Bacteria, Viruses and Immunity Flashcards
Explain the mechanism of action of complement proteins 5-9.
What pathogens are they specific for?
C5b, C6 and C7 bind. The complex then binds the cell membrane via C7. C8 binds this complex and inserts into cell membrane. C9 binds and 10 to 16 molecules polymerise, forming a pore in the bacteria. It’s cytosol is then in continuum with the exterior and it undergoes osmotic lysis.
neisseria gonorrhoeae and neisseria meningitidis
List three enveloped DNA viruses
Hepatitis B
Herpes
Smallpox
What colour would a gram positive bacteria stain?
Purple
What colour would a gram negative bacteria stain?
Pink
Describe the method of gram staining:
Stain with crystal violet - it binds with negatively charged cell components.
Add iodine - forms complexes with crystal violet.
Extract the complexes with acetone or methanol - cannot be extracted through peptidoglycan cell wall.
Stain with red dye.
What can you deduce about a gram positive bacteria?
It has a peptidoglycan cell wall.
What is the structure of the cell wall of a gram negative bacteria?
Plasma membrane, then a thin peptidoglycan cell wall, then an outer membrane consisting of phospholipid and lipopolysaccharide
What is the consequence of a bacteria having a lipopolysaccharide component to its outer cell membrane?
LPS is toxic and causes sepsis, even when the bacteria are dead.
What is the microbiome?
10^14 bacteria that are normally resident on and in the human body.
What would you use an acid fast stain for?
Identify mycobacterium tuberculosis and mycobacterium leprae- bacterial causes of tuberculosis and leprosy.
What name is given to bacteria that are observed as clumps of round cells?
Staphylococci
What name is given to the shape of bacteria that appear as strings of round cells?
Streptococci
What is the name given to bacteria that have an elongated shape?
Rods or bacilli
What name is given to bacteria that appear as clumps of two cells?
Diplococci
What are the external structures that may be observed on a bacteria?
Pili, including fimbriae
Flagella
Capsule
What internal structures may be noted?
Spores, inclusion granules.
What cell envelope types cannot be visualised with a gram stain?
Mycobacterium
Bacteria that are too small - chlamydia, treponemes(syphilis), rickettsia
Mycoplasmas - no peptidoglyca
What stains can be used to identify mycobacterium?
PAS, auramine - fluorescent, Ziehl-Neelsen - bright field
What is the structure of the cell wall of mycobacterium, and what implication does this have for treatment?
Plasma membrane, then a peptidoglycan cell wall, then arabinogalactan which holds together the peptidoglycan and the mycolic acid (hydrophobic 90 carbon lipid).
On the surface are glycolipids
Lipoarabinomannan is also present.
Hardy cell wall, therefore difficult to treat.
What antibiotics can be used to treat a gram positive bacteria?
Penicillins and cephalosporins, glycopeptides.
What would you treat tuberculosis with?
Isoniazid.
By what means do bacteria replicate?
Binary fission
What are the three phases of growth of bacteria in broth?
Lag, exponential and stationary.
What can form on implanted medical devices, and what is the implication?
Biofilms - device must be removed.
What is the benefit of growing colonies?
Can easily identify and count bacteria
What is the gram stain of staphylococcus, and what diseases do they cause?
Gram positive.
Abscesses, food poisoning, toxic shock syndrome, osteomyelitis, endocarditis, scalded skin syndrome.
What is the gram stain of streptococcus pneumoniae, what does it cause?
Gram positive, pneumonia
What is the gram stain of streptococcus pyogenes, what diseases does it cause?
Gram positive, strep throat, scarlet fever, impetigo.
Non suppurative sequels - rheumatic fever, glomerulonephritis.
What is the gram stain of streptococcus agalactiae, what diseases does it cause?
Gram positive, neonatal sepsis and meningitis.
How do the clostridium bacteria stain, what are the four main ones, and what diseases do they cause?
What shape are they?
Gram positive. Clostridium perfringens - gas gangrene Clostridium tetani - tetanus Clostridium botulinum - botulism Clostridium difficile - diarrhoea. Bacilli
How do the neisseria stain, what shape are they, and what are the two main types, and what diseases do they cause?
Gram negative cocci.
Neisseria gonorrhoeae - gonorrhoea (pelvic inflammatory disease, epididymitis)
Neisseria meningitidis - meningitis, septicaemia
What pathogen causes cholera, what is its shape and gram stain?
