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Micro - Intro + Classification of Microorganisms (microbe classification…
Micro - Intro + Classification of Microorganisms
germ theory
germs, depending on the kind, can cause or prevent disease
microbe classification
viruses
obligate intracellular pathogens
simple structure
nucleocapsid (nucleic acid + capsid)
+/- envelope (host cell derived)
can be cultured - grown in susceptible host cells
dependent on growth characteristic + serotype (group with same antigen)
not done regularly
visible under EM
usually detected using molecular methods
NOT CELLS
can't produce their own metabolic energy
can't replicate on their own
e.g. Norovirus (winter vomiting bug/food poisoning), HSV (cold sores/genital herpes
bacteria
have plasmids (extranuclear DNA)
cytoplasm, cytoplasmic membrane, cell wall
In most bacteria the most numerous intracellular structure is the ribosome
appendages
flagellae for locomotion
pili/fimbriae for adherence
e.g. treponema pallidum - gram -ve - syphilis
mostly classified on phenotypic characteristics
observable features
colonial morphology (shape, size, colour)
growth characteristics
gram staining characteristics
purposes
typing (separating 1 strain from another)
confirm the ID of an isolate
types
biotyping (biochemical tests)
serotyping (surface antigens)
phage typing (virus susceptibility)
antibiograms (antibiotic susceptibility)
increasingly being classified on genotypic characteristics (genetic makeup)
uses PCR, whole genome sequencing, microarray techniques
most accurate + quickest method of typing + confirming ID
mycoplasma
smallest known cells
lack a cell well
have cytoplasmic + outer membrane
cause pneumonia in children + young adults
fungi
more closely related to human cells than bacteria
hence more limited Tx options (hard to make a drug selectively toxic to fungal cells + not human cells)
classification
by growth form
filamentous
mould
grows as multinucleate branching hyphae (a mycelium)
yeasts
e.g. oral/vaginal thrush
ovoid/spherical single cells
multiply by budding + division
by infection type
superficial mycoses (e.g. sporothrix)
deep mycoses (e.g. candida)
e.g. Aspergillus fumigatus: harmless except in immunocompromised
parasites
protozoa
unicellular eukaryotes
classified based on infection type
GI (e.g. cryptosporidium parvum)
blood + tissue (e.g. plasmodium falciparum - malaria)
helminths
parasite worms usually in tropics
3 categories
nematodes (e.g. roundworm)
trematodes (e.g. flukes)
cestodes (e.g. tape worms)
NB in tropical + travel-related medicine
arthropods
invertebrate animals (arachnids, insects)
not directly pathogenic to humans - usually act as vectors for infectious agents
mosquitoes - malaria
scabies
ticks (exodus species) - Lyme disease
archaea
unicellular prokaryotes
have a different cell wall to bacteria
extremophiles - found in extreme environments
in gut, vagina, oral cavity
part of microbiome
produce methane
degrade biological compounds (e.g. lipids)
evidence of roles in CR cancer, IBD, constripation
bacteria + archaea = prokaryotes (single chromo/genome, no organelles)
fungi + protozoan = eukaryotes (multiple chromos, nucelus, mt, golgi app, ER)
Binomial naming system
genus + species
species = similar interbreeding organisms within a genus
e.g. S aureus
Prions
not microbes (no nucleic acid)
transmissible small hydrophobic glycoproteins closely related to human protein
unclear pathogenesis - possible prion-human interaction leads to amyloid-like plaque formation
e.g. CJD, Kuru, scrapie, bovine spongiform encephalopathy (mad cow disease)