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Phase 2a > Microbiology > Flashcards

Microbiology Flashcards

1
Q

Define colonisation

A

The microorganism can be cultured from the host but is not causing disease.

Other words - commensal or asymptomatic carriage

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2
Q

Define infection

A

The microorganism can be cultured from the host and it is causing disease

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3
Q

Define opportunistic pathogen/infection

A

Microorganism that only cause disease when the host defence is somehow compromised

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4
Q

Define virulence/pathogenicity

A

The degree to which a given organism is pathogenic

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5
Q

Describe the nomenclature of bacteria

A

Staphylococcus (genus) aureus (species)

Name commonly reflects the shape

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6
Q

Describe the colonial morphology of staph aureus

A

Gold and round

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7
Q

Describe the colonial morphology of staph epidermiditis and saprophyticus

A

White and round

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8
Q

Describe the colonial morphology of strep pyogenes

A

White, round, beta haem

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9
Q

Describe the colonial morphology of pseudomonas aeruginosa

A

Green, irregular, mucoid, smells like swimming pool

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10
Q

Describe the colonial morphology of e.coli

A

Greyish, round, faecal smell

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11
Q

Describe the colonial morphology of Neisseria

A

Greyish, round

Only grows on chocolate agar

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12
Q

What is grown on blood agars

A

Streptococcus and other

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13
Q

What is grown on chocolate agars

A

(cooked blood)

Fastidious Neisseria

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14
Q

What is grown on MacConkey agars

A

Lactose status

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15
Q

What is grown on CLED agars

A

Stops motile proteus swarming

Lactose status

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16
Q

What is grown on xylose lysine deoxycholate agar (XLD) agar

A

Selective growth

Salmonella and shigella from clinical samples and food

Both go red - ferment lactose

Salmonella - turns back dots - due to hydrogen sulphide production

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17
Q

What layer soaks up crystal violet

A

Peptidoglycan layer

Gram negative - washed away
Gram positive - cannot be

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18
Q

What colour do gram positive bacteria stain

A

Purple

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19
Q

What colour do gram negative bacteria stain

A

Pink

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20
Q

Describe the steps of gram stain

A

Crystal violet
Iodine
Alcohol (gram negative will become colourless)
Safranin (gram negative becomes pink)

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21
Q

What is the mnemonic for gram staining

A

Come in and stain

Crystal violet
Iodine
Alcohol
Safranin

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22
Q

What gram stain is staphylococcus aureus

A

Gram positive cocci (bunch of grapes)

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23
Q

What gram stain is e.coli

A

Gram negative rod, short and stubby

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24
Q

What gram stain is Neisseria meningitidis

A

Gram negative diplococci

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25
Q

What gram stain is bacillus cereus

A

Gram negative rod, long rod, some occurring in chains

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26
Q

What is the role of the catalase test

What would show on the test

A

Differentiates between staphylococcus and streptococcus genus

Staph = +

strep = -

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27
Q

On a catalase test does staph show are

A

Positive (weak bubbling)

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28
Q

On a catalase test what does strep show as

A

Negative (no bubbling)

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29
Q

Describe the method of catalase test

A

Apply hydrogen peroxide 3% to a small sample of pure colony

Observe for any bubbling

Any weak bubbling = positive

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30
Q

What is the role of the coagulase test

A

Is it staph aureus?

Differentiates staph aureus (which produces enzyme coagulase) from s. epidermis and s. saprophyticus

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31
Q

A +ve coagulase test would be which bacteria

A

Staph aureus

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32
Q

Describe the method of the coagulase test

A

Apply rabbit plasma to a small sample of pure colony

Observe for fibrin clot clumps

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33
Q

Describe the role of optochin

A

Differentiating alpha-haemolytic streps

S. pneumonia = susceptible

All other alpha streps are resistant

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34
Q

What is the role of the Lancefield serotyping

A

Differentiates beta haemolytic streps

Relies on different, group-specific carbohydrates antigen presents on the cell wall

