Microbiology Flashcards
1
Q
What is a pathogen?
A
Organism that causes disease
2
Q
What is a commensal?
A
Organism that colonises host but causes no disease normally
3
Q
What is an opportunist pathogen?
A
Microbe that only causes disease if host defence is compromised
4
Q
What is virulence/pathogenicity?
A
The degree to which an organism is pathogenic
5
Q
What is the first stage of gram staining?
A
Fixation of clinical materials to microscope slide (heat/methanol)
6
Q
What happens in gram staining after fixation?
A
Application of primary stain: crystal violet (all cells turn purple)
7
Q
What happens after the primary stain in gram staining?
A
Application of mordant (iodine): crystal violet-iodine complex formed
8
Q
What happens after application of mordant in gram staining?
A
Decolourisation step: distinguishes gram +ve and gram -ve, use acetone or ethanol
9
Q
What happens after decolourisation in gram staining?
A
Application of counterstain: safranin to stain gram -ve pink
10
Q
What do gram positive bacteria look like after gram staining?
A
Stains purple
11
Q
What do gram negative bacteria look like after gram staining?
A
Stains pink
12
Q
How can you remember the gram staining method?
A
“Come In and Stain” Crystal violet Iodine Alcohol Safranin
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)
14
Q
What are the 2 different types of gram positive cocci?
A
Staphylococcus and streptococcus
15
Q
What are the characteristics or staphylococcus?
A
Clusters/catalase +ve
16
Q
What are the characteristics of streptococcus?
A
Chains/catalase -ve
17
Q
Give some examples of gram positive rods.
A
Corneybacteria, Mycobacteria, Listeria, Bacillus, Nocardi
18
Q
What test can be done to determine the type of staphylococcus?
A
Coagulase test
19
Q
What bacteria is it if it tests positive after a coagulase test?
A
S.aureus or MRSA
20
Q
What bacteria is it if it tests negative after a coagulase test?
A
Coagulase negative staph (S.epidermidis/S.saphrophiticus)
21
Q
What is coagulase?
A
Enzyme produced by S.aureus that converts soluble fibrinogen in plasma to insoluble fibrin
22
Q
What test can be done to determine the type of streptococcus?
A
Haemolysis on blood agar
23
Q
What does alpha haemolysis indicate?
A
Alpha haemolytic strep
24
Q
What does beta haemolysis indicate?
A
Lancefield A, B, C + G - S.pyogenes
25
What does gamma haemolysis indicate?
Lancefield D (S.bovis/enterococcus)
26
What does alpha haemolysis look like?
Partial lysis (greening)
27
What does beta haemolysis look like?
Complete lysis (clear)
28
What does gamma haemolysis look like?
No lysis
29
What is the haemolysis test?
Uses hydrogen peroxide to test reaction with haemoglobin
30
Give some examples of alpha haemolytic chains.
S.pneumoniae
| Viridans group streptococci
31
Give some examples of beta haemolytic chains.
Group A strep (S.pyogenes)
Group B strep (S.agalactiae)
Group G strep (S.dysgalactiae)
32
Give examples of gamma (non) haemolytic chains.
Group D strep (S.bovis, enterococcus)
33
What infections are associated with S.aureus?
Impetigo, boils, cellulitis, endocarditis, toxic shock syndrome (skin infections)
34
What infections are associated with S.epidermidis?
Surgical wound infections, septicaemia, endocarditis
35
What infections are associated with S.saphrophiticus?
Acute cystitis
36
What infections are associated with S.pneumoniae?
Pneumonia, otitis media, sinusitis, meningitis
37
What infections are associated with viridans group strep?
Oral strep, deep organ abscesses
38
What infections are associated with group A strep (S.pyogenes)
Cellulitis, tonsillitis, impetigo, scarlet fever, pharyngitis (throat + skin infections)
39
What infections are associated with group B strep (S.agalactiae)?
