Pathogens, spread of human disease and control of infection Flashcards
What is the definition of pathogen?
A disease causing organism
Why do many bacterial disease not result in the death of the host
Bacteria infect a host in order to exploit the food potential of the hosts body tissue. It is not in the bacteria’s interest for the host to be dead.
Examples of pathogenic bacteria
- Vibrio cholerae (cholera)
- Salmonella bacteria (salmonella)
- Staphylococcus aureus (food poisoning)
- Mycobacterium tuberculosis (tuberculosis)
Classification of bacteria
Its shape and its cell wall.
What are all bacteria’s cell wall made up of
Peptidoglycan (murein) which is made up of polysaccharide and amino acids.
If a bacteria was gram positive, what colour would it stain and why?
Stain purple because it will retain colour from crystal violet. Cell wall made up of peptidoglycan but lacks lipopolysaccharide layer.
If a bacteria was gram negative, what colour would it stain and why?
Stain red because of counterstain safranin. as the lipopolysaccharide is washed away by the alcohol. meaning the cell wall consists of a thin layer of lipopolysaccharide and peptidoglycan underneath.
what happens to the cell wall in a gram-positive bacteria when there is an antibiotic?
Cell wall gets easily disrupted with antibiotic such as penicillin or enzymes such as lysozyme, causing the cell to lyse due to osmosis.
What happens to the cell wall in a gram-negative bacteria when there is an antibiotic?
The cell wall is impermeable meaning nothing will happen but they can be controlled with antibiotic tetracycline.
What are antibiotics?
Antibiotics are chemical substances produced by microorganisms (e.g fungi and bacteria) which are used to interfere with the biochemistry of bacteria.
Why can antibiotics be used without harming human cells
because they target reactions in the bacterium which are different to humans.
What can’t antibiotics be used against?
Viruses, because they multiply by taking over human cells. and any toxic chemicals acting against them would also affect our cells.
What does bacteriostatic antibiotics mean
slows down or stops bacteria growth
What does bactericidal antibiotics mean
kills bacteria
what does broad spectrum antibiotics mean?
Kills many types of bacteria.
What does narrow spectrum antibiotics mean?
Kills only certain types of bacteria.
An example of bactericidal and narrow spectrum antibiotic
Penicillin - affects formation of cross-linkages in cell wall of gram-positive bacteria. Weakens cell wall and makes bacteria vulnerable to be attacked by antibodies and enzymes.
An example of bacteriostatic and broad spectrum antibiotic
Tetracycline - prevents transcription of DNA during protein synthesis (stops cell manufacturing new proteins such as enzymes). this will be effective against a wider range of bacteria.
When is antibiotic resistant bacteria more likely to occur
- antibiotics prescribed for trivial infections.
- people do not complete a prescribed course
- used routinely by farmers.
Why is it important that we reduce our use of antibiotics
low levels of the chemicals to be present in the environment could kill most susceptible bacteria, leaving the stronger ones to multiply and gradually produce resistant strains.
What type of bacteria is Salmonella and how does it affect people?
Gram-negative, rod-shaped. It enters body cells lining the small intestine and they multiply. Some die and realize endotoxins which irritate the lining of the intestine and cause gastroenteritis.
What are the symptoms of salmonella
nausea, vomiting, fever, chills, diarrhoea, muscle aches.
What can salmonella do to make ‘things worse’
Salmonella can escape from the intestine and go into the blood and travel to other organs. it may become chronic infection in some people, who can be symptom-free yet capable of spreading the disease to others.
Where can salmonella be found
pork, poultry, eggs, unpasteurised milk
How can salmonella be spread
when slaughtering the animals gut may contaminate other parts of the animals body.
if meat is frozen or chilled very little bacterial growth will occur so when the meat is defrosting bacterial growth and multiplication is rapid and any water and juices dripping from the meat onto other foods will contaminate them.
Also can be transmitted by handling raw chicken.
inadequate cooking of meats accelerates bacterial growth and the temperature is not high enough, therefore it won’t destroy the bacteria.
Salmonella can also be passed on through raw eggs and unpasteurised milk.
How to prevent salmonella.
Adequate thawing of frozen foods
thorough cooking of foods
raw and cooked foods stored separately
hands, surfaces, utensils washed thoroughly
How long does salmonella food poisoning occur and how to treat?
It is left to run its own course and the infection lasts from 5-7 days. loss of fluid may be severe so rehydration therapy may be needed. or use of an intravenous drip to replace bodily fluids. antibiotic treated is possible but not usual.
What type of bacteria is Cholera?
Gram-negative, caused by bacterium Vibrio Cholerae. An endemic in much of the developing world.
Where does Vibrio Cholerae live
it lives and multiplies in the intestine
What does the Vibrio Cholerae do?
It produces a powerful endotoxin which causes a violent inflammation of mucous membrane of the gut. however, many pathogens are required to cause the disease as the acid in the stomach can kill them. It also can survive outside the body, humans can act as reservoirs and carriers of the bacteria.
what is the main source of infection for Vibrio Cholerae?
Water contaminated by faeces
contaminated food
direct contact - rare
Symptons of vibrio cholerae
diarrhoea due to irritation of the bowel by the endotoxin released by the bacteria
severe fevers
dehydration
What are asymptomatic carriers
Carriers of a bacteria but does not develop symptoms.
Treatment of cholera (Vibrio Cholerae)
Using rehydration salts and non-contaminated fluid. which are taken orally or in severe cases infused into vein.
