pneumoniae infections. Therefore, differences among strains in the resistance to complement and/or to antimicrobial peptides Emricasan mediated killing may account for differences in virulence [11, 15, 39]. In addition, a wealth of evidence clearly indicates the importance of the inflammatory responses in clearing K. pneumoniae infection and have provided substantial evidence for the protective role of a Th1-mediated response [40–42]. Thus, differences in the

induction of inflammatory responses among strains may also underline in vivo eFT508 molecular weight behavior. In summary the available data support the notion that CPS-dependent cytotoxicity, together with other bacterially triggered events, is required for virulence. Further studies will attempt to elucidate SC79 these novel virulence mechanisms, which may differ among capsulated strains, in order to achieve a comprehensive understanding of K. pneumoniae pathogenesis. Conclusion This study allocates a novel role to K. pneumoniae capsule, i.e. the induction of cytotoxicity during the infection of lung epithelial cells. This effect, which has been analysed

by using four different approaches, is not capsule serotype dependent, does require the presence of live bacteria, and does not seem to be directly related to bacterial adhesion. Host cell cytotoxicity could be associated with virulence. However, strains expressing different capsule levels were not equally virulent, suggesting that additional bacterial elements could be involved in Klebsiella virulence. Acknowledgements Salary support to V.C. from Govern Balear is gratefully acknowledged.

J.G. is a recipient of a Contrato de Investigador “”Miguel Servet”" from Instituto de Salud Carlos III. This work has been funded by grants from FIS (CP05/00027 to J.G. and PI06/1629 to J.A.B.). Ciberes is an initiative from Instituto de Salud Carlos III, Spain. The authors sincerely thank Dr. Christian selleck chemical Frank for critical reading of the manuscript. References 1. Carpenter JL:Klebsiella pulmonary infections: occurrence at one medical center and review. Rev Infect Dis 1990, 12:672–682.PubMed 2. Gupta A: Hospital-acquired infections in the neonatal intensive care unit- Klebsiella pneumoniae. Semin Perinatol 2002, 26:340–345.CrossRefPubMed 3. Jarvis WR, Munn VP, Highsmith AK, Culver DH, Hughes JM: The epidemiology of nosocomial infections caused by Klebsiella pneumoniae. Infect Control 1985, 6:68–74.PubMed 4. Bartlett JG, O’Keefe P, Tally FP, Louie TJ, Gorbach SL: Bacteriology of hospital-acquired pneumonia. Arch Intern Med 1986, 146:868–871.CrossRefPubMed 5. Straus DC: Production of an extracellular toxic complex by various strains of Klebsiella pneumoniae. Infect Immun 1987, 55:44–48.PubMed 6. Strauss E: A symphony of bacterial voices [news]. Science 1999, 284:1302–1304.CrossRefPubMed 7.