Human microbiota Flashcards
What percentage of cells in the human body are of human origin?
10%
What does it mean if a micro-organism is described as ‘virulent’ or ‘pathogenic’?
It causes disease
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.
What are the problems with Koch’s postulates?
difficulty of isolation of causative agent, impossible to grow some pathogens in artificial culture, ethical objections, animal models not sufficient
What type of parasites are viruses?
obligate intracellular parasites
What is the generic structure of a virus?
nucleic acid core wrapped in a protein coat (some also have an envelope)
What makes retroviruses unusual?
The virion carries an RNA copy of the genome but upon infection of host cell, a cDNA copy of the virus genome is made using the enzyme reverse transcriptase
What is the name of the units making up the protein coat of a virus?
capsomeres
Which special class of virus attacks bacteria?
bacteriophages
What are believed to cause spongiform encephalopathies?
prions
Are all fungi prokaryotic or eukaryotic?
eukaryotic
Most fungi have a cell wall made of what?
chitin
Define moulds
fungi that grow in mats of tiny filaments (hyphae) forming mats called mycelia
What are unicellular fungi?
yeasts
Name 2 common superficial infections caused by mould
ringworm and athletes foot
Name the 4 classes of protista
apicomlexa, flagella Protista, ciliate Protista, amoebae
Name a Protista that can cause vaginal infection
trichomonas vaginalis
What do bacterial cells lack?
membrane bound nucleus
Are bacteria prokaryotes or eukaryotes?
prokaryotes
What are the two most common shapes of bacteria?
cocci or bacilli
What does the gram reaction test in bacteria?
Their ability to retain a crystal violet-iodine dye complex
What does the envelope of a gram-positive bacteria mainly comprise of ?
30-40 layers of peptidoglycan
What is the outer leaflet of gram negative bacteria mainly comprised of?
lipopolysaccharide
Are gram positive or negative bacteria surrounded by fimbriae?
Gram negative
What is the function of fimbriae?
aid adhesion onto particular surfaces
How do gram-negative bacteria exchange genetic material?
Through sex pili tubes
What is the purpose of a bacterial cell’s capsule?
protects the bacterium, even within phagocytes
What type of bacteria produce a slime allowing them to stick to plastics?
coagulase-negative staphylococci
What are endospores?
highly resistant structure produced by some bacteria
What is a common means of spreading GI infections?
faecal-oral route
Define fomites
inanimate objects that can act as the vectors of infection
Define normal flora
organisms found in a given location in a state of health
Define colonisation
establishment at a site in the body
Define symbiosis
two or more organisms co-exist in close physical association
What are the 4 types of symbiosis?
mutualism, neutralism, commensalism, parasitism
Define mutualism
both organisms benefit from symbiosis
Define neutralism
neither organism derives benefit or harm from symbiosis
Define commensalism
one organism benefits, while the other does receive not benefit or harm from symbiosis
Define parasitism
one organism (parasite) benefits at the expense of the other (host_)
Define a sterile site and give an example
a site with no normal flora, for example to lower respiratory tract
How is sterility of sterile sites maintained?
surface cleaning, barriers that allow uni-directional flow, physical separation from non-sterile sites
What is tissue tropism?
cells and tissues of a host which support growth of a particular virus or bacteria
Where is coagulase-negative staphylococci found as normal human flora?
skin
At what sites in the body can staphylococcus aureus be found as normal flora?
skin, nostrils, pharynx
What is produced in the vagina post-puberty due to circulating oestrogens?
glycogen
What normal flora is found in the vagina post-puberty?
LACTOBACILLUS, skin flora, a few C. albicans
What characteristic of the stomach and small intestine prevents bacterial growth?
low gastric pH
Are the bacteria of the stomach and the small intestine mainly aerobic or anaerobic?
aerobic
Name the 2 main normal flora found in the stomach and small intestine
acid-tolerant lactobacilli and H. pylori
Are the bacteria of the large intestine mainly aerobic or anaerobic?
anaerobic
What prevents overgrowth of pathogens in the large intestines?
colonisation resistance by normal gut flora
What are the 3 main benefits of normal flora?
synthesis and excretion of vitamins, colonisation resistance, induction of cross-reactive bodies
What is the main risk factor for clostridium difficile infection?
antibiotic treatment
What type of treatment has made a ‘come-back’ in treating C.diff?
faecal transplants
What are the 3 main pathologies of normal flora?
overgrowth, translocation, cross-infection
Give an example of normal flora overgrowth?
vaginal thrush
Give an example of a translocation infection
conjunctivitis
