1. CLASSIFICATION & STRUCTURE OF BACTERIA
Assistant Professor Microbiology

2. OBJECTIVES Classify Bacteria
Identify Unicellular nature of Bacterial cell
Review selective toxicity of antimicrobials

3. CLASSIFICATION OF BACTERIA
Nomenclature
Binomial Linnean System
Genus species
Italicize
Example Escherichia coli
Used for bacteria, fungi and parasites
Not used for viruses(single name e.g. Poliovirus)

4. CLASSIFICATION OF BACTERIA
Criteria for classification
Growth requirement
O2 requirements e.g. Aerobe, Anaerobe, Facultative anaerobe, Strict anaerobe, Strict aerobe
CO2 requirements e.g. Carboxyphilic
Salt requirements e.g. Halophilics (Salt loving)
Microscopy
Gram staining e.g. Gram Pos & Gram Neg due to cell wall differences

5. CLASSIFICATION OF BACTERIA
Biochemical Reactions
Oxidase test, Catalase test
Serology
Strep pyogenes –Rheumatic fever nephritogenic strain, M types 2, 42, 49, 56, 57, and 60
DNA-DNA Similarity
Ribosomal RNA analysis

6. CLASSIFICATION OF BACTERIA
Bergey's Manual of Systematic Bacteriology
Classification of medically imp bacteria based upon criteria like Gram reaction, motility, cell structure, etc

8. CLASSIFICATION OF BACTERIA
I. Gram-negative eubacteria that have cell walls
Group 1: The spirochetes
Treponema, Borrelia, Leptospira
Group 2: Aerobic/microaerophilic, motile helical/vibroid gram-negative bacteria
Campylobacter , Helicobacter, Spirillum,
Group 4: Gram-negative aerobic/microaerophilic rods and cocci
Bordetella, Brucella, Legionella, Neisseria,
Pseudomonas
Group 5: Facultatively anaerobic gram-negative rods
Escherichia (and related coliform bacteria)
Klebsiella, Proteus, Salmonella, Shigella, Vibrio
Group 6: Gram-negative, anaerobic, straight, curved, and helical rods
Bacteroides, Fusobacterium
Group 9: The rickettsiae and chlamydiae
Rickettsia, Coxiella, Chlamydia

9. CLASSIFICATION OF BACTERIA
II. Gram-positive bacteria that have cell walls
Group 17: Gram-positive cocci
Enterococcus, Staphylococcus, Streptococcus
Group 18: Endospore-forming gram-positive rods and cocci
Bacillus,Clostridium
Group 19: Regular, nonsporing gram-positive rods
Listeria
Group 20: Irregular, nonsporing gram-positive rods
Actinomyces, Corynebacterium
Group 21: The mycobacteria
Mycobacterium
Group 22–29: Actinomycetes
Nocardia
III. Cell wall-less eubacteria: The mycoplasmas or mollicutes
Group 30: Mycoplasmas
Mycoplasma, Ureaplasma

10. STRUCTURE OF BACTERIAL CELL
Shape, Arrangement, Color & Size
Three basic shapes- Cocci (round), Bacilli (rod), Spirochetes (spiral)
Pleomorphism
Shape due to cell wall
Arrangement is due to orientation at cell division
Pairs-Diplococci
Chains-Streptococci
Clusters-Staphylococci

11. STRUCTURE OF BACTERIAL CELL
Shape, Arrangement, Color & Size
Color-Gram Staining gives purple or red color to bacteria
Staining reaction-cell wall differences
Size-0.2 to 5µ
Clinical importance
Above parameters help us identify certain bacteria

12. BASIC STRUCTURE OF PROKARYOTE

13. Unicellular nature of Bacterial cell
Prokaryotic cell is a unicellular structure
It has nucleoid, cytoplasm and outer covering called Cell envelop
Prokaryotic cell lacks nuclear membrane- DNA is present loosely in area called Nucleoid
Cytoplasm contains ribosome- smaller size 70S with 30S & 50Ssubunits
Insoluble granules stores-e.g. metachromatic granules of Corynaebacterium diphtheriae
Metachromatic granules

