Salmonella and Shigella Flashcards by Hoi Wan

What is the O antigen?

The polysaccharide component of LPS

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What is the H antigen?

The flagellar antigen

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What is the K antigen?

A polysaccharide capsule component

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What is a serotype?

Strain differentiated through antibody recognition of antigens

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Salmonella, Shigella, and E. Coli all belong to what family?

Enterobacteriaciae

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Salmonella, shigella, and E coli–are they gram positive or negative? What morphology do they have?

Gram negative rods

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What are the three clinical syndromes related to salmonella?

Typhoid
Septicemias
Acute gastroenteritis

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What salmonella strain causes typhoid or enteric fever?

Salmonella Typhi

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What salmonella strain causes septicemias?

Salmonella cholerasuis

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What salmonella strain causes acute gastroenteritis?

Salmonella typhimurium/enteriditis

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What are the symptoms of typhoid fever?

bradycardia, rose spot, leukopenia, enlarged liver and spleen

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What is the incubation period for typhoid fever?

7-14 days

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Describe the pathogenesis of S Typhi

ingested through contaminated food/water
adhesins allow attachment to intestinal epithelium
S.Typhi is ingested by macrophages
Survives in macrophage phagocytic vacuoles through Vi antigen
Kills macrophage to moves through thoracic duct to blood, liver, spleen, and gall bladder.
Re-enters GI tract through gall bladder

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What are pathogenicity islands?

Areas of chromosome that has genes for virulence factors. These pathogenicity islands are acquired through horizontal gene transfer

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What is an identifying feature of pathogenicity islands?

High G+C content

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Salmonella pathogenicity island 1 encodes for:

invasion

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Salmonella pathogenicity Island 2 encodes for:

intracellular survival

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What is Type 3 secretion system?

Specialized form of secretion where a protein moves across the bacterial cytoplasmic and outer membrane AND host membrane through a needle injection

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What is delivered by the salmonella T3SS?

toxins that induce membrane ruffling by stimulating actin polymerization and endocytosis

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What would you use to treat S typhi?

Fluoroquinolones like Cipro

3rd generation cephalosporin (Ceftriaxone)

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How would you treat chronic carriers of S. Typhi?

Ampicillin/ciprofloxacin

2. Gall bladder removal

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Are vaccines available for S Typhi?

yes, Oral attenuated and Vicapsular polysaccharide vaccine

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What is the source of Salmonella cholerasuis?

Swine, can be transferred via contaminated food

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What is an infectious dose of aslmonella cholerasuis?

1000 organisms

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What is the incubation period for S. Cholerasuis?

6-72 hours. Short.

What are the symptoms for salmonella cholerasuis?

high fever and bacteremia after gastroenteritis

What is the most common salmonella infection in the US?

Salmonella enteriditis and salmonella typhimurium

What are the symptoms are S enteriditis and S typhimurium?

diarrheal disease mostly confined to GI tract

What is the incubation period of salmonella typhimurium?

8-48 hrs after consumption

What is responsible for many of the symptoms of S. Typhimurium?

LPS release during invasion of epithelial cells of the intestines

What sort of secretion system is used by the S typhimurium?

T3SS

Does salmonella ferment lactose

Are salmonella strains motile?

Yes. Shigella is not motile

Can salmonella produce H2S?

Yes. DIagnostic. Produces a black precipitate.

Is salmonella positive for urease or indole?

No. Negative for both. In contrast, E coli is positive for indole.

Shigella-How is it spread?

Food, fingers, feces, and flies (4Fs)

Which form of shigella is most common in the developing world?

Shigella dysenteriae

Which form of shigella is most common in the US?

Shigella Sonnei

Which form of shigella is most common in the indian subcontinent?

Shigella Boydii

What are the symptoms of shigella?

bloody diarrhea, fever, and abdominal cramps

What is the bacterial load necessary for Shigella infection?

