MICROBES AND DISEASE

1. MICROBES AND DISEASE F 6

2. PATHOGEN- a micro-organism which causes a disease when it infects. • VIRULENCE-ability of a pathogen to cause disease • INFECTIOUS DISEASE- which can be passed from one sufferer to another • An infection does not always result in disease

3. Mode of Transmission • Direct contact—person to person via the mucous membrane, which is thinner, softer and moister and thru blood • Horizontal kissing, sexual intercourse, sneezing less than 1 meter, touching • Vertical Placenta , breast milk

4. Indirect contact Air /dust—Fungi spores ---influenza and SARS viruses Food, Water, Fomites Vector borne Insects , Protozoans, poor hygiene, Cholera and Typhoid bacteria-sewage- contaminated water Salmonella bacteria (raw meat) Prion as disease agent(CJD)-Creutzfeldt-Jacob disease

5. Human pathogenic diseases and their means of transmission

6. Mode of transmission Indirect contact – vector borne Example: bacterial dysentery • * The bacterium Shigella causes a type bacterial dysentery . • * Flies can spread Shigella when they carry infected faecal matter on their feet to drinking water or food. • * Symptoms can vary from mild diarrhoea through to a more severe disease with watery or bloody diarrhoea, fever, stomach cramps and vomiting .

7. Mode of transmission Indirect contact – vehicle borne Example: athlete’s foot • * The fungus Trichophyton that causes athlete’s foot can be spread indirectly through towels, changing room floors etc. • * The fungus thrives in the damp warm environment found between the toes. • * The skin between the fourth and fifth toe is usually affected first. A flaky itchy red rash develops. The skin becomes cracked and sore and small blisters may appear. • * If the infection is left untreated it can spread to other parts of the body. • Fomite - a non-living object that can carry disease-causing organisms.

8. Mode of transmission Indirect contact – vehicle borne Example: tuberculosis (TB) • * Air/dust • * The bacterium Mycobacterium tuberculosis causes tuberculosis (TB). • * TB is spread from person to person through the air. • * When a person with active TB coughs or sneezes, droplets loaded with the infectious organism are propelled into the air. • * The moisture evaporates from these particles to leave droplet nuclei that can remain airborne for days and spread long distances. • * The Mycobacterium has a waxy coat, which protects it fromdrying out allowing it to survive for many months in the air and dust.

9. Mode of transmission Direct contact – person to person Example: German measles • * Rubella virus causes German measles. • * When infection occurs during pregnancy the virus crosses the placenta in the blood leading to infection of the fetus . • * The virus can affect all the organs of the developing fetus . • * T he risk to the baby is highest in the first 3 months – up to 85% of babies are affected if infected during this period. • Eight week old fetus attached to its placenta by the umbilical cord. Vertical across the placenta or via breast milk

10. Mode of transmission Direct contact – person to person Example: German measles • * Congenital rubella syndrome is the name given to a group of defects that occur in a child when infected as a fetus. • * Defects are • # deafness (most common) • # eye problems such as cataracts • # heart disease • # impaired mental development • # bone deformities • # liver damage • * The number of cases has dropped significantly due to the introduction of rubella vaccine which is offered to all children as part of the MMR jab.

11. Mode of transmission Direct contact – person to person Example: SARS • * Horizontal – sneezing closer than 1 metre • * SARS - associated coronavirus causes severe acute respiratory syndrome (SARS). • * SARS is transmitted when an infected person coughs or sneezes infectious droplets onto a nearby person . • * T he droplets land on another person ’ s face or hands, and become introduced to the nose or mouth. • Jets of droplets erupt from a man’s nose as he sneezes.

12. Mode of transmission Direct contact – person to person Example: SARS • * The main symptoms of SARS are a high fever >38.0°C, dry cough and breathing difficulties. • * Other symptoms may include headaches, loss of appetite and body aches. • * About 10 -20% of patients have diarrhoea. • * Most patients develop pneumonia.

