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Phase 2a > Microbiology > Flashcards

Microbiology Flashcards

1
Q

What is a pathogen?

A

Organism that causes disease

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2
Q

What is a commensal?

A

Organism that colonises host but causes no disease normally

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3
Q

What is an opportunist pathogen?

A

Microbe that only causes disease if host defence is compromised

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4
Q

What is virulence/pathogenicity?

A

The degree to which an organism is pathogenic

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5
Q

What is the first stage of gram staining?

A

Fixation of clinical materials to microscope slide (heat/methanol)

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6
Q

What happens in gram staining after fixation?

A

Application of primary stain: crystal violet (all cells turn purple)

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7
Q

What happens after the primary stain in gram staining?

A

Application of mordant (iodine): crystal violet-iodine complex formed

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8
Q

What happens after application of mordant in gram staining?

A

Decolourisation step: distinguishes gram +ve and gram -ve, use acetone or ethanol

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9
Q

What happens after decolourisation in gram staining?

A

Application of counterstain: safranin to stain gram -ve pink

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10
Q

What do gram positive bacteria look like after gram staining?

A

Stains purple

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11
Q

What do gram negative bacteria look like after gram staining?

A

Stains pink

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12
Q

How can you remember the gram staining method?

A 
“Come In and Stain”
Crystal violet
Iodine 
Alcohol
Safranin
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13
Q

What is the difference between gram positive and gram negative bacteria?

A

Gram positive: thick layer of peptidoglycan (cell wall)

Gram negative: thin layer of peptidoglycan (high lipid content)

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14
Q

What are the 2 different types of gram positive cocci?

A

Staphylococcus and streptococcus

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15
Q

What are the characteristics or staphylococcus?

A

Clusters/catalase +ve

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16
Q

What are the characteristics of streptococcus?

A

Chains/catalase -ve

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17
Q

Give some examples of gram positive rods.

A

Corneybacteria, Mycobacteria, Listeria, Bacillus, Nocardi

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18
Q

What test can be done to determine the type of staphylococcus?

A

Coagulase test

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19
Q

What bacteria is it if it tests positive after a coagulase test?

A

S.aureus or MRSA

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20
Q

What bacteria is it if it tests negative after a coagulase test?

A

Coagulase negative staph (S.epidermidis/S.saphrophiticus)

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21
Q

What is coagulase?

A

Enzyme produced by S.aureus that converts soluble fibrinogen in plasma to insoluble fibrin

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22
Q

What test can be done to determine the type of streptococcus?

A

Haemolysis on blood agar

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23
Q

What does alpha haemolysis indicate?

A

Alpha haemolytic strep

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24
Q

What does beta haemolysis indicate?

A

Lancefield A, B, C + G - S.pyogenes

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25
Q

What does gamma haemolysis indicate?

A

Lancefield D (S.bovis/enterococcus)

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26
Q

What does alpha haemolysis look like?

A

Partial lysis (greening)

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27
Q

What does beta haemolysis look like?

A

Complete lysis (clear)

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28
Q

What does gamma haemolysis look like?

A

No lysis

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29
Q

What is the haemolysis test?

A

Uses hydrogen peroxide to test reaction with haemoglobin

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30
Q

Give some examples of alpha haemolytic chains.

A

S.pneumoniae

Viridans group streptococci

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31
Q

Give some examples of beta haemolytic chains.

A

Group A strep (S.pyogenes)
Group B strep (S.agalactiae)
Group G strep (S.dysgalactiae)

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32
Q

Give examples of gamma (non) haemolytic chains.

A

Group D strep (S.bovis, enterococcus)

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33
Q

What infections are associated with S.aureus?

A

Impetigo, boils, cellulitis, endocarditis, toxic shock syndrome (skin infections)

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34
Q

What infections are associated with S.epidermidis?

A

Surgical wound infections, septicaemia, endocarditis

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35
Q

What infections are associated with S.saphrophiticus?

A

Acute cystitis

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36
Q

What infections are associated with S.pneumoniae?