100 bugs. Because it is highly tolerant to acidity of the stomach

Describe in brief the pathogenesis of shigella

``` Invasion of intestinal epithelial cells Uptake by macrophages through T3SS Escape into the cytoplasm through T3SS Induced apoptosis of macrophages IL-1 and TNF released ```

Describe the shiga toxin

Exotoxin with A and B subunits. A subunit inhibits 60S ribosomal RNA. Subunit B binds receptor on intestinal cells

How can you diagnose shigella?

Culture from feces. No gas with only glucose fermentation. lactose non fermenters. No H2S. Nonmotile.

Which antigens does shigella have?

O antigens only, no H antigen

Is shigella positive/negative for indole and urease?

negative for both

How do you treat shigella?

Fluid and electrolyte replacement, may be antibiotics in severe cases

What are the alternative hosts of shigella?

None. Only carried in humans

Is there an effective vaccine for shigella?

No.

What function do nonpathogenic E coli have in our normal microflora?

Synthesis of vitamin K and protection against other pathogens

How are strains of E. Coli categorized?

As either shiga toxin producing (STEC) or diarrheagenic (everything else)

What is the main serogroup type for Enterohemorrhagic E.Coli (Shiga toxin E coli)?

O157:H7

How can E Coli (hemorrhagic and shiga toxin producing) be transmitted?

Food, petting zoos, personal contact

What are the symptoms of EHEC and STEC?

abdominal pain, bloody diarrhea, hemolytic uremic syndrome, renal failure

Do EHEC and STEC cause bacteremia?

No. remain extracellular though.

Describe the pathogenicity pathway of EHEC and STEC

1. Weak pili attachment 2. T3SS creates attachment lesions 3. Tir is secreted allowing for strong E coli attachment 4. Tir binds to Intimin on surface of E coli 5. Proteins also recruit host cell actin, causing a raised structure and lesions 6. Microvilli are destroyed 7. Shiga like toxin is produced preventing protein synthesis causing hemolytic uremic syndrome

What is hemolysin?

Protein produced often by E coli strains that cause meningitis. It forms a pore that inserts into the host cell membranes

What are the diarrheagenic E coli strains?

``` eneteropathogenic E coli (EPEC) Enterotoxigenic E Coli (ETEC) Enteroaggregative E coli (EAEC) Enteroinvasive E Coli (EIEC) Diffuse adhering E Coli (DAEC) ```

Hemolytic uremic syndrome is caused by what?

shiga-like toxin. Results in hemolytic anemia, thrombocytopenia, and destruction of red blood cells

Can EHEC cause bacteremia?

T3SS and effectors of Ecoli are endoed by which pathogenicity island?

LEE-locus of enterocyte effacement

How does Shiga-like toxin work?

Subunit B mediates toxin uptake. Subunit A interferes with protein synthesis of 28S rRNA

Why are cows unaffected by EHEC?

Shiga toxin binds to Gb3/CD77 on host cells. This is not present on cattle.

Does EHEC have a capsule?

Yes

What is unique about enteropathogenic E Coli's method of adherence?

Adherence is through the bundle forming pili.

What is unique about the secretions and adherence of Enterotoxigenic E coli? What is its colloquial name?

Produces ST(heat stable) and LT(heat labile) toxins. Also has fimbriae for colonization of small intestine. Commonly called traveller's diarrhea.

How does ETEC's heat labile toxin work?

Similar to cholera toxin, it targets adenylate cyclase to increase cAMP levels, PKA, and secretion of water and electrolytes into the gut

How does ETEC's heat stable toxin (ST) work?

Stimulates membrane bound guanylate cyclase, increasing intracellular cyclic GMP also causing water and electrolyte excretion

What does enteroaggregative E coli secrete (EAEC)?

Hemolysins and Enteroaggregative stable toxin (EAST) and plasmid-encoded toxin (PET)

How does enteroinvasive E coli attach to cells? What toxins does it secrete?

Attaches through adhesins. Does not produce toxins

How can you diagnose E coli?

Lactose fermenting.

How can you diagnose EHEC?

O157:H7 serotype is sorbitol negative. Cannot grow on that medium. Can also perform toxin analysis. stx1 and stx2, eae and hlyA. Also, serotyping and DNA analysis

What population does diffuse adhering E coli affect?

Older children in developing countries

Which E coli strains produce shiga like toxin?

EHEC,

Which E coli strains produce hemolysin

EHEC and EAEC

Which E coli strains produce attaching and effacing lesions?

EHEC and EPEC

Which type of E coli is only spread person to person?

EPEC

How do you treat EAEC?

fluoroquinolones

How do you treat ETEC?

Loperamide, fluoroquiolones, azithromycin, or rifaximin

How would you treat EPEC and EHEC?

Supportive care. May use antibiotics in severe cases