Salmonella and Shigella Flashcards
what is a bacterial strain?
a population of organisms within a species that descends from a single organism
- evolve by mutation and/or by acquiring additional genes by horizontal gene transfer
- surface components often vary
- sub population of a species
what is a bacterial serotype?
a strain that is differentiated by serological means
based on antibody recognition of antigens
what are O antigens?
the polysaccharide component of LPS
Side chains vary to aid in immunevasion
what is the H antigen?
the flagellar antigen
what is the K antigen?
polysaccharide capsule component
what are the possible clinical syndromes of salmonellosis? (3)
1) Typhoid/enteric fever
2) septicemias
3) acute gastroenteritis
what is the genus of salmonella? what type of bacteria is it? (gram, shape)
member of Enterobacteriaciae
gram-negative rod
where is salmonella typhi often found?
what disease does it cause?
what is it’s incubation period?
common in developing world
causes typhoid fever
Incubation period: 7-14 days
what species does S. Typhi infect?
-only infects humans via food/water
How does S. typhi survive phagocytic vacuoles?
enabled by Vi antigen of polysaccharide capsule
how are Salmonella typhi pathogenicity islands acquired? what do they consist of?
acquired through horizontal gene transfer
G+C content, phage/transposon sequences, non-native adjacent sequences
SPI-1 and SPI-2
what does the SPI-1 (Salmonella pathogenicity island 1) encode for?
encodes genes for invasion
Type 3 secretion system (T3SS)
what is the T3SS (type 3 secretion system)?
a specialized form of secretion wherein a protein moves across the bacterial cytoplasmic and outer membrane AND across the host cell membrane through an injection needle
Salmonella T3SS delivers?
toxins that induce membrane ruffling by stimulating actin polymerization, and endocytosis
what does SPI-2 (salmonella pathogenicity island 2) encode for?
encodes genes for intracellular survival
what is endotoxin a component of? what does it cause?
lipid A component of LPS
causes fever and shock
how would you diagnose S. typhi? (at 1 week, 2-3 weeks, after 3 weeks)
Week 1: subclinical, positive stool culture
Weeks 2-3: symptomatic, positive blood cultures
After week 3: stool culture positive again following gall bladder colonization
how do you treat S. typhi? (acute, chronic)
Acute: Fluoroquinolones, 3rd generation cephalosporin
Chronic carrier:
1) Ampicillin/Ciprofloxacin
2)cholecystectomy
how can S. typhi be prevented?
- control of water and sewage (humans only host)
- food safety and pasteurization
- 2 vaccines: oral attenuated and Vi capsular polysaccharide
are there vaccines for S. typhi? if so, what are they and what type?
Ty21a: live attenuated
ViCPS: capsular polysaccharide
how is Salmonella cholerasuis spread? how many organisms are required for infection?
oral ingestion of contaminated swine
infectious dose: 1000 organisms
where are Salmonella enteriditis and Salmonella typhimurium most common? what are the normal symptoms? what tests could be used to detect it?
most common Salmonella infection in U.S.
diarrheal disease mostly confined to GI tract
infrequent positive blood cultures
what are the sources of S. enteriditis and S. typhimurium?
poultry, pork, dog food, eggs (eggs most common, inside and outside shell)
contaminated fruits/vegetables
turtles and other reptile pets
sandbox
what is the incubation period of S. enteriditis and S. typhimurium? what are the clinical symptoms? how long do they last?
4-48hr incubation
sudden onset of headache, chills, abdominal pain, vomiting, diarrhea, fever
lasts 1-4 days
describe the pathogenesis of S. enteriditis and S. typhimurium.
LPS release during invasion of epithelial cells of intestine causes many symptoms
T3SS mediates invasion of epithelial cells
extracellular cells produce toxins (including pertussis-like toxin) that promote inflammation and secretion
how are S. enteriditis and S. typhimurium treated?
mostly self-limiting
fluid and electrolyte replacement
pts with predisposing conditions get antibiotics but resistance is possible
Salmonella diagnosis (What does it ferment? Is it motile? Oxidase, urease, nitrate, indole?)
Isolation in feces or blood Ferments glucose, does not ferment lactose Motile oxidase negative can reduce nitrate Urease negative Indole negative Produce H2S
what is the genus of Shigella? what type of bacteria is it (gram, shape)?
