respiratory chain components
✓Energy-transducing systems
✓Site for the H+-ATPase of the proton pump
✓Membrane stages in the biosynthesis of
phospholipids, peptidoglycan, LPS, and
capsular polysaccharides.

41. 2. Cell Wall - a rigid structure that maintains the
shape of the cell and prevents the bursting of the
cell from intracellular high osmotic pressure.
Gram positive cell wall
Gram negative cell wall

42. Mycobacteria have a modified Gram- positive cell
wall called Acid-fast cell wall.
Mycoplasmas have no cell wall, contains sterols in
their cell membrane

44. ✓ 80% Water (20% Salts-Proteins)
❖ Osmotic Shock important
✓DNA is circular, Haploid
❖More efficient; grows quicker
❖Mutations allow adaptation to
environment quicker

45. ✓Plasmids; extra circular DNA
❖Antibiotic Resistance
✓No organelles (Mitochondria, Golgi, etc.)

46. o The bacterial nucleoid is a structure containing a
single chromosome
o The number of copies of the chromosome in a
cell depends on the stage of the cell cycle
(chromosome replication, cell enlargement,
chromosome segregation, etc

47. oBacterial chromatin does not contain basic
histone proteins, instead low-molecular-weight
polyamines and magnesium ions may fulfill a
function similar to that of eukaryotic histones

48. ✓Prokaryotic and eukaryotic cells are distinguished
on the basis of structure
✓Bacterial nucleoid, which contains the DNA fibrils,
lacks a limiting membrane
✓Under the light microscope, the nucleoid of the
bacterial cell can be visualized with the aid of
Feulgen staining, which stains DNA

49. ✓The DNA is then seen to be a single,
continuous, "giant" circular molecule with a
molecular weight of approximately 3 X 109