Microbiology Flashcards
(184 cards)
1
Q
Define pathogen.
A
Organism that causes or is capable of causing a disease.
2
Q
Define commensal.
A
Organism that colonises the host without causing a disease, in normal circumstances.
3
Q
List 5 locations commensals are found.
A
1) skin
2) mouth
3) mucosal surfaces
4) urethra
5) vagina
4
Q
List 7 locations commensals are not found, i.e. sterile.
A
1) blood
2) cerebrospinal fluid
3) pleural cavity
4) peritoneal cavity
5) lower respiratory tract
6) urinary tract
7) joints
5
Q
Define virulence.
A
The degree to which a pathogen is pathogenic.
6
Q
What is a synonym of virulence?
A
Pathogenicity.
7
Q
Define virulence factor. (5)
A
Molecules produced by pathogens that enable them to:
1) colonise host
2) obtain host nutrients
3) immunoevade
4) immunosuppress
5) enter and exit cells (intracellular pathogen)
8
Q
Define asymptomatic carriage.
A
Pathogen in a tissue site without causing a disease.
9
Q
List Koch’s postulates of disease. (4)
A
1) microbe must be found in all diseased individuals
2) microbe must be isolated from diseased individual and grown into a pure culture
3) individual inoculated with pure microbe culture should develop disease
4) microbe must be reisolated from inoculated diseased individual
10
Q
Define coccus.
A
Round bacteria.
11
Q
Define bacillus.
A
Rod-shaped bacteria.
12
Q
Define diplococcus.
A
Paired round bacteria.
13
Q
Define vibrio.
A
Curved rod-shaped bacteria.
14
Q
Define spirochaete.
A
Spiral rod-shaped bacteria
15
Q
Define spore.
A
Dormant form of bacteria that is highly resistive to physical and chemical influences.
16
Q
Define opportunistic pathogen.
A
Organism that causes disease only in immunocompromised individuals.
17
Q
Define desiccation.
A
A state of extreme dryness.
18
Q
What temperature is the bacterial environment?
A
-80C to +80C.
19
Q
What pH is the bacterial environment?
A
pH 4 to pH 9.
20
Q
List 3 forms of mutation that lead to genetic variations in bacteria.
A
1) substitution
2) deletion
3) insertion
21
Q
List 3 forms of gene transfer that lead to genetic variation in bacteria.
A
1) transformation, e.g. plasmid
2) transduction, e.g. phage
3) conjugation, e.g. sex pilus
22
Q
How long can spores be desiccated?
A
> 50 years.
23
Q
How long can bacteria be desiccated?
A
2 hours to 3 months.
24
Q
Define endotoxin.
A
Lipopolysaccharide (LPS), found on outer membrame of Gram negative bacteria.
25
Define exotoxin.
Proteins secreted by bacteria.
26
Which has a specific action, exotoxin or endotoxin?
Exotoxin.
27
List the 3 components of LPS of Gram negative bacteria.
1) lipid A - toxic
2) core antigen (R) - short sugar chain
3) somatic antigen (O) - repeating oligosaccharide chain
28
Which is stable in high temperatures, exotoxin or endotoxin?
Endotoxin.
29
What is Gram staining?
Staining method used to separate bacteria into two groups, Gram positive and Gram negative.
30
Which doesn’t bind well to immune cell receptors, exotoxin or endotoxin?
Endotoxin.
31
What property does the Gram stain use to differentiate bacteria? (2)
Peptidoglycan in cell walls.
1) Gram positive bacteria have a single membrane cell wall with large amounts of peptidoglycan.
2) Gram negative bacteria have a double membrane cell wall with small amounts of peptidoglycan.
32
List the steps of Gram staining. (4)
1) crystal violet stain - purple primary stain
2) iodide - fixes crystal violet to peptidoglycan
3) ethanol/acetone - decolorisation
4) safranin/carbyfuscin - pink counter stain
33
Why do Gram negative bacteria find secreting proteins harder?
