Klebsiella pneumoniae is an encapsulated gram-negative bacillus that frequently causes outbreaks of nosocomial infections in hospitalized patients. It can also afflict ambulatory persons and cause community-acquired invasive diseases—including pyogenic liver abscess, endophthalmitis, meningitis, empyema, lung abscess, and necrotizing fasciitis. The worldwide emergence of multidrug-resistant strains and hypervirulent strains of K. pneumoniae has become an increasing clinical challenge and public health concern. A new molecular diagnostic method, based on detection of the two genetic determinants of O1 lipopolysaccharides, has been developed by Dr. Chi-Tai Fang of National Taiwan University to rapidly and accurately identify hypervirulent K. pneumoniae strains. This study has been published in March on Journal of Clinical Microbiology, a distinguished journal of the American Society for Microbiology.
[Photo: Dr. Chi-Tai Fang, two students, Ms. Yun-Jui Shih and Ms. Cheng-Man Cheong, and their parents in 2011 College of Public Health Graduation Ceremony]
The research was conducted by Dr. Chi-Tai Fang, associate professor at the Institute of Epidemiology and Preventive Medicine, College of Public Health, National Taiwan University, Taipei, Taiwan, and two Master students, Ms. Yun-Jui Shih and Ms. Cheng-Man Cheong.
K. pneumoniae strains can be distinguished by their capsular polysaccharide (CPS) K-antigen types (77 serotypes) and lipopolysaccharide (LPS) O-antigen types (9 serotype). Strains with K1 capsular polysaccharide are extremely virulent, causing metastatic endophthalmitis, meningitis from pyogenic liver abscess. However, only 60 percent of strains causing pyogenic liver abscess are K1 strains. The remaining are of K2, K5, K20, K54, K57, and other K types. On the other hand, more than 90 percent of strains causing pyogenic liver abscess have O1 lipopolysaccharides. Therefore, O1 is a better marker for virulent K. pneumoniae strains capable of causing pyogenic liver abscess. However, there was a lack of simple and reliable method for detecting O1 in clinical and epidemiological samples, because K. pneumoniae O-serotyping is cumbersome and the reagents are not commercially available.
To develops a new molecular diagnostic method to quickly and accurately identify O1 K pneumoniae, Dr. Fang and his students sequenced the genetic determinants of LPS O-antigen from O1, O2a, O2ac, O3, O4, O5, O8, O9, and O12. They identified the two genetic determinants of O1 lipopolysaccharides. They then successfully develop PCR primers that detects the O1-specific genes. They further tested the sensitivity and specificity of the new molecular detection method against the O and K reference strains provided by World Health Organization Collaborative Center for Escherichia coli and Klebsiella at Statens Serum Institut (Copenhagen, Denmark). The sensitivity and specificity were found to be 100 percent and 100 percent, respectively.
Given the high accuracy and the great convenience, the new PCR detection method represents an important breakthrough in the molecular diagnosis of hypervirulent K. pneumoniae. This new technology provides a highly useful tool for the clinical and epidemiological investigations of K. pneumoniae and its associated diseases.