Post on 19-Dec-2015
What are pathogens?• Some pathogens can be classified as micro-organisms
(microscopic living things):
Bacteria Protists (worms, mites, lice, amoebae)
Fungi (yeasts & moulds)• Some pathogens can be classified as non-living biological
agents:
Viruses Prions
Most micro-organisms live harmlessly on our skin, in our water and soil and on surfaces all around us.
Some micro-organisms that are generally harmless to healthy people can sometimes cause illness in susceptible people.
About microorganisms
This photograph
taken by a special
electron microscope,
demonstrates the
size of bacteria
(yellow) in relation to
the tip of a pin
(mauve).
Viruses are even
smaller than bacteria.
Bacteria These are widely distributed in nature (including on/in our body)
Eg: Golden Staph, Salmonella, Meningococcus, E.coli etc
The majority of bacteria are not
pathogens, in fact some are
beneficial to humans
Microscopy Bacteria under the microscope are analysed by their shape and colour reaction (after a specialised stain is added to slide)
Round purple bacteria calledGram positive cocci
Large pink cellsWhite blood cells
Growth on agar plates
Bacteria grow as colonies on the surface of plates containing nutritional agar gel
Specimen placed here & spread out
Individual colonies used for analysis
Plates containing nutrient gel
Reproduction
Bacteria multiply very rapidly by simply ‘snapping’ into two.
Each bacterium doubles itself in 8-10 minutes, so one bacterium will produce millions of ‘offspring’ within hours
Antibiotics
Penicillin, the first antibiotic discovered, was
produced from a fungus called Penicillium
Sir Alexander Fleming who discovered Penicillin
Antibiotics can be used to cure diseases
caused by bacteria.
They are chemical substances which kill or
prevent the reproduction of bacteria.
Protists This is a very broad group of pathogens that can include worms, lice, mites, and protozoans such as amoebae
Protist caused infections are usually associated with poor hygiene or low immunity.
They may be very small (microscopic) or larger worms or insects
Eg: Giardia, Amoeba, Malaria, Hookworm, Threadworm, Headlice, Scabies (itch) mite
Giardia
Parasitic infectionsDiagnosed by directly detecting the
parasite or its eggs in the specimen with a microscope
Difficult to grow in laboratory
Eggs of Thread worm
Itch miteItch mite
Giardia in faecesGiardia in faeces
Malaria in Red Blood Cells
Normal RBC
RBC with malarial parasite
Life-cycles
Some protists have complex life-cycles with more than one host
A host is an organism that carries the pathogen during one or more stages of its life cycle
A primary host is the organism which carries the pathogen during its parasitic stage (is harmed by it)
An intermediate host is the organism which carries the pathogen during its larval phase
Giardia
FungiWidely distributed in nature.
Two types: yeasts and moulds
Fungi don not often infect healthy people. They usually infect people with low immunity, people who have puncture their skin or people who have been using antibiotics
Eg: Candida (causes thrush), Aspergillus, dermatophytes etc
Aspergillus
Fungal infections
Diagnosed by directly detecting the fungus in
the specimen with a microscope
Fungi reproduce by producing spores which
are very light, airborne and are resistant to
damage
Like bacteria, fungi can be grown on plates with
agar gel
Candida seen under the microscope
Yeast cells
Candida grown on nutrient plates
Aspergillus seen under the microscope
Aspergillus (mould) grown on nutrient plates
Viruses Are not classified as living because they are only active once they invade living cells
Eg: Influenza, Hepatitis, HIV, Herpes, SARS, Measles, common cold, Rubella etc
Model of HIV virus enlarged millions of times
Herpes viruses seen by an electron microscope
Cell-hijackers
Viruses cause disease by invading cells
and using cell organelles to survive and
reproduce more copies of themselves
They disrupt normal cell functioning and
kill the cells they invade by causing them
to burst as they release the newly made
viruses
Viruses
Extremely small – cannot be seen by
ordinary microscope (only seen by
electron microscope)
Difficult to grow in laboratory because
they need to be grown within other cells
Antibiotics are not effective against
viruses
Prions Can be considered as infectious proteins. They are thought to be a form of protein that is folded in an unusual manner and able to replicate themselves and invade/kill cells
Only discovered recently and not much is known about them
Eg: Kuru, Cruetzfeld Jacob’s disease, Scra[ie. Bovine Spongiform Encephelopathy
Some good sites to learn about micro-organisms
• http://www.cdc.gov/
• http://www.who.int/health_topics/en/
• http://www.tmvc.com.au/info10.html
• http://www.dhs.vic.gov.au/phd/topics/diseases.htm
What is infection?Infection occurs when:• pathogens multiply in the body • Overcome the body's defences • pathogens cause general illness (eg. fever) or
a localised effect (eg. pus in a wound or urinary tract burning).