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Infect Immun, July 1998, p. 3113-3119, Vol. 66, No. 7
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Phenotypic Effect of Isogenic uspA1 and uspA2 Mutations on Moraxella catarrhalis 035E

Christoph Aebi,1,2,dagger Eric R. Lafontaine,1 Leslie D. Cope,1 Jo L. Latimer,1 Sheryl L. Lumbley,1 George H. McCracken Jr.,2 and Eric J. Hansen1,*

Departments of Microbiology1 and Pediatrics,2 University of Texas Southwestern Medical Center, Dallas, Texas 75235-9048

Received 2 January 1998/Returned for modification 13 February 1998/Accepted 14 April 1998

The UspA surface antigen of Moraxella catarrhalis was recently shown to be comprised of two different proteins (UspA1 and UspA2) which share an internal region containing 140 amino acids with 93% identity (C. Aebi, I. Maciver, J. L. Latimer, L. D. Cope, M. K. Stevens, S. E. Thomas, G. H. McCracken, Jr., and E. J. Hansen, Infect. Immun. 65:4367-4377, 1997). Isogenic uspA1, uspA2, and uspA1 uspA2 mutants were tested in a number of in vitro systems to determine what effect these mutations, either individually or together, might exert on the phenotype of M. catarrhalis 035E. Monoclonal antibodies specific for UspA1 or UspA2 were used in an indirect antibody accessibility assay to prove that both of these proteins were expressed on the surface of M. catarrhalis. All three mutants grew in vitro at the same rate and did not exhibit autoagglutination or hemagglutination properties that were detectably different from those of the wild-type parent strain. When tested for the ability to adhere to human epithelial cells, the wild-type parent strain and the uspA2 mutant readily attached to Chang conjunctival cells. In contrast, the uspA1 mutant and the uspA1 uspA2 double mutant both attached to these epithelial cells at a level nearly 2 orders of magnitude lower than that obtained with the wild-type parent strain, a result which suggested that expression of UspA1 by M. catarrhalis is essential for attachment to these epithelial cells. Both the wild-type parent strain and the uspA1 mutant were resistant to the bactericidal activity of normal human serum, whereas the uspA2 mutant and the uspA1 uspA2 double mutant were readily killed by this serum. This latter result indicated that the presence of UspA2 is essential for expression of serum resistance by M. catarrhalis.

* Corresponding author. Mailing address: Department of Microbiology, Hamon Building, NA6.200, University of Texas Southwestern Medical Center, 6000 Harry Hines Blvd., Dallas, TX 75235-9048. Phone: (214) 648-5974. Fax: (214) 648-5905. E-mail: hansen01{at}utsw.swmed.edu.

dagger Present address: Department of Pediatrics, University of Bern, Inselspital, CH-3010 Bern, Switzerland.

Infect Immun, July 1998, p. 3113-3119, Vol. 66, No. 7
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.


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