Vibrio cholerae, comma shaped, gram negative.
What is the shape and gram stain of helicobacter pylori, what diseases do they cause?
Gram negative spiral. Peptic ulcers and adenocarcinoma of the stomach.
What is the shape and gram stain of pseudomonas aeruginosa? What disease does it cause?
Gram negative coccobacilli. Ubiquitous pathogen, causes hospital acquired infections, important in patients with CF, burns and diabetes.
What are the three chlamydiae, how do they stain, what diseases do they cause?
Gram negative
Chlamydiae trachomatis - genital tract infections
Chlamydiae pneumoniae - pneumonia
Chlamydiae psittaci - psittacosis
What is the shape and stain of bacteroides, name one and the diseases they cause:
Gram negative rods, bacteroides fragilis, abscesses in peritoneal cavity.
What is the shape and stain of salmonella, what diseases does it cause?
Gram negative bacilli. Nontyphoidal gastroenteritis, typhoid fever.
What causes legionnaires disease, and what is its shape and stain?
Legionella pneumophilia. Gram negative bacilli.
What is the shape and stain of escherichia coli, and what diseases does it cause?
Gram negative bacilli.
Secretory diarrhoea and UTIs
What diseases does shigella cause, and what is its shape and stain?
Dysentery - gram negative bacilli.
What does enterohaemorrhagic escherichia coli cause, and what is its shape and stain?
Haemorrhagic colitis.
Gram negative bacilli
How are mitochondria inherited?
Maternal lineage
What is infection?
The establishment of an organism on or in a host, associated with its multiplication and damage to or dysfunction of the host specifically related to that organism or its products.
What causes infection?
Bacteria, viruses, prions, fungi, arthropods, archaea, protozoa, helminths.
What are the main differences between prokaryotes and eukaryotes?
Transcription and translation are coupled in prokaryotes, compartmentalised in eukaryotes.
Prokaryotes have no membrane bound organelles.
They have no introns
They have one chromosome
They have 70s ribosomes (50s and 30s subunits), eukaryotes have 80s ribosomes (40s and 60s subunits)
All bacteria have a peptidoglycan cell wall, not present in eukaryotes.
The mRNA in prokaryotes is very labile (degrades spontaneously)
Name a group of non enveloped DNA viruses, and the diseases they might cause.
Papilloma viruses - warts, cervical cancer.
What are the RNA enveloped viruses? What diseases are caused by them?
Rubella, rotavirus (gastronteritis), HIV, ebola, orthomyxoviruses and paramyxoviruses (flu, measles and mumps), coronaviruses (colds and SARS)
What are the non enveloped RNA viruses? What diseases do they cause?
Picornaviruses
Polio, hepatitis A, colds.
How would you describe a virus?
Obligate intracellular parasites
What do viruses consist of?
Nucleic acid core.
Protein capsid
May or may not have an envelope
What part of the virus is targeted by detergent?
Envelope.
By what three methods do viruses enter cells?
Initially bind receptors.
Then either receptor mediated endocytosis, or fusion with host cell membrane, or cross membranes via coated pits.
What genes necessary for reproduction of the virus are not carried in the viruses genome?
Genes that code for proteins required in metabolism, or proteins required in protein synthesis. It may not have genes that code for proteins involved in nucleic acid synthesis.
How are non enveloped viruses released?
Cell lysis
How are enveloped viruses released?
Budding.
What are inclusion bodies?
Nuclear or cytoplasmic aggregates of stainable substances such as proteins.
Are ions or polysaccharides present in viruses?
No
What is a syncytia?
Multinucleated cell.
How do syncytia arrive?
Viral fusion proteins (that are usually used by virus to enter cell) travel to cell membrane and cause it to fuse with neighbouring cells.
What would you observe about the growth curve of a virus?
It is stepped
What is the outer protein coat that may be present on a virus, and what is its subunit?
Capsid, capsomere.
What is the function of the capsid?
Protection of genome
Attachment to host cells
What are the possible structures of the capsid?
Icosahedral or helical
Why does a pathogen damage the host if this will alert the immune system?
It is an inevitable consequence of breaking barriers.
What role do epithelia play in defence against pathogens?
Produce natural antibiotics (Cationic antibacterial peptides- defensins and cathelicidins)
Produce cytokines and chemokines
Removal of pathogens (rapid renewal, tears, coughing, mucociliary escalator, vomiting, sneezing, ear wax, digestive enzymes, peristaltic gut movement, regular urine flow, nasal hear, blinking)
What happens when epithelial cells are activated by a pathogen?
