Microbiology Flashcards
(206 cards)
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
Draw a flowchart of the bacterial identification process for gram positive cocci.
A
18
Q
Draw a flowchart of the bacterial identification process for gram negative bacilli.
A
19
Q
Give some examples of gram positive rods.
A
Corneybacteria, Mycobacteria, Listeria, Bacillus, Nocardi
20
Q
What test can be done to determine the type of staphylococcus?
A
Coagulase test
21
Q
What bacteria is it if it tests positive after a coagulase test?
A
S.aureus or MRSA
22
Q
What bacteria is it if it tests negative after a coagulase test?
A
Coagulase negative staph (S.epidermidis/S.saphrophiticus)
23
Q
What is coagulase?
A
Enzyme produced by S.aureus that converts soluble fibrinogen in plasma to insoluble fibrin
24
Q
What test can be done to determine the type of streptococcus?
A
Haemolysis on blood agar
25
What does alpha haemolysis indicate?
Alpha haemolytic strep
26
What does beta haemolysis indicate?
Lancefield A, B, C + G - S.pyogenes
27
What does gamma haemolysis indicate?
Lancefield D (S.bovis/enterococcus)
28
What does alpha haemolysis look like?
Partial lysis (greening)
29
What does beta haemolysis look like?
Complete lysis (clear)
30
What does gamma haemolysis look like?
No lysis
31
What is the haemolysis test?
Uses hydrogen peroxide to test reaction with haemoglobin
32
Give some examples of alpha haemolytic chains.
S.pneumoniae
| Viridans group streptococci
33
Give some examples of beta haemolytic chains.
Group A strep (S.pyogenes)
Group B strep (S.agalactiae)
Group G strep (S.dysgalactiae)
34
Give examples of gamma (non) haemolytic chains.
Group D strep (S.bovis, enterococcus)
35
What infections are associated with S.aureus?
Impetigo, boils, cellulitis, endocarditis, toxic shock syndrome (skin infections)
36
What infections are associated with S.epidermidis?
Surgical wound infections, septicaemia, endocarditis
37
What infections are associated with S.saphrophiticus?
Acute cystitis
38
What infections are associated with S.pneumoniae?
Pneumonia, otitis media, sinusitis, meningitis
39
What infections are associated with viridans group strep?
Oral strep, deep organ abscesses
40
What infections are associated with group A strep (S.pyogenes)
Cellulitis, tonsillitis, impetigo, scarlet fever, pharyngitis (throat + skin infections)
41
What infections are associated with group B strep (S.agalactiae)?
Postpartum infection, neonatal sepsis, neonatal meningitis
42
What infections are associated with group G strep (S.dysgalactiae)
Severe mastitis, rheumatic fever, throat infections
43
What infections are associated with S.bovis?
Endocarditis, UTIs, sepsis (colorectal)
44
What infections are associated with enterococcus?
Endocarditis, UTIs, intra-abdominal + pelvic infections
45
Where is S.aureus found?
Nasal passages + skin
46
Where is S.epidermidis found?
Skin
47
Where is S.saphrophiticus found?
Female genital tract + perineum
48
Where is S.pneumoniae found?
Nasopharynx (+ rest of upper resp tract)
49
Where is viridans group strep found?
Oral cavity mostly, also upper resp tract, female genital tract + GI tract
50
Where is S.pyogenes found?
Resp tract
51
Where is S.agalactiae found?
Lower GI tract + female genital tract
52
Where is S.dysgalactiae found?
GI tract + genital tract
53
Where is S.bovis found?
GI tract
54
Where is enterococcus found?
GI tract
55
What antibiotics can be used to treat S.aureus?
Flucloxacillin, Co-Amoxiclav, Macrolides (susceptible to most)
56
What antibiotics can be used to treat MRSA?
Gentamicin, Vancomycin
57
What antibiotics can be used to treat S.epidermidis?
Co-Amoxiclav
58
What antibiotics can be used to treat S.saphrophiticus?
Nitrofurantoin, trimethoprim
59
What antibiotics can be used to treat S.pneumoniae?
Oral Amoxicillin, IV Benzylpenicillin
60
What antibiotics can be used to treat viridans group strep?
Amoxicillin
61
What antibiotics can be used to treat S.pyogenes?