A

Pneumonia, otitis media, sinusitis, meningitis

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37
Q

What infections are associated with viridans group strep?

A

Oral strep, deep organ abscesses

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38
Q

What infections are associated with group A strep (S.pyogenes)

A

Cellulitis, tonsillitis, impetigo, scarlet fever, pharyngitis (throat + skin infections)

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39
Q

What infections are associated with group B strep (S.agalactiae)?

A

Postpartum infection, neonatal sepsis, neonatal meningitis

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40
Q

What infections are associated with group G strep (S.dysgalactiae)

A

Severe mastitis, rheumatic fever, throat infections

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41
Q

What infections are associated with S.bovis?

A

Endocarditis, UTIs, sepsis (colorectal)

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42
Q

What infections are associated with enterococcus?

A

Endocarditis, UTIs, intra-abdominal + pelvic infections

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43
Q

Where is S.aureus found?

A

Nasal passages + skin

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44
Q

Where is S.epidermidis found?

A

Skin

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45
Q

Where is S.saphrophiticus found?

A

Female genital tract + perineum

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46
Q

Where is S.pneumoniae found?

A

Nasopharynx (+ rest of upper resp tract)

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47
Q

Where is viridans group strep found?

A

Oral cavity mostly, also upper resp tract, female genital tract + GI tract

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48
Q

Where is S.pyogenes found?

A

Resp tract

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49
Q

Where is S.agalactiae found?

A

Lower GI tract + female genital tract

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50
Q

Where is S.dysgalactiae found?

A

GI tract + genital tract

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51
Q

Where is S.bovis found?

A

GI tract

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52
Q

Where is enterococcus found?

A

GI tract

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53
Q

What antibiotics can be used to treat S.aureus?

A

Flucloxacillin, Co-Amoxiclav, Macrolides (susceptible to most)

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54
Q

What antibiotics can be used to treat MRSA?

A

Gentamicin, Vancomycin

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55
Q

What antibiotics can be used to treat S.epidermidis?

A

Co-Amoxiclav

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56
Q

What antibiotics can be used to treat S.saphrophiticus?

A

Nitrofurantoin, trimethoprim

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57
Q

What antibiotics can be used to treat S.pneumoniae?

A

Oral Amoxicillin, IV Benzylpenicillin

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58
Q

What antibiotics can be used to treat viridans group strep?

A

Amoxicillin

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59
Q

What antibiotics can be used to treat S.pyogenes?

A

Amoxicillin (any penicillins)

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60
Q

What antibiotics can be used to treat S.agalactiae?

A

Amoxicillin

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61
Q

What antibiotics can be used to treat S.dysgalactiae?

A

Amoxicillin

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62
Q

What antibiotics can be used to treat S.bovis?

A

Amoxicillin

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63
Q

What antibiotics can be used to treat enterococcus?

A

Amoxicillin

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64
Q

What antibiotics do beta haemolytic strep respond to?

A

Any penicillin (amox, co-amox, fluclox etc)

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65
Q

Who is most vulnerable to S.epidermidis?

A

Immunocompromised patients

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66
Q

What percentage of cystitis infections are caused by S.saphrophiticus?

A

5-8%, most commonly in young women

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67
Q

What is the most virulent viridans group strep?

A

S.milleri

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68
Q

What is the most commone cause of bacterial infections in newborn babies?

A

S.agalactiae

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69
Q

What is group A strep?

A

S.pyogenes

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70
Q

What is group B strep?

A

S.agalactiae

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71
Q

What is group G strep?

A

S.dysgalactiae

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72
Q

What is group D strep?

A

S.bovis, enterococcus

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73
Q

What test is used to determine the type of gram negative bacillus?

A

Appearance on MacConkey agar

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74
Q

What does a pink appearance on a MacConkey agar suggest?

A

Lactose fermenting: E.coli, klebsiella

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75
Q

What does a white appearance on a MacConkey agar suggest?

