Lect 9 - Introduction & Classification of Human Microbiota Flashcards
what percentage of cells in the human body are of human origin?
10 % of cells
whats the name for cells that live in the body but are not human?
The remaining cells comprise the human commensal microbiota.
Certain viruses may also persist in the human body.
are most bacteria harmful? how would you describe these bacteria?
No.
Microorgansims that do cause disease may be described as “virulent” or “pathogenic”.
Historically, how would we define an organism as pathogenic?
using koch’s postulates.
what are Koch’s Postulates?
The causative organism must be isolated from every individual suffering from the disease in question;
The causative organism must be cultivated artificially in pure culture;
When the causative organism is inoculated from pure culture, the typical symptoms of the infection must result;
The causative organism must be recoverable from individuals who are infected experimentally.
how can koch’s postulates be applied to genetics?
the gene encoding the trait of interest should be present and transcribed/translated in a virulent strain;
the gene encoding the trait of interest should NOT be present or should be silent in a strain that does not cause disease;
disruption of the gene in a virulent strain should result in the formation of a strain that is incapable of casing disease;
what comprises a virus?
They comprise of a nucleic acid core wrapped in a protein coat.
Some viruses have an envelope. other viruses are naked.
do viruses carry DNA or RNA?
Viruses have a nucleic acid core, either DNA or RNA but not both.
Retroviruses (RNA) are unusual.
what are the units that make up the protein coat of a virus called?
capsomeres.
what is the class of virus that attacks bacteria called?
bacteriophages.
what is the class of virus that attacks plants?
viroids: naked, infectious RNA molecules that are not associated with any proteins.
whats the difference between a naked virus and a prion?
a prion has no genetic material
are fungi all eukaryotic?
what is their cell wall made of?
All fungi are eukaryotic.
Most possess a cell wall made of chitin.
what is the typical “hairy” type of fungi called?
moulds
mould can grow tiny filaments, which form mats. what are these filaments and mats called?
hyphae (singular: hypha, Greek for a thread)
mycelia. (singular: mycelium, from the Greek mukes, meaning a mushroom).
what are unicellular fungi called?
yeasts.
what is the most common yeast infection?
“thrush” caused by Candida albicans.
give some examples of infections caused y moulds
ringworm and athlete’s foot.
What are protista?
a grouping of diverse unicellular eukaryotic organisms that are not animals, plants or fungi.
what are the classes of protista?
apicomplxa (formerly sporozoa),
flagellate protista,
ciliate protista
and amoebae.
give examples of diseases caused by protists
toxoplasmosis, amoebic meningitis, malaria, trypanosomiasis, leishmaniasis (Kala-Azar) amoebic dysentery diarrhoea.
What protista causes foul smelling vaginal discharge in women?
Trichomonas vaginalis. NOTE MEN CAN BE ASYMPTOMATIC CARRIERS.
are bacteria pro or eukaryotes?
The bacterial cell lacks a membrane-bound nucleus. Because of this, bacteria are described as prokaryotes,
what are the most common shapes of bacteria?
Most bacteria are either round (cocci) or rod-shaped (bacilli)
how else do we divide bactera?
Gram reaction
how do we do gram testing?
look at the ability to retain a crystal violet-iodine dye complex when cells are treated with acetone or alcohol.
(reveals fundamental differences in the structure of bacteria.)
what is the difference between the structure of a gram + and - bacteria?
positive has a membrane of 30-40 layers of “peptidoglycan”, while a negative has far less of this.
negative bacteria have an extra, complex “outer membrane” instead.
what do sugars form the surface antigen of gram negative bacteirum, along with the complex lipid known as lipid A cause?
they act as an endotoxin and cause Gram-negative shock
what do bacteria use to increase their motility?
flagella
what do gram neg bacteria use to aid adhesion onto surfaces?
hair-like structures known as fimbriae.
Some bacteria produce slime to help them to stick to surfaces. (like Streptococcus mutans on teeth, leading to plaque)
what can gram negative bacteria use to exchange genetic material during conjugation?
sex pili (singular: pilus)
what other feature have bacteria developed to prevent them from being phagocytosed?
capsules.
what bacteria cause infections associated with implanted plastic medical devices.
‘Coagulase-negative’ staphylococci.
they live on the skin, and produce a slime that enables them to stick to plastics.
what is the most resistant structure a bacterium can produce; resisting a range of hazardous environments by protecting against heat, radiation and desiccation?
endospores
name some routes of infection
airborne faecal-oral route (GI) sexually transmissible direct inoculation (HIV) via animals (MALARIA) via Inanimate objects (known as fomites)
how does one control infection?
by identifying the mode of spread and interrupting the cycle of infection, replication and spread.
what term describes a pathogen’s ability to complete the cycle of infection?
“virulence factors”.
what class of diseases can still spead without the victim encountering live microorganisms?
Intoxication illnesses, such as tetanus or botulism. these are unusual.
disease results from exposure to a toxin
what are the different types of toxins?
exotoxins and endotoxin
what are the mechanisms by which bacteria cause disease?
production of “aggressins”;
initiating undesirable consequences of the host defences.
