Week 6 - Microorganisms Flashcards
Describe viruses
18-300nm
Obligate - cannot replicate outside of host cell
DNA or RNA enclosed in a virus encoded protein coat (nucleocapsid)
Some have an outer most host cell membrane-derived envelope
Infectious virus particle - virion
What can the nucleic acid be like in viruses?
DNA or RNA
Double or single stranded (ds or ss)
Circular or linear
One piece or segmented
What is the capsid made of?
Capsomeres - determine symmetry
Icosahedral/cuboidal - 20 sided
Helical
Complex
How does a virus replicate?
Adsorbs to cells via receptor binding proteins
If the nucleic acid is positive sense ss RNA it is treated as mRNA
If it is negative sense ss RNA it is converted to positive by viral RNA polymerase
Retroviruses have ss RNA which is reversely transcribed to double stranded DNA by reverse transcriptase which is then transcribed to mRNA.
These all then produce new viral proteins
How to viruses egress?
Budding - most likely in viruses with envelopes
Cytolysis
How can a virus be transmitted?
Oral Direct skin contact Droplet transmission Direct inoculation Trans-placental Sexual
Stages of infection of viruses
Infection Spread Multiplication Evasion Shedding or egress resulting in transmission Pathology
Describe fungal infections
Often in immunocompromised patients
Aspergillus - opportunistic and often fatal
Cryptococcus neoformans - indicates AIDS - causes meningitis and fungaemia
Fungi are uni or multicellular and have a hard carbohydrate cell wall and membrane bound organelles
Describe parasites
Protozoa are single celled - malaria
Helminths are worms
arthropods carry Lyme’s disease or yellow fever
What are prions
Host proteins which are abnormally folded and so disrupt cell function
Form fibrils in brain or cause refolding of other proteins
Resistant to treatment
Often transmitted through food or other contaminated items
Creutzfeldt Jacob disease can cross species barrier
What are bacteria
Single celled
Prokaryotic - don’t have membrane bound organelles
DNA in cytoplasm, mostly as circular chromosomes.
Often have plasmids
Reproduce through binary fission or spore formation
Genetic variation from horizontal gene transfer
What do bacteria need to survive?
Energy source (e.g. glucose) Water Nitrogen, sulphur, iron etc Some need complex organic materials Temperature, pH Atmosphere - strict aerobes -facultative -strict anaerobes
What are the three types of horizontal gene transfer?
Transformation - bacteria takes in DNA fragments outside of the cell and integrates them into its own
Conjugation - bacteria replicates plasmid and transfers it to another bacteria via a sex pilus
Transduction - via bacteriophages - viruses which infect bacterial cells - inject cells with DNA fragments when they infect another cell
Describe the phases of the bacterial growth curve
Logarithmic scale
Lag phase - synthesising RNA, adapting to environment
Exponential phase - exponential growth, straight due to log scale
Stationary phase - growth limiting factor such as lack of a nutrient
Death phase - toxin buildup, lack of nutrients or adverse conditions
What are gram positive bacteria
Thick peptidoglycan layer
Purple gram stain
Mostly sensitive to penicillin and vancomycin
Some have spores
What are gram negative bacteria?
Thin peptidoglycan layer
Lipopolysaccharide layer
Pink on gram stain
Mostly resistant to penicillin and vancomycin
What are the two types of haemolysis?
Alpha-incomplete degradation of haemoglobin
Green on blood agar
Beta - complete lysis of RBCs - more pathogenic
Yellow and transparent on blood agar
What are yeasts
Unicellular fungi
Candida causes thrush and athlete’s foot
In blood called candidaemia - much worse
Directions in which bacteria can divide
Three planes - staphylococcus (makes grape-like clusters)
One plane - streptococcus and enterococci- chains
- diplococci - pairs
- bacilli
Staphylococcus aureus
Gram positive Clusters beta haemolysis - haemolysins Catalase positive - breaks down hydrogen peroxide Coagulase positive - turns fibrinogen to fibrin - coats bacterial cells and prevents phagocytosis Facultative anaerobe pore forming alpha toxin o Skin and soft tissue infections - CELLULITIS o Pneumonia o Bone and joint infections o ENDOCARDITIS Scalded skin syndrome Toxic shock syndrome - exotoxin Gastroenteritis
protein A - binds to antibodies, preventing strong immune response
hyaluronidases - hyaluronic acid –> hyaluronan - used as a source of carbon for growth
flucloxacillin for succeptible
MRSA - vancomycin
Streptococcus pneumoniae
Gram positive diplococci Facultative anaerobe alpha haemolytic Most common cause of Community acquired pneumonia (CAP) pneumococcal menigitis
Streptococcus pyogenes
Form chains Facultative anaerobe gram positive Beta haemolytic (group A) One of the most important bacteria pathogens in humans hyaluronidases - hyaluronic acid --> hyaluronan - used as a source of carbon for growth DNAases fimbriae for adhesion haemolysins Protein M - helps gain entry to cells o Pharyngitis o Scarlet fever o Rheumatic fever o Post-streptococcal glomerulonephritis o Bacteraemia o Necrotizing fasciitis
strep throat
Clostridium tetani
Gram positive
Bacilli
anaerobe
Spores in soil – contaminates wounds
Excitation of motor neurons by blocking release of inhibitory neurotransmitter GABA
Spastic paralysis – rigidity of voluntary muscle e.g. “lock jaw”
Hyper-sympathetic state as catelcholamine not inhibited
Fatal
Clostridium botulinum
Gram positive Bacilli anaerobe Food-borne usually Neurotoxin - prevents acetylcholine release Symmetrical flaccid descending paralysis Oculomotor muscles affected, dysphagia, respiratory depression Botox
