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biology year 2 > topic 6 : microbiology and pathogens > Flashcards

topic 6 : microbiology and pathogens Flashcards

1
Q

why are microorganisms cultured?

A

they are too small to be seen by the naked eye

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2
Q

what is the definition of a pathogen

A

microorganisms that cause diseases

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3
Q

what is a culture?

A

measures growth of microorganisms (bacteria and fungi) in a culture/nutrient medium under controlled conditions

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4
Q

what is a nutrient/culture medium?

A

substance used for the culture of microorganisms which can be in a liquid form (nutrient broth) or solid form (nutrient agar)

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5
Q

selective media

A

only a selected group of microorganisms
- has specific nutrients for the bacteria

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6
Q

what does inoculation mean?

A

getting bacteria on agar/broth with inoculating loop (which scrapes bacteria from solid surface to medium)

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7
Q

definition of sterile

A

free from living microorganisms and their spores

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8
Q

how to obtain a pure culture?

A
  • desired microorganism must be isolated
  • growing under anaerobic/aerobic conditions means that only certain bacteria survive
  • medium can favour the growth of one organisms by controlling the nutrients or adding growth inhibitors
    indicator media cause certain bacteria to change colour
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9
Q

how do cell counts measure the growth of bacteria?

A
  • bacteria and s.c fungi can be counted using haemocytometer
  • dead cells stain blue from the trypan blue stain
  • count the bacterial cells in each 4 sets of 16 squares and take a mean
  • pre calibrated haemocytometer, to allow number of microorganisms in a standard volume of broth to be calculated
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10
Q

what does it mean if something is turbid?

A

opaque/cloudy/thick with suspended matter, in the context of water
- as turbidity increases, transmission of light decreases and absorbance increases.

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11
Q

how do optical methods (turbidity) show and measure the growth of bacteria?

A

As the number of bacterial cells in a culture increases, it becomes more cloudy or turbid
- turbid solutions absorb more light - LIGHT PASSING THROUGH MEASURED BY COLORIMETER - show how many microorganisms are present
- calibration curve produced by growing a control culture and taking samples at regular tie intervals
- turbidity and cell count (with haemocytometer) measured for each sample - relationship between turbidity and num. of cells present

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12
Q

how can dilution plating be used to measure the growth of bacteria?

A
  • finds total viable cell count
  • use assumption that each colony grows from a single microorganism
  • eg. 30 patches of mycelia means that there were 30 fungal cells on plat when inoculated.
  • solid mass of microbes is present after culturing
    0 this is done by diluting the original culture in stages until a point is reached when the colonies can be counted - each colony assumed to come from one cell (refer to picture in sia’s notes)
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13
Q

how can the area and mass of fungi be used to measure the growth of culture?

A
  • measure diameter of patches of mycelium
  • used to compare growth rate in different conditions
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14
Q

what is the lag phase

A

microorganisms adapting to their environment and reproduction rate increases slowly

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15
Q

what is the log phase

A

microorganisms grow at their maximum rate, as long as there are SUFFICIENT RESOURCES

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16
Q

what is stationary phase?

A

death rate = reproduction rate (due to buildup of waste products and lack of nutrients).

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17
Q

what is death phase

A

deaths exceed new cell population as conditions continue to worsen

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18
Q

what are the different types of mediums ?

A

broth cultures, agar and selective media

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19
Q

what is a medium ?

A

mediums can favour the growth of one organism by controlling the nutrients or adding growth inhibitors

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20
Q

different methods of measuring growth of bacterial culture

A

cell counts, dilution plating, mass and optical methods

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21
Q

different phases of bacterial growth curve?

A

lag phase, log phase, stationary phase and death phase

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22
Q

how can bacteria enter the body

A
  • cuts on skin/eyes
    droplets through nose/mouth
  • reproductive tract
  • can be through direct contact or by a vector (exterior organism)
23
Q

what can bacteria do as pathogens?

A

can be :
- agents of infection
- invading and destroying host tissues
- producing toxins

24
Q

what is an exotoxin and how do they cause damage?

A

(gram pos and neg bacteria)
- exotoxins proteins are released from their cytoplasm
- An exotoxin can cause damage to the host by destroying cells or disrupting normal cellular metabolism.

25
Q

example of exotoxin
- how they cause disease
- gram pos or neg
- where is it found on body
- pathogenic effect
- how is it treated

A

staphylococcus (S.aureus)
- only cause disease if they get into tissue due to another disease, or if the person is immunocompromised
- gram positive bacteria
- found on the skin
- can cause skin and joint infections, infections of membranes around the heart, toxic shock syndrome, bacterial meningitis if it has access to the brain.
- treated with antibiotics, but becoming increasingly resistant –> cause death rapidly

26
Q

what is an endotoxin and how do they cause damage?

A

(gram neg bacteria)
- endotoxins are a part of the cell’s surface membrane
- they initiate a host inflammatory response to Gram-negative bacterial infection (fever esc).

