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Threats and Defence > Introduction to microbiology > Flashcards

Introduction to microbiology Flashcards

1
Q

What is the important of looking at a microorganism under a microscope?

A

Helps you to identify what microogranism is causing an infection and therefore this influences your treatment approach

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2
Q

What bacteria can cause pneumonia?

A

Asperigillus

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3
Q

What are the key groups of microorganisms?

A

bacteria (prokaryotes - biggest group), virus, fungi and parasites
2 groups of parasites - protozoa (similar to plants) and worms

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4
Q

Where do infections usually come from?

A

from ourselves = more bacterial cells than human cells - from our own flora

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5
Q

What are common endogenous infectious micro-organisms on the skin?

A

Staphylococcus aureus

Staphylococcus epidermidis

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6
Q

What are common endogenous infectious micro-organisms in the mouth/throat?

A

Viridans streptococci - can cause dental infections and also associated with endocarditis

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7
Q

What are common endogenous infectious micro-organisms in the gut?

A

Escherichia coli = aerobes

Bacteriodes species = anaerobes

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8
Q

What are common endogenous infectious micro-organisms in the vagina?

A

Lactobacilli = rarely cause infection - colonise in the vagina and protect it against infection

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9
Q

What is a common endogenous infectious micro-organisms in the vagina/mouth/skin?

A

Candida albicans - it occurs when lactobacillus is knocked out = causes thrush

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10
Q

Where do you catch exogenous infections?

A

From another person - e.g. chicken pox or from mother to child
From an animal - E.g. E.Coli 0157- carried in cow’s guts but not occurs and therefore contaminated burgers can infect us causing us to become very unwell
Vector - indirect method e.g. needle stick, beef burger Is the vector, malaria
Environment - certain organisms are just in the environment e.g. legionella can be found in water and can cause pneumonia

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11
Q

What is the structure of bacteria?

A

Prokaryotes
Single celled organisms
Divide by binary fission- divide rapidly e.g. E.coli divides every 20 mins
Single chromosome of circular DNA
Their cell wall is important for classification

Capsulated bacteria = helps to protect them
some have pili to help them adhere to surfaces

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12
Q

How are bacteria classified?

A

Shape = Cocci, Bacilli (rods), Spirochaetes (spirally), filamentous (grow in chains)
Gram stain - not all stain with this stain
Dependence on oxygen = anaerobes or aerobes
Spore formation = this function is very useful for bacteria because it means they are very resistant and can survive in the environment more easily
Metabolism - what they do to sugar filamentation

DNA sequencing e.g. of 16s- using mass spectrometry you can identify the organism in 10 minutes whereas it used to take 24 hours

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13
Q

What are the chemical used in gram staining?

A

Crystal violet
Iodine
Acetone
Neutral red

1) stain with crystal violet
2) fix with iodine
3) wash with acetone
4) counterstain with neutral red

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14
Q

What is the cell wall/membrane structure of gram positive and gram negative bacteria?

A

Almost all bacteria have a cell wall but the structure of it depends on the bacteria
Gram positive bacteria only have a thick peptidoglycan cell wall and no cell membrane

Gram negative bacteria have a thinner peptidoglycan cell wall which doesn’t bind crystal violet and they have an additional cell membrane on top of their cell wall

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15
Q

What are some examples of gram +ve cocci?

A

Staphylcocci aureus (clusters)

  • round purple circles grouped together like a bunch of grapes
  • about 30% of us carry it
  • if it invades tissue it acts as a pathogen
  • produces a golden colony on plates

Staphylcocci epidermis

  • tends not to be pathogenic
  • on our skin it helps to protect us from invasion
  • can cause a problem though if it breaches the skin barrier e.g. central line
  • it isn’t particularly nasty but it will still cause infection

Streptococci (chains)

  • produce a toxin that surrounds their colony
  • streptococci pneumonia = occurs in pairs and has a green clearing
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16
Q

What are some examples of gram +ve bacilli?

A

Lysteria

  • associated with soft chest
  • many people are not able to consume soft cheese due to this bacteria= immunosuppressed, elderly and pregnant

Clostridium = anaerobic

  • large family
  • difficile = infection can lead to diarrhoea
  • tetani = produces tetanus toxin
  • botulinum = producers botulinum = paralysis of muscles
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17
Q

What is an example of gram -ve bacilli?