Protein has to pass through two membranes.
34
How do you differentiate Gram positive cocci into Staphylococci and Streptococci?
Catalase testing.
35
What are the results of catalase testing? (2)
1) Staphylococcus, catalase positive.
| 2) Streptococcus, catalase negative.
36
Define Staphylococcus.
Clusters of Gram positive cocci.
37
How do you differentiate Staphylococci?
Coagulase test.
38
What is the coagulase test?
Test for the enzyme coagulase.
39
What is coagulase?
A virulence factor that clots blood plasma, forming a fibrin clot around the bacteria protecting it from phagocytosis.
40
What are coagulase negative bacteria generally?
Opportunistic.
41
How do you differentiate Staphylococci aureus? (5)
1) cocci
2) clustered
3) Gram positive
4) coagulase test positive
5) golden colour
42
How do you differentiate Staphylococcus saprophyticus? (4)
1) cocci
2) clustered
3) Gram positive
4) coagulase negative
43
Define Streptococcus.
Chains of Gram positive cocci.
44
List 3 ways of differentiating Streptococci.
1) haemolytic testing
2) Lancefield grouping
3) optochin disc testing
45
List the 3 outcomes of haemolytic testing.
1) α - partial lysis —> greening
2) β - complete lysis —> clearing
3) γ - no lysis —> red
46
List 5 α haemolytic Streptococci.
1) Streptococci pneumoniae
2) viridans Streptococci
3) Streptococci oralis
4) Streptococci milleri
5) Streptococci sanguis
47
List 2 β haemolytic Streptococci.
1) Streptococci pyogenes
| 2) Streptococci agalactiae
48
Name a γ haemolytic Streptococci.
Streptococci bovis.
49
How do you differentiate Staphylococcus epidermidis? (4)
1) cocci
2) clustered
3) Gram positive
4) coagulase negative
50
What is Lancefield grouping.
Using antibodies to test for carbohydrate cell surface antigens.
51
What is a positive result in Lancefield grouping?
Suspension of bacteria, agglutination.
52
What are the Lancefield types.
A-H and K-V, but A and B are most important.
53
What Streptococci is Lancefield group A postive?
Streptococci pyogenes.
54
What Streptococci is Lancefield group B positive?
Streptococci agalactiae.
55
Describe optochin disc testing. (3)
1) disc is placed on agar
2) if growth is inhibited around the disc, positive
3) if growth is normal around disc, negative
56
What is optochin testing used to differentiate?
Streptococci pneumoniae.
57
How do you differentiate Streptococci pneumoniae? (5)
1) cocci
2) chained
3) Gram positive
4) α haemolytic
5) optochin disc sensitive
58
How do you differentiate viridans Streptococci? (5)
1) cocci
2) chained
3) Gram positive
4) α haemolytic
5) optochin disc resistant
59
Where do viridans Streptococci generally infect?
Orally.
60
How do you differentiate Streptococci pyogenes? (5)
1) cocci
2) chained
3) Gram positive
4) β haemolytic
5) Lancefield group A
61
How do you differentiate Streptococci agalactiae? (5)
1) cocci
2) chained
3) Gram positive
4) β haemolytic
5) Lancefield group B
62
How do you differentiate Streptococcus bovis? (4)
1) cocci
2) chained
3) Gram positive
4) γ haemolytic
63
What are the 2 groups of Gram positive bacilli?
1) aerobic
| 2) anaerobic
64
List the 3 types of aerobic Gram positive bacilli.
1) Cornybacterium, e.g. C. diphtheria
2) Listeria, e.g. L. monocytogenes
3) Bacillus, e.g. B. anthracis
65
Name a type of anaerobic Gram positive bacilli.
Clostridium.
66
List 4 examples of Clostridium.
1) Clostridium perfringens
2) Clostridium tetani
3) Clostridium botulinium
4) Clostridium dificile
67
List 3 types of Gram negative cocci.
1) Neisseria
2) Moraxella
3) Veillonella
68
How do you differentiate Gram negative bacilli?