A

Non-lactose fermenting: shigella, salmonella, pseudomonas, proteus

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76
Q

How is the type of lactose fermenting bacteria determined?

A

Biochemical identification (API strip) + sensitivity tests

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77
Q

How is the type of non-lactose fermenting bacteria determined?

A

Oxidase test

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78
Q

What does a positive oxidase test indicate?

A

Pseudomonas

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79
Q

What does a negative oxidase test indicate?

A

Shigella, salmonella, proteus

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80
Q

What does a positive oxidase test look like?

A

Purple

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81
Q

What does a negative oxidase test look like?

A

Cream coloured

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82
Q

What is an oxidase test used for?

A

To determine if a bacterium produces certain cytochrome c oxidases

83
Q

Give some examples of gram negative cocci.

A

Neisseria (gonorrhoea), Moraxella, anaerobic cocci - Veillonella

84
Q

Give some examples of lactose fermenting bacteria.

A

E.coli

Klebsiella

85
Q

Give some examples of non-lactose fermenting bacteria.

A

Pseudomonas
Shigella
Salmonella
Proteus

86
Q

What are the 2 types on non-lactose fermenting bacteria?

A

+ve and -ve oxidase

87
Q

What infections are associated with E.coli?

A

UTIs, traveller’s diarrhoea, cholecystitis, cholangitis

88
Q

What infections are associated with klebsiella?

A

Pneumonia, meningitis, surgical wound infections

89
Q

What infections are associated with pseudomonas?

90
Q

What infections are associated with shigella?

A

Shigellosis (diarrhoea, fever)

91
Q

What infections are associated with salmonella?

A

Salmonellosis (diarrhoea)

92
Q

What infections are associated with proteus?

A

UTIs, related to stone formation

93
Q

What infections are associated with neisseria?

A

Gonorrhoea, meningitis

94
Q

Where is E.coli found?

95
Q

Where is klebsiella found?

96
Q

Where is pseudomonas found?

97
Q

Where is shigella found?

A

N/A (from water)

98
Q

Where is salmonella found?

A

Intestines (from raw meats, poultry, eggs)

99
Q

Where is proteus found?

A

Intestines

100
Q

What antibiotics are used to treat E.coli?

A

Co-amoxiclav, Trimethoprim, Nitrofurantoin

101
Q

What antibiotics are used to treat pseudomonas?

A

Tazocin, Gentamicin, Quinolones

102
Q

How is klebsiella treated?

A

Do sensitivity testing

103
Q

What antibiotics are used to treat shigella?

A

Quinolones, Azithromycin

104
Q

What antibiotics are used to treat salmonella?

A

Amoxicillin, Quinolones, Macrolides

105
Q

What antibiotics are used to treat proteus?

A

Penicillins, cephalosporins

106
Q

What antibiotics are used to treat neisseria?

A

Cephalosporins

107
Q

What bacterium causes the majority of UTIs?

108
Q

Why is klebsiella hard to treat?

A

Some strains highly resistant

109
Q

How does pseudomonas present?

A

Do not usually cause infections in healthy people - if so infection is mild

110
Q

What is the pathology behind meningitis?

A

Inflammation of the pia + arachnoid mater - microorganisms infect the CSF
Not always an infective cause - can have chemical/ post-surgical etc

111
Q

What are the symptoms of meningitis?

A

Stiffness of the neck, photophobia + severe headache
Infective: fever, malaise
Petechial rash associated with meningococcal meningitis

112
Q

What causes bacterial meningitis in neonates?

A

E.coli (-ve), Group B Strep (+ve), Listeria monocytogenes (+ve)

113
Q

What causes bacterial meningitis in infants?

A

Neisseria meningitidis (-ve), Haemophilus influenzae (-ve), S.pneumoniae (+ve)

114
Q

What causes bacterial meningitis in young adults?

A

Neisseria meningitidis (-ve), S.pneumoniae (+ve)

115
Q

What causes bacterial meningitis in the elderly?

A

Neisseria meningitidis (-ve), S.pneumoniae (+ve), Listeria monocytogenes (+ve)

116
Q

What are the 2 most common causes of bacterial meningitis?

