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Biology > Chapter 6: Microbiology and Pathogens > Flashcards

Chapter 6: Microbiology and Pathogens Flashcards

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1
Q

6.1 Microbial techniques

To investigate microorganisms they need to be…

A

cultured.

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2
Q

6.1 Microbial techniques

What is culturing?

A

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.

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3
Q

6.1 Microbial techniques

Why is it important to be careful when culturing microorganisms?

A
  1. Even if they are harmeless there is risk of a mutant strain arising that can be pathogenic
  2. Contamination of the culture by pathogenic microorganisms
  3. Growing a pure strain will be contaminated by any new microorgnaism entering it.
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4
Q

6.1 Microbial techniques

What do most microorganisms require a good source of?

A

Carbon nitrogen and other minerals

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5
Q

6.1 Microbial techniques

How is the nutrient medium found?

A
  1. Nutrient broth (liquid)
  2. Nutrient solid form
  3. Nutrient agar (jelly)-this is extracted from seaweed
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6
Q

6.1 Microbial techniques

Most microorganisms need nutrient enriching substances to grow such as…

A

blood, yeast or meat extract

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7
Q

6.1 Microbial techniques

What is a selective medium?

A

A nutrient medium with very specific ingredients in which only a select group of microorganisms will grow.

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8
Q

6.1 Microbial techniques

What is innoculation?

A

The process of introducing (placing) bacteria onto the agar.

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9
Q

6.1 Microbial techniques

What is used to complete innoculation?

A

Use an innoculating loop and a process called streaking by scraping bacteria off one solid plate and transferring to a chosen medium.

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10
Q

6.1 Microbial techniques

What is an alternative method to a loop for innoculation?

A

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.

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11
Q

6.1 Microbial techniques

After plate/flask has the bacteria added what is done to ensure the bacteria will grow properly?

A

The flask is incubated at a suitable temperature
The flask is shaken often making sure it is aerated

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12
Q

6.1 Microbial techniques

What are the effects of culturing bacterias in oxygen and not in oxygen?

A

Not in oxygen: only anaerobic bacteria survive
Oxygen: aerobic bacteria survive

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13
Q

6.1 Microbial techniques

Define a pathogen

A

Microorganism that is a disease causing agent

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14
Q

6.1 Microbial techniques

Define a culture

A

A growth medium where a microorganism is provided with the correct organisms to grow in large numbers

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15
Q

6.1 Microbial techniques

Define a nutrient medium and nutrient broth/agar

A

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.

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16
Q

6.1 Microbial techniques

How do you count single celled fungi in nutrient broth?

A
  • 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.
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17
Q

6.1 Microbial techniques

Which of the blue or purple is counted?

A

Only purple is counted. They MUST be touching the top and left line to be counted.

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18
Q

6.1 Microbial techniques

Explain the use of optical methods to measure the number of cells in a culture

A
  • 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.
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19
Q

6.1 Microbial techniques

Explain the relationship between turbidity and cell concentration

A

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.

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20
Q

6.1 Microbial techniques

Describe how a colorimeter measures turbidity

A

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)

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21
Q

6.1 Microbial techniques

How do you make a calibration curve?

A
  1. Growing a control culture and taking samples at regular time intervals.
  2. Measuring the turbidity of each sample using a colorimeter.
  3. Performing a direct cell count on each sample, e.g. using a haemocytometer.
  4. Plotting a graph with turbidity on the x-axis and cell count on the y-axis.
  5. The resulting calibration curve shows the relationship between turbidity and cell concentration.
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22
Q

6.1 Microbial techniques

Define dilution plating

A

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.

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23
Q

6.1 Microbial techniques

Explain the purpose of dilution plating (when is it useful)

A
  • 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
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24
Q

6.1 Microbial techniques

What is the process of dilution plating?

A
  • 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)
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25
Q

6.1 Microbial techniques

How do you interpret the dilution plating results?

A
  1. Counting the colonies: Carefully count the number of colonies on each agar plate.
  2. Calculating the dilution factor: Determine the overall dilution factor by multiplying the dilution factors at each step.
  3. 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.
  4. Assessing the accuracy: Compare results across replicate plates to ensure consistency. The more plates counted, the more accurate the final estimate.
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26
Q

6.1 Microbial techniques

How do you calcualte the optimum temperature for growth?

A
  • 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.
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27
Q

6.1 Microbial techniques

Testing optimum nutrients or pH

A
  • 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
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28
Q

6.1 Microbial techniques

Time between bacterial divisions is referred to as…

A

Generation time.

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29
Q

6.1 Microbial techniques

What acts as a barrier to infinity reproduction of bacteria?

A

Waste products and lack of nutrients

30
Q

6.1 Microbial techniques

Why is a logarithmic scale used when considering bacterial growth?

A

The numbers are too large when increasing to put on a graph so a logarithmic scale condenses the data to plot on a graph.

31
Q

6.1 Microbial techniques

What is the formula to calculate the no of bacteria in a population?

A
32
Q

6.1 Microbial techniques

What is the exponential growth rate constant and what does it represent?

A

The no. of times the population doubles in one unit of time.

33
Q

6.1 Microbial techniques

What are the four stages of the growth curve?