A

Aerobic or anaerobic

e.g. E.coli

18
Q

What are some examples of gram -ve cocci?

A

Nisseria

  • 2 infections: meningitis and gonnorhoea
  • To test for meningitis you take some CSF via lumbar puncture

Gram -ve diplococci =meningitis
Gram +ve diplococci = streptococcus pneumonia = also causes meningitis

19
Q

What are some examples of bacteria that don’t stain with the gram stain?

A

Spirochetes e.g. syphilis

  • cell wall is too thin
  • identified by PCR or dark stain microscopy

Tuberculosis - use acid-fast stain

20
Q

What is the key pathogen for cellulitis?

A

Staph. aureus, streptococcus progenis

21
Q

What is the key pathogen for pneumonia?

A

Streptococcus pneumonias (gram +ve diplococci), Haemophilus influenza (rod)

22
Q

What is the key pathogen for meningitis?

A

Nisseria meningitis, streptococci pneumonia

23
Q

What is the key pathogen for UTI?

A

most commonly from gut bacteria
Occurs more often in women than men due to their shorter ureter
E.Coli - from own flora

24
Q

What is the key pathogen for cholecystitis?

A

E.Coli

25
Q

What is the key pathogen for appendicitis, diverticulitis?

A

E.Coli - gut anaerobes coming from bowel

26
Q

What is the key pathogen for gastroenteritis?

A

Campalobacter, salmonella = both gram -ve bacilli

27
Q

What is the key pathogen for bacteraemia?

A

bacteria from outside

Brushing of teeth - potentially this happens everyday

28
Q

How do bacteria cause disease?

A

1) invasion > inflammation
2) Toxin production - release of toxins e.g. botulinum
3) Immunopathogeneis

29
Q

What antibiotics act on cell wall synthesis?

A

1) beta-lactams e.g penicillins, cephalosporins, carbapenems
2) Glycopeptides e.g. vancomycin, teicoplanin.

30
Q

What antibiotics act on protein synthesis?

A

1) tetracyclines
2) Aminoglycosides (e.g. gentamicin)
3) Macrolides (e.g. erythromycin)

31
Q

What antibiotics act on Metabolic pathways (folate synthesis)?

A

1) Trimethoprim

2) Sulphonamides

32
Q

What antibiotics act on nucleus (DNA synthesis)?

A

1) Quinolones

2) Metronidazole

33
Q

Are antibiotics that act against cell wall synthesis safe?

A

they can’t damage our own cell wall, so they are not particularly toxic
- Used in pregnancy

34
Q

Why can’t penicillins be used against lots of staph. aureus?

A

Penicillin is a beta-lactam and staph. aureus bacteria have adapted to confer resistance against them

35
Q

What do antibiotics against protein synthesis take advantage of?

A

It takes advantage that our ribosomal subunits are different to bacterias (30s and 50s subunits)

36
Q

What antibiotic is used to treat cellulitis?

A

Flucloxadin

37
Q

What are some of the side effects of antibiotics?

A

Rash, anaphylaxis, diarrhoea
C.difficile infection - antibiotics against other infections cause c. diff to grown and therefore this can lead to the production fo toxins, which can in serious conditions lead to mortality
Antibiotic resistance

38
Q

How do you test for antibiotic resistance?

A

On a plate, you have the bacteria and then plates with disks of antibiotics on them to see if the bacteria can grow in the presence of the bacteria

If there is a zone of sparing this means the antibiotics are effective

39
Q

What is MRSA resistant to and what do you treat it with instead?

A

resistant to flucloxacillin and methicillin, so you have to treat it with vancomycin

40
Q

What are the antibiotic resistance mechanisms?

A

1) Antibiotic degrading/altering enzyme (e.g. penicillinase, extended spectrum beta-lactamase, carbapenemase)
2) Alteration of target site (e.g. penicillin binding protein in MRSA)
3) Reduction in permeability (porin proteins)
4) Efflux pumps (e.g. macrolides) - pump antibiotic back out

Threats and Defence (10 decks)

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