introduction to microbiology - wydział lekarski...introduction to microbiology prof. dr hab. beata...
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Introduction to
microbiology
Prof. dr hab. Beata M. Sobieszczańska
Department of Microbiology
University of Medicine
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• http://www.lekarski.umed.wroc.pl/mikrobiologia
• schedules, rules, important information
• Sick leaves (original) must be shown to the
teacher just after an absence but not longer
than after two weeks otherwise a sick note
will not be honored - a copy of the sick note
must be delivered to the secretary office
• Consulting hours – teachers are always
available for students during consulting
hours or classes – apart from consulting
hours – you must chase !
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• Class tests – 10 open questions
• Terms: 1st, 2nd – if failed commission test
from the whole material at the end of
semester
• Students with the average 4.8 will be
released from the final exam
• Presence on lectures and classes are
obligatory
• The final grade from classes is the average
of all grades during semester
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Your best friend in this year:
Medical Microbiology by Patrick R. Murray, Ken S. Rosenthal,
Michael A. Pfaller
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Answer questions:
• Name important cell wall structures of GP and GN
bacteria
• What is a role of these structures in human
diseases?
• Name other than bacterial cell wall structures and
explain their role in bacterial pathogenicity
• Do you understand the term pathogenicity?
• Name five different genera GP and GN bacteria and
indicate the colour they have after Gram staining
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Answer questions:
• Name clinically important bacteria producing
endospores – why endospores are important?
• What is the difference between capsule and
glycocalyx layer on GP bacteria?
• What is axial filament? What role it plays? What
bacteria produce axial filaments?
• Name two types of pili and their role in bacterial
pathogenicity
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Most bacteria come in one of three basic
shapes: coccus, rod or bacillus & spiral
The COCCI
Spherical or oval bacteria having one of
several distinct arrangements based on their
planes of division
MURRAY 7th ed. chapters: 12 – 16
Immunology: section 3
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The rods and bacilli
• rod-shaped bacteria
• divide in one plane
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The spiral Spirals come in one of three forms:
• vibrio - a curved or comma-shaped rod
• spirillum - a thick, rigid spiral
• spirochete - a thin, flexible spiral
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Spirillum
Spirochete
The spirochete Borrelia
(arrows) in a blood smear
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Bacteria :unicellular, microscopic,
prokaryotic organisms that reproduce by binary fission
Prokaryotic cell
Simple structure:
a) The nuclear body (nucleoid) is not bounded by a nuclear membrane
b) It contains one circular chromosome composed of DNA associated with histone-like proteins - prokaryotic cells are haploid
c) There is no nucleolus
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Structurally a typical bacterium
usually consists of:
• a cytoplasmic membrane surrounded by a
peptidoglycan cell wall & maybe an outer
membrane
• a fluid cytoplasm containing a nuclear region
(nucleoid) & numerous ribosomes
• often various external structures such as a
glycocalyx, capsule, flagella & pili
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Cytoplasmic membrane
Is a fluid phospholipid bilayer imbedded with
proteins & usually lacking sterols – exception:
mycoplasmas
The electron transport system is located in the
cytoplasmic membrane
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Bacterial cell wall
• Contains a semirigid, tightknit molecular
complex called peptidoglycan
• Mycoplasmas & ureaplasmas are the
only bacteria that naturally lack a cell
wall
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Peptidoglycan A peptidoglycan monomer consists of two
joined amino sugars:
N-acetylglucosamine (NAG)
N-acetylmuramic acid (NAM)
with a pentapeptide coming off of the NAM
The types & the order of amino acids in the
pentapeptide are almost identical in most
bacteria
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The peptidoglycan
monomer of
Escherichia coli
The peptidoglycan
monomer of
Staphylococcus aureus
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Most bacteria can be placed into one of
three groups based on their colour after
specific staining procedures performed:
gram-positive (GP)
gram-negative (GN)
acid-fast
These staining reactions are due to
fundamental differences in their cell wall
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Gram-positive (GP) bacteria
They retain the initial dye during the Gram stain
procedure & appear purple
Common GP bacteria of medical importance
include:
Streptococcus pyogenes, Streptococcus
pneumoniae, Staphylococcus aureus, Enterococcus
faecalis & Clostridium species
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Gram-positive bacteria cell wall
structure
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Gram-negative bacteria (GN)
They decolorize during the Gram
stain procedure & appear red
Common GN bacteria of medical
importance include:
Salmonella species, Shigella species,
Neisseria species, Haemophilus
influenzae, Escherichia coli, Klebsiella
pneumoniae, Proteus species &
Pseudomonas aeruginosa
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Gram-negative bacteria cell wall
structure
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Structures on the cell wall
a) Glycocalyx - is usually a viscous polysaccharide or polypeptide slime layer in GP cocci (Staphylococci & Streptococci)
b) Capsule - a viscous thick covering surrounding a cell composed of polysaccharides
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Structures outside the cell wall
Flagella - a rotating appendages arising from the bacterial surface and used for locomotion (axial filaments in spiral bacteria)
c) Pili (fimbria) - a tubular protein structure extending from a bacterial surface used for attachment to environmental surfaces or cells
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Flagellar Arrangements
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Pili (fimbria) They are found in:
- virtually all Gram-negative bacteria
- not in many Gram-positive bacteria
The pilus has:
• a shaft composed of a protein called pilin
• adhesive tip structure having a shape corresponding to that of specific glycoprotein or glycolipids receptors on a host cell
Adhesive tip of bacterial
pili binding to host cell
receptors
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Pili (fimbriae)
There are two basic types of pili:
1) short attachment pili (fimbria) -
quite numerous
2) long conjugation pili
("F" or sex pili) - very few in
number
Conjugation (sex) pilus
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Effect of oxygen on bacteria
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Culture media
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Hemolytic activity on blood agar
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Summary
• Shapes and arrangements of bacteria: cocci,
rods/bacilli, spiral. These may grow singly, in
clusters or in chains
• Gram-positive bacteria are dark violet and Gram-
negative bacteria are pink /red
• The Gram reaction is related to the structure of the
cell envelope
• Peptidoglycan: responsible for shape and strength
of the cell wall of bacterium
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• Teichoic acids in Gram-positives
• Lipopolysaccharide (endotoxin, LPS) in Gram-
negative outer membrane
• Capsules, slime layers, glycocalyx: role in
adhesion/biofilm and in protection (anti-phagocytic)
• Surface appendages: flagella = motile, fimbriae/pili
= attachment
• Sporulation in Bacillus and Clostrdium (spores)
survival in hostile environment
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Pathogenesis of infections
• Adhesion (pili, proteins)/invasion (invasins)
= spreading in tissues
• Immune system evasion (e.g. survival in
macrophages)
• Toxin & enzymes production (cells & tissue
damage)
• Multiplication at the site of infection (biofilm
formation)
• Stimulation of the immune response
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Next lecture and classes:
staphylococci and streptococci –
prepare from Murray chapters:
18, 19, 20
Thank you for your
attention