Transcript Bacterial Infections

Bacterial Infections
HB6
2010
Bacteria are:
Unicellular
 Small (1-4mm)
 Prokaryotes- no nucleus or membrane bound
organelles
 Different metabolic reactions to us (peptidoglycan
cell wall)
 Different sources of energy

 Photosynthetic
bacteria
 Chemosynthetic bacteria
 Pathogenic bacteria are heterotrophs- get energy from
other organisms
Generalised bacterial cell
Escherichia coli
Bacterial shapes
Bacterial naming

Bacteria are usually referred to by
their binomial name:
Genus species
 e.g. Escherichia coli


This may include Latin words referring to
the shape, disease caused by the
bacterium, or other properties
Some examples:
Helicobacter pylori
 Staphylococcus aureus
 Staphylococcus epidermis
 Streptococcus pneumoniae
 Vibrio cholerae
 Neisseria meningitidis
 Neisseria gonorrhoeae
 Mycobacterium tuberculosis
 Mycobacterium leprae





Gram positive
 Thick cell wall containing
mostly peptidoglycan
Gram negative
 Cell wall contains less peptidoglycan
& more lipid
Aerobic
 Use oxygen for metabolism
Anaerobic
 Don’t use oxygen for metabolism,
oxygen may be highly toxic to them
Bacterial
reproduction
Bacteria have a short
generation time (as short as
20min)
 Bacteria reproduce binary
fission:

The DNA is replicated
 The cell elongates in the middle
 The cell wall & cell membrane
pinch inwards
 Two cells separate

Why are bacteria so successful?
They reproduce quickly
 They evolve quickly (e.g. antibiotic
resistance)
 They can live in extreme environments (e.g.
in hot pools- 90oC)
 Some can form endospores, which can
survive for many years (e.g. anthrax)

Not all bacteria are bad!

Lactobacillus- ferment milk to make
yoghurt and cheese
 Bacteria are decomposers- break
down dead organisms and sewage
and recycle the nutrients
 There are millions of bacteria in our
digestive systems- these produce
vitamin K (needed for blood clotting)
Bacteria as pathogens
Some bacteria which gain their energy
from other organisms can act as
pathogens
 The negative effects on the host are
generally either from toxins produced by
the bacteria or from chemicals released
by damaged cells

Tetanus
Wound infection by Clostridium tetani
 Produces a neurotoxin which causes a
prolonged muscle contraction
 Death due to spasm of the breathing
muscles
 About 10 cases each year in Australia, of
which one will die
 Neonatal tetanus (often infection of the
umbilical stump) has a death rate of
approximately 75%

Gram positive
 Obligate anaerobe
 Forms spores which can be found in soil
 Rod-shaped (‘tennis racket’)

Some pathogenic cocci

Streptococcus
pyogenes


Causes skin
infections
Chains of cocci

Staphylococcus
aureus


Causes wound
infections
Groups of cocci

Neisseria
gonorrhoeae


Causes gonorrhoea
Diplococci (pairs)

Neisseria meningitides


Causes meningococcal
disease
Diplococci
Some pathogenic spirilli

Treponema pallidum
Causes syphilis
 Spirochetes (long spiral shape)

Bacterial pneumonia

Anthrax forms
spores which
remain dormant
in the ground
until they are in
hospitable
surroundings.
Some bacterial diseases
Pneumonia
 Appendicitis
 Meningococcal disease
 Skin infections
 Food poisoning

Some pathogenic bacilli

Escherichia coli


Normally found in
human intestines &
faeces
Some strains cause
severe food poisoning

Haemophilus influenzae

Causes some types of
pneumonia