A
  1. Lag phase
  2. Log phase
  3. Stationary phase
  4. Death phase
34
Q

6.1 Microbial techniques

Draw the growth curve and label each of the 4 stages

A
35
Q

6.1 Microbial techniques

Describe the lag phase

A

When bacteria are adapting to their new environment and are not yet reproducing at their maximum rate.

36
Q

6.1 Microbial techniques

Describe the log phase

A

When the rate of bacterial reproduction is close to or at its theoretical maximum, repeatedly doubling in a given time period.

37
Q

6.1 Microbial techniques

Describe the stationary phase

A

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.

38
Q

6.1 Microbial techniques

Describe the death phase

A

When reproduction has almost ceased and the death rate of cells is increasing.

39
Q

6.2 Bacteria as pathogens

How do pathogenic bacteria cause disease?

A

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.

40
Q

6.2 Bacteria as pathogens

What are the two classifications of bacterial pathogens?

A

Endotoxins and Exotoxins

41
Q

6.2 Bacteria as pathogens

What type of molecule are endotoxins and where are they located?

A
  • lipopolysaccharides
  • on outerlayer of cell wall of gram negative bacteria
  • lipid part of the lipopolysaccharides produce the toxin while the polysaccharides produce an immune response
42
Q

6.2 Bacteria as pathogens

What is a key example of endotoxins?

A

** 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.

43
Q

6.2 Bacteria as pathogens

What types of molecules are exotoxins and where are they found?

A

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.

44
Q

6.2 Bacteria as pathogens

What is a key example of exotoxins?

A
  • 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.
45
Q

6.2 Bacteria as pathogens

What is host tissue invasion?

A

Invading host cells and damaging tissue is the way bacteria acts as a pathogen.

46
Q

6.2 Bacteria as pathogens

What is a key example of host tissue invasion?

A

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.

47
Q

6.2 Bacteria as pathogens

Define primary infection

A

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

48
Q

6.3 Action of antibiotics

How do antimicrobial drugs work?

A

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.

49
Q

6.3 Action of antibiotics

What are antimetabolites with an example?

A
  • Action: Interrupts metabolic pathways, such as blocking nucleic acid synthesis, causing death.
  • Example: Sulfonamides
  • Bacteriostatic
50
Q

6.3 Action of antibiotics

What are Protein Synthesis Inhibitors with an example?

A
  • Action: Interrupts or prevents transcription and/or translation of microbial genes, affecting protein production.
  • Example: Tetracyclines, Chloramphenicol
  • Bacteriostatic
51
Q

6.3 Action of antibiotics

What are Cell Wall Agents with an example?

A
  • Action: Prevents formation of cross-linking in cell walls, leading to bacterial lysis (bursting).
  • Example: Beta-lactams (e.g., Penicillins)
  • Bactericidal
52
Q

6.3 Action of antibiotics

What are Cell Membrane Agents with an example?

A
  • Action: Damages the cell membrane, causing metabolites to leak out or water to move in, killing the bacteria.
  • Example: Some Penicillins, Cephalosporins
  • Bactericidal
53
Q

6.3 Action of antibiotics

What are DNA Gyrase Inhibitors with an example?

A
  • Action: Stops bacterial DNA coiling up, making it too large to fit within the bacterium.
  • Example: Quinolones
  • Bactericidal
54
Q

6.3 Action of antibiotics

What is bacteriostatic?

A

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.

55
Q

6.3 Action of antibiotics

What is bactericidal?

A

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

56
Q

6.3 Action of antibiotics

What factors do antimicrobial drug effectiveness depend on?

A
  • concentration of the drug
  • pH
  • wether pathogen or host tissue destroy pathogen
  • sucesptibility
57
Q

6.4 Antibiotic resistance

What is a superbug and what are examples of it?

A

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.

58
Q

6.4 Antibiotic resistance

What is MRSA and how has it become a superbug?

A
  • 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.

59
Q

6.4 Antibiotic resistance

What is colostorum difficil and its toxins?

A

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.

60
Q

6.4 Antibiotic resistance

you didnt do pg58 text book

A
61
Q

6.4 Antibiotic resistance

pg58 text book

A
62
Q

6.5 Other pathogenic agents

The main way that viruses can cause disease is by…

A

lysis of host cell

63
Q

6.5 Other pathogenic agents

How does the flu cause epidemics or pandemics?

A

It mutates frequently making it very difficult to treat.
Pandemic-worldwide
Epidemic-within the country

64
Q

6.5 Other pathogenic agents

What is the key example of a virus that acts as a pathogen?

A

Influenza

65
Q

6.5 Other pathogenic agents

What are influenzas mode(s) of transmision?

A

**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.

66
Q

6.5 Other pathogenic agents

What is influenzas mode of infection?

A
  1. The flu virus targets the ciliated epithelial cells in the respiratory system.
  2. The viral RNA enters the host cell’s nucleus
  3. The virus takes over the cell’s biochemistry to produce new viral particles.
  4. The infected cell eventually ruptures (lyses), releasing the newly created viruses.
  5. The body’s reaction to cell lysis contributes to various flu symptoms.
67
Q

6.5 Other pathogenic agents

A
68
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6.5 Other pathogenic agents

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69
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6.5 Other pathogenic agents

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70
Q

6.5 Other pathogenic agents

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Biology (7 decks)

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