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Infection and Immunity, March 2007, p. 1255-1264, Vol. 75, No. 3
0019-9567/07/$08.00+0     doi:10.1128/IAI.01484-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Analysis of the Polysaccharide Capsule of the Systemic Pathogen Streptococcus iniae and Its Implications in Virulence{triangledown}

Beth A. Lowe, Jesse D. Miller,{dagger} and Melody N. Neely*

Department of Immunology and Microbiology, Wayne State University School of Medicine, Detroit, Michigan 48201

Received 15 September 2006/ Returned for modification 4 November 2006/ Accepted 14 December 2006

Systemic pathogens have developed numerous strategies for evading the defenses of the host, permitting dissemination and multiplication in various tissues. One means of survival in the host, particularly in the bloodstream, has been attributed to the ability to avoid phagocytosis via capsular polysaccharide. To further define the virulence capacity of Streptococcus iniae, a zoonotic pathogen with the ability to cause severe systemic disease in both fish and humans, we performed an analysis of the capsule locus. The initial analysis included cloning and sequencing of the capsule synthesis operon, which revealed an approximately 21-kb region that is highly homologous to capsule operons of other streptococci. A genetic comparison of S. iniae virulent strain 9117 and commensal strain 9066 revealed that the commensal strain does not have the central region of the capsule operon composed of several important capsule synthesis genes. Four 9117 insertion or deletion mutants with mutations in the beginning, middle, or end of the capsule locus were analyzed to determine their capsule production and virulence. Virulence profiles were analyzed for each mutant using three separate criteria, which demonstrated the attenuation of each mutant in several tissue environments. These analyses also provided insight into the different responses of the host to each mutant strain compared to a wild-type infection. Our results demonstrate that capsule is not required for all host environments, while excess capsule is also not optimal, suggesting that for an "ideal" systemic infection, capsule production is most likely regulated while the bacterium is in different environments of the host.

* Corresponding author. Mailing address: Wayne State School of Medicine, Department of Immunology and Microbiology, 540 E. Canfield, Detroit, MI 48201. Phone: (313) 577-1314. Fax: (313) 577-1155. E-mail: mneely{at}med.wayne.edu.

{triangledown} Published ahead of print on 28 December 2006.

Editor: A. Camilli

{dagger} Present address: 3M Corporate Research Analytical Laboratory, 3M Center, Building 0201-BW-11, St. Paul, MN 55144-1000.

Infection and Immunity, March 2007, p. 1255-1264, Vol. 75, No. 3
0019-9567/07/$08.00+0     doi:10.1128/IAI.01484-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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