Topic 6 Microbiology And Pathogens + 2.2 Viruses Flashcards
(111 cards)
1
Q
What are microbial techniques?
A
Aseptic techniques
- Bunsen burner: create updraft, sterilise air around Bunsen burner
- use disinfectant to clean surfaces
- flame the inoculating loop - sterilise and kills all microorganisms
- autoclave (heat and high pressure to sterilise Petri dish)
2
Q
Where to culture bacteria and how? 6 marker
A
Petri dish containing agar (nutrients like glucose, nitrates)
Put Petri dish on heat proof mat next to Bunsen
Flame and cool inoculating loop, and neck of sample bottle
Dip into bacteria
Slightly open lid of Petri and zig-zag streak on agar
Use tape to seal lid (12, 6 o’clock)
Store in incubator
3
Q
What temperature would the the incubator for bacteria culture be at and why isn’t it higher?
A
25 C , 3-5 days
Prevent overgrowth and mutation that could become harmful
4
Q
Why do we want to culture bacteria?
A
- test antibiotic resistance
- compare growth rate of bacteria
- identify bacteria then try to invent cure
5
Q
Agar is a type of…
A
Culture medium that you grow bacteria on
6
Q
What requirements are needed for microbial growth?
A
- organic C source
- N source
- mineral salts K, Mg, Fe
- vitamins
- purine and pyrimidines
All are needed
7
Q
What are forms of culture media? What are their pros and cons?
A
- liquid culture (stir w magnet to evenly distribute mineral ions, circulation of Oxygen as well) (can batch or continuous culture)
- solid culture (Agar)(no spillage, useful storage)
8
Q
What are broad and narrow spectrum culture media?
A
Broad: can grow lots of generic/different bacteria containing general nutrients
Narrow: only specific bacteria can grow in it, designed specifically for particular microorganism. Inhibits growth of other microbes
9
Q
How to make sure only specific bacteria grow on agar?
A
Use antibiotics
10
Q
What makes antibiotics?
A
Bacteria to kill other species of bacteria to reduce competition
11
Q
How do you know you’ve grown the specific species of bacteria you want?
A
Look at
- colour of colony
- shape/structure
- height
- texture
- colour
- form
12
Q
What is a selective media?
A
Isolates bacteria
Can only grow gram positive/negative bacteria
13
Q
What can grow on MacConkey Agar?
A
Gram -ve bacteria
14
Q
How to measure population size of bacteria?
A
- serial dilution (so sample is less saturated)
- Then count (4 ways)
15
Q
What are 4 ways of counting bacteria population size?
A
- haemocytometer (direct count)
- dilution plating (direct count)
- dry mass
- colorimeter
16
Q
Define the total cell count of bacteria
A
Dead and alive bacteria cell population
17
Q
Define the viable cell count of bacteria
A
Alive number of bacteria only
18
Q
What can bacteria do?
A
- agents of infection
- invade and destroy host tissues
- produce toxins
19
Q
What produces exotoxins?
A
Staphylococcus
20
Q
What produces endotoxins?
A
Salmonella
21
Q
What invades host tissues?
A
Mycobacterium tuberculosis
22
Q
What are endotoxins?
A
Released from dead/broken down bacteria
Are lipopolysaccharide in cell wall membrane
Released by gram negative bacteria only
23
Q
What are exotoxins?
A
Released from living bacteria
Are proteins
Released by both gram positive and negative
24
Q
Evaluate methods of controlling malaria
A
Ethical- consent and insecticides affect other organisms
Social- social change, vaccines need to become accepted
Economical-treatment, other better uses of money than malaria treatment
25
What is a pathogen?
Infects another organism by invading the host, causing harm to it
26
What is an example of a bacterial disease caused by host tissue invasion?
Tuberculosis
Caused by bacteria Mycobacterium tuberculosis
27
What do antibiotics target?
- cell wall synthesis
- nuclei acid synthesis
- does NOT kill bacteria!!!
28
What are the 2 types of antibiotic resistance and describe
Primary resistance: natural resistance to narrow spectrum antibiotics
Secondary resistance: acquire resistance to antibiotics they are previously susceptible to
29
What’s the difference between lytic and latency?