Enterobacteriaciae
Gram-negative rods
what is the most common Shigella species in U.S.?
Shigella sonnei
what is the most common Shigella species in developing world?
Shigella dysenteriae
what are the clinical symptoms of Shigella?
Fever (due to LPS), diarrhea and abdominal cramps (due to Shiga toxin)
Bloody, mucous diarrhea
Usually self-limiting
Bacteremia rare
describe the pathogenesis of Shigella. (how does it infect and spread?)
Invade intestinal cells in terminal ileum and colon
Uptake by macrophages followed by escape and cell-to-cell spread
describe the virulence of Shigella? (ie how does it create disease)
T3SS-secreted Shigella protein induces macrophage uptake and escape
Induces apoptosis of macrophages and release of IL-1 and TNF
Shiga toxin causes intestinal ulceration
Diarrhea due to fluid malabsorption
what is Shiga toxin? what are the subunits? what does it do?
Exotoxin produced by Shigella
2 subunits: A & B
causes intestinal ulceration
May lead to apoptosis of mucosal cells
what does the Shiga toxin subunit A do?
interferes with function of 60S ribosomal RNA inhibiting protein synthesis
what does the Shiga toxin subunit B do?
binds to receptor on intestinal cells
how is Shigella diagnosed?
clinical Sx NOT diagnostic
Isolation of microorganisms from feces
detection of PMNs in stool indicates invasive disease
Shigella important diagnostic traits (Ferments? Motile? Antigens? Indole, Urease?)
Ferments glucose (no gas), does not ferment lactose Nonmotile Contains O antigens only (no H) Indole negative Urease negative
how is Shigella treated?
fluid and electrolyte replacement
antibiotics in severe cases, resistance is increasing
What is the incubation period for Salmonella typhi? What are the diagnostic symptoms and clinical syndrome?
Incubation period: 7-14 days
Dx Sx: Episodic fever, bradycardia, skin rash (Rose spot)
Bacteremic phase: leukopenia, hepatosplenomegaly
late GI phase: intestinal hemorrhage or perforation
Word association: Rose Spots
Salmonella typhi
how is Shigella prevented? is there a vaccine? if so, what type?
Improve sanitation (humans are only host)
No effective vaccine
Recombinant O-antigen vaccine conjugated to Shiga toxin is promising vaccine candidate
How is S. Typhi diagnosed? (what symptoms would you see?)
- Episodic fever
- bradycardia
- skin rash (Rose spot)
describe the pathogenesis of S. Typhi. how does it enter cells and the body? what symptoms does it cause?
- resistant to stomach acid
- adhesins promote attachment to intestinal epithelium
- induce bacterially-mediated endocytosis into epithelial cells
- ingested by macrophage, survives inside phagocytic vacuoles and lysosome
- kills macrophage and disseminate via thoracic duct
- causes fever and shock when in blood stream
- reinvasion of GI tract from gall bladder
what symptoms occur during the bacteremic phase of S. Typhi?
- leukopenia
- hepatosplenomegaly
what symptoms occur during the late GI phase of S. Typhi?
intestinal hemorrhage or perforation
what disease does shigella cause?
causes dysentery (shigellosis)
how is shigella spread?
spread by Food, Fingers, Feces, and Flies (4Fs)
who is most susceptible to shigella?
Children under 10 more susceptible
what are the reservoirs of shigella?
No animal reservoir
how long can shigella be detected in feces after recovery?
Organisms detectable in feces 1-4 wks after recovery
what is the incubation period of Salmonella cholerasuis?
short incubation: 6-72hrs
what are the symptoms of Salmonella cholerasuis?
high fever and bacteremia with gastroenteritis
microabsesses
how many shigella organisms are required to infect?
Low inoculum (100 bugs)
how does shigella respond to acid?
acid tolerant
how long is the incubation period of shigella?
1-4 day incubation
How do strains arise?
Mutation and/or acquiring additional genes
What is a serotype? What is stereotyping?
Group of organisms that are recognized by the same antibodies
Useing specific antisera that contains antibodies to specific bacterial antigens
Can be different strains within a serotypes and different strains can have the same serotype - the serotype is specifically only the group of bacteria for which the same antibody reacts
