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Phase 1: weeks 1-5 > PBL 2: viruses and bacteria > Flashcards

PBL 2: viruses and bacteria Flashcards

1
Q

What is a virus?

A

A small infectious agent that is only able to replicate in a host cell (why it is called an obligate intracellular parasite)

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2
Q

Describe the structure of a virus

A

Nucleic acid: Either RNA (most commonly) or DNA which congas the viral genome
Capsid: protective protein coat made up of capsomeres
Outer envelope: some cells have an envelope made up of lipid bilayer with projecting spikes of glycoproteins. This is acquired when the virus buds through the host membrane upon leaving.

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3
Q

Name five different ways in which a virus may enter

A 
Conjunctiva (eye membrane)
Genitals
Skin
Respiratory tract 
Digestive tract
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4
Q

Explain how a virus infects a host cell

A

Adsorption: Virus binds to host cell surface by specific binding of its glycoprotein spikes to cell receptors

Virus enters cell in one of 3 ways:
Membrane fusion: lipid bilayer of viral envelope fuses with the host cell membrane bilayer and the viral genome is engulfed into the cell
Endocytosis: a pore forms in the cell membrane allowing viral genome to enter
Virus penetrates cell membrane and its genome is injected into cytoplasm

Virus envelop is uncoated and viral genome is exposed

Virus takes control of host cell membrane and recruits host enzymes to replicate viral genome.

In DNA viruses, the host’s own RNA polymerase is used to produce mRNA and Host’s ribosome is used to make viral proteins.
In RNA viruses, virus’s own RNA polymerase is used to make mRNA.

Progeny viral particles assemble with caspids and viral enzymes to form viral proteins.

Viral proteins leave in one of 2 ways:
They bud through the host membrane, acquiring a viral envelope as the host cell membrane is incorporated with glycoproteins. Cell is not damaged.

They burst out of the host, resulting in cell death and the virus is ready to infect another host cell.

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5
Q

Does a virus contain organelles e.g. mitochondria, ribosomes?

A

NO

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6
Q

Describe the structure of bacteria

A

Bacteria is prokaryotic and does not contain membrane bound organelles e.g. mitochondria or nucleus.
But it does contain ribosomes.

Genetic material is held in circular chromosomes (loosely organised as fibrous mass in cell cytoplasm) and in plasmids (circular pieces of DNA that can replicate independent of the main genome)

Flagella: allow motility by propulsion
Pili: hair like appendages on the host cell surface which allow adhesion of the bacterial cell to other structures and cells.

Outer capsule: tough outer polysaccharide layer which keeps the bacteria hydrated and evades detection and phagocytosis from macrophages. It increases the bacteria’s virility.

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7
Q

Describe the different shapes of bacteria , give some examples

A

Cocci (spherical) e.g. streptococcus pneumoniae and staphylococcus aureus
Bacillus (rod shaped) e.g. E.Coli and salmonella
Vibrios (comma shaped)
Spirilla (spiral shaped)

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8
Q

How do you differentiate between gram positive and gram negative bacteria ?

A

Gram staining is used which uses a primary stain, iodine dye and alcohol.

Gram positive bacteria: Retains a purple colour as it has a thick peptidoglycan layer

Gram negative bacteria: retains a pink colour since it has a thin peptidoglycan layer

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9
Q

Give an example of gram positive coccus and bacillus bacteria

A

Coccus:
Staphylococcus aureus
Streptococcus pneumoniae

Bacillus:
Listeria monocytogenes
Corynebacterium diptheriae

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10
Q

Give an example of gram negative coccus and bacillus bacteria

A

Coccus: Neisseria Meningiditis

Bacillus: Salmonella, E.Coli

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11
Q

Define heterotrophic in relation to bacteria

A

Unable to synthesise its own food

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12
Q

Define fastidious

A

Has specific nutritional requirements, very sensitive, if conditions are not met it will die very quickly

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13
Q

Define facultative

A

Bacteria that is able to adapt its function

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14
Q

Define obligate

A

Bacteria must grow in specific conditions

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15
Q

Define psychrophilic bacteria

A

Bacteria that must grow in cold temperatures

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16
Q

Define mesophilic bacteria

A

Bacteria that must grow in mild temperatures

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17
Q

Define thermophilic bacteria

A

Bacteria that must grow in high temperatures

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18
Q

What is transposition ?

A

Transfer of DNA sequences to another DNA molecule

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19
Q

What are the 3 methods of transposition?

A

Small insertion sequences
Transposons (jumping from one location to another in genome)
between chromosomes and plasmids

20
Q

Heat re the natural methods of gene transfer?

