Microbiology Flashcards
(25 cards)
Re-intro to microbiology: What are the main groups of micro-organisms and how are they classified?
Protozoa e.g. malaria and fungi - eukaryotes
Bacteria - prokaryotes
Viruses
Prions - infectious rogue proteins
Re-intro to microbiology: What are the features of Protozoa?
Unicellular eukaryotes
2-100 mm - small, complex life cycles in some cases
Many are free-living- e.g. euglena (pond-water)
Several are important human pathogens - Malaria
Often affect the immunocompromised
Mainly a threat in developing countries
Protozoa examples- trypanosomiasis (chagas disease),
malaria, cryptosporidium, Toxoplasma gondii
Re-intro to microbiology: What are the features of fungi?
Eukaryotic organisms with a variety of forms
Commercially important- baking, brewing and pharmaceuticals
External, rigid cell wall – containing chitin
Filamentous or yeast forms
Many display both- dimorphic e.g. Candida
Re-intro to microbiology: What are the features of bacteria?
Most numerous organisms on earth
Adapted to inhabit almost all habitats
- Even those not based on sunlight- deep sea vents
Responsible for notable worldwide epidemics- PLAGUE
Prokaryotes- no internal membranous compartments
Specialised cell walls
Produce a range of toxins- virulence factors
Re-intro to microbiology: What is a coccus?
Any spherical or roughly spherical bacterium.
When cocci divide or reproduce they create different patterns, depending on the type.
Re-intro to microbiology: What types of coccus bacteria exist?
Diplococci - 2 Tetrads - 4 Sarcina - 4 stacked on top of 4 Streptococci - twist or string of pearls Staphylococci - bunch of grabs shape
Re-intro to microbiology: What other shapes of bacteria exist?
Bacilli - rod extended irregular rods e.g. fusobacterium corkscrew helical e.g. campylobacter kidney bean
Re-intro to microbiology: What is the difference between gram positive and gram negative?
Gram positive - one cell membrane and a thick peptidoglycan cell wall which retains the stain and goes purple
Gram negative - two membranes with a thin cell wall in-between creating a perioplasm space, also has outer capsule of LPS - does not retain stain and appears pink
Re-intro to microbiology: What is peptidoglycan made up of?
- a polymer of N-acetyl muramic acid (NAM) and N-acetyl glucosamine (NAG)
- crosslinked via amino acid pentapeptides and anchored to cell wall
Re-intro to microbiology: What are pili and fimbriae used for?
proteinaceous filamentous structures
Often used for attachment to host-cells or surfaces
Adhesins at the tip for host interaction e.g. EPEC bfp
Can also be used for twitching motility e.g. Pseudomonas spp.
Re-intro to microbiology: What are pathogens?
Disease causing bacteria e.g. Cholera
Re-intro to microbiology: What are opportunistic pathogens
- Commensals that sometimes cause disease
e.g. MRSA, C. difficile, Major hospital infections
N.meningitidis- isolated epidemics in UK
Re-intro to microbiology: What are commensals?
Mainly harmless
Colonise surfaces and mucosa
harmless and beneficial inhabitants of the body
Re-intro to microbiology: What are the main colonisers of the digestive tract and why are they beneficial?
E coli
- Gram negative rod
- essential commensal
- some strains are Pathogenic
Bacteroides species
- Gram-negative anaerobic bacilli
- Most numerous in the body
Clostridia species
- Gram positive anaerobic spore forming bacilli
- includes C. difficile an increasingly
drug resistant
- related to tetanus and botulism causing bacteria
they degrade some stuff we can/t, they stimulate the immune system and provide us with some vitamins.
Re-intro to microbiology: What are the features of mycobacterium and why are they different?
Gram (positive) rods, unusual cell wall- mycolic acid - major determinant of virulance
Impervious to Gram-staining
Need Ziehl-Neelsen acid-fast staining procedure: mycobacteria in red
Re-intro to microbiology: Why are the mycolic acids of the mycobacteria important in causing TB?
Mycolic acids are strong hydrophobic molecules that form a lipid shell around the organism and affect permeability properties at the cell surface.
Mycolic Acids are are thought to be a significant determinant of virulence in M.TB. Probably, they prevent attack of the mycobacteria by cationic proteins, lysozyme and oxygen radicals in the phagocytic granule. They also protect extracellular mycobacteria from complement deposition in serum
Re-intro to microbiology: What has the high conc of lipids in the cell walls of mycobacterium tuberculosis been associated with?
- Impermeability to stains and dyes
- Resistance to many antibiotics • Resistance to killing by acidic and alkaline compounds
- Resistance to osmotic lysis via complement deposition
- Resistance to lethal oxidations and survival inside of macrophages
Re-intro to microbiology: What bacteria is associated with leprosy?
M. leprae
Re-intro to microbiology: Why is chlamydia (c.trachomatis) unusal?
Unusual Gram negative cell wall
Extremely unusual life cycle:
Elementary body facilitates spread
Reticulate body- intracellular replication
Re-intro to microbiology: What is asymptomatic carriage of pathogenic bacteria?
examples - gonorrhoea, chlamydia
Some pathogens however do not always cause disease or may remain after incomplete treatment and promote passage of disease
Re-intro to microbiology: what are some features of viruses?
Obligate intracellular parasites
Cause of major world epidemics:
e.g. H1N1: 1918 Flu 20 million deaths, HIV, measles
Unable to reproduce without host factors
Viral genome uses host to encode viral proteins
- some have basic parasitic or lytic life cycle where they attach, invade, replicate and break out
Re-intro to microbiology: What is the basic viral structure?
- Nucleic acid encapsulated by proteinaceous capsid
Varying shape and symmetry
Some further coated with lipid coat - enveloped
e.g.
Re-intro to microbiology: What is viral latency?
incorporation into genome – retrovirus, use of reverse transcriptase then host can produce viral proteins etc
Latent infection of host cell away from site of infection e.g. Herpes, Varicella zoster
Re-intro to microbiology: What are the features of prions?
Heat resistant, filterable, stick to instruments
Can be detected in tonsils… but not outside lymphatics so far in humans- but in animals…
Scrapie, BSE, CJD (familial, variant and sporadic)
normal PrPC converted into ‘Rogue’ PrPSC
Aggregate into long fibers and amyloid plaques
- Likely transmission via Brain tissue
