Post on 28-Jun-2020
Introduction to
microbiology
Prof. dr hab. Beata M. Sobieszczańska
Department of Microbiology
University of Medicine
• 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 !
• 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
Your best friend in this year:
Medical Microbiology by Patrick R. Murray, Ken S. Rosenthal,
Michael A. Pfaller
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
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
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
The rods and bacilli
• rod-shaped bacteria
• divide in one plane
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
Spirillum
Spirochete
The spirochete Borrelia
(arrows) in a blood smear
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
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
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
Bacterial cell wall
• Contains a semirigid, tightknit molecular
complex called peptidoglycan
• Mycoplasmas & ureaplasmas are the
only bacteria that naturally lack a cell
wall
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
The peptidoglycan
monomer of
Escherichia coli
The peptidoglycan
monomer of
Staphylococcus aureus
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
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
Gram-positive bacteria cell wall
structure
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
Gram-negative bacteria cell wall
structure
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
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
Flagellar Arrangements
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
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
Effect of oxygen on bacteria
Culture media
Hemolytic activity on blood agar
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
• 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
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
Next lecture and classes:
staphylococci and streptococci –
prepare from Murray chapters:
18, 19, 20
Thank you for your
attention