Postpartum infection, neonatal sepsis, neonatal meningitis
40
What infections are associated with group G strep (S.dysgalactiae)
Severe mastitis, rheumatic fever, throat infections
41
What infections are associated with S.bovis?
Endocarditis, UTIs, sepsis (colorectal)
42
What infections are associated with enterococcus?
Endocarditis, UTIs, intra-abdominal + pelvic infections
43
Where is S.aureus found?
Nasal passages + skin
44
Where is S.epidermidis found?
Skin
45
Where is S.saphrophiticus found?
Female genital tract + perineum
46
Where is S.pneumoniae found?
Nasopharynx (+ rest of upper resp tract)
47
Where is viridans group strep found?
Oral cavity mostly, also upper resp tract, female genital tract + GI tract
48
Where is S.pyogenes found?
Resp tract
49
Where is S.agalactiae found?
Lower GI tract + female genital tract
50
Where is S.dysgalactiae found?
GI tract + genital tract
51
Where is S.bovis found?
GI tract
52
Where is enterococcus found?
GI tract
53
What antibiotics can be used to treat S.aureus?
Flucloxacillin, Co-Amoxiclav, Macrolides (susceptible to most)
54
What antibiotics can be used to treat MRSA?
Gentamicin, Vancomycin
55
What antibiotics can be used to treat S.epidermidis?
Co-Amoxiclav
56
What antibiotics can be used to treat S.saphrophiticus?
Nitrofurantoin, trimethoprim
57
What antibiotics can be used to treat S.pneumoniae?
Oral Amoxicillin, IV Benzylpenicillin
58
What antibiotics can be used to treat viridans group strep?
Amoxicillin
59
What antibiotics can be used to treat S.pyogenes?
Amoxicillin (any penicillins)
60
What antibiotics can be used to treat S.agalactiae?
Amoxicillin
61
What antibiotics can be used to treat S.dysgalactiae?
Amoxicillin
62
What antibiotics can be used to treat S.bovis?
Amoxicillin
63
What antibiotics can be used to treat enterococcus?
Amoxicillin
64
What antibiotics do beta haemolytic strep respond to?
Any penicillin (amox, co-amox, fluclox etc)
65
Who is most vulnerable to S.epidermidis?
Immunocompromised patients
66
What percentage of cystitis infections are caused by S.saphrophiticus?
5-8%, most commonly in young women
67
What is the most virulent viridans group strep?
S.milleri
68
What is the most commone cause of bacterial infections in newborn babies?
S.agalactiae
69
What is group A strep?
S.pyogenes
70
What is group B strep?
S.agalactiae
71
What is group G strep?
S.dysgalactiae
72
What is group D strep?
S.bovis, enterococcus
73
What test is used to determine the type of gram negative bacillus?
Appearance on MacConkey agar
74
What does a pink appearance on a MacConkey agar suggest?
Lactose fermenting: E.coli, klebsiella
75
What does a white appearance on a MacConkey agar suggest?
Non-lactose fermenting: shigella, salmonella, pseudomonas, proteus
76
How is the type of lactose fermenting bacteria determined?
Biochemical identification (API strip) + sensitivity tests
77
How is the type of non-lactose fermenting bacteria determined?
Oxidase test
78
What does a positive oxidase test indicate?
Pseudomonas
79
What does a negative oxidase test indicate?
Shigella, salmonella, proteus
80
What does a positive oxidase test look like?
Purple
81
What does a negative oxidase test look like?
Cream coloured
82
What is an oxidase test used for?
To determine if a bacterium produces certain cytochrome c oxidases
83
Give some examples of gram negative cocci.
Neisseria (gonorrhoea), Moraxella, anaerobic cocci - Veillonella
84
Give some examples of lactose fermenting bacteria.
E.coli
| Klebsiella
85
Give some examples of non-lactose fermenting bacteria.
Pseudomonas
Shigella
Salmonella
Proteus
86
What are the 2 types on non-lactose fermenting bacteria?
