1. PathogensPathogens A biological agent which can cause an infectious disease

2. 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

3. 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

4. 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.

5. 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

6. Microscopy Bacteria under the microscope are analysed by their shape and colour reaction (after a specialised stain is added to slide) Round purple bacteria called Gram positive cocci Large pink cells White blood cells

7. 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

8. 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

9. 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.

10. 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

11. Parasitic infections  Diagnosed by directly detecting the parasite or its eggs in the specimen with a microscope  Difficult to grow in laboratory Eggs of Thread worm Itch mite Giardia in faeces Malaria in Red Blood Cells Normal RBC RBC with malarial parasite

12. 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

13. Human: Primary Host Pig: Intermediate Host

14. Fungi Widely 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

15. Did you know… That mushrooms are fungi?

16. 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

17. Candida seen under the microscope Yeast cells Candida grown on nutrient plates Aspergillus seen under the microscope Aspergillus (mould) grown on nutrient plates

18. 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

19. 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

20. 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

21. 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

23. 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/dis eases.htmhttp://www.dhs.vic.gov.au/phd/topics/dis eases.htm

24. 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).

25. Infection can occur only if: a pathogen can be transmitted from person to person or from the environment to a person, person is prone to infection, and the pathogen can enter and then survive and multiply (e.g. through a wound). Spread of Infection