Latency has incorporation of genetic material but not lytic
Lytic has symptoms, latency doesn’t
Lytic has protein synthesis
30
Describe the lytic cycle of a virus? (2 marks)
- viral proteins made
- virus/genetic material multiply and cell lyse
(- using host cell organelles)
31
State what it is meant by the term latency. (3 marks)
- virus nucleoid acid **incorporated** into host cell
- virus is **inactive**
- virus nucleus acid replicates when host cell divides
- **viral proteins made and assembled**
32
What happens in the lytic cycle?
1. Virus receptors attach to host cell antigens
2. Inject genetic material (DNA or RNA)
3. Viral proteins synthesised
4. New viruses assemble
5. Host cell lyses
33
What happens in the latency cycle?
1. Virus receptors **attach** to host cell antigens
2. **Inject** genetic material (DNA or RNA)
3. **Viral** genome **incorporated** into host cell genome
4. Viral genome **replicates** with Host cell genome
(5. Join lytic cycle)
Or remain, no symptoms shown
- repressor gene stops rest of genome being read
34
What are the 4 types of capsid shapes?
- helical
- polyhedral
- spherical
- complex
35
What is a capsid?
Surrounds (protects) genetic material of virus
36
What virus has helical capsid?
Tobacco mosaic virus
37
What virus has polyhedral capsid?
Adenovirus
38
What virus has spherical capsid?
Influenza virus
39
What virus has complex capsid?
Bacteriophage
40
What virus is DNA based?
Lambda (λ)phage
41
Which 2 viruses are RNA based?
Tobacco mosaic (not enveloped) (both helical capsids)
**E**bola (*E**nveloped)
42
What’s an RNA retrovirus?
HIV
43
What are properties of Lambda (λ)phage virus?
- host: bacteria
- no lipid envelope
- has **complex** protein capsid
- viral **DNA** (double stranded)
- protein synthesis needed to take place
44
What are properties of Tobacco mosaic / all positive-sense RNA virus?
- no envelope
- helical capsid
- single stranded genetic material
- only translation at ribosomes
45
What are properties of all negative ssRNA viruses?
- host: lymphocytes
- have lipid envelope
- helical capsid
- has antisense so transcribe first then translate at ribosomes (?check)
46
What is ssRNA?
Single strand RNA
47
What are properties of RNA retrovirus?
- host: T helper lymphocytes
- cone shaped capsid
- contain enzyme called reverse transcriptase
- lipid envelope
- 2 copies of ssRNA
- reverse transcription (RNA>DNA>RNA>DNA hence ‘retro’)
48
Why are bacteria described as agents of infection?
- they produce exotoxins
- trigger immune responses
- invade and destroy host tissues
49
What are 2 types of antibiotic bacteria?
- bacteriocidal
- bacteriostatic
50
What causes antibiotic resistance?
- random genetic mutations (usually on plasmid). Since they have selective advantage they reproduce and pass on allele
- competitive bacteria
51
What causes antigen variability?
Random mutations on base of DNA
52
What impact does antigen variability have on the incidence of diseases?
Antigens no longer complementary to receptors, so can catch disease more than once.
Vaccinations less likely to work
53
Replicating DNA vs protein synthesis?
DNA Rep / PS
make DNA / proteins
2 identical sets of DNA / mRNA strip
DNA polymerase / RNA polymerase
54
Why does it take time for symptoms of virus to show?
Take time for
- attaching complementary antigens to receptors
- viral genome forming
- (transcription and) translation
- takes time to lyse and exocytose
55
Compare and contrast the structures between bacteria and virus
- bacteria is living cell / virus is not
- no antigens / yes
- double strand bacterial DNA / can be RNA or DNA (single or double)
- has flagellum / no
- has plasmid (circular dna) / no, only linear
- peptidoglycan cell wall / doesn’t, some have lipid envelope
56
Why do antibiotics not work on viruses?
They don’t have Peptidoglycan cell wall to break down so cannot destroy virus
57
What do antiviral drugs do?
- cannot cure virus diseases but can **delay** symptoms
- by inhibiting the ways how viruses replicate (via receptors, assembly, or stop new viruses budding)
58
Things to do to prevent spread of a virus:
- education (esp burial of corpses)
- sterilisation of medical facilities
- clear public spaces
- clean water and sewage works
- isolate people who are infected
59
Ethical implications of using untested drugs (pros and cons)
Pros
- disease may have high mortality rate
- new drug is unlikely to affect other people
- it can help develop the drug for other patients
Cons
- unknown side effects
- patients may not have informed consent
- if there is limited supply, who decides who gets treated?
