This document discusses the morphology and structures of bacterial cells. It begins by outlining the learning objectives which are to describe different bacterial shapes and arrangements, basic bacterial cell structures and their functions, staining characteristics based on structures, and how structure relates to laboratory identification. It then details the various bacterial cell components such as the cell wall, plasma membrane, ribosomes, and other internal structures. It explains how these structures determine staining properties and relates morphology to identification. The document uses diagrams to illustrate the different bacterial forms, components, and arrangements.

1. BACTERIAL MORPHOLOGY I
Dr. Tarek Mahbub Khan
MBBS, M.Phil (virology)
Senior lecturer
Faculty of Medicine
Basic Medical Microbiology
Semester 3, Year 2
Date: December 30, 2014
Time: 0930-1030
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2. TLO (students will be able to)
• describe different morphological form of
bacteria and their arrangements.
• describe basic structures and functions of a
bacterial cell.
• explain staining characteristics on the basis of
structural components
• explain the role of bacterial structure in
laboratory identification.
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3. SHAPE AND ARRANGEMENT OF BACTERIA
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4. STRUCTURES
ESSENTIAL COMPONENTS NONESSENTIAL COMPONENTS
Cell Wall Capsule
Plasma membrane Pilus or Fimbria
Ribosome Flagellum
Mesosome Spore
Nucleoid Plasmid
Periplasm Granules
Glycocalyx
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5. BACTERIAL CELL
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6. CELL WALL
• Multilayered structure outside the cytoplasmic
membrane
• COMPOSED OF:
– Peptidoglycans
– Teichoic acid/ lipoteichoic acid
– Lipopolysaccharide
• Function provides:
– cell shape, osmotic stability, transportation of molecules,
antigenicity
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7. PEPTIDOGLYCANS
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8. A: E.coli B: Staphylococcus
Penicillin
acts
Transpeptidase
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9. Gram positive and Gram negative cell wall
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10. LIPOPOLYSACCHARIDE
ENDOTOXIN
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11. CELL WALL OF ACID FAST BACTERIA
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12. TEICHOIC ACID
• Present on gram positive bacteria
• Chemically glycerol phosphate or ribitol phosphate
• Glycerol teichoic acid are lipoteichoic acid
• Ribitol teichoic acid attached to NAM acid of CHO
• Functions/effects:
– Septic shock
– Attachment to mucosa (e.g., Staphylococcus)
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13. BACTERIAL RIBOSOME (70S)
Antibiotic binds
selectively
Selective toxicity
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14. CYTOPLASM AND GRANULES
• Cytoplasm has two distinct regions:
– Amorphous (e.g, Nutrient granules, ribosome etc.)
– Nucleoid
• Granules often contains high energy phosphates
Red stained metachromatic
granule
Corynebacterium diphtheriae
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15. NUCLEOID
Not a true nucleus
No nuclear membrane
No nucleolus
No mitotic spindle
No histones
No introns
Bacterial genes are
arranged in ‘Operons’
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16. PLASMID
Extra chromosomal
Double stranded
Circular
DNA molecules
Self replicable
Transmissible
Non transmissible
Contains Antibiotic R genes
Genes for sex pilus
Genes for exotoxins
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17. BACTERIAL CAPSULE
A gelatinous layer
Polysaccharide in nature
Antiphagocytic
Antigenic
Helps bacterial adherence
Aids lab diagnosis
Negative staining shows unstained capsule
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18. FLAGELLA: Organ of motility
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19. ARRENGEMENT OF FLAGELLA
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20. PILI (Fimbria)
Hair like filaments
Composed of pilin proteins
Short and straight than flagella
FUNCTIONS
Attachment (Ordinary pili)
Conjugation (Sex pili)
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21. GLYCOCALYX
Often known as ‘Slime layer’
Covers surface as film
Polysaccharides
Components of biofilm
Helps bacterial adherence
Thick glycocalyx forms capsule
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22. BACTERIAL SPORE
Highly resistance form
Forms in adverse condition
RESISTANT FACTORS:
Dipicolinic acid (Ca+ Chelator)
Keratin like Spore coat
Less water
Less cytoplasm
Resistant to boiling
Killed by autoclaving
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23. BACTERIA AND LOCATION OF SPORE
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24. DIRECT OBSERVATION OF A BACTERIUM
• Can not be observed in naked eye
• Microscopy:
• Direct evidence
– Shape
– Arrangement
– Staining characteristics
• Indirect evidence
– Motility
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25. HOW BACTERIAL STRUCTURE
INFLUENCES STAINING METHOD
• GRAM STAIN
– Primary stain (crystal violet) is retained in gram positive
bacteria due to thick cell wall. Hence bacteria stained
purple or blue
– Gram negative bacteria loss the primary stain easily due to
thin cell wall and take the counter stain color (red carbol
fuchsin)
• ACID FAST STAIN
– Due to mycolic acid in the cell wall of acid fast bacteria
primary stained (red carbol fuchsin) is applied in hot state.
Hence the bacteria is red
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27. GRAM
POSITIVE
BACTERIA
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28. ACID FAST BACTERIA
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29. EXAMPLES OF BACTERIA WITH
MORPHOLOGICAL AND BIOCHEMICHEL
PROPERTIES
PROPERTIES EXAMPLES
Capsulated Streptococcus pneumoniae, Neisseria
meningitidis, Klebsiella pneumoniae
Flagellated Escherichia coli, Salmonella, Vibrio, Proteus
Piliated Neisseria gonorrhoeae, E.coli,
Strict aerobe Mycobacterium tuberculosis, Pseudomonas
Anaerobe Clostridium, Bacteriodes
Facultative
anaerobe
E.coli, Salmonella, Shigella other enteric
bacteria
Spore forming Clostridium, Bacillus
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30. REFERENCE
• Warren Levinson. Review of Medical Microbiology and
Immunology, 11th edition (2010). Appleton and Lange.
• Geo. F. Brooks, Karen C. Carroll, Janet S. Butel, Stephen A.
Morse, Timothy A. Mietzner. Medical Microbiology, 25th
edition (2010). Appleton & Lange.
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