13. Mode of transmission Direct contact – person to person Example: cold sore • * The virus particles invade the cells of the skin around the mouth and enter the nerve tissue where they lie dormant until something triggers their reactivation. • * Common reasons for the virus becoming reactivated are tiredness, illness, stress and sunlight.

14. Bacterial infection • Intracellular---Chlamydia • Extracellular---Streptococcus

15. Extra cellular bacteria • Damage tissues from outside cells. • Host cells produce antibodies – OPSONINS • Produce acute disease • Last for short time • Streptococcus--------Gram +ve bacteria • S.agalactiae- mother to infant during child birth • S.pyogenescause-strep throat, rheumatic fever and scarlet fever

16. An Opsonin • is any molecule that acts as a binding enhancer for the process of phagocytosis • Action of opsonins a phagocytic cell recognises the opsonin on the surface of an antigen

17. Capsule of Streptococcus pneumonia produces proteins that inhibits phagocytosis by human immune system

18. Intra cellular bacterial infection • Are able to grow and reproduce only within the cells of other organisms • Eg., Chlamydia, Rickettsia • Chlamydia trachomatis- blindness

19. The Rickettsia survival depends on entry, growth, and replication within the cytoplasm of Eukaryotic host cells. Rickettsia species are carried as Parasites by many ticks, fleas and lice. • Typhus • African tick bite fever

20. Chlamydia spc. • are the most common bacterial sexually transmitted infections in humans • Leading cause of infectious blindness

21. Bacterial toxin • Exotoxin • Endotoxin----- • Lipopolyscaccharides in the wall of the Gram –ve bacteria For eg., Salmonella • Released when the bacteria die or cell wall is damaged • Causes fever and aches • Only gram+ve –Listeriamonocytogenes

22. Exotoxin • A protein secreted by the bacterium. • may produce even in the absence of bacterium. • majority of them can be destroyed by heating • Both gram-ve and +ve produce exotoxin • Can be destroyed by antibodies, but some are so toxic that they may be fatal before immune system can respond. • Vibrio cholera

23. Three main types of exotoxin • Acts on connective tissue-spread the bacteria • Acts as enzymes-enter the cell and effect their metabolism • Membrane damaging toxins-puncture the CM-killing cells.

24. Clostridium tetani-gram +ve • Tetanus • Exotoxin- neurotoxin-tetanospasmin • Infection thru wound contamination • Muscles spasmsin the jaw-lockjaw—difficulty in swallowing, and muscle stiffness and spasms. • Sustained contraction of skeletal muscle

25. Exotoxin • Clostridium botulinum –inhibitor of neuromuscular junction • Small doses of toxin is used in commercial preparation of –botox

26. Methods of controlling microbial growth • Antiseptics—to prevent sepsis • Carbolic acid (phenol) the first antiseptic • Today-chlorohexidine –mouthwash- • and alcohols---ethanol and isopropanol

27. Disinfection • Destruction of infective organisms • Hypochlorite ---purify water in swimming pools • Disinfect feeding bottles • Toilets—bleaching agents-pH 5 • Active ingredient is HOCl-hypochlorous acid • Kills bacteria by releasing oxygen, and act as oxidising agent

28. Effective when used in warm solution • Bacteriocidal- to kill the bacteria • Bacteriostatic –to prevent multiply The action of bacteriocidal and bacteriostatic agents.

29. Pastuerisation • Sterilise food • Milk • Boiling upto72 celsius for 15 seconds

30. Radiation • Gamma radiation • used to sterilise culture media • Medical supplies • Drugs • Bacterial and fungal cells-need low dose • Spores and viruses need higher dose • Spices and condiments

31. In lab • 1.Culture media---all nutrient • Agar-complex polysaccharide ---extracted from seaweed and can be warmed to 370 C. • Agar is mixed with liquid medium to prepare a solid medium. • 2. Inoculation-introduction of bacteria • 3. Incubator • Liquid media/ broth-incubated in a waterbath.