A

N.meningitidis (-ve) + S.pneumoniae (+ve) = diplococci

117
Q

What viruses can cause meningitis?

A

Mumps virus, echo virus, coxsackie virus, herpes simplex virus, poliovirus

118
Q

What drugs can induce meningitis?

A

NSAIDs, trimethoprim

119
Q

How is meningitis diagnosed?

A

Blood culture
CSF sample (lumbar puncture at L4) for microscopy + sensitivity testing
Nose + throat swabs for viral

120
Q

What does a CSF sample look like that indicates bacterial meningitis?

A

Turbid yellow colour, neutrophil polymorphs, raised protein, low glucose

121
Q

What does a CSF sample look like that indicates viral meningitis?

A

Lymphocytes, normal protein, normal glucose

122
Q

What does a CSF sample look like that indicates tuberculous meningitis?

A

Lymphocytes, raised protein, low/normal glucose

123
Q

How is bacterial meningitis treated?

A

Start antibiotics before tests come back if suspected
Cephalosporins: IV cefotaxime/ IV ceftriaxone
If over 50/immunocompromised add IV amoxicillin to cover listeria
One dose oral ciprofloxacin - prophylaxis for contacts

124
Q

How is meningococcal septicaemia treated?

A

Immediate IM benzylpenicillin in community/ IV cefotaxime in hospital

125
Q

How is viral meningitis treated?

A

Supportive treatment, self-limiting in 4-10 days, acyclovir for HSV meningitis

126
Q

What antibiotics inhibit cell wall synthesis? What bacteria are they used to treat?

A

Glycopeptides and beta lactams - gram positive bacteria (have thick cell walls)

127
Q

Give some examples of glycopeptide antibiotics.

A

Vancomycin and teicoplanin

128
Q

What are the different categories of beta lactams?

A

Penicillins
Cephalosporins
Carbapenems

129
Q

Give some examples of penicillins.

A

Benzylpenicillin
Amoxicillin
Flucloxacillin

130
Q

Give some examples of cephalosporins.

A

Cephalexin
Cefotaxime
Ceftriaxone

131
Q

Give some examples of carbapenems.

A

Imipenem

Estapenem

132
Q

Which antibiotics inhibit protein synthesis?

A

Cholaramphenicol
Macrolides
Tetracyclines
Aminoglycosides

133
Q

Give some examples of macrolides.

A

Clarithromycin

Erythromycin

134
Q

Give some examples of tetracyclines.

A

Doxycycline

135
Q

Give some examples of aminoglycosides.

A

Gentamicin

Streptomycin

136
Q

When are macrolides used?

A

We generally use macrolides instead of penicillin for those with a penicillin allergy

137
Q

Which antibiotics inhibit folate synthesis?

A

Trimethoprim

Sulphonamides - Sulphamethoxazole

138
Q

Which antibiotics inhibit DNA gyrase?

A

Fluroquinolones - Ciprofloxacin

139
Q

Which antibiotics bind to RNA polymerase?

A

Rifampicin

140
Q

Which antibiotics cause DNA strand breaks?

A

Metronidazole

141
Q

Why shouldn’t you give trimethoprim to a pregnant woman?

A

Folate is important during pregnancy to prevent spina bifida - inhibits folate synthesis

142
Q

How common are mycobacteria in the UK?

143
Q

Describe the characteristics of mycobacteria.

A

Aerobic, non-spore forming, non-mobile bacilli

144
Q

How does a mycobacteria infection present?

A

Slow-growing causes gradual onset of disease

145
Q

How is a mycobacteria infection treated?

A

Requires multi-antibiotic treatment for a prolonged period

146
Q

What are the 2 main examples of mycobacteria?

A

TB and leprosy

147
Q

What staining technique is used to identify mycobacteria?

A

Ziehl-Neelsen stain used instead of gram staining

148
Q

What colour do acid-fast bacteria stain in Ziehl-Neelsen staining?

