49. Salmonella and Shigella Flashcards Preview

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Flashcards in 49. Salmonella and Shigella Deck (19):
1

what is the real species of S.typhinurium?

Salmonella enterica, subspecies enterica, serovar Typhinurium

2

typhoid vs NTS disease?

- Typhoid: systemic syndrome, enteric fever (life threatening
- NTS: diarrhea (inflammatory)

3

Typhoid vs NTS - which can you treat w/Abx? which has vaccines?

Typhoid for both

4

NTS epidemiology?

- infections assoc w/poultry eggs, and dairy
- raw meat, fruits, veggies
- contaminated prep area
- animal hosts
- infectious dose is low
- self-limiting infections
- carried asymptomatically by lots of vertebrate species
- some NTS in kids

5

NTS disease?

- gastroenteritis (“inflammatory enteritis”)
- watery diarrhea: blood, pus, and mucous
- abd pain, fever
- immunocompromised hosts: bacteremia and systemic suppurative foci (bone, lung, meninges, etc)

6

NTS tx?

- antidiarrheals
- NO ABX

7

Typhoid Salmonella Epi?

- adapted to cause disease in humans only
- world health problem
- ingestion of contaminated food/water
- asymptomatic excretion from gallbladder colonization chronic carriers (gallstones and bile induced biofilm formation may be impt)

8

Typhoid salmonella disease?

- “typhoid fever” = enteric fever
- generalized systemic infection of the reticuloendothelial system
- No diarrhea
- 5-21 days inc period
- malaise, headache, cough, sore throat, constipation, muscle aches, CNS abnormalities
- febrile and ill-appearing
- rose spots, hepatosplenomegaly, abdominal tenderness
- 10-30% mortality untreated (1% treated)
- can lead to pna, meningitis, or intestinal perforation (intestinal hemorrhage is the most common cause of death)

9

typhoid salmonella tx and vaccine?

- remember to think of typhoid fever in febrile pts who have traveled to developing areas as problem when undiagnosed early
- FQ (ciprofloxacin)
- S.enterica MDR to many first line Abx (ie ampicillin, chloramphenicol, TMP-SMX)
- live attenuated oral vaccine (Ty21a)
- Vi capsular polysaccharide (parenteral)
- no vaccine for pts

10

salmonella pathogenesis?

- all salmonella are invasive (mucosal invasion)
- bacterium adheres to small bowel mucosa
-via T3SS, internalized into M cells and enterocytes (cell membrane disrupted transiently to engulf organism, has effects on actin dynamics causing cytoskel alterations)
- 2nd T3SS to prevent lysosomal fusion – multiplies w/in vacuole
- bacteria escape and infect others
- cause inflammation: Typhoidal involves minimal inflammation and neutrophil transmigration w/restrained immune response while NTS causes significant inflammation and neutrophil recruitment which may contain the infection
- inflammation re: T3SS-1 creating inflammasome, LPS binding TLR4, and Flagella binding TLR5
**Inflammation induced by salmonella confers competitive advantage in the intestine:
- host releases antimicrobial peptide lipocalin-2
- lipocalin binds enterobactin (siderophore produced by enteric bacteria)
- salmonella produces salmchelin that is not bound by lipocalin
- thus salmonella has an advantage over other gut microbes (gets the iron it wants)
- also use of tetrathionate for respiration

11

salmonella virulence?

- T3SS encoded on PAIs (pathogenicity islands)
- regulators
- adherence fimbriae
- salmochelin expression - tetrathionate utilization (NTS only)


S.typhi only:
- Vi antigen: capsule that reduces inflammatory response by evading TLR4
- altered flagellin gene regulation evades TLR5
- genome degradation

12

Shigella microbiology?

- GNR
- non-motile
- closely related to EIEC
- enterobacteriaceae

13

most common shigella in US?

S.sonnei - traveler's diarrhea

14

most common shigella in the world?

S. flexneri - traveler's diarrhea

15

most severe shigella?

S. dysenteriae

- Most severe – more virulent and infectious
- explosive outbreaks and epidemics
- all age groups
- high attack rates

16

shigella epidemiology?

- humans are only reservoir
- not usu chronic carriers
- person-person spread
- low inoculum thus institutional outbreaks

17

shigella virulence?

Virulence plasmid:
- T3SS (invasion)
- effectors
- enterotoxins

Avl = antivirulence locus that is lost


S. dysenteriae has shiga toxin that leaves 28S rRNA

18

shigella disease?

- dysentery (freq small volume stools w/blood & mucus)
- strains at the stool (tenesmus)
- inflammatory diarrhea w/cramps, fever, malaise
- Complications: colitis (can cause hemorrhage), persistent diarrhea and dehydration, protein loss, malnutrition and cognitive defects, rectal prolapse, intestinal perforation and bacteremia are rare
- can lead to reactive arthritis (Reiter’s syndrome) (arthritis, urethritis, conjunctivitis – autoimmune)


S. dysenteriae: - Severe colitis
- neurologic complications
- HUS
- high mortality

19

shigella dx and tx?

- blood, pus, and heavy mucus in the stool

- Abx is usually effective (unlike salmonella diarrhea)
- TMP/SMX most commonly used
- watch for complications
- maintain hydration
- pay attention to epidemiology
- no vaccine

S.dysenteriae has MDR strains!