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35
Q

Describe an infection of c. difficle

A

Antibiotic therapy = disruption of colonic microflora

C. diff exposure and colonisation

C. diff toxin A and B cause mucosal injury and inflammation

= pseudomembranous colitis = toxic megacolon = perforation and death

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36
Q

What is the treatment of c. diff

A

10 days oral fidaxomicin or vancomycin

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37
Q

What is the treatment of meningitis

A

Cephalosporins - IV cefotaxime/IV ceftriaxone

Over 50/immunocompromised - IV amoxicillin to cover listeria

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38
Q

What treatment is given for contacts of meningitis

A

One oral dose of ciprofloxacin

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39
Q

What is the treatment of meningococcal septicaemia

A

Immediate IM benzylpenicillin (community)

IV cefotaxime (hospital)

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40
Q

What medication is given to UTIs during pregnancy

A

Cefalexin

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41
Q

What medication is given to UTIs

A

Oral nitrofurantoin or trimethoprim

Simple = 3 days
Complicated = 7 days

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42
Q

Describe the pathophysiology of helicobacter pylori infection

A

Colonise gastric mucosa

Urease enzyme = urea = NH3 + CO2

Disrupts mucous and release toxins = ulcers

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43
Q

What is the gram stain of helicobacter pylori

A

Gram negative

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44
Q

What is the treatment of h. pylori

A

Triple therapy

Abx + Abx + PPI

Amoxicillin + metronidazole + omeprazole

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45
Q

What antibiotics inhibit cell wall synthesis

A

Glycopeptides - vancomycin, teicoplanin

Beta lactams
- penicillin
- cephalosporins
- carbapenems

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46
Q

Give 3 examples of cephalosporins

A

Cephalexin
Cefotaxime
Ceftriaxone

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47
Q

Give 2 examples of carbapenems

A

Imipenem
Ertapenem

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48
Q

What is used to treat MRSA and c. diff infections

A

Glycopeptide vancomycin

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49
Q

What antibiotics inhibit protein synthesis

A

Chloramphenicol

Macrolides

Tetracyclines

Aminoglycosides

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50
Q

Name 2 examples of macrolides

A

Clarithromycin

Erythromycin

51
Q

Name an example of tetracyclines

A

Doxycycline

52
Q

Name 2 examples of aminoglycosides

A

Gentamicin

Streptomycin

53
Q

What antibiotic is generally used for people with penicillin allergies

A

Macrolides

54
Q

Name 4 ways in which antibiotics can inhibit nucleic acid synthesis

A

Inhibit folate synthesis
Inhibit DNA gyrase
Bind to RNA
DNA strand breaks

55
Q

Which antibiotics inhibit folate synthesis

A

Trimethoprim

Sulphonamides - sulphamthoxazole

56
Q

Which antibiotics inhibit DNA gyrase

A

Fluroquinolones - ciprofloxacin

57
Q

Which antibiotics bind to RNA polymerase

A

Rifampicin

58
Q

Which antibiotic causes DNA strand breaks

A

Metronidazole

59
Q

How is antibiotic sensitivity testing performed

A

Lawn of test microorganism onto Mueller-Hinton agar

Place antibiotic discs onto lawn and incubate

Measure diameter

60
Q

What are beta-lactamase producing bacteria resistant to

A

Penicillin-derived Ab

61
Q

Describe how MRSA is resistant

A

Carries a gene called mecA - unique transpeptidase that is not inhibited by B-lactam antibiotics

Is able to continue peptidoglycan crosslinking (PBP2a) and resist

62
Q

What is MRSA resistant to

A

B-lactams

63
Q

What is a common resistance mechanism in bacteria

A

Efflux pumps

64
Q

What is a side effect of isoniazid

A

Numb/tingly extremities

I can’t feel my hands - Ison

65
Q

What is a side effect of ethambutol

A

Eye

Ocular side effects

66
Q

What is a side effect of rifampicin

A

Orange/red urine

Red and orange picin

67
Q

What is a side effect of pyrazinamide

A

Arthralgia

68
Q

Name the 4 treatments for mycobacteria (TB)

