Klebsiella pneumoniae

Klebsiella pneumoniae is a Gram-negative, non-motile, encapsulated, lactose-fermenting, facultative anaerobic, rod-shaped bacterium. It appears as a mucoid lactose fermenter on MacConkey agar. Although found in the normal flora of the mouth, skin, and intestines, it can cause destructive changes to human and animal lungs if aspirated, specifically to the alveoli, resulting in bloody, brownish or yellow colored jelly-like sputum. In the clinical setting, it is the most significant member of the genus Klebsiella of the Enterobacteriaceae. K. oxytoca and K. rhinoscleromatis have also been demonstrated in human clinical specimens. In recent years, Klebsiella species have become important pathogens in nosocomial infections. It naturally occurs in the soil, and about 30% of strains can fix nitrogen in anaerobic conditions. As a free-living diazotroph, its nitrogen-fixation system has been much-studied, and is of agricultural interest, as K. pneumoniae has been demonstrated to increase crop yields in agricultural conditions. It is closely related to K. oxytoca from which it is distinguished by being indole-negative and by its ability to grow on melezitose but not 3-hydroxybutyrate.

History The genus Klebsiella was named after the German microbiologist Edwin Klebs (1834–1913). It is also known as Friedlander's bacillum in honor of Carl Friedländer, a German pathologist, who proposed that this bacterium was the etiological factor for the pneumonia seen especially in immunocompromised individuals such as people with chronic diseases or alcoholics. Community-acquired pneumonia caused by Klebsiella pneumoniae may occasionally be called Friedländer's pneumonia.

Role in disease

Klebsiella pneumonia The most common condition caused by Klebsiella bacteria outside the hospital is pneumonia, typically in the form of bronchopneumonia and also bronchitis. These patients have an increased tendency to develop lung abscesses, cavitation, empyema, and pleural adhesions. Antibiotic resistance is highest in Asia. A study done in Turkey in 2016 revealed that bacteremia from Klebsiella has a death rate around 50%, even with antimicrobial therapy.

Pathophysiology It is typically due to aspiration and alcoholism may be a risk factor, though it is also commonly implicated in hospital-acquired urinary tract infections, and COPD (chronic obstructive pulmonary disease) individuals. In terms of the pathophysiology of Klebsiella pneumonia the neutrophil myeloperoxidase defense against K. pneumoniae is often seen. Oxidative inactivation of elastase is involved, while LBP helps transfer bacteria cell wall elements to the cells.

Signs and symptoms Individuals with Klebsiella pneumoniae tend to cough up a characteristic "currant jelly" sputum, as well as having fever, nausea, tachycardia, and vomiting. Klebsiella pneumoniae tends to affect people with underlying conditions, such as alcoholism.

Diagnosis In terms of the diagnosis of Klebsiella pneumoniae the following can be done to determine if the individual has this infection, with the addition of susceptibility testing to identify drug-resistant organisms:

Blood culture CBC Sputum (culture) Radiography (chest) CT scan

Treatment Treatment for Klebsiella pneumoniae is by antibiotics such as aminoglycosides, piperacillin/tazobactam, and cephalosporins, the choice depending upon antibiotic susceptibility testing, the person's health condition, medical history and severity of the disease.

Klebsiella possesses beta-lactamase giving it resistance to ampicillin. Many strains have acquired an extended-spectrum beta-lactamase with additional resistance to carbenicillin, amoxicillin, and ceftazidime. The bacteria remain susceptible to aminoglycosides and some cephalosporins, and varying degrees of inhibition of the beta-lactamase with clavulanic acid have been reported. Infections due to multidrug-resistant gram-negative pathogens in the ICU have invoked the re-emergence of colistin. However, colistin-resistant strains of K. pneumoniae have been reported in ICUs. In 2009, strains of K. pneumoniae with gene called New Delhi metallo-beta-lactamase ( NDM-1) that even gives resistance against intravenous antibiotic carbapenem, were discovered in India and Pakistan. Klebsiella cases in Taiwan have shown abnormal toxicity, causing liver abscesses in people with diabetes mellitus (DM); treatment consists of third generation cephalosporins.

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