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Phase 2a Gold Standard > Microbiology > Flashcards

Microbiology Flashcards

1
Q

Define pathogen

A

Organism that causes or is able to cause disease

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2
Q

Define commensal pathogen

A

Pathogen which colonises host but causes no disease under normal circumstances

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3
Q

Define opportunist pathogen

A

Microbe only causes disease if host defences are immunocompromised

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4
Q

Define virulence/pathogenicity

A

Degree to which a given organism is pathogenic

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5
Q

What is coagulase

A

Enzyme in bacteria that causes blood to clot around plasma by turning fibrinogen into fibrin

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6
Q

How do staphylococcus appear on microscopy

A

Purple clusters of cocci

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7
Q

How do streptococcus appear on agar

A

Purple chains/pairs of cocci

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8
Q

Staph aureus virulence factors

A

1 - Pore forming toxins
2 - Proteases
3 - Toxic shock syndrome toxin
4 - Protein A (binds antibodies in wrong direction)

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9
Q

How are beta haemolytic bacteria further classified

A

Lancefield grouping using Latex agglutination test used to group by antigens. 20 groups characterised by letter

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10
Q

What group is S. pyogenes. What infection does this cause?

A

Group A
throat, skin, post partum
(tonsilitis, pharyngitis, impetigo, scarlet fever, glomerulonephritis)

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11
Q

What group is S.aglactiae. What infection does this cause

A

Group B
Neonatal infections

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12
Q

S.pyogenes virulence factors with IMPORTANT examples

A

Enzymes (streptokinase)
Toxins (Streptolysins O&S, Ertyhtogenic toxin)
Surface factor (M protein - encourages complement degradation)

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13
Q

S. pneumoniae infections

A

Pneumonia, meningitis, otitis media, sinusitis

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14
Q

S. pneumoniae virulence factors

A

Capsule
Inflammatory wall constituents (peptidoglycan, teichoic acid)
Cyotoxin (pneumolysin)

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15
Q

Viridians streptococci properties, examples, infection

A

A-haemolytic and optochin resistant.
S. sanguinis, S. oralis
Found in mouth, cause deep organ abscesses (IE, brain, liver)

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16
Q

Clostridia properties, examples, infections

A

Anaerobic gram positive bacilli

C.tetani (tetanus - muscle contractions/spasms)
C. botulinum (botulism - paralysis from head to body)
C. difficile (diarrhoea or pseudomembranous colitis)

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17
Q

Main infections caused by Escherichia coli (6)

A

1 - Wound infections
2 - UTI
3 - Gastroenteritis
4 - Travellers’ diarrhoea
5 - Bacteraemia
6 - Meningitis in infants

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18
Q

Main infections caused by H. influenzae (4)

A

Opportunistic

1 - meningitis
2 - Pneumonia
3 - sinusitis, otitis media
4 - bronchopneumonia

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19
Q

What are the growth requirements for H influenzae

A

Factor X (haem) and factor Y (NAD) presence

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20
Q

Legionella infections

A

Man made aquatic environments
E.g. air conditioning, shower heads, humidifiers

Causes legionairres disease (legionaires pneumonia)

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21
Q

Neisseria properties

A

Non-flagellated diplococci
Fastidious requirements
Main ones are N meningitidis and N gonorrhoeae

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22
Q

What are the 7 sterile sites of the body?

A

Blood
CSF
Pleural fluid
Peritoneal cavity
Joints
Urinary tract
Lower respiratory tract

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23
Q

S. enterica infections

A

3 types of Salmonellosis
(Gastroenteritis, Enteric fever and Bacteraemia)

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24
Q

How does staph aureus appear on blood agar?

A

Golden/creamy yellow

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25
Q

How does staph epidermidis appear on blood agar?

A

Colourless/white

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26
Q

What are used in a gram stain

A

“Come In And Stain”
Crystal violet - purple dye that stains all bacteria
Iodine - Fixes crystal violet to cell wall
Acetone or Alcohol - Decolourising agent, removes it from some bacteria
Safranin - Counterstain that stains the decolourised bacteria a contrasting pink.

