Detailed discussion on bacterial anatomy and cell structure for theory class for undergraduates and post graduates

1. Morphology of Bacteria
And
Anatomy of bacterial cell
UNDER GARADUATE STUDENT’S LECTUER ON
BY
GUNJAL PN
ASSIST. PROF.
DEPT OF MICROBIOLOGY
DVVPF’S MEDICAL COLLEGE & HOSPITAL
AHMENDAGAR
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GENERAL BACTERIOLOGY:
MORPHOLOGY OF
BACTERIA

3. At the end of the Lecture, the students will be able to
understand:
• Classification of bacteria depending on their
morphology and Gram staining property.
• Anatomy of Bacterial Cell.
• Bacterial cell wall.
• Various Bacterial cell appendages and their functions.
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LEARNING OBJECTIVES

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MICROORGANISMS
EUKARYOTIC
• Parasites, fungi
• Membrane enclosed
organelles
• Cytoskeleton
PROKARYOTIC
• Bacterial cell
• Do not contain
organelles
• Cell wall, peptidoglycan

5. • SIZE - 0.25-1 µm width
• 1-3 µm length
Depending - on shape, bacteria -
classified into:
• Cocci (meaning berry) - oval or
spherical cells – Staphylococcus.
• Bacilli or rods - rod shaped –E.coli
• Comma shaped- Vibrio.
• Spiral- coiled – Spirillum/Spirochetes.
• Branching filaments – Actinomycetes.
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SHAPE OF BACTERIA

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• Cocci - arranged in groups (clusters), pair or chains.
• Bacilli - arranged in chain, pair, and some bacilli are
curved, comma shaped, or cuneiform shaped.
SHAPE OF BACTERIA

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SHAPE OF BACTERIA

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SHAPE OF BACTERIA
Cocci and bacilli - further classified - based on Gram
staining into:
• Gram-positive cocci
• Gram-negative cocci
• Gram-positive bacilli
• Gram-negative bacilli.

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SHAPE OF BACTERIA
Based on Gram’s staining differentiation

10. Bacterial cell anatomy:
• The outer layer/envelope - consists - (1)rigid cell wall
(2) plasma membrane
• Cytoplasm contains - cytoplasmic inclusions
(mesosomes, ribosomes, etc) and a diffuse nucleoid
containing single circular chromosome.
• Some bacteria - possess additional cell wall
appendages - capsule, flagella and fimbriae.
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ANATOMY OF BACTERIAL CELL

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CLASSIFICATION OF BACTERIA DEPENDING ON THEIR
MORPHOLOGY AND GRAM STAINING PROPERTY
Bacteria Example
Gram-positive cocci arranged in
Cluster Staphylococcus
Chain Streptococcus
Pairs, lanceolate shaped Pneumococcus
Pair or in short chain, spectacle
shaped
Enterococcus
Tetrads Micrococcus
Octate Sarcina
Gram-negative cocci arranged in
Pairs, lens shaped Meningococcus
Pairs, kidney shaped Gonococcus

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Bacteria Example
Gram-positive bacilli arranged in
Chain (bamboo stick
appearance)
Bacillus anthracis
Chinese letter or cuneiform
pattern
Corynebacterium diphtheriae
Palisade pattern Diphtheroids
Branched and filamentous
form
Actinomyces and Nocardia
CLASSIFICATION OF BACTERIA DEPENDING ON THEIR
MORPHOLOGY AND GRAM STAINING PROPERTY

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CLASSIFICATION OF BACTERIA DEPENDING ON THEIR MORPHOLOGY AND
GRAM STAINING PROPERTY
Bacteria Example
Gram-negative bacilli arranged in
Pleomorphic (various shapes) Haemophilus, Proteus
Thumb print appearance Bordetella pertussis
Comma shaped (fish in stream
appearance)
Vibrio cholerae
Curved Campylobacter (Gull-wing shaped) and
Helicobacter
Chain Streptobacillus
Spirally coiled, flexible Spirochetes
Rigid spiral forms Spirillum
Bacteria that lack cell wall Mycoplasma

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BACTERIAL CELL WALL

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STRUCTURE OF BACTERIAL CELL

16. • Tough and rigid structure - surrounding the bacterium.
• 10–25 nm thickness
• Weighs about 20–25% of the dry weight of the cell.
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BACTERIAL CELL WALL

