Chapter 6: Microbiology and Pathogens Flashcards
6.1 Microbial techniques
To investigate microorganisms they need to be…
cultured.
6.1 Microbial techniques
What is culturing?
This involved frowing a large number of microorganisms so they can be measured. This requires that you provide them with nutrients and oxygen as well as ideal pH and temperature for growth.
6.1 Microbial techniques
Why is it important to be careful when culturing microorganisms?
- Even if they are harmeless there is risk of a mutant strain arising that can be pathogenic
- Contamination of the culture by pathogenic microorganisms
- Growing a pure strain will be contaminated by any new microorgnaism entering it.
6.1 Microbial techniques
What do most microorganisms require a good source of?
Carbon nitrogen and other minerals
6.1 Microbial techniques
How is the nutrient medium found?
- Nutrient broth (liquid)
- Nutrient solid form
- Nutrient agar (jelly)-this is extracted from seaweed
6.1 Microbial techniques
Most microorganisms need nutrient enriching substances to grow such as…
blood, yeast or meat extract
6.1 Microbial techniques
What is a selective medium?
A nutrient medium with very specific ingredients in which only a select group of microorganisms will grow.
6.1 Microbial techniques
What is innoculation?
The process of introducing (placing) bacteria onto the agar.
6.1 Microbial techniques
What is used to complete innoculation?
Use an innoculating loop and a process called streaking by scraping bacteria off one solid plate and transferring to a chosen medium.
6.1 Microbial techniques
What is an alternative method to a loop for innoculation?
Use an innoculation broth-mix a known volume of bacterial suspension with nutrient broth in a flask. Then use cotton wool to block other microorganisms from contaminating the broth.
6.1 Microbial techniques
After plate/flask has the bacteria added what is done to ensure the bacteria will grow properly?
The flask is incubated at a suitable temperature
The flask is shaken often making sure it is aerated
6.1 Microbial techniques
What are the effects of culturing bacterias in oxygen and not in oxygen?
Not in oxygen: only anaerobic bacteria survive
Oxygen: aerobic bacteria survive
6.1 Microbial techniques
Define a pathogen
Microorganism that is a disease causing agent
6.1 Microbial techniques
Define a culture
A growth medium where a microorganism is provided with the correct organisms to grow in large numbers
6.1 Microbial techniques
Define a nutrient medium and nutrient broth/agar
Nutrient medium is a substance used to culture microrganisms that can come in a liquid form referred to as nutrient broth or seaweed jelly known as agar.
6.1 Microbial techniques
How do you count single celled fungi in nutrient broth?
- Use a microscope and haemocytometre.
- Place the diluted sample on the haemocytometer, a thick microscope slide with a grid-engraved chamber (volume: 0.1 mm³).
- View the grid under a microscope.
- Focus on the four corner grid squares, each divided into 16 smaller squares.
- Count the cells in these smaller squares for all four corner grids.
- Find the mean cell count across the four sets of 16 squares.
6.1 Microbial techniques
Which of the blue or purple is counted?
Only purple is counted. They MUST be touching the top and left line to be counted.
6.1 Microbial techniques
Explain the use of optical methods to measure the number of cells in a culture
- Turbidimetry is a specialized form of colorimetry used to measure the number of cells in a microbial culture. It provides an alternative to direct cell counting methods like using a haemocytometer.
- The key purpose of turbidimetry in microbiology is to indirectly determine the concentration of cells in a culture by measuring the cloudiness or turbidity of the sample.
6.1 Microbial techniques
Explain the relationship between turbidity and cell concentration
Turbidity refers to the cloudiness or opacity of a liquid caused by the presence of suspended particles, in this case bacterial cells. As the number of cells in a culture increases, the culture becomes more turbid or cloudy.
This is because the suspended cells absorb and scatter more light, making the culture appear darker and less transparent.
6.1 Microbial techniques
Describe how a colorimeter measures turbidity
Colorimeters are instruments used in turbidimetry to measure the turbidity of a sample.
