PBL 2: viruses and bacteria Flashcards
What is a virus?
A small infectious agent that is only able to replicate in a host cell (why it is called an obligate intracellular parasite)
Describe the structure of a virus
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.
Name five different ways in which a virus may enter
Conjunctiva (eye membrane) Genitals Skin Respiratory tract Digestive tract
Explain how a virus infects a host cell
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.
Does a virus contain organelles e.g. mitochondria, ribosomes?
NO
Describe the structure of bacteria
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.
Describe the different shapes of bacteria , give some examples
Cocci (spherical) e.g. streptococcus pneumoniae and staphylococcus aureus
Bacillus (rod shaped) e.g. E.Coli and salmonella
Vibrios (comma shaped)
Spirilla (spiral shaped)
How do you differentiate between gram positive and gram negative bacteria ?
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
Give an example of gram positive coccus and bacillus bacteria
Coccus:
Staphylococcus aureus
Streptococcus pneumoniae
Bacillus:
Listeria monocytogenes
Corynebacterium diptheriae
Give an example of gram negative coccus and bacillus bacteria
Coccus: Neisseria Meningiditis
Bacillus: Salmonella, E.Coli
Define heterotrophic in relation to bacteria
Unable to synthesise its own food
Define fastidious
Has specific nutritional requirements, very sensitive, if conditions are not met it will die very quickly
Define facultative
Bacteria that is able to adapt its function
Define obligate
Bacteria must grow in specific conditions
Define psychrophilic bacteria
Bacteria that must grow in cold temperatures
Define mesophilic bacteria
Bacteria that must grow in mild temperatures
Define thermophilic bacteria
Bacteria that must grow in high temperatures
What is transposition ?
Transfer of DNA sequences to another DNA molecule
What are the 3 methods of transposition?
Small insertion sequences
Transposons (jumping from one location to another in genome)
between chromosomes and plasmids
Heat re the natural methods of gene transfer?
Conjugation
Transduction
Transformation
Define conjugation
Direct transfer of genetic material between bacterial cells which are in contact with one another
Define transduction
Horizontal gene transfer of DNA via viruses or bacteriophages (viruses that attack bacteria)
Define transformation
When DNA is taken up by bacterial cells from the environment
List the sterile sites in the body
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
List the colonised sites of the body
Skin Nose Throat Mouth Large intestine Vagina Urethra
Define colonisation
The abundance of bacteria that doesn’t harm the body and can maintain a mutualistic relationship
Define infection
Colonisation of bacteria and multiplication of pathogens that may cause harm in a vulnerable host which may lead to disease
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)
What are virulence factors?
Factors that contribute to the damage and pathogenicity caused to a host
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)
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
Define sepsis
Sepsis: Body’s response to infection causes damage to body’s own tissues and organs
Outline the broad principles of management of infections
Conservative: Rehydration, drugs, nutrition, oxygen Antibiotics Surgical Infection control Public health
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
List some diseases caused by viruses
HIV HPV Influenza Measles MUmps Rhinovirus Polio Zika virus Rabies Ebola Herpes Simplex Virus
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.
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
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
How is the Zika virus transmitted?
Aedes Mosquito
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.
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
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
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
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.
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.
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
List treatments for cholera
Rehydration salts
Clean water
Vaccinations
