Download Morphology and structure of bacteria

Morphology and structure of bacteria
Prof. Marianna Murdjeva, MD, PhD
Department of Microbiology and Immunology
Medical University-Plovdiv
Lecture course in microbiology
Summer term
Bacterial Morphology studies:
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Bacterial Shape
Bacterial Size
Bacterial Cell Arrangement
Gram staining
According to their shape bacteria are:
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Round (cocci)
– staphylococci, streptococci
– diplococci (pneumococci, meningococci)
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Rod-shaped (rods)
– non-spore forming (M. tuberculosis, C. diphtheriae)
– spore-forming (bacilli) - clostridia, B. anthracis
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Spiral (spirilli)
– vibrios (V. cholerae) – 1 curve
– spirilli (Helicobacter) – 2 curves
– spirochaetes: Treponema, Leprospira, Borrelia – many curves
According to cell arrangement
bacteria are:
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Single – monococci
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Pairs
– diplococci (pneumococci, meningococci)
– diplobacteria (Klebsiella)
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Tetrads (sarcina)
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Chains (streptococci, B. anthracis)
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Clusters (staphylococci)
Bacteria are measured in
micrometers (m)
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Small (0.2-0.3 m).
Haemophillus, Brucella
Medium (0.5-2 m).
Staphylococci, Streptococci, E. coli
Large (3-10 m).
Clostridia, B. anthracis
Bacterial structure:
• Cell envelope = cell wall (CW)+cytoplasmic membrane (CM)
• Cytoplasmic components:
- core material (nucleoid) –N
- ribosomes (Ri)
- inclusions
• External structures
- capsule
- flagella and pilli
- spores
• Essential (obligatory) organels - CW, CM, N, Ri
• Non-essential (additional) organels – capsule, flagella, pilli,
spores
Bacterial Cell wall contains
Peptidoglycan:
1. glycan part:
N-acetyl glucosamine
N-acetyl muramic acid
-1,4 glycoside link
2. peptide part
Difference b/n Gram+ and Gram- cell wall
Gram – Cell Wall
Gram+ Cell Wall
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Thick layer of peptidoglycan
Negatively charged teichoic
acid on surface
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Thin peptidoglycan
Outer membrane: - О Ag, LPS and
core oligosaccharide.
– LPS – Ag and toxic properties. Lipid А
(endotoxin). Causes Endotoxic shock.
– Porins.
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Periplasmic space
Function of CW in B
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Some bacterial groups lack typical cell wall structure i.e. Mycobacterium and
Nocardia:
– They have Gram-positive cell wall structure with lipid mycolic acid (cord
factor) which are responsible for pathogenicity and high degree of
resistance to certain chemicals and dyes
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Some have no cell wall i.e. Mycoplasma:
– their cell structure is stabilized by sterols
– they are pleomorphic
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Lysozyme digests disaccharide in peptidoglycan.
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Penicillin inhibits peptide bridges in peptidoglycan.
Bacterial Cytoplasmic membrane (CM) :
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Three-layered
Target for lipid-dissolving agents and some antibiotics
(Polymyxin and Nistatin)
Lack of inner membranes
Function of bacterial CM :
Respiratory (mitochondrial) equivalent
Selective permeability
Participates in peptidoglycan synthesis and formation of penicillin-binding
proteins, necessary for linkage with some antibiotics
Participates in chromosome replication and large plasmids
Bacterial mesosomes:
• Organels, formed by CM folding
• Functions:
– respiratory (mitochondrial) equivalent
– coordination of core material division and
cytoplasm during binary fission of bacteria
Bacterial cytoplasmic components
• Ribosomes – difference with Eu
• Inclusions:
– volutine (diphtherial bacteria)
– glycogen (enteric bacteria)
– others
• Core (nucleoid)- a single DNA
molecule
• Extra-chromosomal genetic
elements (plasmids, bacteriophages)
Bacteria may have non-essential
structures:
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Capsule
Flagella
Pilli
Spores
Bacterial capsule:
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May be real (S. рneumoniae, B. anthracis), slime (S. mutans),
or microcapsule (S. typhi)
Structure
– polysaccharide (S. pneumoniae)
– polypeptide (B. anthracis)
Staining (Klett, Neuffeld)
Function:
– protection (virulence factor)
– Ag properties (K Ag)
Flagella:
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Structure – 3 parts:
- filament – long, thin, helical structure composed of protein flagellin
- hook- curved sheath
- basal body – stack of rings firmly anchored in cell wall
Composition – protein (flagellin)
Function – motion, virulence factor, antigenic and receptor
Pilli (fimbriae)
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Types
– common (adhesins)
– sex (participate in conjugation)
Composition - protein (pillin=fimbrillin)
Function:
– adhesion to cells (gonococci, E. coli)
– participation in conjugative transfer
– Ag properties (F Ag)
Bacterial spores
• Formation – at high temperature or dehydration
• Structure and composition – less water, thicker wall
• Types:
– according to location in the cell: central (B. anthracis), terminal(С.
tetani), subterminal (C. perfringens)
– according to shape: round or oval
– according to their capacity to deform the cell: deforming
(Clostridium) and non-deforming (B. anthracis)
Sporulation
Microscopy: The Instruments
Brightfield Microscopy
Darkfield Microscopy
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Simplest of all the optical
microscopy illumination.
techniques
Dark objects are visible against
a bright background.
Light objects visible against dark
background.
used to enhance the contrast in
unstained samples.
Instrument of choice for spirochetes
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Microscopic staining methods for bacterial structure:
– simple (Loffler, Pfeiffer)
– differential (Gram, Neisser, Zhiel-Neelsen, Moller, Klett)
Fluorescence Microscopy
Electron Microscopy: for Detailed
Images of Cell Parts
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Uses UV light.
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Uses electrons, electromagnetic lenses, and
fluorescent screens
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Fluorescent substances absorb UV
light and emit visible light.
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Cells may be stained with fluorescent
chemicals (fluorochromes).
Electron wavelength ~ 100,000 x smaller than
visible light wavelength
Specimens may be stained with heavy metal
salts
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