60
How to continuously extend the stationary phase of bacterial growth?
When death rate = growth rate
- keep adding nutrients SUCH AS sucrose, nitrates, water, oxygen to keep up with growth
61
What are bacteriostatic antibiotics? + example
- prevents reproduction in DNA replication
- cells cannot reproduce and multiply
- no cell division
- by attaching to ribosomes
- tetracycline
62
What are bacteriocidal antibiotics? + example
Kills bacteria AND cell burst
Penicillin
63
What are broad and narrow spectrum antibiotics? + examples
Broad: targets a range of bacteria (tetracycline)
Narrow: target limited range (penicillin)
64
How does retrovirus replicate?
- bind complementary receptors to antigens
- viral RNA enters host cell (cannot be used as mRNA)
- viral RNA translate into viral DNA **by reverse transcriptase** in cytoplasm
- viral DNA incorporated into host dna
- new viral particles are assembled
- leave host cell via **exocytosis**
- repeat
65
What are 3 things antibiotics could target?
Synthesis of
- cell wall
- nucleic acid
- proteins
66
How does penicillin kill bacteria?
- targets gram+ bacteria
- act as inhibitor
- stop **cross links** between thick Peptidoglycan cell walls **synthesis**
- weaken cell wall > bacteria cannot lyse as cannot respire > die
67
How does tetracycline destroy bacteria?
- stop protein synthesis
- by stopping tRNA from binding on ribosomes
- stop translation
Hence inhibit growth
68
How are antibiotics formed?
- random mutation
- other competitive bacteria
69
What is primary antibiotic resistance?
Natural resistance to narrow-spectrum antibiotics
70
What is secondary antibiotics resistance?
Bacteria acquire resistance to antibiotics they were previously susceptible to.
71
What are causes of secondary antibiotic resistance?
- decrease in uptake b increase in expulsion
- production of enzymes to modify antibiotic
- development of pathway to bypass effects
DOESNT MAKE SENSE
72
How often and how do bacteria divide?
Via binary fission every 20 mins
73
How and how often does secondary antibiotic mutation occur?
Single gene mutation
1 in every 10^6 pairs
74
How is antibiotic resistant bacteria controlled?
- sub-clinical concentrations create selection pressures for resistance
- UK & EU guidelines to use antibiotics
- measures to reduce HAIs
75
How to prevent the spread of antibiotic resistance?
- guidelines to finish course of treatment
- educating doctors when to prescribe, keep everything sterilised, don’t use for viral infections
- keep prescriptions range small so there’d be backup options if it doesn’t work
76
Why shouldn’t we take antibiotics too much?
- only short term fix
- can kill good bacteria like ones in gut and worsen health!
- don’t take unless you need to
77
What is another saying for capsid?
Protein coat
All **viruses** have it
78
Explain why there is a delay before number of lysed cells start to increase. (3 marks)
- virus **attaches** to host cell
- **protein synthesis**, synthesis of dna
- virus start to **assemble**
79
Give a structural difference between gram +ve and -ve bacteria
Gram +ve has thicker Peptidoglycan cell wall and thinner lipid cell wall
(Or reverse)
80
Give 2 differences between endotoxins and exotoxins
Endo / exo
Lipid / protein
Released from dead bacteria / living
Released from gram -ve only / both +ve and -ve
81
What are properties of Salmonella?
salmoNella
- thiN Peptidoglycan cell wall
- eNdotoxin
82
Why is reducing prescription helpful to reduce antibiotic resistance?
- ensuring prescribed only for illnesses caused by bacteria not viruses
- as antibiotics act as selection pressure for resistant bacteria
83
How do bacteriocidal antibiotics work?
- inhibits new crosslinks formed in Peptidoglycan cell walls of bacteria
- causing cell lyse from osmotic pressure
84
Why are antibiotics ineffective against viruses? (2 marks)
- viruses aren’t living
- no cell wall
85
What is malaria caused by?
Plasmodium
86
What is stem rust fungus caused by?
Puccinia
87
What shape do antibodies have?