1. Shining a beam of light through the sample.
2. Measuring the amount of light that is absorbed or scattered by the suspended cells.
3. Relating the amount of light absorbed/scattered to the turbidity of the sample.
4. The more turbid the sample, the less light will pass through it and be detected by the colorimeter.
(INVERSE RELATIONSHIP)
6.1 Microbial techniques
How do you make a calibration curve?
- Growing a control culture and taking samples at regular time intervals.
- Measuring the turbidity of each sample using a colorimeter.
- Performing a direct cell count on each sample, e.g. using a haemocytometer.
- Plotting a graph with turbidity on the x-axis and cell count on the y-axis.
- The resulting calibration curve shows the relationship between turbidity and cell concentration.
6.1 Microbial techniques
Define dilution plating
Dilution plating is a technique used in microbiology to count the number of viable microorganisms in a sample.
Diluting the original sample in a series of steps and then plating the diluted samples onto agar plates to allow individual colonies to form.
6.1 Microbial techniques
Explain the purpose of dilution plating (when is it useful)
- Quantifying microbial populations: Counting the number of viable cells
- Comparing microbial growth: Measuring changes in cell numbers over time
- Isolating pure cultures: Obtaining single colonies for further study
6.1 Microbial techniques
What is the process of dilution plating?
- Take a small volume of the original sample and dilute it in a larger volume of sterile diluent (e.g. saline or buffer). Then take a small volume of the first dilution and dilute it further, creating the second dilution, and so on.
- Plate the dilutions: Take a small volume (e.g. 0.1 mL) from each dilution and spread it onto the surface of an agar plate. Repeat this for multiple plates per dilution.
- Incubate the plates
- Count the colonies:This represents the number of viable cells in the original volume plated.
- Calculate the total viable count: Multiply the colony count by the dilution factor to determine the total number of viable cells per mL (or g)
6.1 Microbial techniques
How do you interpret the dilution plating results?
- Counting the colonies: Carefully count the number of colonies on each agar plate.
- Calculating the dilution factor: Determine the overall dilution factor by multiplying the dilution factors at each step.
- Determining the viable cell count: Multiply the colony count by the dilution factor to get the total number of viable cells per mL (or g) of the original sample.
- Assessing the accuracy: Compare results across replicate plates to ensure consistency. The more plates counted, the more accurate the final estimate.
6.1 Microbial techniques
How do you calcualte the optimum temperature for growth?
- Use identical Petri dishes with the same growth medium and number of spores.
- Incubate the dishes at different temperatures.
- Measure the diameter of fungal colonies after a set time.
- Calculate the mean colony diameter for each temperature.
- The temperature with the largest mean diameter is the optimum for growth.
- Technique is less effective for bacteria due to smaller, slower-growing colonies.
6.1 Microbial techniques
Testing optimum nutrients or pH
- Use the dry mass of microorganisms to assess growth.
- Grow fungi in a liquid medium and remove samples at intervals.
- Separate fungi from the liquid by centrifugation or filtering.
- Dry the material (e.g., in an oven at ~100°C overnight) until no further mass loss occurs.
- Measure the dry mass to determine growth.
- Conditions producing the greatest dry mass indicate optimal nutrients or pH
6.1 Microbial techniques
Time between bacterial divisions is referred to as…
Generation time.
6.1 Microbial techniques
What acts as a barrier to infinity reproduction of bacteria?
Waste products and lack of nutrients
6.1 Microbial techniques
Why is a logarithmic scale used when considering bacterial growth?
The numbers are too large when increasing to put on a graph so a logarithmic scale condenses the data to plot on a graph.
6.1 Microbial techniques
What is the formula to calculate the no of bacteria in a population?
6.1 Microbial techniques
What is the exponential growth rate constant and what does it represent?
The no. of times the population doubles in one unit of time.
6.1 Microbial techniques
What are the four stages of the growth curve?
- Lag phase
- Log phase
- Stationary phase
- Death phase
6.1 Microbial techniques
Draw the growth curve and label each of the 4 stages
6.1 Microbial techniques
Describe the lag phase
When bacteria are adapting to their new environment and are not yet reproducing at their maximum rate.
