Microbiology Flashcards
1
Q
Define pathogen.
A
An organism capable of causing disease.
2
Q
Define commensal.
A
An organism that colonises the host but causes no disease.
3
Q
Define opportunist pathogen.
A
An organism that only causes disease if host defences are compromised.
4
Q
Define virulence.
A
The degree to which a given organism is pathogenic.
5
Q
What would gram positive bacteria look like down the microscope?
A
Purple/blue.
6
Q
What would gram negative bacteria look like down the microscope?
A
Red/pink.
7
Q
What type of organism would you stain with Ziehl Neelsen?
A
Mycobacteria e.g. TB.
8
Q
How do you apply the gram stain?
A
Apply crystal violet to heat fixed bacteria.
Treat with iodine.
Decolourise the sample (alcohol)
Counterstain with safranin
9
Q
Describe the characteristic features of gram positive bacteria?
A
- Single membrane.
2. Large peptidoglycan area.
10
Q
Describe the characteristic features of gram negative bacteria?
A
- Double membrane.
- Small peptidoglycan area.
- LPS (endotoxin area).
11
Q
Between what temperatures and what pH range can bacteria grow?
A
Between -80 to +80°C. And from a pH of 4 to 9.
12
Q
Give an example of a slow growing bacteria.
A
TB
13
Q
Give an example of a fast growing bacteria.
A
E.coli and S.aureus.
14
Q
What types of bacteria release endotoxin?
A
Gram negative.
15
Q
What types of bacteria release exotoxin?
A
Gram positive and gram negative.
16
Q
Do viruses have a cell wall?
A
NO! Viruses have an outer protein coat that is sometimes surrounded by a lipid envelope but they do not have a cell wall.
17
Q
What part of the virus will enter the host cell?
A
Viruses use cell materials e.g. enzymes, amino acids and nucleotides, for their replication and they evade host defence mechanisms.
18
Q
Where in a cell does viral replication occur?
A
In the nucleus, cytoplasm or both.
19
Q
How can viruses be released from a cell?
A
- Bursting open; lysis of cell.
2. ‘Leaking’ from the cell over a preiod of time; exocytosis
20
Q
What are the 5 ways by which viruses can cause disease?
A
- Damage by direct destruction: cell lysis.
- Damage by modification of cell structure.
- ‘Over-reactivity’ of the host as a response to infection: immuno-pathological damage.
- Damage via cell proliferation and immortalisation.
- Evasion of host defences.
21
Q
What is the catalase test?
A
H2O2 + Staphylococci → Gas bubbles
\+ve = staph -ve = non staph
22
Q
You do a coagulase test for gram +ve cocci in clusters. Give an example of a bacteria that would give a positive/negative result
A
+ve = staph aureus.
It produces coagulase that converts fibrinogen to fibrin
-ve = staph epidermis
23
Q
A gram stain test reveals gram +ve cocci. What two types of bacteria could they be?
A
Clusters = staphlococcus (catalase negative) Chains = streptococcus (catalase positive)
24
Q
How would you distinguish between gram positive cocci in clusters?
A
coagulase test
25
How would you distinguish between gram positive cocci in chains?
Observe blood agar haemolysis
26
Give examples of 2 alpha haemolytic strep?
S. pneumoniae ( optochin +ve)
| S. Viridans (optochin -ve)
27
What is the Lancefield test?
groups bacteria based on carbohydrate composition of bacterial antigen on cell wall, normally for beta haemolytic strep
28
Give examples of Group A/B/D strep?
A: Streptococcus pyogenes (beta haemolytic)
B: Streptococcus agalactiae (beta haemolytic)
D:- Enterococcus
- Strep bovis (group D is non- haemolytic)
29
Give 3 important gram +ve bacilli
1. Listeria monocytogenes
2. Propionibacterium acne – acne
3. Clostridium difficile – diarrhoea from antibiotic
overuse (those starting with C)
30
What is the purpose of MacConkey agar?
Identifies bacteria that can ferment lactose
| normally gram-ve enteric bugs
31
What does MacConkey agar contain?
bile salts
lactose
neutral red (pH indicator)
32
Give examples of the results of MacConkey agar and which bacteria cause them?
YELLOW: non fermenters
- salmonella, shigella, pseudomonas aeruoginosa, proteus mirabilis
PINK: fermenters
- e.coli, klebisella pneumoniae
33
When would you perform an oxidase test?
