W10 Medical Microbiology Flashcards
definition of opportunistic pathogens
microbes that don’t normally cause disease but can be harmful if given the chance such as during weakened immune system
how are cavities formed
bacteria colonise tooth surfaces by attaching to glycoproteins deposited by saliva
extensive growth of oral microbes results in a thick bacterial layer > anaerobic species grow > produce high concentrations of acid that decalcifies tooth enamel
how much microbes are in the gastrointestinal cells
stomach: very little as most microbes killed by acidic conditions (some survive if pass through very quickly or survive in food particles)
small intestine: few organisms
large intestine: largest population in body (10^13 - 10^14 microbial cells)
how are microbes removed from large intestine
by peristalsis, desquamation and movement of mucus
replaced rapidly due to rapid doubling times
most microbes are anaerobes
biochemical/metabolic contributions of intestinal microorganisms
vitamin synthesis
gas production
odor production
organic acid production
glycosides reactions
steroid metabolism
what are bacteroides
bacteria found in large intestines
colonises exfoliated host cells, food particles and sloughed mucus
rapidly eliminated if not attached
adheres to particles in the gut, not the gut itself
degrades complex carbohydrates along either methanogens
relationship between bacteroides and obesity
bacteroides and firmicutes are the main microorganisms that break down food
obese people have less bacteroides and more firmicutes than slim people
why do obese people have more fimicutes
firmicutes have numerous enzymes that break down indigestible carbohydrates
additional nutrients absorbed by intestine
leads to higher caloric intake from food
transmission routes of diseases
person-to-person: airborne, direct contact or sexually transmitted
zoonotic and vector borne
soil borne
waterborne
foodborne
major adherence factors used to facilitate attachment of microbial pathogens to host tissues
capsule/slime layer
adherence proteins
lipoteichoic acid
pili
definition of LD50
indication of how much of a substance is expected to cause death in 50% of a population
lower LD50 > more virulent
little difference between LD50 and LD100 > highly virulent
how do certain enzymes enhance virulence in pathogens
by breaking down other altering host tissue to provide access to nutrients
protect pathogen by interfering with normal host defence mechanisms
what are exotoxins
proteins released from pathogenic organisms as it grows
what are cytolytic toxins
work by degrading cytoplasmic membrane integrity > host cell lysis and death
eg: hemolysins > break down RBC
what are AB toxins
consists of A and B subunits
work by binding to host cell receptor (B subunit) and transfer a damaging agent (A subunit) across cell membrane
what is diphtheria toxin
catalyses ADP-ribosylation of elongation factor 2 > prevents transfer of amino acids to growing peptide chain in ribosome
what is botulinum toxin
blocks release of acetylcholine to muscle tissue > permanent relaxed state
what are super antigen toxins
stimulate large number of immune cells > extensive inflammation and tissue damage
what are endotoxins
lipopolysaccharide portion of cell wall of certain gram negative bacteria is a toxin when solubilised
generally less toxic than exotoxins
risk factors for infection
compromised host: one or more resistance mechanisms are inactive > increased risk of infection
age: very young and very old more susceptible to infection
stress: predisposes healthy individuals to disease
diet and lifestyle choices
genetic conditions can compromise a host