Release cytokines and chemokines.
Permeability of endothelia of capillaries increases - leak complement and immunoglobulin
What are the cardinal signs of inflammation?
Dolor, rubor, tumor, calor
(Pain, redness, swelling, heat)
Loss of function
What are the main features of the innate immune system?
Present from birth
Not specific
No memory, not enhanced by second exposure
Ineffective without adaptive immune system - involved in triggering and amplifying adaptive immune response.
What are the main features of the adaptive immune system?
Learnt by experience
Confers pathogen specific immunity
Enhanced by second exposure - has memory
Inefficient without innate immune response
Antibodies reflect infections that an individual has had.
What immunoglobulins are present in humans?
Five - IgG, IgA, IgM, IgE, IgD
What implies the innate immune system is important?
Inherited deficiencies are rare
Significant impairment in protection when deficiencies do occur.
What cells are involved in innate immunity?
Macrophages (phagocytosis and presentation of antigens to lymphocytes)
Mast cells - protection of mucosal surfaces, allergy-release of histamine, heparin, chemoattractants
Basophils - allergy
Eosinophils - parasites (secreting cytotoxic enzymes)
Neutrophils - phagocytes
How many neutrophils enter the oral cavity in one day?
3x10^9
What conditions are neutrophils specialised for, and what part of the immune response are they involved in?
Anaerobic conditions (prevail in tissue damage) Represent first event of inflammatory response
What happens to a neutrophils once activated?
Cannot synthesise more granules, dies, forms pus.
What is seen in patients with neutrophil deficiencies?
Recurrent infections usually caused by commensal bacteria.
What receptors on a neutrophil bind lipopolysaccharide?
CD14 and CR4
What are macrophages?
Cells that phagocytose microbial cells, and damaged or unwanted cells.
They release cytokines.
They are able to continually produce lysosomes
They are professional antigen presenting cells.
What is opsonisation?
The coating of a microorganism by antibodies or complement so it can be recognised as foreign by phagocytes
What is the role of C3b?
Encapsulated bacteria cannot be engulfed by neutrophils. C3b opsonises such bacteria enhancing phagocytosis.
What mediates the engulfment of bacteria by neutrophils?
Fc receptors and complement receptors
What are natural killer cells?
Part of the innate immune system - neither T cells or B cells.
Have no classical antigen receptors.
Recognise and kill abnormal cells including tumour cells.
Kill virally infected cells by making pores and pumping in proteases.
What activates natural killer cells?
Mast cells (IFNalpha, IFNbeta)
Macrophages (IL-12, TNFalpha)
(Cytokines released in response to viral infection promote proliferation and activation)
What happens to people who lack natural killer cells?
Recurrent viral infections such as herpes
What is the role of transferrin and lactoferrin?
Deprive microorganisms of iron.
What is the role of interferon?
Inhibits viral replication, activates other cells that kill pathogens.
What is the role fibronectin?
Opsonises pathogens
What is the role of TNF alpha?
Suppresses viral replication and activates phagocytes
Where are complement proteins found?
Ubiquitous in blood and lymph
What is the role of C3a, C4a, C5a?
Chemokines - recruit inflammatory cells.
What is the role of C3b?
Opsonisation
What is the role of C5-C9?
Membrane attack complex.
What is the result of a deficiency in C1, C2 or C4?
SLE or another immune complex disease type 3
Hat is the result of a deficiency in C3?
Recurrent bacterial infections -septicaemia, meningitis, pneumonia
What is a result in a deficiency of C5-C9?
Recurrent neisseria infections.
What is the B cell antigen receptor?
Membrane bound antibody - surface immunoglobulin.
Specific for one antigen.
What is the T cell antigen receptor?
Not a membrane bound antibody - distinct receptor.
Specific for one antigen
What are the three ways antibodies protect the host frominfection?
Opsonisation
Activation of complement
Neutralisation
What is clonal selection?
Raising of the frequency of cells with a particular antigen specificity in response to infection.
WhAt are the five stages of adaptive immune responses?
Clonal selection Clonal expansion Differentiation to effector cells (elimination of antigen) T and B cell apoptosis Seeding of memory
What is the nature of the immune response on the second exposure to a pathogen?
Quicker and larger due to memory cells.