On
- non-lactose fermenting
- gram -ve
- bacilli
34
What do the results of an oxidase test indicate?
+ve = Pseudomonas (Additional anti-pseudomonal sensitivity tests required)
-ve = COLIFORMS (shigella, salmonella, proteus)
35
Give 2 significant gram negative cocci.
1. Neisseria meningitidis (diplococci, requires choccy agar)
2. Gonorrhoea
3. Moraxella catarrhalis
36
How do you culture mycobacteria?
Takes long to culture, have to be cultured with
| Löwenstein–Jensen medium
37
Describe the structure of fungi
- eukaryotic
- chitinous cell wall
- can be yeast OR mould
38
When are fungal infections more of a concern?
In the immunocompromised
39
Give 3 significant fungal infections
```
Candida albicans (thrush) – treat with antifungal eg topical
nystatin, oral fluconazole
```
Pneumocystis pneumonia – treat with co-trimoxazole
Aspergilliosis – CF, bronchiectasis patients
40
Give 2 significant helminth infections and their treatment
Schistosomiasis – causes squamous cell bladder cancer
Hookworm - Worldwide cause of iron-deficiency anaemia
Treatment: normally mebendazole
41
Give an example of a protazoa infection (other than malaria)
Giardia: diarrhoea due to alteration of intestinal villi,
reducing absorption
Treat with metronidazole
42
Where in the body might you find staphylococci?
Nose and skin
43
What category of bacteria does shigella fall under?
Gram negative bacilli.
44
Does shigella give a positive result with MacConkey agar?
No. Shigella does not ferment lactose and so gives a negative result.
45
What does mucosal candidiasis look like?
White adherent plaques on oral or genital mucosa
46
What are risk factors for having Candida albicans ?
```
Immunocompromise
Diabetes
Antibiotic use
Dentures
Pregnancy
Poorly ventilated underwear!
```
47
How do you treat Candida albicans?
topical antifungals or oral fluconazole
48
What is the most common presenting illness with HIV?
Pneumocystis pneumonia
| - opportunistic infection, can cause lung infection in immunocompromised people.
49
What is the gold standard test for diagnosing PCP?
PCR of induced sputum or Branchoalveolar lavage (BAL)
50
How do you treat PCP?
co-trimoxazole
51
Why is treating fungi more difficult than bacteria?
Fungi are eukaryotic
52
Give an example of a mould.
Aspergillus fumigatus.
| Aspergillus niger.
53
Which genus does HIV belong to and what is the significance of this?
HIV belongs to the lentivirus genus. These viruses are characterised by having a long incubation period.
54
Why are mutations common in HIV?
HIV is a retrovirus and replicates via reverse transcription. This process is prone to errors and mutations.
55
What cells act as 'host cells' for HIV?
CD4+ cells. Macrophages and dendritic cells can also be invaded by HIV.
56
What is the affect of HIV infection on CD4 count?
HIV leads to uncontrolled CD4 activation and apoptosis. CD4 numbers decrease over time.
57
What enzyme copies HIV RNA into DNA?
Reverse transcriptase.
58
Describe what happens when someone is initially infected with HIV.
1. HIV enters via mucosa.
2. Macrophages ingest HIV and presents an epitope of HIV to a T cell.
3. HIV then infects the T cell.
4. Infection spills into the blood stream - viraemia.
59
HIV leads to immune dysfunction, how are the immune system cells affected?
1. CD4 cells are excessively and inappropriately activated.
2. There is impaired IL-2 production.
3. There is a decrease in the number and function of CD4 cells.
4. B cells produce fewer specific Ab's.
5. There are fewer Natural Killer cells, neutrophils and macrophages.
60
Briefly describe the mechanism of HIV replication.
1. GP120 binds to CD4 receptors.
2. Viral caspid, enzymes and nucleic acids are uncoated and released into the cell.
3. RNA is converted into DNA using reverse transcriptase.
4. Viral DNA is integrated into cellular DNA by intergrase.
5. Viral DNA is transcribed into viral proteins.
6. Splicing.
7. New HIV cells 'bud' from CD4.
61
What does MRSA stand for?
Methicillin-resistant Staphylococcus aureus (vancomycin resistant)
62
How do you treat MRSA?
vancomycin
63
What is a clinically important gram positive resistant bacteria?
MRSA - plasmid transfer resistance.