A

Isoniazid
Ethambutol
Rifampicin
Pyrazinamide

69
Q

What bacteria do not stain using the traditional gram method

A

Mycobacterium, actinomycetes, parasite cryptosporidium

Have waxy, lipid cell walls

Ziehl-Neelson stain used

70
Q

What is acid-fastness a property of

A

Mycobacteria

71
Q

Describe Ziehl-Neelson stain

A

Heating the sample with a strong dye (carbol fuchsin)

Heat makes the bacteria resistant to decolourisation by acid = acid-fast

When slide flooded with acid - mycobacteria retains the pink dye

Everything else decolourised blue

72
Q

Name 3 features of fungi

A

Eukaryotes

Cell wall is made of chitin and glucan

Clinically usually opportunistic

73
Q

What are the two forms of fungi

A

Yeast - single cell that divide via budding

Moulds - form multicellular hyphae or spores

74
Q

Describe the treatment of fungi

A

Antifungal drugs - target the cell wall/plasma membrane (do not work that well)

  • azole

Generally difficult to treat once systemic

75
Q

Describe candida albicans

A

Most pathogenic = candida spp.

Vaginal/oral infections, sepsis line/catheter infections

Can kill rapidly

76
Q

Describe aspergillus fumigatus

A

Most pathogenic = Asp. spp

Lung infections in CF, allergic disease

Poor prognosis - kills slowly

77
Q

Define a virus

A

Infectious, obligate intracellular parasite, compromising of genetic material (DNA or RNA) surrounded by a protein and/or membrane

78
Q

Describe the generic Lifecyle of a virus

A
  1. Attachment
  2. Entry
  3. Genome released
  4. Transcription
  5. Translation
  6. Genome replication
  7. Assembly
  8. Exit
79
Q

Name 5 ways in which virus cause disease with an example

A

Direct destruction of host cells - poliovirus

Modification of host cell - rotavirus

‘Over-reactivity’ of immune system - HBV infection

Damage through cell proliferation - human papillomavirus

Evasion of host defences - varicella zoster virus

80
Q

Name the ways in which virus can be identified

A

PCR

Serology

Histopathology

81
Q

What treatment is used in hepatitis C infection

A

Direct acting antivirals

82
Q

What treatment is used in HIV infection

A

Highly acting anti-retroviral therapies

83
Q

What is the treatment for herpes viral sepsis

A

Aciclovir

84
Q

Describe protozoa

A

Microscopic unicellular eukaryotes

Can be free living or parasitic

Classification based on movements - amoeboid, ciliates, sporozoan, flagellates

85
Q

Name 4 examples of protozoa

A

Malaria
Giardia lamblia
Toxoplasmosis spp.
Trichomonas vaginalis

86
Q

Describe the cycle of malaria

A

Sporozoites (cell type that infects new hosts) develop in the salivary glands of Anopheles mosquitos

Leave the mosquito during a blood meal and enter the hosts liver and multiply

Cell infected with sporozoites eventually burst - releasing merozoites into the bloodstream

These infect red blood cells and rapidly multiply and reproduce, destroying the red blood cell hosts and releasing many new merozoites.

87
Q

Describe the clinical picture of malaria

A

Non-specific symptoms

History of recent travel, possible insect bite or non-compliance with prophylaxis

88
Q

What is the treatment of malaria

A

Oral chloroquine for uncomplicated

IV artesunate for complicated

89
Q

Name the 5 malarial species

A

Most common = p. falciparum

P. malariae

P. vivax

P. ovale

P. knowlesi

90
Q

Where is p. falciparum and p. malariae found

A

Widespread in sub. Saharan Africa, southeast asia, oceania and south america

P. malariae found in lower prevalance

91
Q

Where is p. vivax found

A

Asia, America, Eastern europe, north africa

80% cases occur ethiopia, india and pakistan

92
Q

Where is p. ovale found

A

Africa and west pacific

93
Q

Where is p. knowlesi found

A

Forested areas of southeast asia

94
Q

Name the 2 malaria species which can go dormant in the liver causing relapse

A

P. vivax

P. ovale

95
Q

A bite which causes malaria is from what mosquito

A

Anopheles mosquito

96
Q

Describe the diagnostic test of choice for malaria

A

Giemsa-stained thin and thick blood film smear

97
Q

Describe 3 key features of gram positive bacteria

A

Prefer dry and dusty environments
Skin colonisers
Can spread by breathing in shed skin scales