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27
Q

Why do gram stain results show as they do?

A

Gram positive - Have a thick peptidoglycan cell wall that retains crystal violet, appearing purple
Gram negative - Thinner peptidoglycan layer with outer membrane that is dissolved by the decolourising agent, making them colourless. This allows the Safranin to take effect, appearing pink

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28
Q

What is chocolate agar used for?

A

to detect bacteria with fastidious growth requirements (e.g. H. influenza, Bortadella pertussis, Legionella, Campylobacter jejuni, H pylori)

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29
Q

What is maconkey agar used for?

A

To differentiate lactose fermenting (pink) from non lactose fermenting (yellow/colourless)

Fermenting - E coli
Non lactose fermenting - Shigella, salmonella

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30
Q

How do E coli, shigella and salmonella appear on CLED agar?

A

E coli - yellow
Salmonella and shigella - Blue

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31
Q

What are the notable gram negative cocci

A

Neisseria e.g. N meningitidis
Moraxella

The rest are bacilli!

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32
Q

What are the notable gram positive bacilli

A

Clostridium e.g. C diff
Listeria
Cornybacterium

The rest are cocci!

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33
Q

What does XLD agar differentiate and how?

A

Differentiates salmonella and shigella
Salmonella - Red with black centres
Shigella - Red

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34
Q

What is Sabourard agar used for?

A

For fungal cultures (e.g. candida. aspergillus etc)

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35
Q

What culture medium is used for Mycobacterium e.g. TB

A

Lowenstein-Jensen medium

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36
Q

What 2 ways can Staph aureus be differentiated from other Staphs

A
  • Coagulase test: Coagulase positive
  • Culture on blood agar. S aureus colonies are gold, the rest are colourless/white
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37
Q

What are the 2 methods of virus detection?

A

Viral detection e.g. PCR
Serology testing - detects immune response (Igs created in response to virus)

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38
Q

What virus causes shingles?

A

Varicella Zoster virus

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39
Q

What are the pros and cons for PCR

A

Pros
Cheap and quick
Sensitive
Can test for multiple viruses at once

Cons
Need to suspect virus beforehand
False positive

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40
Q

What swabs are used for bacterial and viral infections?

A

Bacterial - Black charcoal swab
Viral - Green viral swab

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41
Q

What is the main viral cause of infectious glandular fever, as well as the bacterial cause (less typical)

A

Viral: EBV

Bacterial: S. pyogenes

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42
Q

How does glandular fever typically present

A

White/yellow purulent lining over tonsils (both bacterial and viral, must differentiate using black charcoal swab)

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43
Q

What 3 features on investigation would indicate EBV rather than S pyogenes

A

FBC
- Atypical lymphocytes!
Serology (ELISA test)
- IgM active infection
- IgG previous/chronic

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44
Q

What antibody against S pyogenes can be detected for

A

Anti Streptolysin

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45
Q

What is CMV Colitis, and what is its characteristic histological sign

A

An “Aids-Defining” illness, causing inflammation of the colon. It is caused by cytomegalovirus.

Owl-eye inclusion bodies

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46
Q

What are 4 AIDS defining illnesses

A

Pneumocystis jirovecii (FUNGUS) pneumonia
CMV Colitis
Oral Candida
Lymphoma

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47
Q

What are the 3 main HIV markers in the blood

A
  • HIV Igs
  • HIV RNA
  • P24 Antigen
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48
Q

What causes meningism in neonates

A

Bacteria that often colonise the maternal vagina/perianal region
- Group B Beta haemolytic Strep (S. agalactiae)
- E coli
- Listeria

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49
Q

What causes meningism in infants

A

S. pneumoniae
N meningitidis
H influenza

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50
Q

What causes Meningism in adults

A

N meningitidis
S pneumoniae

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51
Q

What causes Meningism in the elderly

A

N meningitidis
S pneumoniae
Listeria (gram positive bacillus, found in cheese, affects immunocompromised more)

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52
Q

What is group A streptococci and where are they found

A

Group A strep - S. pyogenes
Commonly found in healthy throat and on skin.