Antibiotics such as tetracyclines shorten duration of the diarrhoea. still not usually used though because antibiotics are expensive and overuse may result in antibiotic resistance.
Prevention of Cholera
Vaccination gives some protection against the disease. Better measures is water treatment and good hygiene
through education - good hygiene, hand washing, dangers of contaminated water, methods of disinfection of water.
What is tuberculosis
an infectious disease caused by the bacterium Mycobacterium tuberculosis (MTB)
How is tuberculosis spread
transmitted by airborne droplets when infected people cough and sneeze. spread when many people live together in crowded conditions.
Why is tuberculosis growing rapidly in intensity
because of the breakdown in health services in some countries
poor, cramped living conditions
the spread of AIDS?HIV
the emergence of multi-drug resistant TB
Which parts of the body are commonly attacked by tuberculosis
Usually the lungs and the lymph nodes but it can also affect other parts of the body such as the brain. kidney and spine.
Why does some infected people not get sick with the disease of tuberculosis?
Because the bacteria (Mycobacterium tuberculosis) may enter a dormant phase when the body’s immune response walls-off the bacteria in tiny, hard nodules known as tubercules.
6 Major symptons of tuberculosis
coughing up blood fever weakness,fatigue, loss of apetite shortness of breath weight loss chills (chest pain)
treatment and prevention of tuberculosis
Vaccination - people are given the Heaf test. A purified protein is extracted from TB bacterium and then injected under the skin using a six-pointed needle. This is read after 2-3 days.
If test is positive, this is indicated by redness/swelling. meaning they will not need the BCG vaccine.
if there is a negative test there is no reaction therefore the person will need a BCG vaccine.
What is a BCG Vaccine
THE BCG vaccine is also known as the Bacillus Calmette-Guerin vaccine. Which is a freeze-dried live bacterial vaccine prepared from an attenuated strain of M.bovis. used to be routinely given to children in the UK between 10-14 but is now only give to children in high-risk areas in the UK.
What is malaria
malaria is a serious, often fatal parasitic disease that is endemic. it is transmitted by a vector ( female mosquito )
How is malaria caused
Malaria is caused by Plasmodium species which is a protoctistan parasite.
How is malaria transmitted
1 - infected mosquito bites human
2 - Plasmodium in mosquito’s saliva enters bloodstream of human.
3 - Plasmodia invade liver where they multiply and infect blood
4 - another mosquito picks up plasmodia in blood after bite
5 - sexual reproduction of mosquitoes intestines produce plasmodia which migrate to salivary glands.
6 - mosquito infects many more other individuals
Reproduction in plasmodia (malaria)
1 - Plasmodia invade Red blood cell and multiply
2 - plasmodia reproduce asexually in blood
3 - Red blood cell rupture releasing plasmodia
4 - some plasmodia invades more red blood cells.
Major symptoms of malaria
headache, coma, fever, vomiting, shivering, pain in joints, severe anaemia
control malaria
lessen mosquito bites by insecticides nets draining standing water introducing fish (guppies) to eat larvae spray water with diesel oil spray water with insecticide release sterilised male mosquitoes.
Drug treatments that reduce the number of Plasmodium
anti-malarial drugs taken before and the during trip to foreign country.
What differs from the 3 different sub-groups of flu?
They all have different antigenic types (strains)
How can influenza cause death
infects cells of upper respiratory tract - can lead to death by secondary infections of bacteria causing bronchitis or pneumonia
Symptoms of influenza
coughing, sneezing, headache, sore throat and fever
How is influenza spread?
droplet infection
how to prevent influenza?
hygiene, cover mouth when sneezing
withdraw from meeting others.
What are parasites and why do they keep their host alive?
Parasites are organisms that live in or another organism called a host. The obtain nourishment from the host therefore it is it in their interest to keep the host alive.
What is an ectoparasite?
Parasites that are specialised to live on the outside of the host.
example of an ectoparaise
head louse - feeds by sucking blood from the scalp of the host.
what is an endoparasite?
parasites specialised to live inside the body of the host.
examples of endoparasties
Schistosomes(blood flukes) - found in Africa, humans infected when standing in fresh water. The intermediate host is the freshwater snail. the larva in the snail penetrates the skin of a human and enters a vein and pass through the bloodstream moving to lungs and liver where they mature. they feed on RBC. When the larva becomes an adult they have suckers to prevent being washed away by blood. Ascaris lumbricoides (round worm) - all over the world, common in southern Europe. found in the small and large intestine. symptoms are intestinal obstruction, heavy infestation resulting in malnutrition, damage to lungs and coughing, inflammation etc. the eggs are picked up through eating and drinking where faeces contain eggs. To prevent - good hygiene, washing hands. treating sewage etc. how its adapted = large no of eggs, no other host, easy to reinfect humans, body is long and narrow = easy for accommodation in the intestine. TAPEWORMS - primary host is a human secondary host is a pig. eggs get from humans to pig because pigs ingest human faeces. then larvae forms cysts in pig muscle and then humans eat uncooked food. prevention is to cook food thoroughly. features - hooks and suckers to attach to gut wall. Long flattened body - large surface area to volume ratio for absorption. Reproductive structures means vast number of eggs produced.
What does endemic mean?
A disease which is present at low levels in an area
What does epidemic mean
a significant increase in the usual number of cases of a disease
What does infectious mean
a disease which may be passed or transmitted from one individual to another.
