Topic 6 Microbiology And Pathogens + 2.2 Viruses Flashcards
What are microbial techniques?
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)
Where to culture bacteria and how? 6 marker
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
What temperature would the the incubator for bacteria culture be at and why isn’t it higher?
25 C , 3-5 days
Prevent overgrowth and mutation that could become harmful
Why do we want to culture bacteria?
- test antibiotic resistance
- compare growth rate of bacteria
- identify bacteria then try to invent cure
Agar is a type of…
Culture medium that you grow bacteria on
What requirements are needed for microbial growth?
- organic C source
- N source
- mineral salts K, Mg, Fe
- vitamins
- purine and pyrimidines
All are needed
What are forms of culture media?
- 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)
What are broad and narrow spectrum culture media?
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
How to make sure only specific bacteria grow on agar?
Use antibiotics
What makes antibiotics?
Bacteria to kill other species of bacteria to reduce competition
How do you know you’ve grown the specific species of bacteria you want?
Look at
- colour of colony
- shape/structure
- height
- texture
- colour
- form
What is a selective media?
Isolates bacteria
Can only grow gram positive/negative bacteria
What can grow on MacConkey Agar?
Gram -ve bacteria
How to measure population size of bacteria?
- serial dilution (so sample is less saturated)
- Then count (4 ways)
What are 4 ways of counting bacteria population size?
- haemocytometer (direct count)
- dilution plating (direct count)
- dry mass
- colorimeter
Define the total cell count of bacteria
Dead and alive bacteria cell population
Define the viable cell count of bacteria
Alive number of bacteria only
What can bacteria do?
- agents of infection
- invade and destroy host tissues
- produce toxins
What produces exotoxins?
Staphylococcus
What produces endotoxins?
Salmonella
What invades host tissues?
Mycobacterium tuberculosis
What are endotoxins?
Released from dead/broken down bacteria
Are lipopolysaccharide in cell wall membrane
Released by gram negative bacteria only
What are exotoxins?
Released from living bacteria
Are proteins
Released by both gram positive and negative
Evaluate methods of controlling malaria
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
What is a pathogen?
Infects another organism by invading the host, causing harm to it
What is an example of a bacterial disease caused by host tissue invasion?
Tuberculosis
Caused by bacteria Mycobacterium tuberculosis
What do antibiotics target?
- cell wall synthesis
- nuclei acid synthesis
- does NOT kill bacteria!!!
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
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
Describe the lytic cycle of a virus? (2 marks)
- viral proteins made
- virus/genetic material multiply and cell lyse
(- using host cell organelles)
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
What happens in the lytic cycle?
- Virus receptors attach to host cell antigens
- Inject genetic material (DNA or RNA)
- Viral proteins synthesised
- New viruses assemble
- Host cell lyses
What happens in the latency cycle?
- Virus receptors attach to host cell antigens
- Inject genetic material (DNA or RNA)
- Viral genome incorporated into host cell genome
- Viral genome replicates with Host cell genome
(5. Join lytic cycle)
Or remain, no symptoms shown
- repressor gene stops rest of genome being read
What are the 4 types of capsid shapes?
- helical
- polyhedral
- spherical
- complex
What is a capsid?
Surrounds (protects) genetic material of virus
What virus has helical capsid?
Tobacco mosaic virus
What virus has polyhedral capsid?
Adenovirus
What virus has spherical capsid?
Influenza virus
What virus has complex capsid?
Bacteriophage
What virus is DNA based?
Lambda (λ)phage
Which 2 viruses are RNA based?
Tobacco mosaic (not enveloped) (both helical capsids)
Ebola (*E**nveloped)
What’s an RNA retrovirus?
HIV
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
What are properties of Tobacco mosaic / all positive-sense RNA virus?
- no envelope
- helical capsid
- single stranded genetic material
- only translation at ribosomes
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)
What is ssRNA?
Single strand RNA
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’)
Why are bacteria described as agents of infection?
- they produce exotoxins
- trigger immune responses
- invade and destroy host tissues
What are 2 types of antibiotic bacteria?
- bacteriocidal
- bacteriostatic
What causes antibiotic resistance?
- random genetic mutations (usually on plasmid). Since they have selective advantage they reproduce and pass on allele
- competitive bacteria
What causes antigen variability?
Random mutations on base of DNA
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
Replicating DNA vs protein synthesis?
DNA Rep / PS
make DNA / proteins
2 identical sets of DNA / mRNA strip
DNA polymerase / RNA polymerase
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
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
Why do antibiotics not work on viruses?
They don’t have Peptidoglycan cell wall to break down so cannot destroy virus
What do antiviral drugs to?
- cannot cure virus diseases but can delay symptoms
- by inhibiting the ways how viruses replicate (via receptors, assembly, or stop new viruses budding)
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
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?
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
What are bacteriostatic antibiotics? + example
- prevents reproduction in DNA replication
- by attaching to ribosomes
- tetracycline
What are bacteriocidal antibiotics? + example
Kills bacteria
Penicillin
What are broad and narrow spectrum antibiotics? + examples
Broad: targets a range of bacteria (tetracycline)
Narrow: target limited range (penicillin)
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
What are 3 things antibiotics could target?
Synthesis of
- cell wall
- nucleic acid
- proteins
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
How does tetracycline destroy bacteria?
- stop protein synthesis
- by stopping tRNA from binding on ribosomes
- stop translation
Hence inhibit growth
How are antibiotics formed?
- random mutation
- other competitive bacteria
What is primary antibiotic resistance?
Natural resistance to narrow-spectrum antibiotics
What is secondary antibiotics resistance?
Bacteria acquire resistance to antibiotics they were previously susceptible to.
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
How often and how do bacteria divide?
Via binary fission every 20 mins
How and how often does secondary antibiotic mutation occur?
Single gene mutation
1 in every 10^6 pairs
How is antibiotic resistant bacteria controlled?
- sub-clinical concentrations create selection pressures for resistance
- UK & EU guidelines to use antibiotics
- measures to reduce HAIs
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
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
What is another saying for capsid?
Protein coat
All viruses have it
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
Give a structural difference between gram +ve and -ve bacteria
Gram +ve has thicker Peptidoglycan cell wall and thinner lipid cell wall
(Or reverse)
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
What are properties of Salmonella?
salmoNella
- thiN Peptidoglycan cell wall
- eNdotoxin
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
How do bacteriocidal antibiotics work?
- inhibits new crosslinks formed in Peptidoglycan cell walls of bacteria
- causing cell lyse from osmotic pressure
Why are antibiotics ineffective against viruses? (2 marks)
- viruses aren’t living
- no cell wall
What is malaria caused by?
Plasmodium
What is stem rust fungus caused by?
Puccinia
What shape do antibodies have?
Y shape, always
Describe the events that take place resulting in T helper cell activation, following the formation of psuedopodia by the macrophages. (3 marks)
- Bacteria engulfed AND digested
- Antigen attaches to MHC antigen
- Macrophage becomes an antigen presenting cell
- CD4 receptor of T helper cells bind to antigen / macrophage
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
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)
- Skin is a barrier, there are no receptors for the virus
- Viruses only attach to specific receptors, and no present in blood cells. Also destroyed by phagocytes
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
The DNA of the Adenovirus carries genes. Suggest what these genes code for. (2 marks)
- capsid
- spikes
- enzymes
What cell presents antigen to T killer cells? (1 mark)
virus-infected host cell
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