27
Q

example of endotoxin
- pathogenic effect

A

salmonella ( gram negative bacteria)
- invades the intestine lining - endotoxins cause inflammation
- cells no longer reabsorb water

28
Q

what is invasion of host tissue?

A

The response of the host cell to this invasion causes the symptoms

Linked to the production of exotoxins and endotoxins in the cell walls

29
Q

how is TB spread?

A

Spread by droplet infection - the immunocompromised are more at risk

30
Q

how does a primary infection of invasion of host cell work? (of tubercolosis)

A
  • bacteria invade the lung cells and multiply. cause NO SYMPTOMS
  • localised inflammation –> mass of tissue (tubercule)
  • The immune system usually then controls the bacteria and the inflammation dies down
31
Q

how is Tb adapted to avoid the immune system?

A

Can remain dormant and protected from macrophage enzymes, until the person’s immune system is weakened, then it can cause serious lung damage (symptoms like coughing up blood)

  • this will all allow some bacteria to survive this.
32
Q

what are antibiotics and what do they do?

A
  • chemicals that target differences in structure/biochemistry between bacterial and mammalian cells
  • destroy or inhibit reproduction of bacterial cells.
33
Q

what is a bactericidal antibiotic?

A

directly destroys bacterial cells (kills)

34
Q

what is a bacteriostatic antibiotic?

A

inhibit growth and reproduction of bacteria

35
Q

how do bacteria become resistance to antibiotics?

A
  • mutations common in bacteria because they divide so rapidly (can create a difference in structure or biochemistry)
  • meaning that the bacterium is no longer affected by antibiotics (eg. penicillinase)
36
Q

example of bacterial infection which is resistant to antibiotics and how do they come about?

A
  • MRSA
  • resistance to antibiotics results in antibiotic resistance bacterial infections in hospitals
37
Q

how to control the spread of antibiotic resistant infections?

A
  • new patients screened at arrival, isolated and treated if they are infected - prevented spread of bacteria
  • antibiotic only used when needed ant the entire course of antibiotics is completed
  • hygiene - wash with alcohol based antibacterial gells and wearing suitable clothes

all to minimise the transmission of resistant bacteria

38
Q

why should antibiotic courses be completed?

A

ensure that bacteria are destroyed and minimise the selection pressure on bacteria to prevent resistant strains from forming

39
Q

describe the evolutionary race (natural selection behind antibiotic resistance

A
  • in a population of bacteria, there are random mutations that cause antibiotic resistance, and then these bacteria will be resistant to antibiotics
  • there will be a competition for resources (eg. co2) - better adapted ones will survive for longer
  • non-resistant bacteria will die
  • the resistant bacteria will reproduce and eventually all population will have antibiotic resistance.
40
Q

what is a macrophage?

A
  • derived from monocytes, in the leukocytes (WBC) in the blood (4%)
  • monocytes migrate to tissues - become macrophages (now macrophages in tussues)
  • good capacity of ingesting pathogens (can renew their lysosomes).
  • They accumulate at the site of infection.
41
Q

what is a neutrophil?

A
  • granulocytes, in leukocytes in blood (70%)
  • each one can only digest a few pathogens before it dies - cannot renew lysosomes
  • accumulate at the sight of infection
42
Q

why is it difficult to control endemic diseases?

A
  • Widespread
  • Hard to remove all sources of infection, particularly with 2 hosts
  • Large numbers - expensive
43
Q

control measures of endemic disease (specific to malaria)?

A
  • Prevent bites - insect repellants, mosquito nets with insecticide, screens over windows and doors

-Control mosquito numbers - avoid stagnant water and sewage, introduce predators, pesticides

44
Q

ethical implications of controlling endemic disease (specific to malaria) ?

A
  • Safety of vaccines - reservations (some people might want it, while others will not)
  • Difficult to obtain informed consent
    where education on health is poor
  • spraying mosquitoes with insecticides will affect other organisms
45
Q

social implications of controlling endemic disease (specific to malaria) ?

A
  • vaccines needed to become accepted
  • Social changes to reduce infection are difficult to bring about
  • People may need to change customs (eg. sleeping under a mosquito net)
46
Q

economic implications of controlling endemic disease (specific to malaria) ?

A

Treatment, control and prevention is very expensive
Many of the affected countries are poor
Where to place resources - in these countries, issues such as malnutrition are also prevalent

47
Q

what is the definition of a pathogen

A

microorganisms that cause diseases

48
Q

what is agglutination (by antibodies)

A

clumping microorganisms together - makes phagocytosis easier

49
Q

what is lysis (by antibodies)

A

bursting of bacterial cell

50
Q

what is opsonisation (by antibodies)

A

making an antigen/pathogen easily detectable/ recognised by phagocytes

51
Q

what is precipitation (by antibodies)

A

soluble toxin made inactive

52
Q

what is neutralisation (by antibodies)

A

bind to bacterial toxin and neutralise

53
Q

what are HCAI’s

A

healthcare associated infections

biology year 2 (7 decks)

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