morphology of bacteria deepa babin
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Morphology of bacteria
Deepa Babin
Travancore Medical college
Size of Bacteria
Average bacteria 0.2 – 1.5 micrometre (µm)in diam
.Resolution of unaided eye-200 microns
RBC is 7.5 µm in diam.
Cell
• The cell is the basic unit of life
• Based on the organization of the cellular
structures, cells can be divided into 2
groups:
• Eukaryotes-Fungi,Some algae,slime
moulds,Protozoa
• Prokaryotes-Bacteria,blue green algae
Morphology
Differences
Prokaryote Eukaryotes
Nucleus Absent (one circular) Present(linear more than one chromosome)
• Cytoplasm Absent Present
• Sterols Absent Present
• Muramic acid Present Absent
Shapes of Bacteria
• Coccus –Spherical or oval– Chain =- Streptoccus
– Cluster - Staphylococcus
– -Diplo-neisseria
• Bacillus– Chain - Streptobacillus
– Chinese letter pattern-Corynebacterium
• Coccobacillus -Acinetobacter
• Vibrio – curved or comma
• Spirillum –rigid spiral forms
• Spirochetes-flexible spiral forms
• Actinomycetes-branching spiral forms
• Mycoplasma-cell wall deficient
Coccus
Bacillus
Vibrio leptospira
Spirillum&Mycoplasma
Actinomycetes
Bacterial Cell
Bacterial Structures
• Cell Wall
• Plasma Membrane
• Cytoplasm
• Ribosomes
• Mesosomes
• Nucleus,plasmids
• Intracytoplasmic Inclusions
• Pili or Fimbriae
• Flagella
• Capsule/Slime layer
• L forms or Involution forms
• Spores
Cell Wall
• Determine shape of bacteria
• Strength prevents osmotic rupture
• 20-40% of dry weight of bacterial cell
• Does not stain with ordinary stains
• Some antibiotics effect directly– Penicillin
• Cell wall consists of Peptido-glycan Polymer (amino acids + sugars)
• Sugars-NAG (N acetyl glucosamine) & NAM-(N acetyl muramic acid)
• Arranged in alternating chains crosslinked by peptide chain
CELL WALL
• Gram positive cell wall contains thick layers of teichoic acid as surface Ag
• Gram negative thinner cell wall-contains
• 1. Lipopolysaccharide-lipid responsible for endotoxic activity,Polysaccharide for antigen specificity
• 2.Outer membrane –proteins known as porins-which permit the passage of small molecules
Cytoplasmic membrane(cell memb)
• Thin layer between cell wall enclosing
cytoplasm Bilayer Phospholipid
• Acts as a permeability barrier to & from
cytoplasm
• Respiratory enzymes are present
• Damage cause cell death
Cytoplasm
• 80% Water {20% Salts-Proteins)
– Osmotic Shock important
• Nucleus-devoid of nuclear memb so called
nucleoid
• DNA is circular, Haploid
• Attached to plasma membrane and replicates
by binary fission
• Ribosomes-protein synthesis-(Antibiotics like
T,Streptomycin acts on Ribosomes)
• Mesosomes-Invagination of plasma memb in
to cytoplasm- More Respiratory enzymes are
present
• Plasmids- extra circular DNA
– Mutation -Antibiotic Resistance
Intracytoplasmic Inclusions
• -They are reserve of energy mainly seen in
nutrient deficient condition
• -Mainly-Volutin,Lipids –
(Bacillus,TB),Polysaccharides-
(protozoa,fungus),crystals
• -Volutin - Babes-Ernst granules or
Metachromatic granules(reddish purple-
Albert’s or Neisser’s stain)
STRUCTURE OF FLAGELLA
Flagella
• Motility – movement
• Long hollow tubular structures attached to cell membrane(0.2µm)
• Viewed by Electron microscope
• Antigenic
• It consists of a Filament,Hook,Basal body
• Protein subunits called-“flagellin”
• Flagellum is attached to hook made up of different protein
• Basal body consists of outer and inner rings inserted in to small rod like structure,outer ring is attached to cell wall and inner ring attached to cell membrane.
• Basal body rotates flagellum either clockwise and anticlockwise to move bacteria
• Swarming occurs with some bacteria
– Spread across Petri Dish
– Proteus species most evident
• Arrangement basis for classification
– Monotrichous -Single flagella Eg:Vibrio cholerae
– Lophotrichous - Tuft at one end-Spirilla
– Amphitrichous - Single or tuft both ends-Pseudomonas
- Peritrichous- All around bacteria-Salmonella typhi
- Atrichous-No flagella
Arrangement
Lophotrichous -Lophotrichous -Lophotrichous -
Fimbriae
Fimbriae and Pili
• Short,thin hair like protein appendages made of protein subunits-Pillin
– smaller than flagella
– orginate from cell memb- Electron microscope
– organ of adhesion
– Fimbriae are antigenic
– E. coli has numerous types
• K88, K99, F41, etc.
• F1-Sex pili ; used in conjugation
– Exchange of genetic information
Capsule or Slime Layer
• Sticky,viscid bacterial secretion around cell surface
• Glycocalyx - Polysaccharide on external surface
• Adhere bacteria to surface– S. mutans and enamel of teeth
• Virulence factor
• -Prevents Phagocytosis
• Capsule can be demonstrated by negative staining with India ink preparation
• -Clear halo around bacteria against dark background
• Quellung reaction or Capsule swelling-( Neufeld)-Capsulated bacteria is mixed with its specific anticapsular serum and examined under microscope capsule becomes very prominent and appears swollen due to increase its refractivity
Capsule-negative staining
Endospores-
• Resistant structure-RESTING STAGE
– Heat, irradiation, cold
– Boiling >1 hr still viable
• Bacillus stearothermophilus -spores
– Used for quality control of heat sterilization
equipment
• Bacillus anthracis - spores
– Used in biological warfare
Endospore
Spore
• 1.Germinal groove
• 2. Outer cortical layer
3 . Cortex
• 4 .Internal spore coat
• 5 .Sub coat material
• 6. Outer spore coat
• 7 .Cytoplasmic membrane
• 8.Cell wall primordium
• Spores are destroyed by
AUTOCLAVING AT 121º C
FOR 15 MINUTES
1. Central bulging-
2.Central not bulging
3.Subterminal bulging
4. Subterminal not bulging
5.Terminal spherical
6. Terminal oval
Pleomorphism and Involution forms
-Due to defective cell wall synthesis -varies size
and shape
• L forms-Kleineberger-Nobel –Streptobacillus
moniliformis-swollen cells
• Due to Penicillin or other interference
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