17. FUNCTIONS OF CELL WALL
• Protection to cell against osmotic lysis
• Confers rigidity - presence of peptidoglycan layer in the cell
wall
• Protect cell from toxic substances
• Site of action of several antibiotics
• Contains - virulence factors (e.g. endotoxin) - contribute to
pathogenicity
• Antibody against specific cell wall antigens (e.g. antibody to
LPS) - provide immunity against bacterial infection.
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DIFFERENCES BETWEEN GRAM-POSITIVE AND GRAM
NEGATIVE CELL WALL

19. GRAM- POSITIVE CELL WALL
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PEPTIDOGLYCAN:
Thicker (50–100 layers thick, 16–80 nm) than gram-
negative cell wall
• Each layer - Mucopeptide (murein) chain - alternate units
of N-acetyl muramic acid (NAMA) and N-acetyl
glucosamine (NAGA) molecules - cross linked via
tetrapeptide side chains and pentaglycine bridges.
• Tetrapeptide side chain - from NAMA molecule -
composed of L-alanine-D-glutamine - L-lysine - D-alanine.

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GRAM-POSITIVE CELL WALL
Structure of Gram-Positive cell wall

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PEPTIDOGLYCAN LAYER OF GRAM-POSITIVE
CELL WALL

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Teichoic Acid:
• Polymers of glycerol or ribitol - joined by phosphate
groups.
• Maintain - structure of cell wall.
• Two types:
• (i) Cell wall teichoic acid and
• (ii) Lipoteichoic acid.
• Absent in gram-negative bacteria.
GRAM-POSITIVE CELL WALL

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GRAM-NEGATIVE CELL WALL
Peptidoglycan layer:
• Very thin (1–2 layer, 2 nm thick) - composed of a
mucopeptide chain - similar to gram-positive cell
wall.
• Consists - alternate NAMA and NAGA molecules.
• Meso-diaminopimelic acid - present at third position
of the tetrapeptide side chain .
• Pentaglycine bridge is absent.

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Outer Membrane:
• Phospholipid layer - lies outside the thin
peptidoglycan layer
• Serves as - protective barrier to the cell
• Outer membrane proteins (OMP) or porin proteins -
specialized proteins
GRAM-NEGATIVE CELL WALL

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Lipopolysaccharide (LPS): Consists of three parts:
• Lipid A or the endotoxin- pyrogen- fever-causing
agent.
• Core polysaccharide
• O side chain (or O antigen or somatic antigen)
Periplasmic Space
• Space between the inner cell membrane and outer
membrane. It encompasses the peptidoglycan layer.
GRAM-NEGATIVE CELL WALL

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CELL MEMBRANE

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CELL MEMBRANE
• Essential for - survival of the bacteria.
• Fluid mosaic model - most widely accepted model
• 5–10 nm thick -bilayered phospholipid - several proteins
are embedded - integral proteins and peripheral proteins
• Lacks sterols -such as cholesterol (except in Mycoplasma).
• Contain Pentacyclic sterol-like molecules – hopanoids-
used as biomarkers.

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CELL MEMBRANE

30. • Semi permeable membrane
• Transport system -nutrient uptake, and waste
excretion
• Site for metabolic processes
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FUNCTIONS OF CELL MEMBRANE

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CYTOPLASMIC MATRIX
• Bacterial cytoplasm, lacks membrane-bound
organelles.
• Composed of water (70%), salt and proteins.
• Packed with ribosomes, storage granules - inclusions
and cell membrane invaginations - mesosomes.
• Plasma membrane and everything within it - called
as protoplast.

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RIBOSOMES
• Sites for protein synthesis.
• Composed of rRNA and ribosomal proteins.
• Integrated with the mRNA to form
polysomes.
• At this site - genetic codons of the mRNA -
translated into peptide sequences.
• Each 70 S unit - consists of a 30 S and a 50 S
subunits.

