Klebsiella is a genus of Gram-negative, oxidase-negative, rod-shaped bacteria, which is relatively commonly encountered in the healthcare environment. It has numerous species, including K. pneumoniae, K. aerogenes, and K. rhinoscleromatis ¹. Klebsiella may cause a range of infections, most commonly pneumonia (Klebsiella pneumonia), as well as rhinoscleroma (by K. rhinoscleromatis). The remainder of this article refers to Klebsiella pneumoniae.

Classical Klebsiella pneumoniae is a cause of pneumonia, urinary tract infection and bacteremia in those with impaired immunity or hospital exposure. More recently, hypervirulent strains emerged in Asia as a cause of liver abscess in healthy people. Hypervirulent strains have now spread globally and have increasingly developed multi-drug resistance. Bacteremia and metastatic infection increases mortality and morbidity ².

Pathology

Classical Klebsiella pneumoniae (cKp) is a ubiquitous opportunist gram negative organism and is an important cause of nosocomial pneumonia and bacteremia. Rates of gut colonization are increased in hospital patients and this is the likely reservoir for infection.

Hypervirulent Klebsiella pneumoniae (hvKp) commonly causes bacteremia and disseminated infection. Patients are typically younger and the infection is often acquired in the community. Diabetes is an important risk factor. Ventilator-associated infections are increasing in incidence.

Hypervirulence factors include hypermucoviscosity, altered capsule, colibactin toxin (damages DNA), multiple siderophores (which increase affinity for iron, thus promoting growth) and ability to form biofilms. Multi-drug resistance is an increasing problem.

Clinical presentation

CKp typically causes pneumonia, lung abscess, empyema, bacteremia or UTI. Non-specific features of infection include fever, nausea and abdominal pain.

HKp frequently disseminates and important sites of infection include ²:

CNS:

meningitis
brain abscess
epidural abscess

Eye:

endophthalmitis
uveitis

Respiratory:

pneumonia
empyema
septic emboli

Cardiovascular:

thrombosis and embolism
endocarditis
mycotic aneurysm

Musculoskeletal:

soft-tissue abscess
necrotizing fasciitis
osteomyelitis
septic arthritis

Abdominal:

abscess
cholangitis
peritonitis

Treatment and prognosis

Despite combination antibiotic therapy, mortality can exceed 35% for disseminated hKp. Septic shock, necrotizing gas-forming infection, persistent abscess or gastrointestinal fistula are poor prognostic indicators. 70% of cerebral and eye infections lead to permanent neurological disability or visual impairment.

Abscess drainage improves prognosis. Antibiotic regimes might include b-lactam or b-lactamase inhibitors, third-generation cephalosporins, fluoroquinolones, carbapenems or aminoglycosides. Endophthalmitis can be treated with intravitreal injection ².