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Snapshot
  • A 27-year-old man presents to the urgent care clinic for diarrhea. His symptoms began approximately 2 days ago. His symptoms are associated with abdominal pain, malaise, and fatigue. He denies the presence of blood or pus in the stool. He states he returned to the United States 1 week ago from his trip to Ecuador. Physical examination is notable for mild abdominal tenderness upon palpation but there is no appreciable hepatosplenomegaly or skin changes. He is recommended symptomatic treatment. (Traveler's diarrhea by ETEC)
Introduction
  • Classification
    • gram-negative bacteria
      • Escherichia coli
      • Klebsiella
      • Proteus mirabilis
      • Enterobacter
      • Serratia
      • Shigella
      • Salmonella
Enterobacteriaceae
 
Enterobacteriaceae
Organism
Microbiology
Associated Conditions Treatment
E. coli
  • Reservoir
    • gastrointestinal and urinary tract
  • Transmission
    • fecal-oral
    • urethral ascension
    • catheter
    • aspiration
  • Labs
    • lactose fermenting
    • β-hemolytic
  • Properties
    • enterotoxins 
      • heat labile, which increases cAMP
      • heat stable, which increases cGMP
    • fimbriae
    • K-antigen (capsule)
    • H-antigen (flagella)
  • Diarrhea
    • enterotoxigenic (ETEC)
      • causes traveler's diarrhea, which is a watery diarrhea
    • enterohemorrhagic (EHEC)
      • causes bloody diarrhea
      • secretes Shiga-like toxin, which can lead to
        • hemorrhagic colitis
        • hemolytic uremic syndrome
          • associated with E. coli O157:H7
    • enteroinvasive (EIEC)
      • causes bloody diarrhea (with pus and fever)
  • Newborn meningitis
    • irritability
    • bulging fontanelle
  • Urinary tract infection (UTI)
    • dysuria, urinary frequency, and urinary urgency
  • Diarrhea
    • ETEC
      • supportive treatment
    • EHEC
      • supportive treatment
      • monitoring of hemolytic uremic syndrome, which is also managed with supportive treatment
    • EIEC
      • supportive
  • Newborn meningitis
    • ampicillin
    • third-generation cephalosporin with gentamicin
      • in ampicillin-resistant strains
  • Urinary tract infection
    • fluoroquinolone, trimethoprim/sulfamethoxazole (TMP-SMX), or nitrofurantoin
K. pneumoniae
  • Labs
    • lactose fermenter
  • Properties
    • has a capsule and is nonmotile
  • Pneumonia
    • currant-jelly sputum
      • typically seen in patients with underlying lung disease or alcohol use disorder
  • UTI
    • dysuria, urinary frequency, and urinary urgency
    • typically hospital-acquired
  • Typically with a 3rd generation cephalosporin
P. mirabilis
  • Labs
    • splits urea into NH3 and CO2
    • indole negative
    • non-lactose fermenting
  • Properties
    • urease positive
    • motile
  • UTI
    • dysuria, urinary frequency, and urinary urgency
    • urine pH is basic (elevated) due to producing NH3
  • Sepsis
  • TMP-SMX
  • Ampicillin
S. dysenteriae
  • Reservoir
    • humans
  • Transmission
    • fecal-oral
  • Labs
    • non-H2S producing
    • non-lactose fermenting
    • never a part of the normal intestinal flora
  • Properties
    • non-motile
    • invades the small intestine but not the lamina propria
    • produces Shiga toxin
      • acts on the 60s ribosomal subunit of the intestinal epithelia, impairing protein synthesis and causing intestinal damage
  •  Diarrhea
    • bloody with blood and pus (similar to EHEC)
  • Fluoroquinolones
  • Azithromycin
  • Ceftriaxone
S. typhi
  • Reservoir
    • humans
  • Transmission
    • fecal-oral
  • Labs
    • H2S
    • non-lactose fermenting
  • Properties
    • motile
    • capsule
      • patients with an absent or non-functioning spleen are at high risk of infection
    • facultative intracellular
      • can live in macrophages and in the gallbladder
  • Typhoid fever
    • fever
    • hepatosplenomegaly
    • rose abdominal spots 
    • abdominal pain
  • Osteomyelitis
    • seen in patients with sickle cell disease
  • Ceftriaxone
  • Meropenem
  • Fluoroquinolone
 
 

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