LEC 9- Common Bacteria
and Pathogenicity
,Term Definition
Unicellular, prokaryotic
Bacteria
microorganisms lacking a nucleus.
Pathogenicity Ability of bacteria to cause disease.
Virulence Degree of pathogenicity.
Structured community of bacteria
Biofilm
encased in a protective matrix.
,•Bacteria are unicellular, prokaryotic microorganisms.
•They lack a true nucleus and membrane-bound organelles.
•Can be free-living or parasitic.
Basic Structure of Bacteria
1.Cell wall – provides shape and protection. Gram-positive vs Gram-
negative.
2.Cell membrane – regulates entry/exit of substances.
3.Cytoplasm – contains DNA, ribosomes, enzymes.
4.Nucleoid – region with bacterial DNA.
5.Flagella – used for motility.
6.Pili/Fimbriae – used for attachment to surfaces.
7.Capsule – polysaccharide layer for protection from immune
responses.
8.Endospores – formed by some bacteria (e.g., Bacillus, Clostridium) to
survive harsh conditions.
, Classification and Examples of Common Bacteria
A. Based on Gram Staining
•Gram-Positive Bacteria (purple stain)
• Thick peptidoglycan layer.
• Examples: Streptococcus, Staphylococcus, Bacillus.
•Gram-Negative Bacteria (pink/red stain)
• Thin peptidoglycan + outer membrane with LPS.
• Examples: Escherichia coli, Neisseria, Pseudomonas.
B. Based on Shape
•Cocci (spherical): Streptococcus, Staphylococcus
•Bacilli (rod-shaped): E. coli, Mycobacterium tuberculosis
•Spirochetes (spiral-shaped): Treponema pallidum
and Pathogenicity
,Term Definition
Unicellular, prokaryotic
Bacteria
microorganisms lacking a nucleus.
Pathogenicity Ability of bacteria to cause disease.
Virulence Degree of pathogenicity.
Structured community of bacteria
Biofilm
encased in a protective matrix.
,•Bacteria are unicellular, prokaryotic microorganisms.
•They lack a true nucleus and membrane-bound organelles.
•Can be free-living or parasitic.
Basic Structure of Bacteria
1.Cell wall – provides shape and protection. Gram-positive vs Gram-
negative.
2.Cell membrane – regulates entry/exit of substances.
3.Cytoplasm – contains DNA, ribosomes, enzymes.
4.Nucleoid – region with bacterial DNA.
5.Flagella – used for motility.
6.Pili/Fimbriae – used for attachment to surfaces.
7.Capsule – polysaccharide layer for protection from immune
responses.
8.Endospores – formed by some bacteria (e.g., Bacillus, Clostridium) to
survive harsh conditions.
, Classification and Examples of Common Bacteria
A. Based on Gram Staining
•Gram-Positive Bacteria (purple stain)
• Thick peptidoglycan layer.
• Examples: Streptococcus, Staphylococcus, Bacillus.
•Gram-Negative Bacteria (pink/red stain)
• Thin peptidoglycan + outer membrane with LPS.
• Examples: Escherichia coli, Neisseria, Pseudomonas.
B. Based on Shape
•Cocci (spherical): Streptococcus, Staphylococcus
•Bacilli (rod-shaped): E. coli, Mycobacterium tuberculosis
•Spirochetes (spiral-shaped): Treponema pallidum