Whether they ferment in lactose.
69
List 3 agar plates containing lactose that differentiate Gram negative bacilli.
1) MacConkey
2) CLED
3) XLD
70
List 2 lactose fermenting Gram negative bacilli.
1) Escherichia coli
| 2) Klebsiella
71
List 3 non lactose fermenting Gram negative bacilli.
1) Shigella
2) Salmonella
3) Pseudomonas
72
How do you differentiate lactose fermenting Gram negative bacilli? (2)
1) biochemical identification, e.g. API strips
| 2) sensitivity tests
73
What is the colour change in MacConkey agar with the presence of a lactose fermenting Gram negative bacilli?
Yellow —> Red.
74
What type of bacteria does the Gram stain not differentiate?
Mycobacteria.
75
What test is used to differentiate Mycobacteria?
Ziehl-Neelsen staining. Stains red.
76
List 7 Mycobacterium and an associated medical condition.
1) Mycobacterium tuberculosis - tuberculosis
2) Mycobacterium leprae - leprosy
3) Mycobacterium avium - chronic lung infection
4) Mycobacterium kansasii - chronic lung infection
5) Mycobacterium marinum - fish tank granuloma
6) Mycobacterium ulcerans - Buruli ulcer
7) Mycobacterium fortuitum - skin and soft tissue infections
77
List 7 features of Mycobacterium.
1) aerobic
2) bacillus
3) Gram neutral (colourless) to weakly Gram positive
4) non spore forming
5) non motile
6) high molecular weight lipid cell wall
7) slow growing
78
Describe the immunology of Mycobacterium, and the formation of granulomas. (10)
1) Mycobacterium phagocytosed by macrophages
2) Mycobacterium is trafficked into a phagolysosome
3) Mycobacterium adapted to withstand phagolysosome
4) Mycobacterium escapes to cytosol
5) unable to kill the Mycobacterium, macrophages activate into epithelioid histiocytes
6) epithelioid histiocytes fuse forming Langerhan giant cells
7) granuloma forms
8) T cells infiltrate the granuloma
9) fibroblasts surround the granuloma to ‘wall it off’
10) central tissue of granuloma may necrose
79
How long do memory cells take to generate in primary tuberculosis?
4-8 weeks.
80
List 2 outcomes of primary tuberculosis.
1) latent tuberculosis (90%)
| 2) pulmonary tuberculosis (5%)
81
Where do tuberculosis granulomas tend to form?
Lung apexes.
82
Why do tuberculosis granulomas tend to form in lung apexes? (2)
1) more air supply
| 2) less blood supply —> fewer leukocytes
83
List 2 things Mycobacterium high molecular weight lipid cell wall results in.
1) surviving in harsh environments, e.g. macrophage lysosomes
2) resistant to Gram stain
84
List 4 features that is a result of Mycobacterium’s slow growth.
1) slow reproduction
2) slow growth in humans
3) slow growth in culture —> hard to culture
4) slow response to treatment —> 6 months minimum
85
How do you differentiate non lactose fermenting Gram negative bacilli?
Oxidase test.
86
What is the result of Oxidase testing?
Oxidase positive —> Pseudomonas.
87
Define helminths.
Parasitic worms.
88
List the 3 groups of helminth.
1) nematodes - roundworms
2) trematodes - flatworms (flukes)
3) cestodes - tapeworms
89
List 2 locations of nematodes (roundworms).
1) intestines
| 2) skin
90
List 4 locations of trematodes (flatworms).
1) intestines
2) liver
3) lung
4) blood
91
List 2 types of cestodes.
1) non-invasive - remains in intestines
| 2) invasive - leaves intestines
92
List 4 features of helminth related diseases.
1) one of the commonest diseases in world
2) rare in UK
3) helminths reproduce only after developing outside of host
4) helminths produce countless larvae/eggs
93
Define pre-patent period.
Interval between helminth infection and appearance of larvae/eggs in stool.
94
List 6 methods to control helminth related disease.
