Flashcards in salmonella and shigella Deck (31)
how are bacteria classified (what types of groups?)
what is a strain?
population of organisms within a species that descends from a single organism
how do strains evolve within species?
by mutation and/or by acquiring additional genes by horizontal gene transfer
what varies among strains? what is the advantage of this variation?
surface components vary
decreases detection or killing by host or predator
what is a serotype?
strain that is differentiated by serological means
how is serotyping done?
- uses specific antisera that contains antibodies to specific bacterial agents
- based on antibody recognition of antigens
what bacteria surface elements can be recognized by specific antisera?
1: O antigens - polysaccharide component of LPS
2: H antigens - flagellar antigen
3: K antigen - polysaccharide capsule component
what does the O antigen consist of?
repeating oligosaccharide units - up to 20 different sugars, some unique to LPS
how do O antigens vary between species?
can vary between strains
vary to aid in immunoinvasion
what can cause strains to vary within a serotype (ie how is the variation potentially acquired)?
- gene acquisitions
- overall genome rearrangements
what kind of bacteria is salmonella? (family, G+ or G-, shape)
what type of classification is the word salmonilla (ie family, genus, species)?
what are the clinically distinguishable syndromes related to salmonelliosis in man?
1: typhoid or enteric fever
3: acute gastroenteritis
what determines which syndrome related to salmonelliosis you get?
the species of salmonella:
- typhoid fever due to S. Typhi
- septicemia due to S. cholerasuis
- gastroenteritis due to S. enteriditis or S. typhimurium
what species of slamonella causes typhoid fever?
what species of salmonella causes septicemia?
what species of salmonella causes gastroenteritis?
how many cases per year are there of S. Typhi? which countries is it common in?
16 million cases per year
more than 600,000 related deaths (WHO)
rare in N. america, europe and australia
common in developing world
what is the incubation period of S. typhi?
what would the symptoms during the incubation period of S. Typhi be?
in early GI phase may be subclinical but have positive stool culture
what are the symptoms of S. Typhi?
bradycardia (slow heart rate)
skin rash (called rose spot)
leukopenia (low WBC count)
enlarged liver and spleen (during bacteremic phase)
what symptom is diagnostic for S. Typhi?
the rose spot skin rash
what are the symptoms of the late stages of S. Typhi?
intestinal hemorrhage or perforation
GI bleeds and sometimes diarrhea
what species does S. typhi infect?
how is S. typhi transmitted?
via contaminated food and water
how does S. Typhi respond to acid?
somewhat resistent to killing by stomach acid
can survive lysosomal acid in macrophages
how does S. typhi enter cells?
1: adhesins promote attachment to intestinal epithelium
2: bacterially-mediated endocytosis
can also be ingested by macrophages
what happens when S. typhi is ingested by macrophages?
can survive in the phagocytic vacuoles
then kills the macrophages and disseminates via thoracic duct to blood, liver, spleen and gall bladder
reinvades the GI tract from the gall bladder
what enables S. Typhi to survive in macrophages?
possible enabled by Vi antigen = polysaccharide capsule - it's only in S. typhi