6.1 Microbial techniques
Describe the log phase
When the rate of bacterial reproduction is close to or at its theoretical maximum, repeatedly doubling in a given time period.
6.1 Microbial techniques
Describe the stationary phase
When the total growth rate is zero as the number of new cells formed by binary fission is equal to the number of cells dying.
6.1 Microbial techniques
Describe the death phase
When reproduction has almost ceased and the death rate of cells is increasing.
6.2 Bacteria as pathogens
How do pathogenic bacteria cause disease?
Pathogenic bacteria cause disease through various mechanisms:
* Invading and destroying host tissues, leading to symptoms or producing toxins as metabolic by-products that harm the host or its immune system.
6.2 Bacteria as pathogens
What are the two classifications of bacterial pathogens?
Endotoxins and Exotoxins
6.2 Bacteria as pathogens
What type of molecule are endotoxins and where are they located?
- lipopolysaccharides
- on outerlayer of cell wall of gram negative bacteria
- lipid part of the lipopolysaccharides produce the toxin while the polysaccharides produces antigen to be recognized in immune response
6.2 Bacteria as pathogens
What is a key example of endotoxins?
** Case study: Salmonella spp.**
* Antibiotics are generally ineffective for treating Salmonella infections unless the patient is very young, elderly, or immunocompromised.
* Prevention is key: thoroughly cook meat, wash hands after handling raw meat or using the toilet, and avoid contaminated water.
* Some Salmonella strains, like S. typhi, can cause serious illnesses such as typhoid.
6.2 Bacteria as pathogens
What types of molecules are exotoxins and where are they found?
Soluble proteins produced and released by bacteria,both Gram-positive and Gram-negative)
They often act at sites distant from the bacteria and have varied effects, including damaging cell membranes, causing internal bleeding, interfering with neurotransmitters, or directly poisoning cells.
6.2 Bacteria as pathogens
What is a key example of exotoxins?
- Staphylococcus spp. are Gram-positive bacteria, with around 40 types, commonly found in skin and gut flora. They usually do not cause harm unless they invade body tissues.
- The most common species, S. aureus and S. epidermidis, produce exotoxins that cause diseases ranging from mild skin infections (e.g., styes, boils) to severe conditions like septic arthritis,
- While treatable with antibiotics when diagnosed early, S. aureus is becoming increasingly resistant to common antibiotics, such as methicillin.
6.2 Bacteria as pathogens
What is host tissue invasion?
Invading host cells and damaging tissue is the way bacteria acts as a pathogen.
6.2 Bacteria as pathogens
What is a key example of host tissue invasion?
Transmission: TB is spread through droplet infection, especially in crowded conditions.
Risk factors: People with malnutrition, illness, or weakened immune systems (like those with HIV/AIDS) are more susceptible to developing active TB.
Bacterium: The primary cause is Mycobacterium tuberculosis, while Mycobacterium bovis (from cattle) is another source.
Impact: TB primarily affects the lungs, damaging tissue and suppressing the immune system.
Bacterial Survival: Some bacteria can remain dormant in tubercles for years, becoming active when the immune system weakens.
Active TB: Active TB causes rapid bacterial growth, leading to serious damage and disease.
6.2 Bacteria as pathogens
Define primary infection in reference to TB
The initial stage of tuberculosis when the bacteria is inhaled into the lungs, invaded the cells of the lungs and multiplied slowly often causing no obvious symptoms
6.3 Action of antibiotics
How do antimicrobial drugs work?
Principle of Selective Toxicity: Modern antimicrobial drugs work by targeting the metabolism or function of the pathogen while minimizing damage to human cells.
Antibiotics: Antibiotics are the most commonly used and well-known antimicrobial drugs.
Treatment of Fungal Infections: Although less effective than against bacteria, some antibiotics can be used to treat certain fungal infections.
6.3 Action of antibiotics
What are antimetabolites with an example?
- Action: Interrupts metabolic pathways, such as blocking nucleic acid synthesis, causing death.