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53
Q

What can group A strep cause

A

Impetigo, cellulitis, toxic shock syndrome

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54
Q

What is the most common cause of meningitis

A

Viral
- Enteroviruses (coxsackievirus, echovirus)

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55
Q

What is the most common cause of Encephalitis

A

HSV-1
Herpes Simplex Virus - 1

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56
Q

How does CSF appear in meningitis

A

Bacterial: Yellow
Viral: Clear
TB/Fungal: Yellow/fibrous

57
Q

What white cells appear in meningitis CSF

A

Bacterial - Neutrophils
Viral and fungal - Lymphocytes

58
Q

How does glucose appear in meningitis CSF

A

Bacterial and fungal - <50% (low)
Viral - >=60% (normal)

59
Q

How is H influenzae cultured

A

Using factor V and X on chocolate agar

60
Q

S pneumoniae microscopy features

A

Gram Positive diplococci

Optochin sensitive and cultured on blood agar

61
Q

Treatment of Encephalitis

A

IV aciclovir

62
Q

Is C diff anaerobic or aerobic

63
Q

1st line antibiotic for Legionella pneumonia

A

Clarithromycin

64
Q

What are 2 bacterial causes of acute COPD exacerbation

A

H influenzae
S pneumoniae

65
Q

Treatment of H influenzae

A

B lactamase -ve (non resistant) - Amoxicillin

B lactamase +ve (resistant) - Co amoxiclav

66
Q

Treatment of S pneumoniae

A

Amoxicillin

67
Q

Causes of non caseating granuloma

A

Sarcoidosis
Leprosy
Crohns

68
Q

What is the CD4 positive cell count in AIDS conditions?

69
Q

What is the cause of pneumocystis pneumonia, and what is its treatment

A

Pneumocystis jirovecii (fungus)

Co trimoxazole and prednisolone

70
Q

What antibiotic is used against Pseudomonas aeruginosa

A

Piperacillin and Tazobactam

(Tazobactam is a beta lactamase inhibitor - prevents piperacillin breakdown)

71
Q

Signs of cellulitis

A

Typical signs of inflammation (redness, heat, swelling, pain, loss of function).

Skin may be pitted with blisters

72
Q

Main differential of cellulitis

73
Q

Causative pathogens of cellulitis

A

S aureus
S pyogenes

74
Q

If a child presents acutely with an itchy growing spot, what is this and how does it present?

A

Impetigo

  • Honey coloured, clustered lesions on the chin and cheeks of a young person.
  • Otherwise well with no allergies
75
Q

Investigations of impetigo

A

Black charcoal swab
- catalase/coagulase test
- Culture on blood agar (golden colonies = S aureus, haemolysis = S pyogenes)

76
Q

What is MRSA and what should be used against it

A

Methicillin Resistant Staphylococcus aureus

Vancomycin for 2 weeks

77
Q

How should a cellulitis blood culture be taken

A

More than 1 site, more than once. High volume sample

78
Q

Microscopy of strep pyogenes

A

Catalase negative cocci, full haemolysis (pale yellow/transparent on blood agar)

79
Q

If a cannula becomes infected, what 3 samples must be taken?

A
  • Infected cannula tip (4cm)
  • Blood culture (at least 2)
  • Black charcoal swab of exudated/inflamed/infected area
80
Q

What are the main symptoms of upper and lower UTI

A

Upper (pyelonephritis) - Loin pain, fever, nausea/vomiting
Lower - LUTs

81
Q

Investigations in cases of UTI

A
  • Urine dipstick (leukocytes, nitrites, protein)
  • Midstrearm urine sample MC+S
  • Blood culture if bacteraemia suspected
82
Q

What antibiotics are used for uncomplicated UTI

A

Trimethoprim 200mg (2 a day) (teratogen!) and nitrofurantoin 50mg (4 a day)

both for 3 days

83
Q

Most commonly causative pathogen of pyelonephritis

84
Q

Risk factors of UTI

A

BPH
Renal stones
Renal tumours
Catheterisation
Unprotected sex

85
Q

Why should urinalysis never be done from a catheterised urine sample

A

There is likely to be bacteria present in all CSU samples regardless of infection, whereas midstream urine is normally sterile so all bacteria is abnormal.