1) treatment of carriers
2) mass chemotherapy e.g. everyone
3) targeted chemotherapy e.g. haematuric individuals
4) water contamination prevention
5) toilet provisions
6) health education
95
List 7 common viral infections.
1) respiratory
2) herpes group
3) hepatitis group
4) enterovirus
5) diarrhoea causing
6) rash causing
7) HIV
96
List 2 unusual principles of viruses.
1) same virus can cause different diseases, e.g. enteroviruses
2) different viruses can cause same disease, e.g. hepatitis group
97
List 5 basic properties of viruses.
1) inert outside host cell
2) function inside host cell
3) possess only one type of nucleic acid (RNA or DNA)
4) no cell wall —> outer protein coat
5) surface protein receptors —> allows attachment onto host cell
98
List 3 features of viruses that suggest they are living.
1) nucleic acid core
2) outer protein capsid
3) replicate (inside host cell)
99
List 4 features that suggest viruses are non-living.
1) only one type of nucleic acid
2) no cell wall
3) no organelles
4) cannot replicate by themselves
100
List 6 stages of viral replication.
1) attachment
2) cell entry
3) host cell interaction
4) replication
5) assembly
6) release
101
What happens during viral attachment?
Viral surface protein receptors attach to specific cells, e.g. HIV gp120 to CD4 T cells.
102
What happens during viral cell entry?
Central viral core containing nucleic acid and associated proteins enter host cell.
103
What happens during viral host cell interaction.
Virus evades host cell defence mechanisms.
104
What happens during viral replication? (3)
1) virus localises in nucleus, cytoplasm or both
2) virus uses host cell materials (enzymes, amino acids, nucleotides)
3) virus produces progeny viral nucleic acids and proteins
105
What happens during viral assembly?
Progeny viral nucleic acids and proteins are assembled at nucleus, cytoplasm or cell membrane.
106
What happens during viral release?
Virus leaves host cell by either lysis or exocytosis.
107
List 4 methods viruses cause disease.
1) direct destruction of host cells, e.g. HIV
2) modification of host cell structure or function, e.g. rotavirus
3) host overreaction, e.g. hepatitis B
4) cell proliferation/immortalisation, e.g. human papillomavirus
108
List 3 ways viruses evade host defences.
1) persistence
2) variability
3) modulation of host defences
109
What type of cell are fungi?
Eukaryotes.
110
List 4 components of fungal cell walls.
1) chitin
2) mannoproteins
3) B1,3 glucan
4) B1,6 glucan
111
What drugs target fungal cell walls?
Echinocandins.
112
List 3 drugs targeting fungal cell membranes.
1) Amphotericin
2) Azoles
3) Terbinafine
113
What do fungal cell membranes contain instead of cholesterol?
Ergosterol.
114
Is fungal DNA, RNA and protein synthesis similar to mammals?
Yes.
115
Describe fungal nutritional intake.
Heterotrophic.
116
Define heterotrophic.
Inability to produce organic substances from inorganic substances. Rely on outside nutrients.
117
List the 2 forms of fungi.
1) yeast - <1%
| 2) mould - >99%
118
What form are yeasts found in?
Single cells.
119
List 2 forms moulds are found in.
1) multicellular hyphae
| 2) multicellular spores
120
Define dimorphic fungi.
Fungi able to switch between yeasts and moulds depending on conditions.
121
List 2 reasons why fungi are generally not pathogenic.
1) inability to grow at 37ºC - non cell invasive
| 2) no method to combat immune response
122
List 5 common fungal infections.
1) nappy rash
2) vulvovaginal candidiasis - ‘yeast infection’
3) onychomycosis - nail infection
4) otitis externa - swimmer’s ear
5) fungal asthma
123
List 3 instances when fungal infections are life threatening.
1) immunocompromised
2) post-surgical
3) fungal asthma
124
List 3 reasons why is treating fungal infections difficult.