- Example: Sulfonamides
- Bacteriostatic
6.3 Action of antibiotics
What are Protein Synthesis Inhibitors with an example?
- Action: Interrupts or prevents transcription and/or translation of microbial genes, affecting protein production.
- Example: Tetracyclines, Chloramphenicol
- Bacteriostatic
6.3 Action of antibiotics
What are Cell Wall Agents with an example?
- Action: Prevents formation of cross-linking in cell walls, leading to bacterial lysis (bursting).
- Example: Beta-lactams (e.g., Penicillins)
- Bactericidal
6.3 Action of antibiotics
What are Cell Membrane Agents with an example?
- Action: Damages the cell membrane, causing metabolites to leak out or water to move in, killing the bacteria.
- Example: Some Penicillins, Cephalosporins
- Bactericidal
6.3 Action of antibiotics
What are DNA Gyrase Inhibitors with an example?
- Action: Stops bacterial DNA coiling up, making it too large to fit within the bacterium.
- Example: Quinolones
- Bactericidal
6.3 Action of antibiotics
What is bacteriostatic?
Bacteriostatic means that an antibiotic inhibits the growth of bacteria but doesn’t necessarily kill them. The body’s immune system then works to eliminate the remaining bacteria. This level of treatment is often sufficient for many common infections.
6.3 Action of antibiotics
What is bactericidal?
Bactericidal means that a drug or treatment destroys almost all of the pathogens present and kills the cell wall, effectively killing the infection. This type of treatment is often used for severe or dangerous infections
6.3 Action of antibiotics
What factors do antimicrobial drug effectiveness depend on?
- concentration of the drug
- pH
- wether pathogen or host tissue destroy pathogen
- sucesptibility
6.4 Antibiotic resistance
What is a superbug and what are examples of it?
Superbugs are bacteria that are resistant to multiple antibiotics. They are commonly found in healthcare settings like hospitals and care homes where antibiotic use is high.
Methicillin-resistant Staphylococcus aureus (MRSA): This type of bacteria is resistant to many antibiotics, including methicillin. It can cause serious infections, especially in people with weakened immune systems.
**Clostridium difficile: **This bacterium produces toxins that can cause severe diarrhea and other intestinal problems. It is often resistant to many antibiotics.
6.4 Antibiotic resistance
What is MRSA and how has it become a superbug?
- The bacterium Staphylococcus aureus is commonly found on human skin.
- Methicillin, a penicillin-related antibiotic, was effective in treating Staphylococcus infections.
- Some S. aureus bacteria developed a mutation that allows them to produce penicillinase, an enzyme that breaks down methicillin.
Resistance: This mutation makes the bacteria resistant to methicillin and other similar antibiotics.
6.4 Antibiotic resistance
What is colostorum difficil and its toxins?
Anaerobic Bacterium: It’s a type of bacteria that doesn’t need oxygen to survive.
Gut Resident: Found in small numbers in the large intestine of about 5% of the population.
Antibiotic Resistance: Not affected by many common antibiotics.
Tough Spores: Produces spores that can survive for months outside the body.
Antibiotic Disruption: Broad-spectrum antibiotics can destroy normal gut bacteria, allowing C. difficile to overgrow.
Toxin Production: C. difficile produces toxins that damage the intestinal lining.
Severe Symptoms: Can cause severe diarrhea, bleeding, and even death.
6.4 Antibiotic resistance
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6.4 Antibiotic resistance
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6.5 Other pathogenic agents
The main way that viruses can cause disease is by…
lysis of host cell
6.5 Other pathogenic agents
How does the flu cause epidemics or pandemics?
It mutates frequently making it very difficult to treat.
Pandemic-worldwide
Epidemic-within the country
6.5 Other pathogenic agents
What is the key example of a virus that acts as a pathogen?
Influenza
6.5 Other pathogenic agents
What are influenzas mode(s) of transmision?
