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salmonella bacteriology

-gram - rods
-seldom lactose fermenting
-oxidase negative
-urease negative
-H2S producing


salmonella pathogenesisxmk4o

1. enterocolitis
2. enteric fevers (typhoid)
3. septicemia
4. risk of reactive arthritis (Reiter's syndrome)


salmonella enterocolitis

-usually s. typhimurium, s enteritidis, s heidelberg
-bacteria invade gut wall (M cells) by fimbriae - immune containment
-bacteremia rare
-MC in children and nursing homes in US
-high infectious dose
-cause inflammation and diarrhea, nausea, vomiting


salmonella enteric fever

high infectious dose, invasion of gut wall - specifically peyer's patches of distal ileum = transport in macrophages (trojan horse) to lymphatics and major organs and causes macrophage apoptosis, bacteremia, toxemia
-protected from humoral immunity by Vi capsul


virulence factors salmonella

1. ipf operon enhances adhesion to M cells in Peyer's patches
2. Type 3 secretion system injects M cell, enhances bacterial translocation
3. SipB injected by Spi1 type 3 system causes macrophage apoptosis
4. Vi antigen: s. typhi capsule for immune evasion


what is the difference between shigella and salmonella?

shigella lower infectious dose and risk of HUS


salmonella enteric and typhoid fevers symptoms

-onset: fever, malaise, diffuse abdominal pain, constipation
-3-4 week progression: dry cough, stupor, delirium, intestinal hemorrhage, bowel perforation, myocarditis, death


what causes hemorrhage/perforation in salmonella enteric/typhoid fevers

necrosis of the infected peyer patches


what pathogens use macrophage as trojan horse?

salmonella, TB, cryptococcus, histoplasma


penetration of gut by salmonella resisted by what?

CFTR cystic fibrosis allele (heterozygotes)


host risk factors for salmonella

corticosteroids, other immunosuppressants, malignancy, diabetes, HIV


salmonella septicemia

-very rare in previously healthy adults
-underlying chronic disease like sickle cell predisposes


what are the most common sequelae to salmonella septicemia?

osteomyelitis, pneumonia, meningitis


salmonella diagnosis

1. enterocolitis: nonbloody diarrhea, fever, dehydration, culture from stool
2. typhoid: travel abroad, high fever, headache, tender abdomen, anorexia, sometimes rose spots (pink, blanchable, slightly raised), lethargy
3. septicemia: focal symptoms related to affected organ [bone (osteomyelitis), lung (pneumonia), meninges]


salmonella treatment

enterocolitis: self-limited
enteric fevers and septicemia: IV ceftriaxone or ciprofloxacin - drain focal abscesses


Yersinia enterocolitica and pseudotuberculosis bacteriology

-gram - oval rods
-lack yersinia pestis virulence factors (no plague)
-not lactose fermenting
-urease positive
-grows in cold
-motile at 25 C, non motile at 37


what does Yersinia enterocolitica and pseudotuberculosis cause?

foodborne gastroenteritis


Yersinia enterocolitica pathogenesis

high infectious dose
-penetration of mucosa occurs in ileum --> multiplication in Peyer patches (M cells) --> spread to local lymph nodes --> mesenteric lymphadenitis (false appendicitis)


Yersinia enterocolitica virulence factors

carried on chromosome and plasmid
1. pili and Inv adhesin enhance binding to M cells in Peyer's patches
2. CNF dermonecrotic toxin destroys tissue
3. Yop Type 3 secretion system injects proteins in macrophages (no phagocytosis = reduced inflammatory response)


what is there a risk for with Yersinia enterocolitica and pseudotuberculosis

reactive arthritis



similar to yersinia enterocolitica but rarer and seen with immunocompromised or liver disease
-may be associated with izumi fever in children (fever, rash, conjunctival injection, cervical lymphadenitis, inflammation of the lips and oral cavity, edema of hands and feet


Yersinia enterocolitica and pseudotuberculosis diagnosis

-exam: diarrhea, dehydration, false appendicitis
-lab: culture from stool or blood
grow well after cold-enrichment


how is pseudotuberculosis differentiated from enterocolitica?

pseudotuberculosis has fermentation of sorbitol and ornithine decarboxylase activity


listeria monocytogenes bacteriology

-small gram +
-facultative anerobe
-blue-green sheen on non-blood agar
-forms Ls and Vs
-grows well in cold
-tumbling motility by termperature-sensitive flagella
-beta hemolytic


what foods is listeria monocytogenes associated with?

unpasteurized dairy products, undercooked meat, raw veggies (cold food)


what does listeria cause?

gastroenteritis - usually in immunosuppressed and pregnant/fetus


what does listeria infection cause in pregnant women?

3rd trimester - escape GI and proliferate in the placenta
-causes preterm labor, abortion, stillbirth, intrauterine infection


what does listeria cause in the neonate?

-early onset sepsis and premature birth with abscesses and/or granulomas
-transmission from vagina during birth = late-onset meningitis with sepsis


listeria diagnosis on exam

previously healthy: watery diarrhea, fever, headache, cramps
pregnancy: fever, arthralgia, back pain, headache
immunocompromised: (think transplant!) CNS: mental status changes, seizures, cranial nerve deficits, strokelike hemiplegia, tremor, myoclonus, ataxia, brain abscess


listeria lab

gram stain: diphtheroids
culture: small, gray, beta-hemolytic colonies, motility (tumbling), sugar fermentation