14. CELL ENVELOPE Structure that surrounds the cytoplasm of bacteria
In Gram positive, two components:-
Cytoplasmic membrane
Thick peptidoglycan layer (Cell wall)
In Gram negative, three components:-
Cytoplasmic membrane (Also called Inner membrane)
Thin peptidoglycan layer
Outer membrane
Gram + cell envelope

15. CELL ENVELOPE IN GRAM +ve AND GRAM –ve BACTERIA

16. BACTERIAL CELL STRUCTURE
Teichoic Acid
Outer layer of Gram +ve bacteria
Can induce septic shock like Endotoxin of Gram –ve
Attach Staphylococci to mucosal surface

17. BACTERIAL CELL STRUCTURE
LIPOPOLYSACCHARIDE
LPS of outer membrane of Gram –ve is Endotoxin
Produce hypotension, fever, shock
Three components
Lipid A is toxic component
Core polysaccharide of 5 sugars
Outer polysaccharide of up to 25 sugar- O somatic Ag

18. BACTERIAL CELL STRUCTURE Outside Cell Wall
Capsule
Layer covering entire bacterium
Polysaccharide except Bacillus anthracis-polypeptide capsule
Determine sero-type e.g. Strep pneumoniae 84 serotypes
Virulence factor- Negative charge resist phagocytosis. Bacteria that lose capsule-become avirulent

19. BACTERIAL CELL STRUCTURE Outside Cell Wall
Pili (Fimbrae)
Hair-like filament extend from cell surface
Mainly in Gram –ve
Two functions
Attachment of bacterium to specific receptor in human tissue (Mutant Ns lose pili-avirulent)
Sex pili form attachment during conjugation

20. BACTERIAL CELL STRUCTURE Outside Cell Wall
Flagella
Long whip-like appendage-motility
Subunit-flagellin
Energy provided by ATP
Spirochetes have flagellum like-axial filament
Importance for two reasons
UTI causing bacteria move up in bladder
Lab identification using anti-sera e.g. Salmonella

21. BACTERIAL CELL STRUCTURE Outside Cell Wall
Glycocalyx (Slime Layer)
polysaccharide coating
allows the bacteria to adhere firmly to various structures e.g. skin, heart valves, and catheters
Pseudomonas aeruginosa- cystic fibrosis
Staphylococcus epidermidis- endocarditis
Streptococcus mutans-dental plaque and caries

22. BACTERIAL CELL STRUCTURE
Spores
Highly resistant structures
In response to adverse conditions
Sporulation occurs when sources of carbon and nitrogen are depleted
Inside the cell
bacterial DNA, a small amount of cytoplasm, cell membrane, peptidoglycan, very little water
a thick, keratin-like coat -dipicolinic acid

23. Selective toxicity of antimicrobials
Antimicrobials used with aim to target structures and functions of bacteria not present in Eukaryote human cells
Cell Wall
Ribosome
Metabolic pathways

24. Selective toxicity of antimicrobials
Penicillin target the Cell wall not present in Eukaryote cells
Tetracyclin, Macrolides target 30S & 50S subunits of ribosome
Co-trimoxazole attacks Folic acid synthesis pathway unique to Bacteria
Quinolones inhibit Topoisomerase IV enzyme of bacteria

25. MCQs GEN BACTERIOLOGY
You have isolated a cell with a peptidoglycan cell wall. What other structure can you safely assume the cell has?    
a mitochondrion  
a Nuclear membrane
a plasma membrane  
a nucleus
Ans: c

26. MCQs GEN BACTERIOLOGY
A young boy is suffering from acute pharyngitis. You perform a throat swab and isolate a Gram positive cocci β- hemolytic colonies on blood agar. This bacterium protects itself from osmotic lysis by which of following structures?
Cell membrane
Peptidoglycan layer
Hydrolytic enzymes
Ribosomes
DNA
Ans: B

27. MCQs GEN BACTERIOLOGY
All of the following are found in the cell walls of Gram positive bacteria except:    
Lipid A  
Peptidoglycan
N-acetylglucosamine
Lipoteichoic acid  
Teichoic acid
Ans: A