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Infection and Immunity, September 2000, p. 5261-5268, Vol. 68, No. 9
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.

Lipooligosaccharide Pk (Galalpha 1-4Galbeta 1-4Glc) Epitope of Moraxella catarrhalis Is a Factor in Resistance to Bactericidal Activity Mediated by Normal Human Serum

Anthony Zaleski,1 N. Karoline Scheffler,2 Peter Densen,3 Frank K. N. Lee,1 Anthony A. Campagnari,4 Bradford W. Gibson,2 and Michael A. Apicella1,*

Departments of Microbiology1 and Internal Medicine,3 The University of Iowa, Iowa City, Iowa; College of Medicine and Department of Pharmaceutical Chemistry, School of Pharmacy, University of California, San Francisco, California2; and Department of Microbiology, State University of New York at Buffalo, Buffalo, New York4

Received 5 April 2000/Returned for modification 5 June 2000/Accepted 13 June 2000

Moraxella catarrhalis is a respiratory pathogen responsible for acute bacterial otitis media in children and exacerbation of chronic bronchitis in adults. M. catarrhalis strains are frequently resistant to the bactericidal activity of normal human serum. In order to determine if the lipooligosaccharide (LOS) of M. catarrhalis has a role in serum resistance, the UDP-glucose-4-epimerase (galE) gene was identified, cloned, and sequenced and a deletion/insertion mutation was introduced into M. catarrhalis strain 2951. GalE enzymatic activity, measured in whole-cell lysates, was ablated in M. catarrhalis 2951 galE. Mass spectrometric analysis of LOS isolated with hot phenol-water confirmed that strain 2951 produced a type A LOS. These studies showed that the LOS from 2951 galE had lost two hexose residues due to the galE mutation and that the resultant LOS structure lacked the (Galalpha 1-4Galbeta 1-4Glc) Pk epitope found on M. catarrhalis 2951. Wild-type M. catarrhalis 2951 is resistant to complement-mediated serum bactericidal activity. In contrast, a greater than 2-log10-unit reduction in CFU occurred after incubation of 2951 galE in either 50 or 25% pooled human serum (PNHS), and CFU in 10% PNHS decreased by about 1 log10 unit. These studies suggest that the Pk epitope of the LOS may be an important factor in the resistance of M. catarrhalis to the complement-mediated bactericidal effect of normal human serum.

* Corresponding author. Mailing address: Department of Microbiology, The University of Iowa, 51 Newton Rd., Iowa City, IA 52242. Phone: (319) 335-7807. Fax: (319) 335-9006. E-mail: michael-apicella{at}uiowa.edu.

Infection and Immunity, September 2000, p. 5261-5268, Vol. 68, No. 9
0019-9567/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.


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