1) fungi are eukaryotic
2) similar to host cells
3) difficult to treat without host cell toxicity
125
What drugs target fungal DNA, RNA and protein synthesis? (1)
Flucytosine.
126
Define Protozoa.
Single-called eukaryotes.
127
List 2 environments Protozoa are found.
1) aqueous environments
| 2) soil
128
List the 5 major classifications of Protozoa.
1) flagellates
2) amoebae
3) sporozoa
4) microsporidia
5) cilliates
129
Give an example of a Protozoa.
Malaria.
130
List the 5 species of malaria that infect human.
1) Plasmodium falciparum
2) Plasmodium ovale
3) Plasmodium vivas
4) Plasmodium malariae
5) Plasmodium knowlesi
131
List 4 signs of malaria.
1) anaemia
2) jaundice
3) heptosplenomegaly
4) black water fever - dark urine
132
List 8 symptoms of malaria.
1) fever*
2) chills
3) headache
4) myalgia
5) fatigue
6) abdominal pain
7) diarrhoea
8) vomiting
133
What type of malaria causes complicated symptoms.
Plasmodium falciparum.
134
List 5 symptoms of complicated malaria.
1) cerebral
2) acute respiratory distress syndrome (ARDS)
3) renal failure
4) sepsis
5) bleeding/anaemia
135
Define antibiotic.
Molecules that bind to a target site on a bacteria, causing either growth inhibition or direct death.
136
Define target sites.
Points of biochemical reactions, crucial to survival of the bacterium.
137
List the 5 functional classes of antibiotics.
1) inhibitors of cell wall synthesis
2) inhibitors of nucleic acid synthesis
3) inhibitors of protein synthesis
4) inhibitors of cell membrane function
5) anti-metabolites
138
Define anti-metabolites.
Molecules that inhibit the use of a metabolite, e.g. anti-folates.
139
List 3 groups of antibiotics that inhibit cell wall synthesis.
1) beta lactams, e.g. penicillin
2) vancomycin
3) bacitracin
140
How does penicillin inhibit cell wall synthesis?
Disrupts peptidoglycan production.
141
What process must bacteria be undergoing for penicillin to be effective?
Replication.
142
What type of bacteria are penicillin more effective against, and why?
Gram positive. Gram negative bacteria have an extra lipopolysaccharide layer that decreases penetration to peptidoglycan.
143
List 2 ways that antibiotics inhibit nucleic acid synthesis.
1) affect DNA replication, e.g. rifampicin (RNA polymerase)
| 2) affect DNA folding, e.g. fluoroquinolone (DNA gyrase)
144
List 4 types of antibiotics that inhibit protein synthesis.
1) aminoglycosides, e.g. gentromycin
2) tetracyclines
3) lincosamides
4) macrolides, e.g. erthyromycin
145
What are bacteriostatic antibiotics?
Antibiotics that prevent bacteria growth.
146
Describe bacteriostatic antibiotic’s efficacy.
Kill >90% in 18-24 hours.
147
List 3 ways bacteriostatic antibiotics work.
1) inhibit nucleic acid synthesis
2) inhibit protein synthesis
3) anti-metabolite
148
List 2 beneficial effects of bacteriostatic antibiotics.
1) reduce exotoxin production
| 2) reduce endotoxin surge likeliness
150
What are bactericidal antibiotics?
Antibiotics that kill bacteria.
151
Describe bactericidal antibiotic’s efficacy.
Kill 99.9% in 18-24 hours.
152
List 2 ways bactericidal antibiotics work.
1) inhibit cell wall synthesis
| 2) inhibit cell membrane function
153
Can antibiotics be both bacteriostatic and bactericidal?
Yes.
154
List 3 things that affect whether a antibiotic is bacteriostatic or bactericidal.
1) conditions
2) pathogen
3) concentration
155
List 3 instances when bactericidal antibiotics are useful.
1) poor tissue penetration, e.g. endocarditis
2) difficult to treat infections, e.g. tuberculosis
3) need to eradicate infection quickly, e.g. meningitis
157
List 2 things an antibiotic must do to be effective.
