Salmonella, Shigella Campylobacter, Helicobacter, Yersinia Flashcards
What is a way that many people have been contracting Salmonella recently?
Backyard poultry flocks
What two organisms cause the most foodborne outbreaks?
Salmonella and Campylobacter
Which species of Salmonella has Vi capsule?
S. Typhi
What is the clinical presentation of Non-typhoid Salmonella (NTS)?
Typical gastroenteritis
Diarrhea
Caused by many serotypes
What is the clinical presentation of typhoid Salmonella?
Systemic syndrome (malaise, headache, cough, etc.) Enteric fever Rose spots Hepatosplenomegaly Caused by S. Typhi and S. parathyphi
How do you treat Typhoid v. non-Typhoid Salmonella?
Typhoid - antibiotics
Non-typhoid - no antibiotics
What are the reservoirs for Typhoid v. non-Typhoid Salmonella?
Typhoid - only humans
Non-typhoid - animals
What is the mechanism by which people are carriers of S. Typhi?
S. typhi gets associated with gall stones (biofilm)
Can have asymptomatic excretion from gallbladder colonization
What is a major complication of S. Typhi infection?
Intestinal hemorrhage and perforation
What are the virulence factors of Salmonella?
Pathogenicity islands
Two Type III secretion systems:
- One allows bacteria into cell (affects actin)
- Second ejects effectors into cytosol and prevents lysosomal fusion
Can then multiply in vacuole
How does host response differ from Typhoidal v. non-typhoidal salmonella?
Typhoidal - minimal intestinal inflammation, not many neutrophils
Non-typhoidal - lots of inflammation, lots of neutrophils
What is the purpose of the Vi capsule in S. Typhi?
Prevents immune system from recognizing TLR4 (with capsule, TLR4 cannot bind LPS on bacterial surface)
How does Typhoidal Salmonella prevent inflammatory response?
Capsule, evades TLR4
Downregulation of flagellin gene, evades TLR5
How is the inflammation produced in non-typhoidal salmonella beneficial?
Expresses Salmochelin and can use tetrathionate
What is the mechanism of salmochelin?
In response to inflammation, host produces lipocalin, that binds siderophores produced by other enteric bacteria like E. Coli. Siderophores bring iron to the bacteria, so lipocalin binding to siderophores = no iron. Salmonella produces salmochelin (it’s own siderophore) that cannot be bound by lipocalin, so more iron for Salmonella = advantage over other gut microbes.
What is the morphology of Salmonella?
Gram neg rod
What is the morphology of Shigella?
Gram neg rod
What is the most common Shigella species in the US?
Shigella sonnei
What is the most common Shigella species worldwide?
Shigella flexneri
What is the reservoir for Shigella?
Humans only (no animal reservoir), transmitted person to person
Is the infectious dose of Shigella large or small?
Very small! Similar to EHEC
What are characteristics of dysentery?
Scanty stools of blood and mucus
Tenesmus
Abdominal cramps
Many fecal leukocytes on microscopy
What are major complications of Shigella?
Severe Colitis
Persistent diarrhea and dehydration
Rectal prolapse
Reactive arthritis
Does Salmonella affect large or small bowel?
Small
Does Shigella affect large or small bowel?
Large
What is the pathogenesis of Shigella?
Invades M cells using Type III secretion system
Propel from basolateral side (unique) into cytoplasm, rockets through lateral membranes from one cell through to the other
Does this using nucleation of the actin cytoskeleton behind one pole.
What are the virulence factors of Shigella?
Virulence plasmid containing genes for Type III secretion system, effectors, enterotoxins
What makes Shigella dysenteriae the most virulent and infectious?
Secretes Shiga toxin
What other organism expresses Shiga toxin besides Shigella dysenteriae?
EHEC (Enterohemorrhagic E. Coli)
What are the two species of Yersinia that cause gastroenteritis?
Y. enterocolitica
Y. pseudotuberculosis
(NOT Y. pestis)
What is the pathogenesis of Yersinia?
Enters M cells
Injects effectors via Type III secretion system (resists phagocytosis, downregulates inflammation)
Colonizes Peyers patches and mesenteric lymph nodes
What food is Campylobacter associated with?
Raw milk
How do Campylobacter appear on culture?
Curved gram negative (sea gull)
Microaerophilic
Flagellated
What is the clinical presentation of Campylobacter?
Causes inflammatory diarrhea much like Non typhoidal salmonella and Shigella
When should antibiotics be used for Campylobacter?
Very early in the infection, otherwise ineffective
What is a complication of Campylobacter?
Guillain-Barre syndrome
What is the pathogenesis of Guillain-Barre syndrome?
Lipooligosaccharides (LOS) on outside of Campylobacter look similar to nerve gangliosides. Immune system makes antibodies to the LOS, end up cross-reacting with the gangliosides
What makes Helicobacter pylori unique?
Pathogen of the stomach
What is the clinical presentation of H. pylori?
Can by asymptomatic!
Gastritis
Duodenal Ulcers
Gastric carcinoma
What is the key virulence factor of H. pylori?
Urease
Allows H. pylori to neutralize low pH of stomach and then attach and invade gastric mucosa.
What is the treatment for H. pylori?
Triple drug therapy