64
What types of bacteria does vancomyocin work against?
Gram positive only!
| Good for MRSA treatment.
65
What key additional tests need to be performed in someone with MRSA?
1. Echo - to rule out endocarditis.
| 2. Spinal MRI.
66
Name 4 enzymes involved in HIV replication.
1. Reverse transcriptase.
2. Integrase.
3. RNA polymerase.
4. Proteases.
67
Name 4 'sanctuary sites' for HIV.
1. Genital tract.
2. GI tract.
3. CNS.
4. Bone marrow.
68
Define antibiotics.
Agents produced by micro-organisms that kill or inhibit the growth of other micro-organisms.
69
What are the markers for HIV in the blood?
Antigens, antibodies, HIV RNA.
70
What are the markers for HIV in the blood?
```
P24 ANTIGEN (at 4 weeks)
v. sensitive and specific
```
71
Name 5 groups of people who are at high risk of HIV infection.
1. Homosexual men.
2. Sex workers.
3. IV drug users.
4. Truck drivers.
72
What are the 3 stages of the HIV epidemic?
1. Nascent; <5% prevalence in risk groups.
2. Concentrated; >5% prevalence in one or more risk groups.
3. Generalised; >5% prevalence in the general population.
73
How can the impact of HIV be reduced?
1. Behaviour change; education, condom use, needle exchange.
2. Know your status; testing.
3. Specific interventions; PMTCT, PEP, VMCC, PrEP etc.
74
Briefly explain why voluntary medical male circumcision can reduce sexual transmission of HIV.
Male circumcision leads to a change in mucosa. HIV is less able to penetrate due to an increase in keratinisation.
75
How can HIV among young children be eliminated?
To reduce MTCT; prevent breast feeding where possible; give lifelong antiretroviral treatments to the mother.
76
What are the problems with trying to ensure everyone living with HIV has access to antiretroviral treatments?
1. Lack of awareness.
2. Understaffed clinics.
3. Medication needs monitoring.
4. Cost.
5. Adherence.
77
What are the problems with trying to ensure everyone living with HIV has access to antiretroviral treatments?
1. Lack of awareness.
2. Understaffed clinics.
3. Medication needs monitoring.
4. Cost.
5. Adherence.
78
How can awareness of HIV be increased?
TESTING! Ensure it is accurate, high quality and provides care, support and ultimately treatment.
79
What are the 4 main phases in the natural history of HIV?
1. Acute primary infection.
2. Asymptomatic phase.
3. Early symptomatic HIV.
4. AIDS.
80
What signs and symptoms might you see when someone is in the acute primary infection phase of HIV?
Abrupt onset of non-specific symptoms e.g. fever, rash. Weight loss, lethargy and depression can also occur.
81
What happens in the asymptomatic phase of HIV?
There is a progressive loss of CD4+ cells. This is the latent phase and can last for years.
82
What signs and symptoms might you see when someone is in the asymptomatic phase of HIV?
This phase is the latent phase and so you will rarely see symptoms. However, you might sometimes see enlarged lymph nodes.
83
What is the CD4+ count when someone is diagnosed with having AIDS?
CD4+ <200.
84
Name 3 types of people who are likely to rapidly progress and develop AIDS.
1. Elderly people.
2. Children.
3. People with a high viral load.
85
Name 2 markers that are used for monitoring HIV.
1. CD4+ count.
2. HIV RNA copies (viral load).
- These markers are important in determining prognosis.
86
Name 3 respiratory diseases associated with HIV.
1. Bacterial (pneumococcal) pneumonia.
2. TB.
3. Pneumocystis pneumonia (PCP).
87
What are the characteristic signs of pneumocystis pneumonia (PCP)?
Decreased CD4+ count.
Decreased O2 sats on exertion.
Decreased exercise tolerance.
88
Name 3 CNS diseases associated with HIV.
1. Mass lesions e.g. primary CNS lymphoma, cerebral toxoplasmosis.
2. Meningitis e.g. pneumococcal, cryptococcal.
3. Opthalmic lesions e.g. CMV, toxoplasmosis, choroidal tuberculosis etc.
89
What does HAART stand for?
Highly active anti-retroviral treatment.
90
What is HAART? What does it aim to do?
Anti-retroviral treatment where 3 drugs are taken together.
| The aim is to reduce viral load and increase CD4+ count. Good compliance = good prognosis.
