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

PBL 2: viruses and bacteria Flashcards

(47 cards)

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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?

Study These Flashcards
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?

Study These Flashcards
A

Conjugation
Transduction
Transformation

21
Q

Define conjugation

Study These Flashcards
A

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

22
Q

Define transduction

Study These Flashcards
A

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

23
Q

Define transformation

Study These Flashcards
A

When DNA is taken up by bacterial cells from the environment

24
Q

List the sterile sites in the body

Study These Flashcards
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
List the colonised sites of the body
``` Skin Nose Throat Mouth Large intestine Vagina Urethra ```
26
Define colonisation
The abundance of bacteria that doesn't harm the body and can maintain a mutualistic relationship
27
Define infection
Colonisation of bacteria and multiplication of pathogens that may cause harm in a vulnerable host which may lead to disease
28
State common pathogens of different body systems (including the infection to make it easier)
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
What are virulence factors?
Factors that contribute to the damage and pathogenicity caused to a host
30
List some virulence factors
Replication rate Speed of colonisation Toxigenic factors (cause damage to host) Invasive factors (proteins that promote entry of pathogens into host)
31
List some host and environmental factors that lead to infection
``` 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
Define sepsis
Sepsis: Body's response to infection causes damage to body's own tissues and organs
33
Outline the broad principles of management of infections
``` Conservative: Rehydration, drugs, nutrition, oxygen Antibiotics Surgical Infection control Public health ```
34
Describe the chain of infection
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
List some diseases caused by viruses
``` HIV HPV Influenza Measles MUmps Rhinovirus Polio Zika virus Rabies Ebola Herpes Simplex Virus ```
36
How does virus divergence come about?
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
What can viral divergence lead to?
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
Where does Ebola usually reside and how is it transmitted?
In bats where it is non-pathogenic | Transmitted via touch and body fluids e.g. sweat
39
How is the Zika virus transmitted?
Aedes Mosquito
40
What is lymphatic filariasis and what transmits it?
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
What causes malaria, how is it transmitted and what doe sit do to the body?
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
What precautions can be taken to reduce malaria?
Drain swamps as these are breeding grounds for mosquitoes Insect repellant Nets when sleeping Prophylaxis e.g. anti-malarial tablets
43
Explain what Chagas disease is?
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
Explain what African trypanosomiasis is
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
Describe the causes and effect of cholera
Caused by bacterium: vibrio cholerae which is transmitted by oral-faecal transmission. It causes severe diarrhoea and dehydration.
46
Describe some methods of prevention for cholera
Boiling water Filter Bottled water Avoiding foods that may have been washed in dirty water e.g. salad
47
List treatments for cholera
Rehydration salts Clean water Vaccinations

Phase 1: weeks 1-5 (23 decks)

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