A

Conjugation
Transduction
Transformation

21
Q

Define conjugation

A

Direct transfer of genetic material between bacterial cells which are in contact with one another

22
Q

Define transduction

A

Horizontal gene transfer of DNA via viruses or bacteriophages (viruses that attack bacteria)

23
Q

Define transformation

A

When DNA is taken up by bacterial cells from the environment

24
Q

List the sterile sites in the body

A 
Blood, tissue and organ systems
CNS
Eye (behind conjunctiva)
Sinuses, inner and middle ear 
Lower respiratory tract 
Renal system down to posterior urethra 
Female reproductive tract down to cervix
25
Q

List the colonised sites of the body

A 
Skin
Nose
Throat 
Mouth 
Large intestine
Vagina
Urethra
26
Q

Define colonisation

A

The abundance of bacteria that doesn’t harm the body and can maintain a mutualistic relationship

27
Q

Define infection

A

Colonisation of bacteria and multiplication of pathogens that may cause harm in a vulnerable host which may lead to disease

28
Q

State common pathogens of different body systems (including the infection to make it easier)

A

Respiratory: Streptoccocus Pneumoniae (pneumonia)
Gut: Salmonella (food poisoning)
Cardiovascular: staphylococci (endocarditis)
Eye: Staphylococci (Conjunctivitis)
CNS: neisseria meningiditis (meningitis)
Renal: E.Coli (UTI)
Genital: Chlamydia trachomatis (uerthritis)
Bone and joint: staphylococcus aureus (septic arthritis)
Skin and soft tissue: SA (cellulitis)

29
Q

What are virulence factors?

A

Factors that contribute to the damage and pathogenicity caused to a host

30
Q

List some virulence factors

A

Replication rate
Speed of colonisation
Toxigenic factors (cause damage to host)
Invasive factors (proteins that promote entry of pathogens into host)

31
Q

List some host and environmental factors that lead to infection

A 
Age
Gender
Ethnicity
Personal Hygiene 
Nutrition 
Other medical conditions 
Immunocompromise - immune deficiency disorders e.g. chemotherapy and Immunocompromising infections e.g. HIV
Presence of foreign objects 
Vaccination history 
Overcrowding, sanitation, socioeconomic and public health factors
32
Q

Define sepsis

A

Sepsis: Body’s response to infection causes damage to body’s own tissues and organs

33
Q

Outline the broad principles of management of infections

A 
Conservative: Rehydration, drugs, nutrition, oxygen
Antibiotics
Surgical 
Infection control
Public health
34
Q

Describe the chain of infection

A

Mode of transmission: vector, airborne, food handling, ingestion
Portal of entry: mucous membranes, GI tract, respiratory tract, broken skin
Susceptible host: immunosuppression, diabetes, burn
Type of infectious agent: bacteria, virus, protozoa, fungi
Reservoirs: people, equipment, food/water
Portal of exit: excretions, secretions, droplets, contact

35
Q

List some diseases caused by viruses

A 
HIV
HPV
Influenza
Measles
MUmps
Rhinovirus
Polio
Zika virus
Rabies
Ebola
Herpes Simplex Virus
36
Q

How does virus divergence come about?

A

Viruses can exchange genetic material between cells. RNA has its own replicase which copies RNA genomes and in doing so, it can often make mistakes. This leads to mutations and viral divergence.

37
Q

What can viral divergence lead to?

A

Spread of virus to different species
Lead to Epidemics as viruses can mutate to escape immune surveillance
Give rise to resistance to vaccines and therapies

38
Q

Where does Ebola usually reside and how is it transmitted?

A

In bats where it is non-pathogenic

Transmitted via touch and body fluids e.g. sweat

39
Q

How is the Zika virus transmitted?

A

Aedes Mosquito

40
Q

What is lymphatic filariasis and what transmits it?

A

Caused by nematode worms called filarial worms. Transmitted by Aedes mosquito

They invade the lymphatic system and cause inflammation by blocking lymphatic vessels. This results in proliferation of lymph fluid.

41
Q

What causes malaria, how is it transmitted and what doe sit do to the body?

A

Caused by plasmodium parasite
Transmitted by mosquitoes.

Once bitten, parasites enter the bloodstream and travel to the liver where they mature. They then burst out and infect RBCs, causing a fever

42
Q

What precautions can be taken to reduce malaria?

A

Drain swamps as these are breeding grounds for mosquitoes
Insect repellant
Nets when sleeping
Prophylaxis e.g. anti-malarial tablets

43
Q

Explain what Chagas disease is?

A

Caused by the protozoan parasite and is transmitted by triatomine bug. They crawl all over your face and defecate. Their faeces contains parasites in them which spreads to your body.
Chagas disease causes malaise, intestinal problems elating to mega colon and enlargement of heart causing heart failure

44
Q

Explain what African trypanosomiasis is

A

Caused by the parasite trypanosomiasis and is spread by tsetse flies. When these bite you, they inject the parasite and this causes malnourishment and wasting away. The parasite can also cause sleeping sickness by changing sleeping patterns.

45
Q

Describe the causes and effect of cholera

A

Caused by bacterium: vibrio cholerae which is transmitted by oral-faecal transmission. It causes severe diarrhoea and dehydration.

46
Q

Describe some methods of prevention for cholera

A

Boiling water
Filter
Bottled water
Avoiding foods that may have been washed in dirty water e.g. salad

47
Q

List treatments for cholera

A

Rehydration salts
Clean water
Vaccinations

Phase 1: weeks 1-5 (23 decks)

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