Bacterial Structure
Extracytoplasmic structures
Pili
 Also called fimbriae.
 Hair like filaments that extend from the cell surface.
 Consist of protein called pilin.
 Carry fimbrial or F antigen.
 Shorter and thinner than flagella.
 There are two types of pili:
 Ordinary pili: adherence function
 Sex pili: through which plasmids pass between
bacterial cells.
Capsule
 Gelatinous layer outside the cell wall of some bacteria.
 It is formed invivo (inside the host tissues).
 Chemical nature:
o Polysaccharide: in most bacteria
o Polypeptide: in Bacillus anthracis
o Hyaluronic acid: in streptococci
 Not stained by Gram stain. So, they appear as unstained
halo around the bacteria.
 Stained by special capsule stain.
 Functions:
o Protect bacteria against phagocytosis by host phagocytic
cells.
o Bacterial capsule is antigenic . So, it is used in preparation
of vaccines to produce protective antibodies in the host.
Glycocalyx (slime): Loose polysaccharide meshwork
of fibrils extending from the cell surface of some
bacteria. It has adherence function.
Capsules and slime layers
Attachment
Protection from phagocytic
engulfment.
Resistance to drying.
Depot for waste products.
Reservoir for certain
nutrients.
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protection
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These are structures surrounding the outside of the cell envelope. They •
usually consist of polysaccharide; however, in certain bacilli they are
composed of a polypeptide (polyglutamic acid). They are not essential
to cell viability and some strains within a species will produce a capsule,
whilst others do not. Capsules are often lost during in vitro culture.
Glycocalyx - term to describe substances that
surround bacterial cells
1. Capsule
if substance is organized and firmly attached to
cell wall
2. Slime Layer
if substance is unorganized and loosely attached
to cell wall
Function of Capsule
1. Contribute to Virulence of bacteria by
preventing phagocytosis by WBC’s
A. Streptococcus pneumoniae
B. Bacillus anthracis
Functions of Capsules
2. Prevents drying out or desiccation
3. Allows bacteria to adhere to various surfaces
Streptococcus mutans - enamel on teeth to cause
dental carries
Klebseilla pneumoniae - attaches to respiratory tract
Bacterial endospores
 The bacteria form the spores on exposure to
unfavorable conditions (‫ )ظروف غير مواتية‬such as
depletion (‫ )نضوب‬of nutrients.
 Spores develop only invitro. They do not
develop in the host tissues as it contains adequate
nutrients (‫)العناصر الغذائية الكافية‬.
 Spores are formed mainly by Gram positive
bacilli like clostridium and bacillus.
 Spores are not stained by Gram stain.
 They are stained by special stain.
Bacterial spores are not stained with Gram stain
Central non projecting spores
Terminal projecting spores
Steps of sporulation
 In growth of the cell membrane cutting a portion of
cytoplasm containing nuclear material, ribosomes, little
water (Spore core).
 The spore core becomes surrounded by a second layer
of cell membrane.
 Calcium dipicolinate precipitates in the spore core.
 In between the two layers, (spore cortex) which is
formed of peptidoglycan develops.
 Outer to the spore cortex, (spore coat) which is formed
of keratin develops.
 Spores are markedly resistant because of:
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o
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Spore cortex
Spore coat
Calcium dipicolinate
Its little water
Very low metabolic activity
 Spores contaminating medical instruments are only
destroyed by autoclaving at 121 degree for 20-30
minutes.
 Germination of the spores to vegetative form occurs
after the hazard ‫ خطر‬is removed.
Steps of sporulation
Structure of the spore
Endospores
(spores)
• Dormant cell
• Resistant to adverse
conditions
- high temperatures
- organic solvents
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Identification of
Bacteria
 Pathogenesis
 Resistance
• Produced when starved
• Contain calcium dipicolinate
DPA, Dipicolinic acid
• Bacillus and Clostridium
Endospores - formed under periods of
environmental stress
Only found in Gram (+) Bacteria •
• Bacillus
– Bacillus cereus
– Bacillus anthracis
• Clostridium
– Clostridium tetani
– Clostridium botulinum
– Clostridium perfringens
Endospores
• Extremely resistant to heat, cold, chemicals,
lack of water, etc.
• Most vegetative bacterial cells are killed at
temps. above 70 C (160 F)
– Endospores can survive boiling water for several
hours (some for as long as 20 hours)
GOOD LUCK