Y shape, always
88
Describe the events that take place resulting in T helper cell activation, following the formation of psuedopodia by the macrophages. (3 marks)
1. Bacteria engulfed AND digested
2. Antigen attaches to MHC antigen
3. Macrophage becomes an antigen presenting cell
4. **CD4** receptor of T helper cells bind to antigen / macrophage
89
Give 2 differences between the RNA activity of a common cold virus and HIV. (2 marks)
Common cold / HIV
No DNA formed / DNA formed
No reverse transcriptase used / yes
No latency delay of symptoms / yes
90
Suggest why viruses cannot infect cells on unbroken skin nor skin with cut and entered into blood. (2 marks each so 4 marks) (they only enter through the nose)
1. Skin is a barrier, there are no receptors for the virus
2. Viruses only attach to specific receptors, and no present in blood cells. Also destroyed by phagocytes
91
Compare structures of Adenovirus and HIV. (3 marks)
Adeno / HIV
one strand of DNA / 2 strands RNA
no envelope / does
does not / has reverse transcriptase
92
The DNA of the Adenovirus carries genes. Suggest what these genes code for. (2 marks)
- capsid
- spikes
- enzymes
93
What cell presents antigen to T killer cells? (1 mark)
virus-infected host cell
94
Describe the role of T killer cells in the immune response to a viral infection. (4 marks)
- destruction of virus-infected host cells
- by enzymes / chemicals
- virus released from cells
- antibodies can bind to virus (opsonisation)
- virus can be phagocytosed by macrophages
- T memory cells form for secondary immune response
95
Compare dilution plating vs optical methods. (6 marks)
Dilution / Optical
Takes longer / quicker to obtain results
Due to incubation period in DP
Count living cells only / living and dead
Direct cell count / turbidity reading
Easily avail apparatus / expensive colorimeter
Must have one known conc to start with/ can make calibration curve to find out
96
What are risks of errors in dilution plating and optical methods?
DP- if colonies run into each other
OM - error if tube not shaken
97
Explain why antibiotics recommendations for only certain diseases could reduce the spread of antibiotic resistance. (2 marks)
Antibiotics shouldn’t be prescribed if the illness is only caused by a virus
Because antibiotics act as a **selection pressure** for resistant bacteria
98
What are the advantages of using the salmonella rapid culture technique to confirm a salmonella infection? (3 marks)
- food poisoning spreads easily
- quicker identification = quicker treatment and containment of infection
- so correct antibiotic can be used to help prevent spread of infection
- prevent antibiotic resistance if wrong antibiotics used
99
Explain how an antibiotic has a bacteriostatic effect on bacteria. (2 marks)
Cell division prevented
So number of living bacteria doesn’t increase
100
What are the effects of pathogens / stem rust fungus?
- weakens stem
- less nutrients are able to be taken up
- less magnesium ions
101
What is Influenza
A virus
102
How does malaria cause anaemia? (2 marks)
Malaria parasite invades/destroys erythrocytes
Reduced haemoglobin red cell count causes anaemia
103
How does stem rust fungus result in a reduction ingrained yield? (3 marks)
- stem rust fungus takes up glucose
- less glucose to form starch
- weakens stems
- damage vascular system, plants fall over and die
104
What method is best preventing the transmission of Influenza?
Wearing face masks
As it is airborne, so covering your face from inhaling droplets would prevent spread to you
105
Explain how the influenza virus has a pathogenic effect. (4 marks)
- virus can bind to cells of throat/lung
- viruses have receptors
- inject viral dna into host cell
- leads to **lysis**
- immune response triggered, leading to fever, sore throat
106
State 2 methods other than mosquito nets to reduce number of new cases of malaria. (2 marks)
- drain land to reduce mosquito larvae habitats
- use mosquito repellent to prevent bites
- reduce mosquito population by using insecticides
107
Decide a method to distinguish between two BLOOD samples. (3 marks)
- a small volume of blood is spread into a thin layer and viewed under **microscope**
- blood is examined to look for the presence of the malaria, parasite Plasmodium
- use of personal protective equipment when handling blood samples
108
Which 2 viruses have a helical capsid and envelope?
Influenza
Ebola
109
Describe how M. tuberculosis bacteria evade the immune system. (2 marks)
- It survives inside macrophages
- inhibits T helper cells, suppresses immune response
110
111
Compare the time for symptoms to show for exotoxins and endotoxins in food poisoning.
Exotoxins are much quicker, within a few hours of meal
Endotoxins will take longer, after several hours ~12