33. • Storage sites of nutrients/energy.
• Formed by bacteria under
nutritional deficiency conditions
and disappear when the deficient
nutrients are supplied.
• Two types of inclusions:
Organic inclusion bodies.
Inorganic inclusion bodies.
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INTRACYTOPLASMIC INCLUSIONS

34. • Invaginations of plasma membrane -
in the shape of vesicles, tubules.
• Prominent in gram-positive bacteria.
• Involved in:
Bacterial respiration
Cell wall formation
Chromosome replication
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MESOSOMES

35. • Bacteria do not have a true nucleus - genetic material -
located in an irregularly shaped region called - nucleoid.
• Bacteria possess a single haploid chromosome.
• Comprises of super coiled circular double stranded DNA
• Seen by electron microscopy or on staining with Feulgen
stain
• Bacteria also possess extrachromosomal DNA - plasmids
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NUCLEOID

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CELL WALL APPENDAGES

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CELL WALL APPENDAGES
Composed of:
• Capsule and Slime Layer
• Flagella
• Fimbriae or Pili

38. • Layer of amorphous viscid material lying outside the
cell wall called glycocalyx.
• Capsule -well organized and not easily washed off
• Slime layer - diffuse, unorganized loose material that
can be removed easily
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CAPSULE AND SLIME LAYER

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CAPSULE AND SLIME LAYER
Capsulated bacteria Composition
Pneumococcus Polysaccharide
Meningococcus Polysaccharide
Haemophilus influenzae Polysaccharide
Klebsiella pneumoniae Polysaccharide
Pseudomonas aeruginosa Polysaccharide
Bacteroides fragilis Polysaccharide
Bacillus anthracis Polypeptide (glutamate)
Streptococcus pyogenes (some
strains)
Hyaluronic acid

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FUNCTIONS OF CAPSULES
Bacterial virulence :
• Prevent cell from drying out (desiccation)
• Protects the bacterium from the action of lysozyme and
bacteriophages.
• Toxic to the host cells and induces abscess formation (e.g.
Bacteroides fragilis)
Capsules as vaccine:
• Capsular vaccines are available for bacteria such as
Pneumococcus, Meningococcus and Haemophilus influenzae
serotype-b.

41. Biofilm Formation
• Biofilm - Living ecosystem made up of millions of
adherent bacterial cells, which are embedded within a
self-produced matrix of extracellular polymeric
substance.
• Capable of adherence to damaged tissues and plastic
surfaces.
• Adhesion is a first step in colonization and sometimes
leads to disease.
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FUNCTIONS OF CAPSULES

42. Capsule can be detected by various methods:
• Negative staining by India ink and Nigrosin stain.
• M’Faydean capsule stain.
• Serological test
Quellung reaction
Capsular antigen
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DEMONSTRATION OF CAPSULE
S.pneumoniae capsule
seen by India ink staining

43. • Thread-like appendages - protruding from the cell wall.
• Confer motility to the bacteria.
• 5–20 µm in length and 0.01 - 0.02 µm in thickness.
• ARRANGEMENT OF FLAGELLA
• Monotrichous - e.g. Vibrio cholerae, Pseudomonas and Campylobacter.
• Lophotrichous - e.g. Spirillum.
• Peritrichous - e.g. Salmonella typhi, Escherichia coli .
• Amphitrichous - e.g. Alcaligenes faecalis.
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FLAGELLA

44. ARRANGEMENT OF FLAGELLA
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45. On electron microscope -
bacterial flagellum is - composed
of three parts.
1. Filament - longest portion of
the flagellum that extends
from the cell surface to the
tip.
2. The basal body
3. Hook
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ULTRASTRUCTURE OF FLAGELLA
Hook

46. Direct demonstration of
flagella:
Tannic acid staining
(Leifson’s method)
Electron microscopy.
Indirect means by
demonstrating the motility:
• Craigie tube method
• Hanging drop method
• Semisolid medium, e.g.
mannitol motility medium
• Dark ground or phase
contrast microscopy.
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DETECTION OF FLAGELLA

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TYPES OF MOTILITY SHOWN BY DIFFERENT BACTERIA
Types of motility Bacteria
Tumbling motility Listeria
Gliding motility Mycoplasma
Stately motility Clostridium
Darting motility Vibrio cholerae,
Campylobacter
Swarming on agar plate Proteus, Clostridium tetani
Corkscrew, lashing, flexion extension
motility
Spirochete

48. • Short, fine, hair-like appendages -
help in bacterial adhesion.
• Special type of pili (called sex pilus) -
helps in conjugation.
• Pili - made up of protein called pilin.
• Antigenic; but, the antibodies
against pilin antigens are not
protective.
• Not related to motility
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FIMBRIAE OR PILI

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TYPE OF PILI
According to functions, pili are of two types.
1. Common pili or fimbriae
2. Sex pili

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DETECTION OF FIMBRIAE
• Electron microscope
• Surface pellicle - thin layer formed at the surface of a
liquid culture of strongly aerobic bacteria such as
Pseudomonas.