86
Q

Why can microscopy not be done on catheterised patients

A

Catheterisation irritates the bladder, causing an inflammatory response. Neutrophils will be positive regardless of infection

87
Q

Why are urine samples taken from pregnant women

A

Check for preeclampsia

88
Q

Immunological signs of Endocarditis

A
  • Oslers nodes
  • Janeway lesions
  • Splinter haemorrhages
  • Septic emboli
  • Petechiae
  • Roth spots
89
Q

What differentiates S pneumoniae from other a haemolytic streps

A

Optochin sensitivity test.

Optochin sensitive - S. pneumoniae
Optochin resistant - Viridians streptococci

90
Q

What 2 streptococci are known as viridans streptococci, and where are they normally found?

A
  • S oralis
  • S sanguis

Normally found in mouth, throat, GI tract

91
Q

Treatment of viridans streptococci Endocarditis

A

IV Benzylpenicillin +- Gentamicin

92
Q

What is the most common cause of IE and how does this come about?

A

Staph aureus - IV drug use

93
Q

What are other causes of IE

A

Staph epidermidis
Candida albicans (Fungal)

94
Q

How does candida albicans appear on gram staining

A

Stains positive, but is larger than bacteria and shows “budding”.

Grows as creamy colonies on sabourard agar

95
Q

What complication can arise from candida IE

A

Candida ophthalmitis

  • Septic embolus of fungus causes infection of eye
96
Q

What do the b haemolytic streptococci groups cause?

A

a haemolytic
A - pyogenes - Cellulitis, pharyngitis, glomerulonephritis, septicaemia
B - agalactiae - neonatal meningitis, septicaemia
C - Pharyngitis, cellulitis
G - Cellulitis

97
Q

What do alpha haemolytic streptococci cause?

A

Viridans - dental abscesses, IE

S. pneumoniae - Otitis media/sinusitis, pneumonia, meningitis,

98
Q

Define gastroenteritis

A

Syndrome of nausea/vomiting, diarrhoea and abdominal pain

99
Q

Define dysentry

A

Inflammatory, bloody diarrhoea

100
Q

Define diarrhoea

A

Frequent, loose stools, associated with water and electrolyte loss

Usually 5-7 on bristol stool chart

101
Q

Bacterial causes of diarrhoea

A

E coli
Salmonella
Shigella
Campylobacter jejuni
Clostridium difficile

102
Q

Viral causes of diarrhoea

A

Norovirus
Rotavirus
Adenovirus
Astrovirus

103
Q

Treatments for the bacterial causes of diarrhoea

A

Ecoli - Usually self limiting, but Abx = ciprofloxacin
Salmonella - Self limiting, but ciprofloxacin or azithromycin
Shigella - Ciprofloxacin or azithromycin
Campylobacter jejuni - usually self limiting but can use ciprofloxacin

C diff - vancomycin or metronidazole if severe

104
Q

What bacteria causes cholera

A

Vibrio cholerae

105
Q

What are some possible stool tests

A

Stool culture
Faecal calprotectin
Faecal occult blood
Faecal immunochemical test (FIT)

106
Q

How are diarrhoea causing bacteria cultured

A

On MacConkey agar

Lactose fermenters (pink)
- E coli
(Klebsiella also)

Non lactose fermenters (pale yellow/ colourless)
- Shigella
- Salmonella
(Proteus also)

All aerobic, gram negative, bacilli.

107
Q

What is the diarrhoea causing pathogen that is gram positive and anaerobic

A

Clostridium difficile

108
Q

After MacConkey, how can salmonella and shigella be further differentiated?