91
How would you define a 'late diagnosis' of HIV?
CD4+ count < 350.
92
Name 4 diseases that haemophilus influenzae can cause.
1. Meningitis.
2. Otitis media.
3. Pharyngitis.
4. Exacerbations of COPD.
93
What does the HIV envelope contain?
RNA, caspid, reverse transcriptase.
94
What are some of the signs and symptoms of HIV?
General: Fever, night sweats, diarrhea, weight loss, generalised rash/ lymphadenopathy/oral candida/ recurrent mouth lesions
Opportunistic diseases: recurrent herpes simplex, pneumococcal pneumonia
95
What would you do with a negative/positive HIV test?
negative = repeat again if within 'window' period
positive = refer to GUM/ID within 48 hrs
96
What is ringworm?
A fungal infection that can cause an itchy, red, scaly, circular rash.
97
True or False. Mycobacteria can withstand phagolysosome killing.
True. The bacterium has adapted to the intracellular environment can can withstand phagolysosome killing and escape to the cytosol.
98
Give 3 defining features of systemic inflammatory response syndrome (SIRS).
- Temperature >38℃ or <36 ℃.
- Heart rate >90.
- White cell count >12.
- Hyperglycaemia.
99
Infection control. What are the five moments of hand hygiene?
1. Before patient contact.
2. Before aseptic procedure.
3. After bodily fluid exposure.
4. After touching a patient.
5. After touching patient surroundings.
100
Name 6 vaccine preventable diseases that are notifiable.
1. Diptheria.
2. Measles.
3. Mumps.
4. Rubella.
5. Tetanus.
6. Whooping cough.
101
Name 5 diseases that are notifiable.
1. Anthrax.
2. Cholera.
3. Rabies.
4. Smallpox.
5. Yellow fever.
6. Acute encephalitis.
7. Botulism.
8. Enteric fever.
9. Leprosy.
10. Malaria.
102
Why is it important to tell public health England about notifiable diseases?
It can aid disease surveillance: changes can be tracked. Interventions can be developed to protect the community.
103
What is passive immunisation?
Injecting immunoglobulins. Temporary increase in antibody levels.
104
What is active immunisation?
Vaccination that stimulates an immune response against toxoid.
105
What does meningococcal infection usually present as?
Meningitis or septicaemia (blood poisoning).
106
How is Neisseria meningitidis transmitted?
Droplet transmission from person to person.
107
What kind of bacteria is Neisseria meningitidis?
Gram negative diplococci.
108
How can further cases of meningitis be prevented?
1. Notification.
2. Contact tracing.
3. Prophylaxis e.g. advice, medication, vaccination (serogroup dependent).
109
CD4+ cells can differentiate into T helper 1 and T helper 2 cells. What is the function of TH1 cells?
TH1 produce interleukins that help coordinate the immune response. They activate macrophages and CD8+.
110
CD4+ cells can differentiate into T helper 1 and T helper 2 cells. What is the function of TH2 cells?
TH2 produce interleukins that help B cells produce immunoglobulins.
111
What is the first line treatment for meningitis?
Cefotaxime.
112
A 9 month child who has not had any vaccinations is found to have meningitis. His CSF is analysed and the gram film shows gram negative coccobacili. What organism has caused the meningitis?
H.influenzae.
Normally children are vaccinated against this.
113
A 1 day old baby is found to have a group B strep infection. What is the most likely source of this organism in this baby?
From the birth canal.
114
Describe the appearance of listeria monocytogenes on a gram film.
Gram positive bacili.
115
Name 3 groups of people who are at risk of listeria monocytogenes infection.
1. Immunocompromised.
2. The elderly.
3. Neonates.
116
Describe the antibiotic therapy for meningitis caused by listeria monocytogenes?
Cefotaxime and amoxicillin.
117
What would the CSF cell count look like for viral meningitis?
- High lymphocytes.
- Normal/high protein.
- Normal glucose.
118
What would the CSF cell count look like for bacterial meningitis?
- Raised neutrophils.
- High protein.
- Low glucose.
119
Name 5 AIDS defining conditions.
1. Oesophageal candidiasis.
2. TB.
3. PCP (pneumocystis jirovecii pneumonia).
4. Recurrent bacterial pneumonia.
5. Kaposi's carcinoma.
6. Hodgkins and Non-Hodgkin's lymphoma.
7. HIV dementia.
