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

Endospores: Clostridium and

Bacillus

http://commtechlab.msu.edu/sites/dlc-me/zoo/zdc0310.jpg

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