1. Bacterial disease Learning objectives: To be able to describe the factors affecting pathogenicity of bacteriaTo be able to describe the factors affecting pathogenicity of bacteria To be able to describe modes of transmission.To be able to describe modes of transmission. To be able to describe precautions to avoid contamination of food and water.To be able to describe precautions to avoid contamination of food and water.

2. Types of disease Disease is a general term meaning disorder of the body. There are several different kinds of disease: Infectious Genetic Dietary deficiency Environmental Ageing

3. The factors affecting pathogenicity of bacteria Pathogenicity is how ill an infection can make youPathogenicity is how ill an infection can make you It is a result of the toxins produced by the bacteria.It is a result of the toxins produced by the bacteria. Those released by the bacteria as waste products are called exotoxinsThose released by the bacteria as waste products are called exotoxins Endotoxins are part of the bacterial cell itself and are released when the bacterial cell dies and breaks upEndotoxins are part of the bacterial cell itself and are released when the bacterial cell dies and breaks up

4. Infectivity This is the number of bacteria needed to cause an infectionThis is the number of bacteria needed to cause an infection Most diseases require large numbers, for example salmonella, although some, for example typhoid, requires relatively few.Most diseases require large numbers, for example salmonella, although some, for example typhoid, requires relatively few. The fewer bacteria required to trigger a disease, the more virulent the disease isThe fewer bacteria required to trigger a disease, the more virulent the disease is

5. Invasiveness How easily the bacteria can spread within the body.How easily the bacteria can spread within the body. Bacteria must avoid phagocytosis and overcome the bodies defence mechanisms.Bacteria must avoid phagocytosis and overcome the bodies defence mechanisms. How easily the bacteria can penetrate connective and fibrous tissueHow easily the bacteria can penetrate connective and fibrous tissue Bacteria who can penetrate tough tissue have to secrete enzymes. Very few bacteria can do this – those that can (eg bubonic plague and anthrax) are highly invasiveBacteria who can penetrate tough tissue have to secrete enzymes. Very few bacteria can do this – those that can (eg bubonic plague and anthrax) are highly invasive

6. Attachment Once the microbes has infected a new host they need to attach themselves firmly to the host's cells. Why?Once the microbes has infected a new host they need to attach themselves firmly to the host's cells. Why? In order to avoid being removed by cilia, sneezing, vomiting, diarrhoea, etc.In order to avoid being removed by cilia, sneezing, vomiting, diarrhoea, etc.

7. To do this microbes use molecules called adhesins, which are protein or carbohydrate molecules on the cell wall of bacteria.To do this microbes use molecules called adhesins, which are protein or carbohydrate molecules on the cell wall of bacteria. These adhesin molecules bind to specific protein receptor molecules on the cell membranes of host cells forming adhesin- receptor complexes, so firmly attaching(or adhering) the microbe to the host cell.These adhesin molecules bind to specific protein receptor molecules on the cell membranes of host cells forming adhesin- receptor complexes, so firmly attaching(or adhering) the microbe to the host cell. Because this involves specific binding, this attachment is called specific adherence.Because this involves specific binding, this attachment is called specific adherence.

8. Specific adherence explains why microbes tend to be specific for particular species and tissue.Specific adherence explains why microbes tend to be specific for particular species and tissue. For example the malaria parasite only grows in red blood cells; the diphtheria bacterium only colonises the membranes of cells in the trachea; and the polio virus only invades nerve cells.For example the malaria parasite only grows in red blood cells; the diphtheria bacterium only colonises the membranes of cells in the trachea; and the polio virus only invades nerve cells. It also explains one reason why different people have susceptibility to certain infections. Individuals without the "correct" receptor cannot attach the pathogen and so cannot catch that particular disease.It also explains one reason why different people have susceptibility to certain infections. Individuals without the "correct" receptor cannot attach the pathogen and so cannot catch that particular disease. Bacterium Adhesions Receptor Cell membrane

9. Transmission

10. Transmission by Water. Many pathogens can survive (though not reproduce) in water and so infect humans drinking that water.Many pathogens can survive (though not reproduce) in water and so infect humans drinking that water. Water-borne infections include cholera, typhoid, dysentery, gastroenterisis and food poisoningWater-borne infections include cholera, typhoid, dysentery, gastroenterisis and food poisoning

11. Transmission by Food. Food is an even better way of transmitting pathogens, since microbes can grow and reproduce in food, which they can't do in water.Food is an even better way of transmitting pathogens, since microbes can grow and reproduce in food, which they can't do in water. Food can become contaminated by contact with humans or insects.Food can become contaminated by contact with humans or insects. Food-borne infections include TB, botulism, cholera, amoebic dysentery, typhoid and gastroenteritis.Food-borne infections include TB, botulism, cholera, amoebic dysentery, typhoid and gastroenteritis.

