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Flashcards in salmonella and shigella Deck (31)
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1

how are bacteria classified (what types of groups?)

family
genus
species
subspecies
strains

2

what is a strain?

population of organisms within a species that descends from a single organism

3

how do strains evolve within species?

by mutation and/or by acquiring additional genes by horizontal gene transfer

4

what varies among strains? what is the advantage of this variation?

surface components vary
decreases detection or killing by host or predator

5

what is a serotype?

strain that is differentiated by serological means

6

how is serotyping done?

- uses specific antisera that contains antibodies to specific bacterial agents
- based on antibody recognition of antigens

7

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

8

what does the O antigen consist of?

repeating oligosaccharide units - up to 20 different sugars, some unique to LPS

9

how do O antigens vary between species?

can vary between strains
vary to aid in immunoinvasion

10

what can cause strains to vary within a serotype (ie how is the variation potentially acquired)?

- mutations
- gene acquisitions
- overall genome rearrangements

11

what kind of bacteria is salmonella? (family, G+ or G-, shape)

enterobacteriaciae
gram-negative rods

12

what type of classification is the word salmonilla (ie family, genus, species)?

genus

13

what are the clinically distinguishable syndromes related to salmonelliosis in man?

1: typhoid or enteric fever
2: septicemias
3: acute gastroenteritis

14

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

15

what species of slamonella causes typhoid fever?

S. Typhi

16

what species of salmonella causes septicemia?

S. cholerasuis

17

what species of salmonella causes gastroenteritis?

S. enteriditis
S. typhimurium

18

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

19

what is the incubation period of S. typhi?

7-14 days

20

what would the symptoms during the incubation period of S. Typhi be?

in early GI phase may be subclinical but have positive stool culture

21

what are the symptoms of S. Typhi?

episodic fever
bradycardia (slow heart rate)
skin rash (called rose spot)
leukopenia (low WBC count)
enlarged liver and spleen (during bacteremic phase)

22

what symptom is diagnostic for S. Typhi?

the rose spot skin rash

23

what are the symptoms of the late stages of S. Typhi?

intestinal hemorrhage or perforation
GI bleeds and sometimes diarrhea

24

what species does S. typhi infect?

only humans

25

how is S. typhi transmitted?

via contaminated food and water

26

how does S. Typhi respond to acid?

somewhat resistent to killing by stomach acid
can survive lysosomal acid in macrophages

27

how does S. typhi enter cells?

1: adhesins promote attachment to intestinal epithelium
2: bacterially-mediated endocytosis

can also be ingested by macrophages

28

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

29

what enables S. Typhi to survive in macrophages?

possible enabled by Vi antigen = polysaccharide capsule - it's only in S. typhi

30

what is the symptomatic result of S. typhi in the blood stream?

fever and shock