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Infection and Immunity, July 2007, p. 3594-3603, Vol. 75, No. 7
0019-9567/07/$08.00+0     doi:10.1128/IAI.01945-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

The Neisseria meningitidis Capsule Is Important for Intracellular Survival in Human Cells{triangledown} ,{dagger}

Maria Rita Spinosa,{ddagger} Cinzia Progida,{ddagger} Adelfia Talà, Laura Cogli, Pietro Alifano,* and Cecilia Bucci*

Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, Università degli Studi del Salento, Via Monteroni, 73100 Lecce, Italy

Received 12 December 2006/ Returned for modification 18 January 2007/ Accepted 18 April 2007

While much data exist in the literature about how Neisseria meningitidis adheres to and invades human cells, its behavior inside the host cell is largely unknown. One of the essential meningococcal attributes for pathogenesis is the polysaccharide capsule, which has been shown to be important for bacterial survival in extracellular fluids. To investigate the role of the meningococcal capsule in intracellular survival, we used B1940, a serogroup B strain, and its isogenic derivatives, which lack either the capsule or both the capsule and the lipooligosaccharide outer core, to infect human phagocytic and nonphagocytic cells and monitor invasion and intracellular growth. Our data indicate that the capsule, which negatively affects bacterial adhesion and, consequently, entry, is, in contrast, fundamental for the intracellular survival of this microorganism. The results of in vitro assays suggest that an increased resistance to cationic antimicrobial peptides (CAMPs), important components of the host innate defense system against microbial infections, is a possible mechanism by which the capsule protects the meningococci in the intracellular environment. Indeed, unencapsulated bacteria were more susceptible than encapsulated bacteria to defensins, cathelicidins, protegrins, and polymyxin B, which has long been used as a model compound to define the mechanism of action of CAMPs. We also demonstrate that both the capsular genes (siaD and lipA) and those encoding an efflux pump involved in resistance to CAMPs (mtrCDE) were up-regulated during the intracellular phase of the infectious cycle.

* Corresponding author. Mailing address: Dipartimento di Scienze e Tecnologie Biologiche ed Ambientali, Università degli Studi del Salento, Via Monteroni, 73100 Lecce, Italy. Phone for Cecilia Bucci: (39) 0832 298900. Fax: (39) 0832 298626. E-mail: cecilia.bucci{at}unile.it. Phone for Pietro Alifano: (39) 0832 298856. Fax: (39) 0832 298626. E-mail: alifano{at}ilenic.unile.it

{triangledown} Published ahead of print on 30 April 2007.

{dagger} Supplemental material for this article may be found at http://iai.asm.org/.

Editor: J. N. Weiser

{ddagger} M.R.S. and C.P. contributed equally to this work.

Infection and Immunity, July 2007, p. 3594-3603, Vol. 75, No. 7
0019-9567/07/$08.00+0     doi:10.1128/IAI.01945-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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