149
Q

What colour do non-acid fast bacteria stain in Ziehl-Neelsen staining?

150
Q

How do viruses survive?

A

Dependent on host cells for living - have no organelles or cell wall

151
Q

How do viruses cause disease?

A

Can cause disease via direct destruction (polio), modification (rotavirus), over-reactivity (hepatitis B), damage through cell proliferation (HPV)

152
Q

Why are viruses difficult to identify?

A

Not visible in light microscopy, can’t culture as only reproduce inside live cells

153
Q

How are viruses identified?

A

PCR + nucleic acid amplification tests (NAAT) used, can also do serology (look for antibodies in response to virus)

154
Q

What will be the results of a serology test if there is a virus present?

A

IgM within 1 week of onset, IgG appears later

155
Q

How are viral infections treated?

A

Viral infections are often self-resolving, in severe cases antivirals can be given ‘-vir’, eg acyclovir

156
Q

What are protozoa?

A

Microscopic unicellular eukaryotes

157
Q

How do protozoa survive?

A

Can be free living or parasitic

158
Q

How are protozoa classified?

A

Ameoboids, ciliates, sporozoan, flagellates

159
Q

Give some common examples of protozoa.

A

Malaria, giardia lamblia, toxoplasmiosis, trichomonas vaginalis

160
Q

What type of organism are fungi?

A

Eukaryotes

161
Q

Describe the structure of fungi.

A

Have a cell wall - chitin + glucans (polysaccharides)

162
Q

How do fungi move?

A

Move by growing across or through structures or by dispersion in air/ water

163
Q

What are the 2 forms that fungi exist in?

A

Yeast and moulds

164
Q

What is a yeast?

A

Single cell that divide via budding

165
Q

What is a mould?

A

Form multicellular hyphae or spores

166
Q

How do fungi cause infections?

A

Only a few can actually cause infection in humans - eg candida, athlete’s foot, nappy rash

167
Q

How are fungal infections treated?

A

Antifungals target cell wall/ plasma membrane - ‘-azole’

168
Q

How common are worm infections?

A

Common worldwide but rare in UK

169
Q

What are the 3 groups of worms?

A

Nematodes (roundworms), trematodes (flatworms), ceratodes (tapeworms)

170
Q

How do worms reproduce?

A

Adult worms cannot replicate inside body without a period of development outside the body

171
Q

What is the pre-patent period?

A

Interval between infection + appearance of worm eggs/larvae in stool

172
Q

Describe the immune system’s response to worms.

173
Q

Which antibodies are involved in worm infections?

A

Mainly IgG + IgE mediated

174
Q

Give some examples of common worm infections.

A

Hookworm, schistosomiasis

175
Q

What will be the result of the optochin test if the bacteria are sensitive to it?

A

Streptococci pneumoniae - clear zone of no growth around disc

176
Q

What will be the result of the optochin test if the bacteria are resistant to it?

A

Viridans streptococci and other alpha haemolytic streptococci - there will be growth around the disc

177
Q

What is the result of the oxidase test if oxidase positive?

A

Blue - bacteria is AEROBIC e.g. V. cholerae

178
Q

What is the result of the oxidase test if oxidase negative?

A

No colour change - bacteria may be aerobic or anaerobic

179
Q

What does XLD agar look like with salmonella?

A

Red/pink colonies some with black spots

180
Q

What does an XLD agar look like with shigella?

A

Red/pink colonies

181
Q

What are the 3 ways of classifying streptococci?

A
  • Haemolysis
  • Lancefield typing
  • Biochemical properties
182
Q

How are streptococci differentiated with haemolysis?

A

Alpha haemolysis - greenish/brownish e.g Strep. intermedius Beta haemolysis - clear/colourless e.g. Strep. pyogenes Gamma haemolysis - no lysis e.g. Strep. mutans

183
Q

What are the 4 species of malaria that cause human disease?

A
  • P. falciparum (most common)
  • P. ovale
  • P. vivax
  • P. malariae
184
Q

How is malaria transmitted?