**Droplet Infection: ** The primary mode, involving respiratory droplets.
**Direct Contact: ** Touching contaminated surfaces (fomites) or viral-filled mucous.
**Zoonotic Infection: ** Transmission from animals to humans.
Mutation and Cross-Species Transmission: Mutations in the virus can allow it to jump from animals to humans, and potentially from human to human.
6.5 Other pathogenic agents
What is influenzas mode of infection?
- The flu virus targets the ciliated epithelial cells in the respiratory system.
- The viral RNA enters the host cell’s nucleus
- The virus takes over the cell’s biochemistry to produce new viral particles.
- The infected cell eventually ruptures (lyses), releasing the newly created viruses.
- The body’s reaction to cell lysis contributes to various flu symptoms.
6.5 Other pathogenic agents
How is Puccinia graminis transmitted, and what is its life cycle?
Transmission:
* Spores spread via wind from infected wheat plants or alternate hosts (e.g., barberry shrubs).
* Spores can travel long distances, infecting crops hundreds of miles away.
Life Cycle: Requires two hosts:
* Primary Host: Cereals (wheat, barley) – produces reddish urediniospores for repeated infection.
* Alternate Host: Barberry shrubs – produces basidiospores for genetic diversity.
* This complex cycle allows rapid spread and adaptation.
6.5 Other pathogenic agents
Describe the infection process of Puccinia graminis in cereal crops.
- Spore Germination: Requires moisture (rain/dew) and temperatures of 15–20°C.
- Hyphae Penetration: Spores land on wheat, germinate, and hyphae invade stomata (leaf pores).
- Nutrient Absorption: Hyphae secrete enzymes (e.g., cellulases) to digest plant cells, absorbing nutrients.
- Mycelium Growth: Hyphae form a mycelium network within stems/leaves, remaining hidden until symptoms appear.
- Sporulation: Red pustules erupt, releasing urediniospores to infect neighboring plants.
6.5 Other pathogenic agents
How does stem rust reduce grain yield and damage wheat plants?
- Nutrient Theft: Absorbs sugars and minerals, starving developing grains.
- Epidermal Damage: Pustules rupture the epidermis, impairing transpiration control and increasing water loss.
- Vascular Disruption: Hyphae block xylem/phloem, reducing water/nutrient flow to grains.
- Structural Weakness: Infected stems lodge (collapse) in wind/rain, making harvest impossible.
- Yield losses can reach 90%, devastating food production.
6.5 Other pathogenic agents
What strategies are used to control stem rust, and what challenges exist?
- Crop Management: Wider plant spacing, reduced nitrogen fertilizers, removing barberry shrubs.
- Chemical Fungicides: Expensive and environmentally harmful.
- Genetic Resistance: Breeding wheat with resistance genes (e.g., Sr31).
- Challenges:
- New Strains: Ug99 strain (discovered in 1999) overcomes most resistance genes, threatening 80–90% of global wheat.
- Climate Change: Warmer, wetter conditions favor spore germination and spread.
- GM Crops: Public resistance to genetically modified wheat slows adoption.
6.5 Other pathogenic agents
What is the malaria parrasite?
Plasmodium spp. which is a blood parasite, that is protozoa.
6.5 Other pathogenic agents
Why is the Plasmodium life cycle complex?
Involves two hosts: humans and Anopheles mosquitoes
6.5 Other pathogenic agents
How is malaria transmitted?
Vector: Female Anopheles mosquitoes
The parasite passes between the mosquito and human host
6.5 Other pathogenic agents
What role does mosquito saliva play in transmission?
Contains an anticoagulant to prevent blood clotting
The parasite enters the mosquito’s body and develops further
6.5 Other pathogenic agents
How does malaria transmission occur between humans and mosquitoes?
- Gametocytes from an infected human enter a mosquito during feeding.
- The parasite develops in the mosquito’s gut.
- Sporozoites (new stage) move to the mosquito’s salivary glands.
- The mosquito bites another human, injecting the parasite into the bloodstream.
6.5 Other pathogenic agents
What happens when the malaria parasite enters the human body?
Initially infects the liver, staying dormant for some time
Moves into the bloodstream, invading red blood cells
Reproduces asexually within red blood cells
6.5 Other pathogenic agents
How does the malaria parasite destroy red blood cells?