+ve and -ve oxidase
87
What infections are associated with E.coli?
UTIs, traveller’s diarrhoea, cholecystitis, cholangitis
88
What infections are associated with klebsiella?
Pneumonia, meningitis, surgical wound infections
89
What infections are associated with pseudomonas?
Pneumonia
90
What infections are associated with shigella?
Shigellosis (diarrhoea, fever)
91
What infections are associated with salmonella?
Salmonellosis (diarrhoea)
92
What infections are associated with proteus?
UTIs, related to stone formation
93
What infections are associated with neisseria?
Gonorrhoea, meningitis
94
Where is E.coli found?
GI tract
95
Where is klebsiella found?
GI tract
96
Where is pseudomonas found?
GI tract
97
Where is shigella found?
N/A (from water)
98
Where is salmonella found?
Intestines (from raw meats, poultry, eggs)
99
Where is proteus found?
Intestines
100
What antibiotics are used to treat E.coli?
Co-amoxiclav, Trimethoprim, Nitrofurantoin
101
What antibiotics are used to treat pseudomonas?
Tazocin, Gentamicin, Quinolones
102
How is klebsiella treated?
Do sensitivity testing
103
What antibiotics are used to treat shigella?
Quinolones, Azithromycin
104
What antibiotics are used to treat salmonella?
Amoxicillin, Quinolones, Macrolides
105
What antibiotics are used to treat proteus?
Penicillins, cephalosporins
106
What antibiotics are used to treat neisseria?
Cephalosporins
107
What bacterium causes the majority of UTIs?
E.coli
108
Why is klebsiella hard to treat?
Some strains highly resistant
109
How does pseudomonas present?
Do not usually cause infections in healthy people - if so infection is mild
110
What is the pathology behind meningitis?
Inflammation of the pia + arachnoid mater - microorganisms infect the CSF
Not always an infective cause - can have chemical/ post-surgical etc
111
What are the symptoms of meningitis?
Stiffness of the neck, photophobia + severe headache
Infective: fever, malaise
Petechial rash associated with meningococcal meningitis
112
What causes bacterial meningitis in neonates?
E.coli (-ve), Group B Strep (+ve), Listeria monocytogenes (+ve)
113
What causes bacterial meningitis in infants?
Neisseria meningitidis (-ve), Haemophilus influenzae (-ve), S.pneumoniae (+ve)
114
What causes bacterial meningitis in young adults?
Neisseria meningitidis (-ve), S.pneumoniae (+ve)
115
What causes bacterial meningitis in the elderly?
Neisseria meningitidis (-ve), S.pneumoniae (+ve), Listeria monocytogenes (+ve)
116
What are the 2 most common causes of bacterial meningitis?
N.meningitidis (-ve) + S.pneumoniae (+ve) = diplococci
117
What viruses can cause meningitis?
Mumps virus, echo virus, coxsackie virus, herpes simplex virus, poliovirus
118
What drugs can induce meningitis?
NSAIDs, trimethoprim
119
How is meningitis diagnosed?
Blood culture
CSF sample (lumbar puncture at L4) for microscopy + sensitivity testing
Nose + throat swabs for viral
120
What does a CSF sample look like that indicates bacterial meningitis?
Turbid yellow colour, neutrophil polymorphs, raised protein, low glucose
121
What does a CSF sample look like that indicates viral meningitis?
Lymphocytes, normal protein, normal glucose
122
What does a CSF sample look like that indicates tuberculous meningitis?
Lymphocytes, raised protein, low/normal glucose
123
How is bacterial meningitis treated?
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
How is meningococcal septicaemia treated?
Immediate IM benzylpenicillin in community/ IV cefotaxime in hospital
125
How is viral meningitis treated?
Supportive treatment, self-limiting in 4-10 days, acyclovir for HSV meningitis
126
What antibiotics inhibit cell wall synthesis? What bacteria are they used to treat?
Glycopeptides and beta lactams - gram positive bacteria (have thick cell walls)
127
Give some examples of glycopeptide antibiotics.