A

Transmitted by the bite of the FEMALE ANOPHELES MOSQUITO

185
Q

How do you treat C. difficile?

A 
In general ANY antibiotic that begins with the letter C can result in clostridium difficile:
• Ciprofloxacin
• Clindamycin
• Cephalosporins
• Co-amoxiclav (augmentin)
• Carbapanems e.g. meropenem
186
Q

How do you treat staph aureus?

A

Flucloxacillin

187
Q

How do you remember gram positive bacteria?

A 
Sexy - Streptococcus spp. 
Students - Staphylococcus spp. 
Can - Corynebacterium spp. 
Look - Listeria spp.
Bad - Bacillus spp.
Come morning - Clostridium spp.
188
Q

How do you remember gram negative bacteria?

A 
Huge - Helicobacter 
Vaginas - Vibrio cholera 
Can - Coliforms
Never - Neisseria 
Provide - Parvobacteria 
Pleasure - Pseudomonas
189
Q

How do you remember DNA viruses?

A 
H - Herpes viridae
A - Adenovirus
P - Parvovridae
P - Papopviridae
H - Hepaviridae 
Mneumonic - HAPPH
190
Q

How do you treat gram positive bacteria?

A

Penicillins

191
Q

Are staphylococci catalase positive or negative?

192
Q

Are streptococci catalase positive or negative?

193
Q

Which type of bacteria are most catalase positive?

A

Many GRAM NEGATIVE bacteria e.g. E.coli and fungi (aspergillus spp.) are catalase POSITIVE

194
Q

Which bacteria are coagulase positive?

A

Staphylococcus. aureus is coagulase POSITIVE - clumping

195
Q

Which bacteria are coagulase negative?

A

Other staphylococci are coagulase NEGATIVE - no clumping

196
Q

What is the structure of gram positive bacteria?

A
  • Have a single cytoplasmic membrane
  • Have a large amount of peptidoglycan on outer surface
  • DO NOT have endotoxin (lipopolysaccharide)
197
Q

What is the structure of gram negative bacteria?

A
  • Have two membranes; an inner
    and outer
  • Have a smaller amount of peptidoglycan between the membranes
  • Antibiotics target the peptidoglycan
  • The outer membrane has lipopolysaccharide (ENDOTOXIN) which the immune system can react to - endotoxic shock
198
Q

What is the general structure of bacteria?

A
  • Capsule:
    • A polymer of sugar that protects bacteria from host immune system - can inhibit parts of the innate immune system
    • Pneumonia bacteria has a capsule
  • Cell wall:
    • Made up of phospholipid membrane
  • Bacteria are prokaryotes i.e. they do not have a nuclear membrane (eukaryotes do)
  • Bacteria usually have one circular chromosome
  • RNA polymerase is present in bacterial cytoplasm
  • Cell envelope
199
Q

Where in the body is open to bacterial colonisation?

A

Mucosal surfaces are areas open to bacterial colonisation:

  • Nasal cavity
  • Larynx
  • Stomach
  • Colon
  • Need to keep the lungs, gall-bladder, kidneys & eyes STERILE
200
Q

What shape are cocci?

A

Round and spherical

201
Q

What shape are bacilli?

A

Rod-like and straight

202
Q

What can bacteria look like?

A 
Diplococcus (2)
Chain of cocci
Cluster of cocci
Chain of rods
Curved rod (vibrio)
Spiral rod (spirochaete)
203
Q

What are the clinical features of malaria?

A
  • Chills & sweats
  • Headache
  • Myalgia
  • Fatigue
  • Nausea & vomiting - Diarrhoea
204
Q

Give some examples of resistant bacteria.

A
  • Aerobic bacteria are unable to reduce metronidazole to its active form thus the antibiotic is harmless to them
  • Anaerobic bacteria lack oxidative metabolism required to uptake aminoglycosides
  • Vancomycin is not taken up by gram negative bacteria - it cannot penetrate their outer membrane since its too large

Phase 2a (25 decks)

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