Bursts out of RBCs every 48–72 hours
Destroys RBCs before infecting new ones
Leads to cycles of fever and chills
6.5 Other pathogenic agents
What symptoms does malaria cause?
- Cycles of fever, sweating, muscle pain, and headaches
- Caused by the breakdown (lysis) of red blood cells
6.5 Other pathogenic agents
What are the long-term effects of malaria?
- Severe anaemia due to RBC destruction
- Organ failure in severe cases
- Death, especially in vulnerable populations
6.5 Other pathogenic agents
What is an endemic disease?
A disease constantly present in a specific country or area, such as malaria.
6.5 Other pathogenic agents
What are the challenges of treating endemic diseases?
- Widespread nature → Difficult to eradicate
- Pathogen persistence in the environment → Hard to track and remove sources
- Requires large population cooperation → Needs education and policy enforcement
- Expensive to control → Healthcare investment is necessary
6.5 Other pathogenic agents
How does malaria’s lifestyle make it harder to eliminate?
- Can remain dormant in the body for long periods
- Hides inside liver cells and red blood cells, evading the immune system
- Requires multiple strategies for effective control
6.5 Other pathogenic agents
What are common malaria treatments?
- Quinine, chloroquine, artemisinin
- Kill parasites but are most effective if taken early
6.5 Other pathogenic agents
Why is malaria becoming harder to treat?
Drug resistance is increasing, especially to older drugs like chloroquine
WHO now recommends combination therapy to prevent resistance
6.5 Other pathogenic agents
Why is it difficult to create a malaria vaccine and therefore, what are the most effective methods to control malaria spread?
- Malaria parasite spends most of its time inside host cells, evading the immune system
- Its surface antigens frequently change, making recognition difficult
SOLUTIONS: - Controlling mosquitoes (eliminating breeding sites, insecticides)
- Using insecticide-treated bed nets (LLINs)
- Improving access to effective treatment
6.5 Other pathogenic agents
Why are malaria control measures challenging in some regions?
- Many affected populations live far from medical help
- Medicines and healthcare services are expensive
6.5 Other pathogenic agents
What are effective ways to avoid contact with mosquitoes?
- Have mosquito screens on doors and windows
- Sleep under mosquito nets (preferably treated with insecticide)
- Use insect repellents and insecticides in the home and on people
- Wear long-sleeved clothes and long pants to cover as much skin as possible
6.5 Other pathogenic agents
How can mosquito breeding be controlled?
- Removing breeding sites: Emptying standing water (e.g., garden ponds, old tires, flowerpots, drink cans)
- Proper disposal of sewage: Managing human waste to prevent stagnant water accumulation
- Biological control: Seeding water supplies with organisms that feed on mosquito larvae
- Chemical control: Spraying water sources with pesticides to kill eggs and larvae
6.6 Problems of controlling endemic diseases
What are the social/ethical/economic issues surrounding mosquito breeding control?
- Persuading people to change behaviors (e.g., sleeping under nets, clearing stagnant water) requires social engagement.
- Significant investment is required, and governments must decide whether to spend funds on mosquito nets, antibiotics, or other healthcare interventions.
- Individual autonomy vs. public health needs (e.g., vaccinations, insecticide use)
- Risks involved in medical treatments
- Cultural and ethical differences in healthcare decisions
6.6 Problems of controlling endemic diseases
What role does the scientific community play in validating malaria control methods?
Conducts rigorous trials, peer-reviews data, and monitors resistance to ensure methods are safe, effective, and evidence-based.
6.7 Response to infection
What is the role of cell recognition in the immune system?
It allows the body to distinguish between its own cells (‘self’) and foreign cells or organisms (‘non-self’).
6.7 Response to infection
What are antigens?
Antigens are non-self glycoproteins on the surface of foreign cells that are recognized by white blood cells during the immune response.
6.7 Response to infection
How do pathogens trigger non-specific responses?
