Enterobacteriaceae

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
Organism	Microbiology	Associated Conditions	Treatment
E. coli	Reservoirgastrointestinal and urinary tractTransmissionfecal-oralurethral ascensioncatheteraspirationLabslactose fermentingβ-hemolyticPropertiesenterotoxins heat labile, which increases cAMPheat stable, which increases cGMPfimbriaeK-antigen (capsule)H-antigen (flagella)	Diarrheaenterotoxigenic (ETEC)causes traveler’s diarrhea, which is a watery diarrheaenterohemorrhagic (EHEC)causes bloody diarrheasecretes Shiga-like toxin, which can lead to hemorrhagic colitishemolytic uremic syndromeassociated with E. coli O157:H7enteroinvasive (EIEC)causes bloody diarrhea (with pus and fever)Newborn meningitisirritabilitybulging fontanelleUrinary tract infection (UTI)dysuria, urinary frequency, and urinary urgency	DiarrheaETECsupportive treatmentEHECsupportive treatmentmonitoring of hemolytic uremic syndrome, which is also managed with supportive treatmentEIECsupportiveNewborn meningitisampicillinthird-generation cephalosporin with gentamicinin ampicillin-resistant strainsUrinary tract infectionfluoroquinolone, trimethoprim/sulfamethoxazole (TMP-SMX), or nitrofurantoin
K. pneumoniae	Labslactose fermenterPropertieshas a capsule and is nonmotile	Pneumoniacurrant-jelly sputumtypically seen in patients with underlying lung disease or alcohol use disorderUTIdysuria, urinary frequency, and urinary urgencytypically hospital-acquired	Typically with a 3rd generation cephalosporin
P. mirabilis	Labssplits urea into NH₃ and CO₂indole negativenon-lactose fermentingPropertiesurease positivemotile	UTIdysuria, urinary frequency, and urinary urgencyurine pH is basic (elevated) due to producing NH3Sepsis	TMP-SMXAmpicillin
S. dysenteriae	ReservoirhumansTransmissionfecal-oralLabsnon-H2S producingnon-lactose fermentingnever a part of the normal intestinal floraPropertiesnon-motileinvades the small intestine but not the lamina propriaproduces Shiga toxinacts on the 60s ribosomal subunit of the intestinal epithelia, impairing protein synthesis and causing intestinal damage	Diarrheabloody with blood and pus (similar to EHEC)	FluoroquinolonesAzithromycinCeftriaxone
S. typhi	ReservoirhumansTransmissionfecal-oralLabsH2Snon-lactose fermentingPropertiesmotilecapsulepatients with an absent or non-functioning spleen are at high risk of infectionfacultative intracellularcan live in macrophages and in the gallbladder	Typhoid feverfeverhepatosplenomegalyrose abdominal spots abdominal painOsteomyelitisseen in patients with sickle cell disease	CeftriaxoneMeropenemFluoroquinolone

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