98
Q

Describe 2 key features of gram negative bacteria

A

Prefer wet and damp environments
Majority prefer to colonise mucous membranes

99
Q

Describe h. pylori

A

Gram negative, spiral bacterium

100
Q

What is the transmission of h. pylori

A

Oral-oral

Faecal-oral

101
Q

Describe campylobacter

A

Traveller’s diarrhoea

Spread by raw or improperly cooked poultry, untreated water, unpasteurised milk

Treatment = clarithromycin

Most common cause of gastroenteritis worldwide

102
Q

What bacteria produced shiga toxins and what do they do

A

E.coli

Abdominal cramps
Bloody diarrhoea
Vomiting
Haemolytic uraemia syndrome

103
Q

What virus causes gastroenteritis would be seen in a healthcare setting

A

Norovirus

104
Q

Name the cause of meningitis

A

Usually bacterial - meningococcus, pneumococcus

Viruses
Less common infections

Non-infectious (rare)
medications
cancers
Autoimmune diseases - SLE

105
Q

What is the structure of Neisseria meningitidis

A

Gram-negative diplococci

106
Q

Describe the general infection of Neisseria meningitidis

A

Carried by 10-24% of the population

Humans only known reservoir

Transmission by respiratory droplets/naso-pharyngeal secretions

Incubation period 2-10 days - usually 3-4

107
Q

What are the two manifestations of Neisseria meningitidis

A

Meningitis - a localised infection of the meninges, with local symptoms

Septicaemia - a systemic infection with widespread signs, and generalised organ damage

108
Q

How many serogroups of Neisseria meningitidis are there

A

12 - based on the capsular polysaccharide

6 cause majority of cases of meningococcal disease

109
Q

Describe the epidemiology of Neisseria meningitidis

A

Highest conc. sub-saharan countries

4-15% mortality

Most prevalent during winter

Frequent or prolonged close contact

Extremes of age (<2 months and > 60 years)

110
Q

Describe the Brudzinski’s neck sign

A

For meningitis

Flex neck when lying flap on back. Results in flexion of the hips and knees

111
Q

What is petechiae

A

Rash seen in meningitis

Rash does not fade when glass is pressed firmly against

112
Q

Name a complication of sepsis

A

Disseminated intravascular coagulation

113
Q

Describe disseminated intravascular coagulation

A

Activation of coagulation pathways that results in formation of intravascular thrombi (clots) and depletion of platelets and coagulation facts.

Clots can cause arterial occlusions leading to gangrene of extremities and auto-amputations

114
Q

How is a diagnosis of meningitis made

A

Before initiating antibiotics

  • Blood sample
  • CSF
  • Throat swab for culture
115
Q

What does group A streptococcus bacteria cause

A

Scarlet Fever

Sandpaper rash
Strawberry tongue

116
Q

What does salmonella typhi bacteria cause

A

Typhoid fever

Risk factors - travel

Risk groups - food handlers, health and care staff, young children, doubtful hygiene

117
Q

What does legionella pneumophilia bacteria cause

A

Legionnaires disease

Think - travel and water-related exposure

118
Q

Name 6 opportunistic infections

A

 Kaposi’s sarcoma.
 Pneumocystis jirovecii pneumonia (PCP).
 Cytomegalovirus infection.
 Candidiasis (oesophageal or bronchial).
 Lymphomas
 Tuberculosis.

119
Q

Septic arthiritis - what is the most common cause

A

Staph aureus

120
Q

Septic arthiritis - what is the most common cause in prosthetic joints

A

Staph epidermidis

121
Q

Septic arthiritis - what is the most common cause in immunosuppressed, elderly, IVDU

A

Pseudomonas epidermidis

122
Q

Septic arthiritis - what is the most common cause in children

A

Haemophilus influenza

123
Q

Septic arthiritis - what is the most common cause in sexually active young adults

A

N. gonococcus

124
Q
A

Phase 2a (15 decks)

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