Hypermucoviscosity: An Extremely Sticky Phenotype of Klebsiella pneumoniae Associated with Emerging Destructive Tissue Abscess Syndrome

Klebsiella pneumoniae is an opportunis-tic pathogen found in the environment and on mammalian mucosal surfaces. K. pneumoniae has been characterized as a community-acquired pulmonary pathogen since it was discovered 1100 years ago. The classic clinical symptoms are represented by rapid onset, high fever, and he-moptysis (currant jelly–like sputum), in conjunction with the radiographic findings of bulging interlobar fissures and cav-itations [1]. The incidence of community-acquired K. pneumoniae has apparently decreased [2, 3], whereas the mortality rate for pneumonia due to Klebsiella species remains fairly high as a result of the underlying disease that tends to be present in affected patients [2]. In Western countries , most K. pneumoniae infections occur in the lungs and urinary tract. At the same time, however, K. pneumoniae has been found to be the leading cause of liver abscess in Taiwan [4]. K. pneumoniae–medi-ated liver abscess occurred almost exclusively in patients from Taiwan, followed by Singapore and Korea, in reports from 1990 to 1999 [2, 5]. A few cases of liver abscess due to K. pneumoniae have also recently been reported from Hong Kong, Thailand, and Japan [2]. During the 1990s and early 2000s, 1900 patients with liver abscess due to K. pneumoniae were reported from East and Southeast Asian countries, whereas only ∼50 reports of such cases were reported from countries outside of East and Southeast Asia in this same period [2, 6, 7]. It has also been shown that patients with diabetes mellitus in Taiwan are more susceptible to K. pneu-moniae infection than are those without diabetes mellitus [4]. Emerging in Taiwan are K. pneumoniae infections in addition to liver abscess that involve destructive clinical syndromes, such as metastatic meningitis and endophthalmitis, osteo-myelitis, and brain abscess [4, 8]. Despite the production of possible virulence factors , such as polysaccharide capsule, different adhesins, lipopolysaccharide, and iron-scavenging proteins [9], the patho-genicity of K. pneumoniae has not been completely elucidated. In this issue of Clinical Infectious Disease , Yu et al. [10], based in Taiwan, investigated the possible correlation between the incidence of bacteremia due to K. pneumoniae and the frequency of putative pathogenic genes, such as kfu, rmpA, and magA, and the hypermucoviscosity phenotype in clinical isolates of K. pneumon-iae from a total of 151 clinical cases at the 2 largest medical centers in southern Tai-The results demonstrated that nosocomial strains are significantly less prone to form abscesses than are community-acquired K. pneumoniae and that …