Vancomycin and teicoplanin
128
What are the different categories of beta lactams?
Penicillins
Cephalosporins
Carbapenems
129
Give some examples of penicillins.
Benzylpenicillin
Amoxicillin
Flucloxacillin
130
Give some examples of cephalosporins.
Cephalexin
Cefotaxime
Ceftriaxone
131
Give some examples of carbapenems.
Imipenem
| Estapenem
132
Which antibiotics inhibit protein synthesis?
Cholaramphenicol
Macrolides
Tetracyclines
Aminoglycosides
133
Give some examples of macrolides.
Clarithromycin
| Erythromycin
134
Give some examples of tetracyclines.
Doxycycline
135
Give some examples of aminoglycosides.
Gentamicin
| Streptomycin
136
When are macrolides used?
We generally use macrolides instead of penicillin for those with a penicillin allergy
137
Which antibiotics inhibit folate synthesis?
Trimethoprim
| Sulphonamides - Sulphamethoxazole
138
Which antibiotics inhibit DNA gyrase?
Fluroquinolones - Ciprofloxacin
139
Which antibiotics bind to RNA polymerase?
Rifampicin
140
Which antibiotics cause DNA strand breaks?
Metronidazole
141
Why shouldn't you give trimethoprim to a pregnant woman?
Folate is important during pregnancy to prevent spina bifida - inhibits folate synthesis
142
How common are mycobacteria in the UK?
Rare
143
Describe the characteristics of mycobacteria.
Aerobic, non-spore forming, non-mobile bacilli
144
How does a mycobacteria infection present?
Slow-growing causes gradual onset of disease
145
How is a mycobacteria infection treated?
Requires multi-antibiotic treatment for a prolonged period
146
What are the 2 main examples of mycobacteria?
TB and leprosy
147
What staining technique is used to identify mycobacteria?
Ziehl-Neelsen stain used instead of gram staining
148
What colour do acid-fast bacteria stain in Ziehl-Neelsen staining?
Red
149
What colour do non-acid fast bacteria stain in Ziehl-Neelsen staining?
Blue
150
How do viruses survive?
Dependent on host cells for living - have no organelles or cell wall
151
How do viruses cause disease?
Can cause disease via direct destruction (polio), modification (rotavirus), over-reactivity (hepatitis B), damage through cell proliferation (HPV)
152
Why are viruses difficult to identify?
Not visible in light microscopy, can’t culture as only reproduce inside live cells
153
How are viruses identified?
PCR + nucleic acid amplification tests (NAAT) used, can also do serology (look for antibodies in response to virus)
154
What will be the results of a serology test if there is a virus present?
IgM within 1 week of onset, IgG appears later
155
How are viral infections treated?
Viral infections are often self-resolving, in severe cases antivirals can be given ‘-vir’, eg acyclovir
156
What are protozoa?
Microscopic unicellular eukaryotes
157
How do protozoa survive?
Can be free living or parasitic
158
How are protozoa classified?
Ameoboids, ciliates, sporozoan, flagellates
159
Give some common examples of protozoa.
Malaria, giardia lamblia, toxoplasmiosis, trichomonas vaginalis
160
What type of organism are fungi?
Eukaryotes
161
Describe the structure of fungi.
Have a cell wall - chitin + glucans (polysaccharides)
162
How do fungi move?
Move by growing across or through structures or by dispersion in air/ water
163
What are the 2 forms that fungi exist in?
Yeast and moulds
164
What is a yeast?
Single cell that divide via budding
165
What is a mould?
Form multicellular hyphae or spores
166
How do fungi cause infections?
Only a few can actually cause infection in humans - eg candida, athlete’s foot, nappy rash
167
How are fungal infections treated?
Antifungals target cell wall/ plasma membrane - ‘-azole’
168
How common are worm infections?
Common worldwide but rare in UK
169
What are the 3 groups of worms?