32. Condition for growth • Temperature- bacterial growth increases with slight increase in temperature • Wide range of temperatures. • Most grow at neutral pH –use buffers • Obligate aerobes require molecular oxygen so on solid agar they grow on surface and if growing in liquid medium it must be well aerated.

33. 4. Culture-bacteria grows in a medium one bacterial strain or many strains growing together. Colony- visible growth of bacteria on an agar plate Streak Plate is a method of inoculating an agar plate with bacteria so that they are gradually diluted. Lawn- is a layer of bacteria growing on the surface of agar plate. To test the effectiveness of antibiotics or antiseptics.

34. Viruses • Obligate parasites • Grow in specific living host cells. • Tissue culture techiques

35. Growth of bacterial cells • Counting number of cell • Hemeocytometer- individual cells under microscope-used for large cells such as yeast

36. Turbidometry-less accurate • Liquid culture in a cuvette in colorimeter or spectrophotometer and the absorbance of light is measured.

37. Mechanisms of action of antibiotics • Originally defined as susbstance produced by microorganism that kill or inhibit growth of microorganisms • Sir Alexander Fleming in 1928 • first antibiotic discovered Penicillin from a fungus Penicilliumnotatum

38. Antibiotics • Treat infectious bacterial diseases • Microbicidal –kill the bacteria • Microbistatic- slow down the growth of bacteria • Generally gram+ve bacteria are more sensitive to antibiotics than gram-ve bacteria. • Chloramphenicol and Tetracyclines- are broad spectrum of antibiotics and acts on wide range of bacterias

39. Action of antibiotics

40. Effectiveness of antibiotics---resistance • Natural resistance– mutation,conjugation

41. Epidemiology • Study of spread of disease • To find the source of an infection • To establish mechanism of transmission • Pathogens come from infected person or from other reservoir of infection. Three main reservoirs of human infection- a. Person who have had an infection but do not show symptom. Carriers. b. Some animals contain pathogens, which infect both animals and human called zoonosis. c. Many pathogens are found in soil and water

42. Some pathogens

43. English doctor in 1799 • Edward Jenner • Vaccine to prevent a human disease. Small pox.

44. W H O Epidemic-occurs when a large number of people in several communities suffer from the infection Pandemic- occurs when a large number of people in several countries all suffer from the same infection Pandemic-emergence of a disease or new strain to the human population, infects human, causing serious illness and spreads among human.

45. Influenza virus • A, B, C, D. • New strains of A commonly emerge • C and D are stable • Epidemics occur on regular seasonal basis • Pandemics- 1918, Spanish flu(A2 strain) killed more than 20 million people. • -attack the epithelial lining of bronchioles • infection ----Droplet

46. 2004- avian influenza(H5N1) was detected in birds in S .E. Asia 1300 –Bubonic plague ---Yersinapestisspread by fleas HIV infection

47. Spongiform encephalopathy (SE) • Affects the brain of Humans and animals • tiny hole appears in cortex of the brain , look like a sponge. • BRAIN FUNCTION IS IMPAIRED • Memory loss • Personality changes • Problem in movement • Creutzfeldt Jacob disease (CJD) most common form of SE. • Rare • Ages 60-65.

48. Prions (proteinaceous particle) • Misfolded, single type of proteins—lack nucleic acid, • Carry disease , cause deterioration of the brain leading to death • They can be inherited, occurs spontaneously or spread via infection • Transmission occurs when healthy animals eat infected tissues • Britain in 1980s cows were infected by eating the processed remains of sheep nervous tissue. • Bovine form of spongiform encephalopathy (BSE- mad cow disease)

49. A new variant Creutzfeldt Jacob (nvCJD) • Occurs early in their life -20s • Believed that nvCJD is transmitted by eating nervous tissue of cows infected with BSE.

50. Prions • Lack nucleic acid • Single type of protein • To infect and propagate by refolding into abnormal shape • Resistant to denaturation, radiation and heat