Pathogens, Bacteria and Viruses
What is a pathogen?
A pathogen is a microbe that causes a disease.
- A bacterial pathogen- Salmonella
- A viral pathogen- Ebola
- A fungi pathogen- Candida
A bacteria enters your body and releases toxins. These toxins make you feel unwell.
A bacteria is bigger than a virus.
Antibiotics can be used to treat only bacterial infections. Viruses are harder to treat because any treatment would need to get inside a cell or kill the cell itself.
A virus infects a cell by entering the cell and repoducing using the cell's resources. This causes the cell to explode, releasng thousands of copies of the virus into the body.
First Line of Defence
First line of defence protect you from any foreign micro organism. These are:
- Stomach Acid
- Cilia and Mucus
- Blood Clots
- Acidic Vaginal Fluid
- Eye lashes
- Nose Hair
The first line of defence is non- specific. I.E. it keeps ALL types of pathogens out, not just one specific type.
Second Line of Defence
How does the Second Line of Defence work?- Phagocytosis
This is how phagocytosis works:
- The phagocyte moves toward the bacterium.
- The phagocyte engulfs/ingests bacterium
- After the bacterium has been ingested, it is digested with enzymes.
- The phagocyte absorbs any useful products and releases any useless material.
Third Line of Defence
Our third line of defence is our specific immune system. It targets a specific type of pathogen and eliminates it. Our lymphocytes take care of this:
- There is antibody receptor of a specific shape on the lymphocyte.
- There are antigens on the pathogen's surface (proteins on the surface of pathogen.)
- The antibody complements (fits) on to the antigen perfectly.
- This triggers lymphocyte to produce lots of copies of itself.
- All these lymphocytes release antibodies which attach onto the antigens.
- This immobolises the pathogen.
- Some lymphocytes stay on as memory cells to protect us from any secondary exposure.
How does immunity work.
Immunity works in the following manner:
- The body has just been exposed to a disease. It has breached both first and second line of defence. It takes time for the body to identify the correct lymphocyte and then for the lymphocyte to divide to produce copies of itself. All the lymphocytes produce antibodies (leading to an increase in antibodies concentration)
- After the body has produced enough antibiotics to succesfully overcome the pathogen, the level of antibody decreases. However some of the memory cells remain in the blood.
- When the host is infected again, the memory cells divide and produce antibodies quickly and divide with the infection before symtoms can be felt. They produce many more antibodies quicker than in comparison to the first infection.
TO SUM IT UP:
If you ever meet the pathogen again, the immune system can make the same antibodies very quickly.
You have become immune to the disease.
Ignaz Semmelweis was a Hungarian doctor who discovered the significance of hand washing.
- In the 1840s, Semmelweis noticed that the mothers in Ward 1 (staffed by medical students) were more likely to die than those in Ward 2 (staffed by student midwives)
- His friend died after cutting himself whilst dissecting dead bodies and had displayed the same symtoms as the mothers giving birth- he had died from childbed fever.
- Semmelweis realised that his medical students didn't wash his hands and were dissecting dead bodies. The student midwives did not dissect dead bodies.
- He ordered his students to wash their hands.
- In places where they did, death rates reduced. In places where they didn't, death rates remained high.
- Other doctors did not believe Semmelweis' theory. They thought that they didn't have enough proof- they didn't know about bacteria and had not proved that they cause diseases.
- Semmelweis died because of an infected wound.
- After Robert Koch's discovery proving that bacteria causes diseases in the 1870s, modern society considered Semmelweis as the father of infection control. It was one of main ways in which MRSA can be prevented.
Active and Passive immunity (natural and artificia
- NATURAL- When the immune response occurs automatically during an infection. i.e. You suffered from the disease yourself
- ARTIFICIAL- When the immune response is activated by injecting antigens into the body/ taken by mouth. i.e. vaccines.
- NATURAL- Antibodies cross during pregnancy, Colostrum (mother's milk) is rich in antibodies.
- ARTIFICIAL- Antibodies are provided in the form of an anti-toxin/anti-venom which provides animmediate (and temporary) protection.
- Active immunity is permanent. Passive is temporary.
- Natural immunity is gained naturally. Artificial is given artificially.
Difference between antibodies and vaccines
Induces the formation of memory cells which create antibodies when an infection is detected.
Kills bacteria directly- only bacteria (not virus) are susceptible to antibiotics because they have a cell wall (viruses do not). Antibiotics target the cells wall.
Painkillers (e.g. Paracetamol) are given to relieve the symtoms of a disease. However, they cannot kill the pathogens which cause it.
Antibiotics and Penicillin
An antibiotic is a drug that destroys bacteria inside the body without damaging human cells. The first antibiotic to be discovered isPenicillin, discovered by Alexander Fleming.
He discovered penicillin by accident- he left his culture plates unwashed and went on a holiday. After he returned, he discovered a clear ring in the jelly around some of the spots of mould- something had killed the bacteria.
He tried hard to extract the drug, which he called penicillin, but couldn't get it to survive- even in a fridge. Due to this problem, he could never prove that penicillin can be used to treat bacterial infections.
It has been exceeding succesful in treating Typhoid Fever.
We cultured bacteria in the following way:
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