bacteriology

1. Structure Of
Bacteria
Maj M. Omair Riaz
Assistant Professor of Pathology
QIMS

2. Difference Between Prokaryotes
and Eukaryotes
Prokaryotes
 DNA not within nuclear membrane
 No mitotic division
 DNA not associated with histones
 Single chromosome
 No Membrane bound organelles
 70S Ribosome
 Cell wall with peptidoglycan
 Examples: Bacteria
Eukaryotes
 DNA within nuclear membrane
 Mitotic division present
 DNA associated with histones
 More than one chromosome
 Membrane bound organelles
present
 80S Ribosome
 No cell wall with peptidoglycan
 Examples: Fungi & protozoa

4. Bacteria
 Are Prokaryote cells
 Contain both DNA and RNA
 Divide by Binary Fission
 Have a cell wall
 Cell wall differs in Gram positive and Gram
negative organisms
 Nomenclature is Binomial e.g. Escherichia coli.

5. Bacteria
 Size Range 0.2 – 5 um
 The smallest bacteria are Mycoplasma and they
are the same size as the largest viruses i.e.
poxviruses.
 The longest bacteria (rods) approach the size of
some yeasts and human red blood cells

6. Shapes of Bacteria
 Coccus
 Cluster - Staphylococcus
 Chain - Streptococcus
 Bacillus
 Coccobacillus
 Vibrio (Curved Rod)
 Spiral (Spirochete)

7. Basic Shapes

9. Bacterial Structures
 Flagella
 Pili
 Capsule
 Plasma Membrane
 Cytoplasm
 Cell Wall
 Lipopolysaccharides
 Teichoic Acids
 Inclusions
 Spores

10. Flagella
 Motility - movement
 Swarming occurs with some bacteria
 Spread across Petri Dish
 Proteus species most evident
 Arrangement basis for classification
 Monotrichous; 1 flagella
 Lophotrichous; tuft at one end
 Amphitrichous; both ends
 Peritrichous; all around bacteria

12. Pili
 Short protein appendages
 smaller than flagella
 Adhere bacteria to surfaces
 E. coli has numerous types
 F-pilus; used in conjugation
 Exchange of genetic information
 Flotation; increase boyancy

14. Capsule or Slime Layer
 Glycocalyx - Polysaccharide on external
surface
 Adhere bacteria to surface
 S. mutans and enamel of teeth
 Prevents Phagocytosis
 Complement can’t penetrate sugars

15. Cytoplasm
 80% Water {20% Salts-Proteins)
 DNA is circular, Haploid
 Plasmids; extra chromosomal DNA
 Antibiotic Resistance
 No organelles (Mitochondria, Golgi, etc.)

16. Cell Membrane
 Bilayer Phospholipid
 Water can penetrate
 Flexible
 Not strong, ruptures easily
 Osmotic Pressure created by cytoplasm

18. Cell Wall
 Peptido-glycan Polymer (amino acids +
sugars)
 Unique to bacteria
 Sugars; NAG & NAM
 N-acetylglucosamine
 N-acetymuramic acid
 Amino acids cross link NAG & NAM

19. Cell Wall Summary
 Determine shape of bacteria
 Strength prevents osmotic rupture
 20-40% of bacteria
 Unique to bacteria
 Some antibiotics effect directly
 Penicillin

20. Gram Positive vs Gram Negative
Gram Positive
 Thick Peptidoglycan layer
 Teichoic acid present
 Lipopolysaccharide
absent
 Outer membrane absent
 Periplasmic space absent
Gram Negative
 Thin Peptidoglycan layer
 Teichoic acid absent
 Lipopolysaccharide
present
 Outer membrane present
 Periplasmic space present

21. Teichoic Acids
 Gram + only
 Glycerol, Phosphates, & Ribitol
 Attachment for Phages

23. Lipopolysaccharide (LPS)
 Endotoxin or Pyrogen
 Fever causing
 Structure
 Lipid A
 Polysaccharide
 O Antigen of E. coli, Salmonella
 Gram Negative bacteria only

24. LPS (cont’d.)
 Appearance of Colonies
 Mucoid = Smooth (lots of LPS or capsule)
 Dry = Rough (little LPS or capsule)
 O Antigen of Salmonella and E. coli
 2,000 different O Ags of Salmonella
 100’s different O Ags of E. coli
 E. coli O157
 O Ags differ in Sugars, not Lipid A

25. Endospores
 Resistant structure
 Heat, irradiation, cold
 Boiling >1 hr still viable
 Takes time and energy to make
spores
 Location important in classification
 Central, Subterminal, Terminal

26. Chapter 4

27. Comparison