salmonella and shigella

Question 1

how are bacteria classified (what types of groups?)

Answer 1

family
genus
species
subspecies
strains

Question 2

what is a strain?

Answer 2

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

Question 3

how do strains evolve within species?

Answer 3

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

Question 4

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

Answer 4

surface components vary

decreases detection or killing by host or predator

Question 5

what is a serotype?

Answer 5

strain that is differentiated by serological means

Question 6

how is serotyping done?

Answer 6

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

Question 7

what bacteria surface elements can be recognized by specific antisera?

Answer 7

1: O antigens - polysaccharide component of LPS
2: H antigens - flagellar antigen
3: K antigen - polysaccharide capsule component

Question 8

what does the O antigen consist of?

Answer 8

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

Question 9

how do O antigens vary between species?

Answer 9

can vary between strains

vary to aid in immunoinvasion

Question 10

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

Answer 10

• mutations
• gene acquisitions
• overall genome rearrangements

Question 11

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

Answer 11

enterobacteriaciae

gram-negative rods

Question 12

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

Answer 12

genus

Question 13

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

Answer 13

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

Question 14

what determines which syndrome related to salmonelliosis you get?

Answer 14

the species of salmonella:

• typhoid fever due to S. Typhi
• septicemia due to S. cholerasuis
• gastroenteritis due to S. enteriditis or S. typhimurium

Question 15

what species of slamonella causes typhoid fever?

Answer 15

S. Typhi

Question 16

what species of salmonella causes septicemia?

Answer 16

S. cholerasuis

Question 17

what species of salmonella causes gastroenteritis?

Answer 17

S. enteriditis

S. typhimurium

Question 18

how many cases per year are there of S. Typhi? which countries is it common in?

Answer 18

16 million cases per year
more than 600,000 related deaths (WHO)
rare in N. america, europe and australia
common in developing world

Question 19

what is the incubation period of S. typhi?

Answer 19

7-14 days

Question 20

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

Answer 20

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

Question 21

what are the symptoms of S. Typhi?

Answer 21

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

Question 22

what symptom is diagnostic for S. Typhi?

Answer 22

the rose spot skin rash

Question 23

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

Answer 23

intestinal hemorrhage or perforation

GI bleeds and sometimes diarrhea

Question 24

what species does S. typhi infect?

Answer 24

only humans

Question 25

how is S. typhi transmitted?

Answer 25

via contaminated food and water

Question 26

how does S. Typhi respond to acid?

Answer 26

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

Question 27

how does S. typhi enter cells?

Answer 27

1: adhesins promote attachment to intestinal epithelium 2: bacterially-mediated endocytosis can also be ingested by macrophages

Question 28

what happens when S. typhi is ingested by macrophages?

Answer 28

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

Question 29

what enables S. Typhi to survive in macrophages?

Answer 29

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

Question 30

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

Answer 30

fever and shock

Question 31

what are pathogenicity islands?

Answer 31

``` a distinct class of genomic islands acquired by microorganisms through horizontal gene transfer transferred through horizontal gene transfer events such as transfer by a plasmid, phage, or conjugative transposon.Therefore, PAIs contribute to microorganisms ability to evolve. ``` (wikipedia)