12. Transmission by Aerosol Droplet. When an infected person coughs, sneezes, talks or breathes, they are transmitting their pathogens inside droplets of mucus, saliva or water.When an infected person coughs, sneezes, talks or breathes, they are transmitting their pathogens inside droplets of mucus, saliva or water. Air-borne infections include many of the viral infections such as cold, flu, rubella, and some bacterial infections such as TB, diphtheria and strep throat.Air-borne infections include many of the viral infections such as cold, flu, rubella, and some bacterial infections such as TB, diphtheria and strep throat.

13. Transmission by Direct Contact. The skin is a good barrier to microbial entry, but some infections are still possible by contact with the skin.The skin is a good barrier to microbial entry, but some infections are still possible by contact with the skin. Sexual intercourse is a special case of direct contact, and sexually-transmitted diseases (STDs) include the viral infections Hepatitis B and AIDS and the bacterial infections gonorrhoea and syphilis.Sexual intercourse is a special case of direct contact, and sexually-transmitted diseases (STDs) include the viral infections Hepatitis B and AIDS and the bacterial infections gonorrhoea and syphilis.

14. Transmission by Vectors In the context of disease, a vector is an animal that transmits a pathogenic microbe between other animals.In the context of disease, a vector is an animal that transmits a pathogenic microbe between other animals. Examples include rabies (transmitted by dogs), malaria (transmitted by mosquitoes), sleeping sickness (transmitted by tsetse flies) and yellow fever (transmitted by mosquitoes).Examples include rabies (transmitted by dogs), malaria (transmitted by mosquitoes), sleeping sickness (transmitted by tsetse flies) and yellow fever (transmitted by mosquitoes).

15. Entry Some bacterial and fungal pathogens remain attached to the outer surface of human cells or colonise extracellular spaces in humans, such as the lumen of the gut, alveoli, or tissue fluid.Some bacterial and fungal pathogens remain attached to the outer surface of human cells or colonise extracellular spaces in humans, such as the lumen of the gut, alveoli, or tissue fluid. These are termed extracellular pathogens.These are termed extracellular pathogens.

16. Intracellular pathogens enter the cell. Entry is achieved in different ways:Intracellular pathogens enter the cell. Entry is achieved in different ways: –Some bacteria secrete invasin enzymes, which digest the cell membrane of the host cell, allowing the bacterial cell to enter it. –Sometimes the specific adherence described above stimulates endocytosis by the host cell, which brings the microbe cell inside the host cell. The host cell may then try to digest the microbe cell, but if the bacterium has a capsule it may be protected.

17. By reproducing inside host cells. Viruses, bacteria and protoctists can all colonise living cells and reproduce inside them, using up cellular resources and preventing the cell from carrying out its normal reactions.By reproducing inside host cells. Viruses, bacteria and protoctists can all colonise living cells and reproduce inside them, using up cellular resources and preventing the cell from carrying out its normal reactions. The microbes then usually burst out of the host cell, rupturing the cell membrane and killing the cell in the process.The microbes then usually burst out of the host cell, rupturing the cell membrane and killing the cell in the process.

18. Which bacterium is the main cause of diarrhoea?Which bacterium is the main cause of diarrhoea? How is it spread?How is it spread? What do the toxins cause?What do the toxins cause? How does ORT help patients suffering from diarrhoea?How does ORT help patients suffering from diarrhoea? What does the exotoxin secreted by the diptheria bacterium do?What does the exotoxin secreted by the diptheria bacterium do? The bacterial disease tetanus causes muscle spasms. How?The bacterial disease tetanus causes muscle spasms. How? Exotoxins are detected by the body as foreign proteins. How is this effect exploited?Exotoxins are detected by the body as foreign proteins. How is this effect exploited? What effect do endotoxins have on the body?What effect do endotoxins have on the body?