Salmonella and Shigella Flashcards by Charis Ripley-Hager

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

How well did you know this?

Not at all

Perfectly

what is a bacterial serotype?

a strain that is differentiated by serological means

based on antibody recognition of antigens

How well did you know this?

Not at all

Perfectly

what are O antigens?

the polysaccharide component of LPS

Side chains vary to aid in immunevasion

How well did you know this?

Not at all

Perfectly

what is the H antigen?

the flagellar antigen

How well did you know this?

Not at all

Perfectly

what is the K antigen?

polysaccharide capsule component

How well did you know this?

Not at all

Perfectly

what are the possible clinical syndromes of salmonellosis? (3)

1) Typhoid/enteric fever
2) septicemias
3) acute gastroenteritis

How well did you know this?

Not at all

Perfectly

what is the genus of salmonella? what type of bacteria is it? (gram, shape)

member of Enterobacteriaciae

gram-negative rod

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

what species does S. Typhi infect?

-only infects humans via food/water

How well did you know this?

Not at all

Perfectly

How does S. typhi survive phagocytic vacuoles?

enabled by Vi antigen of polysaccharide capsule

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

what does the SPI-1 (Salmonella pathogenicity island 1) encode for?

encodes genes for invasion

Type 3 secretion system (T3SS)

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

Salmonella T3SS delivers?

toxins that induce membrane ruffling by stimulating actin polymerization, and endocytosis

How well did you know this?

Not at all

Perfectly

what does SPI-2 (salmonella pathogenicity island 2) encode for?

encodes genes for intracellular survival

How well did you know this?

Not at all

Perfectly

what is endotoxin a component of? what does it cause?

lipid A component of LPS

causes fever and shock

How well did you know this?

Not at all

Perfectly

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 well did you know this?

Not at all

Perfectly

how do you treat S. typhi? (acute, chronic)

Acute: Fluoroquinolones, 3rd generation cephalosporin
Chronic carrier:
1) Ampicillin/Ciprofloxacin
2)cholecystectomy

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

are there vaccines for S. typhi? if so, what are they and what type?

Ty21a: live attenuated
ViCPS: capsular polysaccharide

How well did you know this?

Not at all

Perfectly

how is Salmonella cholerasuis spread? how many organisms are required for infection?

oral ingestion of contaminated swine

infectious dose: 1000 organisms

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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

How well did you know this?

Not at all

Perfectly

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