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Infection and Immunity, July 2005, p. 4222-4230, Vol. 73, No. 7
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.7.4222-4230.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Roles of 3-Deoxy-D-manno-2-Octulosonic Acid Transferase from Moraxella catarrhalis in Lipooligosaccharide Biosynthesis and Virulence

Daxin Peng,1 Biswa P. Choudhury,2 Ronald S. Petralia,3 Russell W. Carlson,2 and Xin-Xing Gu1*

Vaccine Research Section,1 Section on Neurotransmitter Receptor Biology, National Institute on Deafness and Other Communication Disorders, Rockville, Maryland 20850,3 Complex Carbohydrate Research Center, University of Georgia, Athens, Georgia 306022

Received 20 December 2004/ Returned for modification 27 January 2005/ Accepted 8 March 2005

Lipooligosaccharide (LOS), a major outer membrane component of Moraxella catarrhalis, is a possible virulence factor in the pathogenesis of human infections caused by the organism. However, information about the roles of the oligosaccharide chain from LOS in bacterial infection remains limited. Here, a kdtA gene encoding 3-deoxy-D-manno-2-octulosonic acid (Kdo) transferase, which is responsible for adding Kdo residues to the lipid A portion of the LOS, was identified by transposon mutagenesis and construction of an isogenic kdtA mutant in strain O35E. The resulting O35EkdtA mutant produced only lipid A without any core oligosaccharide, and it was viable. Physicochemical and biological analysis revealed that the mutant was susceptible to hydrophobic reagents and a hydrophilic glycopeptide and was sensitive to bactericidal activity of normal human serum. Importantly, the mutant showed decreased toxicity by the Limulus amebocyte lysate assay, reduced adherence to human epithelial cells, and enhanced clearance in lungs and nasopharynx in a mouse aerosol challenge model. These data suggest that the oligosaccharide moiety of the LOS is important for the biological activity of the LOS and the virulence capability of the bacteria in vitro and in vivo. This study may bring new insights into novel vaccines or therapeutic interventions against M. catarrhalis infections.

* Corresponding author. Mailing address: 5 Research Court, Room 2A31, Rockville, MD 20850. Phone: (301) 402-2456. Fax: (301) 402-5354. E-mail: guxx{at}nidcd.nih.gov.

Editor: J. D. Clements

Infection and Immunity, July 2005, p. 4222-4230, Vol. 73, No. 7
0019-9567/05/$08.00+0     doi:10.1128/IAI.73.7.4222-4230.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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