A

XLD agar culture

Shigella - Red
Salmonella - Red with black centres

109
Q

What 2 problems do salmonella cause

A
  • Diarrhoea
  • Typhoid fever
110
Q

What is the main type of diarrhoeal salmonella. How does this arise, what is its incubation period and how is it treated?

A

S. enteriditis
- Caused by undercooked poultry and eggs
- Incubation 12-36 hours
- Self limiting, supportive treatment

111
Q

What salmonella species can cause typhoid fever

A

S. typhi, S. paratyphi
Waterborne, found in canned meat and shellfish

112
Q

How is salmonella typhoid treated

A
  • Fluoroquinolones (ciprofloxacin)
  • 3rd gen cephalosporin (ceftriaxone)
  • Azithromycin
113
Q

Is there a vaccine for salmonella typhoid

114
Q

What organ does salmonella typhoid damage most

A

Gallbladder (Especially with relapse, which is common)

115
Q

What does shigella cause and what does it do that aids its virulence

A

Causes shigellosis dysentry

Produces shiga toxin

116
Q

What is usually a preceding case in Campylobacter infection

A

Patient eats shellfish/ BBQ chicken the DAY before. Patient now presents acutely unwell with diarrhoea

117
Q

How does campylobacter present on microscopy

A

Gram negative bacillus

118
Q

What neurological disease is Campylobacter strongly implicated in

A

Guillain barre syndrome

119
Q

What agar is Campylobacter cultured on

A
  • CCDA agar (charcoal based, no blood)
120
Q

What must be done immediately if a norovirus diarrhoea case is found

A

Notify UKHSA (formerly Public Health England)

121
Q

What virus normally causes diarrhoea in children

122
Q

What antibiotics increase risk of C diff

A

“C” antibiotics - kill normal gut flora, allowing colonisation of C diff

  • Co amoxiclav
  • Ciprofloxacin
  • Clarithromycin
  • Cephalosporins
123
Q

How should C diff be treated

A

Stop “C” antibiotics immediately and start vancomycin 4 daily for 10 days.

Patient should be isolated for 48 hours

124
Q

Ruptured appendicitis causes intraabdominal infection. What bacteria are implicated in this?

A

G- - Colliforms: E coli, Klebsiella, Enterobacter
G+ - Entercocci

Anaerobe: Bacteroides fragills

125
Q

Empirical treatment of apprendix rupture

A

Cefuroxime (covers G- and enterococcus)
or Metronidazole for Bacteroides

126
Q

What bacteria are implicated in ascending cholangitis

A

E coli
Klebsiella
Enterococcus
Bacteroides fragillis

127
Q

Treatment of ascending cholangitis

A

Co Amoxiclav

128
Q

Structure of gram positive bacteria

A

Single thick peptidoglycan wall. Produce Exotoxin (produced inside and secreted)

129
Q

Structure of gram negative bacteria

A

Double, thinner cell walls. Less peptidoglycan. Produce endotoxins. Action is non specific

130
Q

What are the 2 main classes of beta lactam, what are they good at treating?

A

Penicillins, cephalosporins

Good at treating gram +ves (streps and staphs)

131
Q

What is used in penicillin allergy

A

Vancomycin

132
Q

What antibiotics largely cover gram positives?

A

Beta lactams
- S aureus, Group ABCG strep - Flucloxacillin
- S pneumoniae - Amoxicillin or Benzylpenicillin (can also be used for ACG)

133
Q

What antibiotic is used for Listeria

A

Amoxicillin

134
Q

What does vancomycin treat

A

C diff and MRSA

135
Q

What antibiotics largely cover gram negatives?

A

Fluoroquinolones (Ciprofloxacin! (2nd gen))

136
Q

What antibiotic is used for UTIs, and what bacteria does this cover?

A

Trimethoprim

  • Klebsiella
  • E coli
  • Enterococcus
  • Proteus
137
Q

Who are at risk of fungal infection

A

The immunocompromised (old/young, HIV, long term steroids)

138
Q

What are 2 antifungal medications used to treat fungal infection

A

Azoles
Amphotericin

Phase 2a Gold Standard (29 decks)

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