Pathogens trigger non-specific responses by breaking down body cells and releasing chemicals, or by being labeled by the specific immune system.
6.7 Response to infection
What is inflammation?
Inflammation is a non-specific response to infection involving redness, swelling, and heat due to increased blood flow and the release of histamines.
6.7 Response to infection
What are histamines, and what is their role in inflammation?
Histamines are chemicals released by mast cells and basophils that dilate blood vessels and increase local temperature to reduce pathogen reproduction.
6.7 Response to infection
What is the purpose of a fever in fighting infection?
A fever raises the body temperature to inhibit pathogen reproduction and boost the efficiency of the immune system.
6.7 Response to infection
What are phagocytes, and what are the two main types?
Phagocytes are white blood cells that engulf and digest pathogens. The two main types are neutrophils and macrophages.
6.7 Response to infection
What is phagocytosis?
Phagocytosis is the process by which phagocytes engulf and digest pathogens in a vesicle called a phagosome.
6.7 Response to infection
How do neutrophils and macrophages differ in their function?
Neutrophils are short-lived and ingest fewer pathogens, while macrophages live longer and can ingest more pathogens due to their ability to renew lysosomes.
6.7 Response to infection
What are cytokines, and what role do they play in the immune response?
Cytokines are chemical signals released by phagocytes that stimulate other immune cells to move to the site of infection and enhance the immune response.
6.7 Response to infection
What is the immune response, and what are its four key characteristics?
The immune response is the specific response of the body to pathogens, enabling recognition and removal of ‘non-self’ antigens.
Characteristics:
Distinguishes ‘self’ from ‘non-self’.
Responds specifically to foreign cells.
Recognizes an estimated 10 million antigens.
Has immunological memory to respond rapidly to previously encountered pathogens.
6.7 Response to infection
What are the two main types of lymphocytes?
B cells: Produced and matured in the bone marrow, they have receptors specific to antigens. Once activated, they form plasma cells that produce antibodies and B memory cells for immunological memory.
T cells: Produced in the bone marrow but mature in the thymus gland. They have receptors specific to infected body cells and are divided into T killer cells, T helper cells, and T memory cells.
6.7 Response to infection
What are lymphocytes, and where are they produced?
Lymphocytes are white blood cells involved in the specific immune system, produced in the bone marrow. They travel in blood and lymph, recognizing and responding to foreign antigens.
6.7 Response to infection
What types of B cells are produced when a B cell binds to an antigen?
B effector cells: Divide to form plasma cell clones.
Plasma cells: Produce antibodies at a high rate (around 2,000 per second).
B memory cells: Provide immunological memory for rapid response to the same antigen.
6.7 Response to infection
What are the different types of T cells and their roles?
T killer cells: Destroy infected body cells using chemicals.
T helper cells: Activate plasma cells to produce antibodies and secrete opsonins to aid phagocytosis.
T memory cells: Provide long-term immunological memory and rapidly divide to produce T killer cells on encountering the same pathogen.
6.7 Response to infection
What is the humoral response, and what are its two main stages?
The humoral response targets antigens found outside the body cells, such as bacteria.
Stages:
T helper activation: Phagocytes present antigens to T helper cells, which activate B cells.
Effector stage: B cells produce antibodies that are carried in the blood to neutralize pathogens.
6.7 Response to infection
What happens during T helper activation in the humoral response?
Pathogens release chemicals that attract phagocytes. Phagocytes digest the pathogens and present their antigens to T helper cells, which activate other immune cells.