Nematodes (roundworms), trematodes (flatworms), ceratodes (tapeworms)
170
How do worms reproduce?
Adult worms cannot replicate inside body without a period of development outside the body
171
What is the pre-patent period?
Interval between infection + appearance of worm eggs/larvae in stool
172
Describe the immune system's response to worms.
Poor
173
Which antibodies are involved in worm infections?
Mainly IgG + IgE mediated
174
Give some examples of common worm infections.
Hookworm, schistosomiasis
175
What will be the result of the optochin test if the bacteria are sensitive to it?
Streptococci pneumoniae - clear zone of no growth around disc
176
What will be the result of the optochin test if the bacteria are resistant to it?
Viridans streptococci and other alpha haemolytic streptococci - there will be growth around the disc
177
What is the result of the oxidase test if oxidase positive?
Blue - bacteria is AEROBIC e.g. V. cholerae
178
What is the result of the oxidase test if oxidase negative?
No colour change - bacteria may be aerobic or anaerobic
179
What does XLD agar look like with salmonella?
Red/pink colonies some with black spots
180
What does an XLD agar look like with shigella?
Red/pink colonies
181
What are the 3 ways of classifying streptococci?
* Haemolysis
* Lancefield typing
* Biochemical properties
182
How are streptococci differentiated with haemolysis?
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
What are the 4 species of malaria that cause human disease?
* P. falciparum (most common)
* P. ovale
* P. vivax
* P. malariae
184
How is malaria transmitted?
Transmitted by the bite of the FEMALE ANOPHELES MOSQUITO
185
How do you treat C. difficile?
```
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
How do you treat staph aureus?
Flucloxacillin
187
How do you remember gram positive bacteria?
```
Sexy - Streptococcus spp.
Students - Staphylococcus spp.
Can - Corynebacterium spp.
Look - Listeria spp.
Bad - Bacillus spp.
Come morning - Clostridium spp.
```
188
How do you remember gram negative bacteria?
```
Huge - Helicobacter
Vaginas - Vibrio cholera
Can - Coliforms
Never - Neisseria
Provide - Parvobacteria
Pleasure - Pseudomonas
```
189
How do you remember DNA viruses?
```
H - Herpes viridae
A - Adenovirus
P - Parvovridae
P - Papopviridae
H - Hepaviridae
Mneumonic - HAPPH
```
190
How do you treat gram positive bacteria?
Penicillins
191
Are staphylococci catalase positive or negative?
Positive
192
Are streptococci catalase positive or negative?
Negative
193
Which type of bacteria are most catalase positive?
Many GRAM NEGATIVE bacteria e.g. E.coli and fungi (aspergillus spp.) are catalase POSITIVE
194
Which bacteria are coagulase positive?
Staphylococcus. aureus is coagulase POSITIVE - clumping
195
Which bacteria are coagulase negative?
Other staphylococci are coagulase NEGATIVE - no clumping
196
What is the structure of gram positive bacteria?
- Have a single cytoplasmic membrane
- Have a large amount of peptidoglycan on outer surface
- DO NOT have endotoxin (lipopolysaccharide)
197
What is the structure of gram negative bacteria?
- 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
What is the general structure of bacteria?
- 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
Where in the body is open to bacterial colonisation?
Mucosal surfaces are areas open to bacterial colonisation:
- Nasal cavity
- Larynx
- Stomach
- Colon
- Need to keep the lungs, gall-bladder, kidneys & eyes STERILE
200
What shape are cocci?
Round and spherical
201
What shape are bacilli?
Rod-like and straight
202
What can bacteria look like?
```
Diplococcus (2)
Chain of cocci
Cluster of cocci
Chain of rods
Curved rod (vibrio)
Spiral rod (spirochaete)
```
203
What are the clinical features of malaria?
- Chills & sweats
- Headache
- Myalgia
- Fatigue
- Nausea & vomiting - Diarrhoea
204
Give some examples of resistant bacteria.
- 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