Amoxicillin (any penicillins)
62
What antibiotics can be used to treat S.agalactiae?
Amoxicillin
63
What antibiotics can be used to treat S.dysgalactiae?
Amoxicillin
64
What antibiotics can be used to treat S.bovis?
Amoxicillin
65
What antibiotics can be used to treat enterococcus?
Amoxicillin
66
What antibiotics do beta haemolytic strep respond to?
Any penicillin (amox, co-amox, fluclox etc)
67
Who is most vulnerable to S.epidermidis?
Immunocompromised patients
68
What percentage of cystitis infections are caused by S.saphrophiticus?
5-8%, most commonly in young women
69
What is the most virulent viridans group strep?
S.milleri
70
What is the most commone cause of bacterial infections in newborn babies?
S.agalactiae
71
What is group A strep?
S.pyogenes
72
What is group B strep?
S.agalactiae
73
What is group G strep?
S.dysgalactiae
74
What is group D strep?
S.bovis, enterococcus
75
What test is used to determine the type of gram negative bacillus?
Appearance on MacConkey agar
76
What does a pink appearance on a MacConkey agar suggest?
Lactose fermenting: E.coli, klebsiella
77
What does a white appearance on a MacConkey agar suggest?
Non-lactose fermenting: shigella, salmonella, pseudomonas, proteus
78
How is the type of lactose fermenting bacteria determined?
Biochemical identification (API strip) + sensitivity tests
79
How is the type of non-lactose fermenting bacteria determined?
Oxidase test
80
What does a positive oxidase test indicate?
Pseudomonas
81
What does a negative oxidase test indicate?
Shigella, salmonella, proteus
82
What does a positive oxidase test look like?
Purple
83
What does a negative oxidase test look like?
Cream coloured
84
What is an oxidase test used for?
To determine if a bacterium produces certain cytochrome c oxidases
85
Give some examples of gram negative cocci.
Neisseria (gonorrhoea), Moraxella, anaerobic cocci - Veillonella
86
Give some examples of lactose fermenting bacteria.
E.coli
| Klebsiella
87
Give some examples of non-lactose fermenting bacteria.
Pseudomonas
Shigella
Salmonella
Proteus
88
What are the 2 types on non-lactose fermenting bacteria?
+ve and -ve oxidase
89
What infections are associated with E.coli?
UTIs, traveller’s diarrhoea, cholecystitis, cholangitis
90
What infections are associated with klebsiella?
Pneumonia, meningitis, surgical wound infections
91
What infections are associated with pseudomonas?
Pneumonia
92
What infections are associated with shigella?
Shigellosis (diarrhoea, fever)
93
What infections are associated with salmonella?
Salmonellosis (diarrhoea)
94
What infections are associated with proteus?
UTIs, related to stone formation
95
What infections are associated with neisseria?
Gonorrhoea, meningitis
96
Where is E.coli found?
GI tract
97
Where is klebsiella found?
GI tract
98
Where is pseudomonas found?
GI tract
99
Where is shigella found?
N/A (from water)
100
Where is salmonella found?
Intestines (from raw meats, poultry, eggs)
101
Where is proteus found?
Intestines
102
What antibiotics are used to treat E.coli?
Co-amoxiclav, Trimethoprim, Nitrofurantoin
103
What antibiotics are used to treat pseudomonas?
Tazocin, Gentamicin, Quinolones
104
How is klebsiella treated?
Do sensitivity testing
105
What antibiotics are used to treat shigella?
Quinolones, Azithromycin
106
What antibiotics are used to treat salmonella?
Amoxicillin, Quinolones, Macrolides
107
What antibiotics are used to treat proteus?
Penicillins, cephalosporins
108
What antibiotics are used to treat neisseria?
Cephalosporins
109
What bacterium causes the majority of UTIs?
E.coli
110
Why is klebsiella hard to treat?
Some strains highly resistant
111
How does pseudomonas present?
Do not usually cause infections in healthy people - if so infection is mild
112
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
113
What are the symptoms of meningitis?
Stiffness of the neck, photophobia + severe headache
Infective: fever, malaise
Petechial rash associated with meningococcal meningitis
114
What causes bacterial meningitis in neonates?
E.coli (-ve), Group B Strep (+ve), Listeria monocytogenes (+ve)
115
What causes bacterial meningitis in infants?