6.7 Response to infection
Describe the in depth process of phagocytosis and draw a diagram
Phagocytosis:
1. Macrophage engulfs pathogen by phagocytosis
1. Vesicle (phagosome) containing pathogen fuses with lysosome
1. Antigens separated (antigen processing)
1. Processed antigen combines with MHC to form complexes that move to the outer cell membrane
1. Macrophages are now called antigen presenting cells (APCs)
6.7 Response to infection
Describe the process of T-helper cell activation and draw a diagram
- CD4 receptor cells on the T helper cells enable it to bind to the specific antigen on the antigen complex on the APC
- This triggers T helper cells to reproduce and produce clone cells with the same CD4 receptor as the original T cel
- All the T cells are now specific for that antigen
- Most of these cloned cells become active T helper cells which are used in the rest of the immune response
- Rest of the cells become memory cells
6.7 Response to infection
Describe the effector stage and draw a diagram
- B lymphocyte recognises the antigen of a pathogen
- Cytokines are released from active T cells
- Clonal selection
- B effector cells become plasma cells. Plasma cell synthesises the specific antibodies, antibodies are released from the plasma cell. Antibodies attach to the pathogen
6.7 Response to infection
What is clonal selection, and what do plasma cells do in the immune response?
- Clonal selection occurs when T helper cells stimulate B cells to divide and form plasma cell clones.
- Plasma cells produce antibodies identical to the parent B cell’s immunoglobulin.
6.7 Response to infection
What are the functions of the antibodies produced by plasma cells?
- Agglutination: Clumps pathogens for easier phagocytosis.
- Opsonisation: Marks pathogens for recognition by phagocytes.
- Neutralisation: Binds to toxins or bacteria to neutralize their effects.
- Plasma cells produce 2000 antibodies/second and are short-lived. Memory cells ensure long-term immunity.
6.7 Response to infection
What happens during the cell-mediated immune response?
- Used for intracellular pathogens like viruses.
- Infected cells present antigens on MHC molecules and become antigen-presenting cells (APCs).
T killer cells: - Bind to infected APCs using complementary receptors.
- Activated by cytokines from T helper cells, causing clonal expansion.
- Release chemicals to cause lysis of infected cell membranes, destroying the cells.
- Targets cancer cells, transplanted organs, and cells infected by viruses or bacteria.
6.7 Response to infection
What is the difference between the primary and secondary immune responses?
Primary Response:
* Takes days/weeks to activate.
* Involves plasma cells producing antibodies and T killer cells destroying infected cells.
* Causes symptoms as pathogens reproduce before being eliminated.
Secondary Response:
* Faster and more effective due to memory cells.
* Memory B and T cells quickly respond to the same pathogen.
6.7 Response to infection
Define vaccination
Vaccination introduces weakened or inactive antigens into the body to stimulate the immune response without causing disease.
6.7 Response to infection
Describe the steps required to produce a vaccine
Step 1: Introduction of antigens into the bloodstream via injection or orally.
Step 2: Lymphocytes recognize the antigens and stimulate an immune response.
Step 3: Antibodies are produced and memory cells are created.
Step 4: Upon future exposure to the same pathogen, the immune system reacts quickly and eliminates the threat.
6.7 Response to infection
What is herd immunity?
A phenomenon where a high percentage of vaccinated individuals in a population protects those who cannot be vaccinated.
6.7 Response to infection
What are the challenges and benefits surrounding herd immunity?
Importance:
* Prevents disease spread.
* Protects vulnerable individuals, including babies, immunocompromised people, and the very sick.
Challenges:
* Requires a significant proportion of the population to be vaccinated.
* Difficult to achieve in communities with limited access to vaccines.
6.7 Response to infection
What are the benefits of vaccination?
Protects the vaccinated individual and reduces disease spread.
Society benefits from overall reduced disease prevalence.
Financially cost-effective: Reduces long-term healthcare expenses.
6.7 Response to infection
What are the issues with vaccination?
Rare side effects and allergies can occur.
Ethical concerns regarding mandatory vaccination.
Potential risks when vaccination rates drop below herd immunity thresholds.
6.7 Response to infection
Define, natural active, natural passive, artifical active and artifical passive immunity
Natural Active Immunity: Immunity from an infection where the body produces its own antibodies.
Natural Passive Immunity: Immunity passed from mother to child through the placenta or breast milk.
Artificial Passive Immunity: Injection of antibodies (e.g., tetanus antitoxin).
Artificial Active Immunity: Immunity developed from vaccines
6.7 Response to infection
What are attentuated pathogens?
Weakened pathogens used in vaccines that don’t cause disease but trigger immunity.