51. • Involution forms: Swollen and aberrant forms of bacteria (e.g. gonococci
and Yersinia pestis) formed in ageing cultures in high salt concentration.
• Pleomorphic bacteria: Exhibit great variation in the shape and size of
individual cells, e.g. Proteus and Haemophilus.
L Form (Cell Wall Deficient Forms) - Cell wall deficient bacteria.
• Discovered by E. Klieneberger, while studying Streptobacillus moniliformis.
• Named it as L form - after its place of discovery, i.e. Lister Institute, London
(1935)
• L forms play a role in the persistence of pyelonephritis and other chronic
infections.
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ATYPICAL FORMS OF BACTERIA

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Unstable L forms: Bacteria lose their cell wall in presence of penicillin, a
mechanism of resistance shown by the bacteria against penicillin.
• Maintained only in presence of penicillin - can revert to the original
morphology once penicillin is removed.
• Protoplasts - Gram-positive bacteria whose cell wall is entirely removed.
• Spheroplasts - Derived from gram-negative bacteria whose cell wall is
partially removed.
Stable L forms: Mycoplasmas lack cell wall permanently - may represent
stable L-forms of bacteria.
ATYPICAL FORMS OF BACTERIA

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BACTERIAL SPORES

54. • Spores are highly resistant resting
(or dormant) stage of the bacteria.
• Formed in unfavorable
environmental conditions - as a
result of the depletion of
exogenous nutrients.
• Bacterial spore comprises of
several layers.
• From innermost towards the
outermost, the layers are: core →
cortex → coat → exosporium
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BACTERIAL SPORES

55. • Refers to - process of formation of spores from vegetative
stage of bacteria.
• Not a method of reproduction - because bacteria do not
divide during sporulation.
• Complex process and takes about 10 hours.
• Mature spore formed is extremely resistant to heat and
disinfectant
• Transformation of dormant spores into active vegetative cells
when grown in a nutrient-rich medium.
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SPORULATION
GERMINATION

56. • For a given species, the precise position, shape and relative
size of the spore are constant.
• Position: Central, subterminal or terminal
• Shape: Oval or spherical in shape
• Width: Diameter of spore may be same or less than the width
of bacteria
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SHAPE AND POSITION OF SPORES
A. Non-bulging, oval and terminal;
B. Non-bulging, round, and
subterminal;
C. Non-bulging, oval and central;
D. Bulging, round and terminal;
E. Bulging, oval and terminal;
F. Bulging, oval, and central

57. • Spores are resistant to most of the routinely used disinfectants.
• Only limited agents called as sterilants are capable of killing the
spores, e.g. autoclave, or ethylene oxide sterilizer, etc.
DEMONSTRATION OF SPORES
• Gram staining: Spores appear as unstained retractile bodies
within the cells
• Modified Ziehl–Neelsen staining: Spores are weakly acid-fast
and appear red color.
• Special techniques for endospore staining include the
Schaeffer–Fulton stain and the Moeller stain.
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SPORICIDAL AGENTS

58. • Indicators of proper sterilization.
Spores of Geobacillus stearothermophilus -
sterilization control for autoclave and plasma
sterilizer.
Spores of Bacillus atrophaeus - sterilization control
for hot air oven and ethylene oxide sterilizer.
• Used as agents of bioterrorism
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APPLICATIONS OF SPORES

59. Q1. Bamboo stick appearance arrangement is characteristic of:
a. Staphylococcus
b. Streptococcus
c. Corynebacterium diphtheriae
d. Bacillus anthracis
Q2. Bacterial capsule can be best demonstrated by:
a. Gram staining
b. Acid-fast staining
c. Negative staining
d. Albert staining
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QUESTIONS:

60. Q3. Lipopolysaccharide is a component of cell wall of:
a. Gram-positive bacteria
b. Gram-negative bacteria
c. Virus
d. Fungi
Q4. Bacterial structure involved in respiration is:
a. Ribosome
b. Pili
c. Mesosome
d. Flagella
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61. Thank you all !
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