Klebsiella Pneumoniae Characteristics

Klebsiella pneumoniae

• Gram-negative rods with a large polysaccharide capsule
• Mucoid, lactose-fermenting colonies on MacConkey agar
• Oxidase negative
• Reservoir: human colon and upper respiratory tract
• Transmission: endogenous
• Pathogenesis:
  • Capsule impairs phagocytosis
  • Endotoxin causes fever, inflammation, and shock (septicemia)

Diseases Caused by Klebsiella pneumoniae

• Pneumonia:
  • Community-acquired, most often in older men with chronic lung disease, alcoholism, or diabetes
  • Endogenous, assumed to reach lungs by inhalation of respiratory droplets from the upper respiratory tract
  • Frequent abscesses make it hard to treat; high fatality rate (40-60%)
  • Sputum is thick and bloody (currant jelly) but not foul-smelling
• Urinary tract infection:
  • Catheter-related (nosocomial) from fecal contamination of catheters
• Septicemia:
  • In immunocompromised patients, may originate from bowel defect or invasion of IV line
• Klebsiella pneumoniae is the second most common gram-negative pathogen associated with various infections, including:
  • Urinary tract infection (UTI)
  • Pneumonia
  • Intra-abdominal infection
  • Bloodstream infection (BSI)
  • Meningitis
  • Pyogenic liver abscess (PLA)

Rhinitis and Rhinoscleroma

• Rhinitis:
  • Infection of the nasal epithelium with K. ozaenae can lead to atrophic rhinitis
  • Characterized by focal areas of squamous metaplasia, wasting of the mucous gland, and impairment of mucous secretion
  • Nasal mucosa looks dry, glazed, and shiny
• Rhinoscleroma:
  • Caused by K. rhinoscleromatis
  • Begins with symptoms resembling an ordinary cold
  • Granulomatous inflammation of the nasal airway leads to the development of tumor-like submucosal masses
  • Masses can become large and may close the nares and cause the face to swell

Enterobacter

• Distinguishing features:
  • Many features in common with Klebsiella, but variant
  • Motility
  • Colonies are slightly mucoid
• Reservoir: soil and water, occasionally found in human feces and the respiratory tract
• Disease(s): opportunistic infections of hospital patients, notably of the urinary tract, and an important cause of bacteremia
• Pathogenesis: poorly understood
• Treatment: highly resistant to penicillins and many cephalosporins

Proteus and Related Genera

• Proteus, Providencia, and Morganella
• Distinguishing features:
  • Morphological variation, but in agar-grown cultures, the microscopical appearance is much like that of other coliform bacteria
  • Strains of Proteus spp. can be differentiated from Morganella spp. and Providencia spp. by their ability to swarm on suitable agar media
• Disease(s):
  • Urinary tract infection in children and bacteremia
  • Other strains of Proteus and Providencia are isolated from hospital patients, especially in elderly men following surgery or instrumentation
  • Complications of urinary tract surgery, septicaemia, and outbreaks of septicaemia, often with meningitis, may occur among newborns in hospitals

Antibiotic Resistance

• Carbapenemase-producing Enterobacteriaceae (CPE) are a major concern
• blaOXA-48 is the most prevalent carbapenemase gene
• Colistin resistance is a growing concern, especially among Enterobacteriaceae isolated from clinical samples
• The emergence of multidrug-resistant (MDR) strains of Enterobacteriaceae and the lack of new antibiotics are worrisome prospects for global health.