Neisseria meningitidis (-ve), Haemophilus influenzae (-ve), S.pneumoniae (+ve)
116
What causes bacterial meningitis in young adults?
Neisseria meningitidis (-ve), S.pneumoniae (+ve)
117
What causes bacterial meningitis in the elderly?
Neisseria meningitidis (-ve), S.pneumoniae (+ve), Listeria monocytogenes (+ve)
118
What are the 2 most common causes of bacterial meningitis?
N.meningitidis (-ve) + S.pneumoniae (+ve) = diplococci
119
What viruses can cause meningitis?
Mumps virus, echo virus, coxsackie virus, herpes simplex virus, poliovirus
120
What drugs can induce meningitis?
NSAIDs, trimethoprim
121
How is meningitis diagnosed?
Blood culture
CSF sample (lumbar puncture at L4) for microscopy + sensitivity testing
Nose + throat swabs for viral
122
What does a CSF sample look like that indicates bacterial meningitis?
Turbid yellow colour, neutrophil polymorphs, raised protein, low glucose
123
What does a CSF sample look like that indicates viral meningitis?
Lymphocytes, normal protein, normal glucose
124
What does a CSF sample look like that indicates tuberculous meningitis?
Lymphocytes, raised protein, low/normal glucose
125
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
126
How is meningococcal septicaemia treated?
Immediate IM benzylpenicillin in community/ IV cefotaxime in hospital
127
How is viral meningitis treated?
Supportive treatment, self-limiting in 4-10 days, acyclovir for HSV meningitis
128
What antibiotics inhibit cell wall synthesis? What bacteria are they used to treat?
Glycopeptides and beta lactams - gram positive bacteria (have thick cell walls)
129
Give some examples of glycopeptide antibiotics.
Vancomycin and teicoplanin
130
What are the different categories of beta lactams?
Penicillins
Cephalosporins
Carbapenems
131
Give some examples of penicillins.
Benzylpenicillin
Amoxicillin
Flucloxacillin
132
Give some examples of cephalosporins.
Cephalexin
Cefotaxime
Ceftriaxone
133
Give some examples of carbapenems.
Imipenem
| Estapenem
134
Which antibiotics inhibit protein synthesis?
Cholaramphenicol
Macrolides
Tetracyclines
Aminoglycosides
135
Give some examples of macrolides.
Clarithromycin
| Erythromycin
136
Give some examples of tetracyclines.
Doxycycline
137
Give some examples of aminoglycosides.
Gentamicin
| Streptomycin
138
When are macrolides used?
We generally use macrolides instead of penicillin for those with a penicillin allergy
139
Which antibiotics inhibit folate synthesis?
Trimethoprim
| Sulphonamides - Sulphamethoxazole
140
Which antibiotics inhibit DNA gyrase?
Fluroquinolones - Ciprofloxacin
141
Which antibiotics bind to RNA polymerase?
Rifampicin
142
Which antibiotics cause DNA strand breaks?
Metronidazole
143
Why shouldn't you give trimethoprim to a pregnant woman?
Folate is important during pregnancy to prevent spina bifida - inhibits folate synthesis
144
How common are mycobacteria in the UK?
Rare
145
Describe the characteristics of mycobacteria.
Aerobic, non-spore forming, non-mobile bacilli
146
How does a mycobacteria infection present?
Slow-growing causes gradual onset of disease
147
How is a mycobacteria infection treated?
Requires multi-antibiotic treatment for a prolonged period
148
What are the 2 main examples of mycobacteria?
TB and leprosy
149
What staining technique is used to identify mycobacteria?
Ziehl-Neelsen stain used instead of gram staining
150
What colour do acid-fast bacteria stain in Ziehl-Neelsen staining?
Red
151
What colour do non-acid fast bacteria stain in Ziehl-Neelsen staining?
Blue
152
How do viruses survive?
Dependent on host cells for living - have no organelles or cell wall
153
How do viruses cause disease?
Can cause disease via direct destruction (polio), modification (rotavirus), over-reactivity (hepatitis B), damage through cell proliferation (HPV)
154
Why are viruses difficult to identify?
Not visible in light microscopy, can’t culture as only reproduce inside live cells
155
How are viruses identified?
