Serratia

Snapshot

• A 56-year-old man is admitted to the hospital for appendicitis. During the appendectomy, he had a foley inserted which was removed successfully post-operatively. A few days after the procedure, the patient started experiencing fevers, chills, and pain with urination. A urinalysis revealed increased white blood cells, red blood cells, and bacteria. A urine culture grew a catalase-positive, weakly lactose fermenting gram-negative bacilli.

Introduction

• Classification 
  • Serratia marcescens
    • a catalase-positive, weakly lactose fermenting, and gram-negative bacillus
    • produces prodigiosin, a pale pink or dark red pigment 
  • clinical syndromes are often associated with recent instrumentation/procedure
    • urinary tract infection 
    • wound infections
    • pneumonia
    • endocarditis
    • meningitis
• Epidemiology
  • demographics
    • male > female
    • children > adults
  • risk factors
    • hospital admission
    • diabetes mellitus
    • kidney failure
    • chronic obstructive pulmonary disease
    • immunocompromised status
    • recent procedure at the site of infection
      • i.e., instrumentation of urinary tract or bronchoscopy
• Pathogenesis
  • the bacteria colonizes the respiratory and urinary tracts and causes nosocomial infections
• Prognosis
• Serratia meningitis and endocarditis have the highest mortality

Presentation

• Symptoms
  • fever and chills
  • shortness of breath
  • frequent urination
  • dysuria
• Physical exam
• suprapubic tenderness

Studies

• Urine dipstick
  • nitrite positive
  • leukocyte esterase positive
• Bacterial culture on EMB agar
  • lactose fermenters grow as purple or black colonies
• Making the diagnosis
• based on clinical presentation and laboratory studies

Differential

• E. coli urinary tract infection
  • distinguishing factors
    • no red pigment
• may not be associated with recent instrumentation

Treatment

• Management approach
  • Serratia is resistant to many antibiotics, including first-generation cephalosporins
  • final choice of antibiotics depends on the sensitivities of cultured bacteria
• Medical
  • 2nd generation or higher cephalosporins (cefoxitin, cefotaxime, and cefepime)
    • indication
      • all patients
  • fluoroquinolones   
    • indications
• all patients

Complications

• Septic shock