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.
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Epidemiology
Classical Klebsiella pneumoniae is a cause of pneumonia, urinary tract infection and bacteremia in those with impaired immunity or hospital exposure. However, hypervirulent strains, which initially emerged in Asia before spreading globally, have been identified as a cause of hepatic abscess (among other manifestations) in healthy people, and are associated with multi-drug resistance. Bacteremia and metastatic infection increases mortality and morbidity 2.
Clinical presentation
Classical Klebsiella pneumoniae typically causes pneumonia (Klebsiella pneumonia), lung abscess, empyema, bacteremia or urinary tract infection. Non-specific features of infection include fever, nausea and abdominal pain.
Hypervirulent Klebsiella pneumoniae frequently disseminates and important sites of infection include 2:
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CNS
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ocular
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respiratory
septic emboli
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cardiovascular
thrombosis and embolism
mycotic aneurysm
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musculoskeletal
soft-tissue abscess
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abdominal
abscess (especially hepatic abscess)
Pathology
Classical Klebsiella pneumoniae 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 commonly causes bacteremia and disseminated infection. Patients are typically younger and the infection is often acquired in the community. Diabetes mellitus 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.
Treatment and prognosis
Antibiotic regimens might include b-lactam or beta-lactamase inhibitors, third-generation cephalosporins, fluoroquinolones, carbapenems or aminoglycosides. Endophthalmitis can be treated with intravitreal injection 2. Abscess drainage improves prognosis.
Despite combination antibiotic therapy, mortality can exceed 35% for disseminated hypervirulent Klebsiella pneumoniae. 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.
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