PCR + nucleic acid amplification tests (NAAT) used, can also do serology (look for antibodies in response to virus)
156
What will be the results of a serology test if there is a virus present?
IgM within 1 week of onset, IgG appears later
157
How are viral infections treated?
Viral infections are often self-resolving, in severe cases antivirals can be given ‘-vir’, eg acyclovir
158
What are protozoa?
Microscopic unicellular eukaryotes
159
How do protozoa survive?
Can be free living or parasitic
160
How are protozoa classified?
Ameoboids, ciliates, sporozoan, flagellates
161
Give some common examples of protozoa.
Malaria, giardia lamblia, toxoplasmiosis, trichomonas vaginalis
162
What type of organism are fungi?
Eukaryotes
163
Describe the structure of fungi.
Have a cell wall - chitin + glucans (polysaccharides)
164
How do fungi move?
Move by growing across or through structures or by dispersion in air/ water
165
What are the 2 forms that fungi exist in?
Yeast and moulds
166
What is a yeast?
Single cell that divide via budding
167
What is a mould?
Form multicellular hyphae or spores
168
How do fungi cause infections?
Only a few can actually cause infection in humans - eg candida, athlete’s foot, nappy rash
169
How are fungal infections treated?
Antifungals target cell wall/ plasma membrane - ‘-azole’
170
How common are worm infections?
Common worldwide but rare in UK
171
What are the 3 groups of worms?
Nematodes (roundworms), trematodes (flatworms), ceratodes (tapeworms)
172
How do worms reproduce?
Adult worms cannot replicate inside body without a period of development outside the body
173
What is the pre-patent period?
Interval between infection + appearance of worm eggs/larvae in stool
174
Describe the immune system's response to worms.
Poor
175
Which antibodies are involved in worm infections?
Mainly IgG + IgE mediated
176
Give some examples of common worm infections.
Hookworm, schistosomiasis
177
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
178
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
179
What is the result of the oxidase test if oxidase positive?
Blue - bacteria is AEROBIC e.g. V. cholerae
180
What is the result of the oxidase test if oxidase negative?
No colour change - bacteria may be aerobic or anaerobic
181
What does XLD agar look like with salmonella?
Red/pink colonies some with black spots
182
What does an XLD agar look like with shigella?
Red/pink colonies
183
What are the 3 ways of classifying streptococci?
* Haemolysis
* Lancefield typing
* Biochemical properties
184
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
185
What are the 4 species of malaria that cause human disease?
* P. falciparum (most common)
* P. ovale
* P. vivax
* P. malariae
186
How is malaria transmitted?
Transmitted by the bite of the FEMALE ANOPHELES MOSQUITO
187
Causes of 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
```
188
How do you treat staph aureus?
Flucloxacillin
189
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.
```
190
How do you remember gram negative bacteria?
```
Huge - Helicobacter
Vaginas - Vibrio cholera
Can - Coliforms
Never - Neisseria
Provide - Parvobacteria
Pleasure - Pseudomonas
```
191
How do you remember DNA viruses?
```
H - Herpes viridae
A - Adenovirus
P - Parvovridae
P - Papopviridae
H - Hepaviridae
Mneumonic - HAPPH
```
192
How do you treat gram positive bacteria?
Penicillins
193
Are staphylococci catalase positive or negative?
Positive
194
Are streptococci catalase positive or negative?
Negative
195
Which type of bacteria are most catalase positive?
Many GRAM NEGATIVE bacteria e.g. E.coli and fungi (aspergillus spp.) are catalase POSITIVE
196
Which bacteria are coagulase positive?
Staphylococcus. aureus is coagulase POSITIVE - clumping
197
Which bacteria are coagulase negative?
Other staphylococci are coagulase NEGATIVE - no clumping
198
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)
199
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
200
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
201
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
202
What shape are cocci?
Round and spherical
203
What shape are bacilli?
Rod-like and straight
204
What can bacteria look like?
```
Diplococcus (2)
Chain of cocci
Cluster of cocci
Chain of rods
Curved rod (vibrio)
Spiral rod (spirochaete)
```
205
What are the clinical features of malaria?
- Chills & sweats
- Headache
- Myalgia
- Fatigue
- Nausea & vomiting - Diarrhoea
206
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