1) occupy an adequate number of binding sites - concentration
2) occupy binding sites for an adequate period of time - time
158
List the 2 types of antibiotic killing.
1) concentration dependant killing
| 2) time dependant killing
159
What is the key parameter of concentration dependant killing?
How high antibiotic concentration is above MIC.
| Peak Concentration/MIC ratio
160
List 2 types of antibiotics that are concentration dependant killers.
1) aminoglycosides
| 2) quinolone
161
What is the key parameter of time dependant killing?
How long antibiotic concentration remains above MIC between doses.
t>MIC
162
List 3 types of antibiotics that are time dependant killers.
1) beta lactams, e.g. penicillin
2) macrolides, e.g. erythromycin
3) oxazolidiones
163
Define minimum inhibitory concentration (MIC).
Minimum concentration of antibiotic required to stop bacterial growth.
164
List 8 considerations before prescribing antibiotics.
1) side effects
2) drug interactions
3) intolerance, allergy, anaphylaxis
4) age
5) kidney function
6) liver function
7) pregnancy and breast feeding
8) risk of Clostridium difficile
165
List 3 ways bacteria develop resistance to antibiotics.
```
Intrinsic
1) naturally resistant
Acquired
2) spontaneous gene mutation
3) horizontal gene transfer
```
166
List 3 methods of horizontal gene transfer.
1) conjugation - plasmid transfer via sex pilli
2) transduction - DNA insertion by bacteriophages
3) transformation - picking up naked DNA
167
List 2 important antibiotic resistant bacteria.
1) methicillin resistant Staphylococcus aureus (MRSA)
| 2) vancomycin resistant Enterococci (VRE)
168
Define minimum bactericidal concentration (MBC).
Minimum concentration of antibiotics required to kill all bacterium.
169
List the 3 groups of HIV.
1) main (M)
2) outlying (O)
3) new (N)
170
List the clades of main group.
1) A-D
2) F-H
3) J-K
171
Where is clade A found?
West and Central Africa.
172
Where is clade B found?
Europe and USA.
173
Where is clade C found?
Southern Africa.
174
List the 9 steps of HIV replication.
1) attachment
2) entry
3) uncoating
4) reverse transcription
5) genome integration
6) transcription
7) translation
8) assembly
9) budding
175
How many genes does HIV contain?
9.
176
List 7 cells HIV can infect.
1) helper T cells*
2) macrophages
3) dendritic cells
4) bone marrow progenitors (CD34+)
5) renal epithelial cells
6) brain micro vascular endothelial cells
7) astrocytes
177
List 3 reasons why is immune response to HIV poor.
1) antibodies to gp120 are slow to develop
2) antibodies to gp120 are ineffective as gp120 is not immunogenic
3) HIV escapes killer T cells through antigen mutations
178
List 5 ways HIV depletes helper T cell numbers.
1) induces apoptosis*
2) cytotoxicity of infected cells
3) decreased production
4) redistribution (peripheries —> lymphoid)
5) bystander cell killing (infected cells kill uninfected cells)
179
Define sanctuary site.
Areas poorly penetrated by drugs, allowing tumours and pathogens evade effects of the drug.
180
List 4 sanctuary sites of HIV.
1) bone marrow
2) central nervous system
3) gastrointestinal tract
4) genital tract
181
List 2 factors used to monitor HIV infection.
1) helper T cell count
| 2) HIV viral load
182
List 3 symptoms that should prompt asking about sexual history.
1) fever
2) rash
3) non-specific symptoms
183
When should you think about doing a HIV test?
No clear reasons for symptoms or recurring infection in unexpected patient.
184
What is the most common opportunistic infection associated with HIV?
Pneumocystis pneumonia (PCP).
185
What is HAART?
Highly active antiretroviral therapy. 3 or more antiretroviral drugs that act on different points of HIV’s replication.
186
What is another name for Lancefield D positive gram negative cocci
Enterococci.
