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Infection and Immunity, October 2002, p. 5759-5769, Vol. 70, No. 10
0019-9567/02/$04.00+0     DOI: 10.1128/IAI.70.10.5759-5769.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Characterization of a Pore-Forming Cytotoxin Expressed by Salmonella enterica Serovars Typhi and Paratyphi A

Jan Oscarsson,1 Marie Westermark,1 Sven Löfdahl,2 Björn Olsen,3,4 Helena Palmgren,3 Yoshimitsu Mizunoe,5 Sun Nyunt Wai,1,5 and Bernt Eric Uhlin1*

Department of Molecular Biology,1 Department of Infectious Diseases, Umeå University, S-90187 Umeå,3 Swedish Institute for Infectious Disease Control, S-17182 Solna,2 Department of Infectious Diseases, Länssjukhuset (LSK), S-39185 Kalmar, Sweden,4 Department of Bacteriology, Faculty of Medical Sciences, Kyushu University, Fukuoka 812-8582, Japan5

Received 19 February 2002/ Returned for modification 15 April 2002/ Accepted 2 July 2002

Cytolysin A (ClyA) is a pore-forming cytotoxic protein encoded by the clyA gene that has been characterized so far only in Escherichia coli. Using DNA sequence analysis and PCR, we established that clyA is conserved in the human-specific typhoid Salmonella enterica serovars Typhi and Paratyphi A and that the entire clyA gene locus is absent in many other S. enterica serovars, including Typhimurium. The gene products, designated ClyASTy and ClyASPa, show >=90% amino acid identity to E. coli cytolysin A, ClyAEC, and they are immunogenically related. The Salmonella proteins showed a pore-forming activity and are hence functional homologues to ClyAEC. The chromosomal clyASTy gene locus was expressed at detectable levels in the serovar Typhi strains S2369/96 and S1112/97. Furthermore, in the serovar Typhi vaccine strain Ty21a, expression of clyASTy reached phenotypic levels, as detected on blood agar plates. The hemolytic phenotype was abolished by the introduction of an in-frame deletion in the clyASTy chromosomal locus of Ty21a. Transcomplementation of the mutant with a cloned clyASTy gene restored the hemolytic phenotype. To our knowledge, Ty21a is the first reported phenotypically hemolytic Salmonella strain in which the genetic determinant has been identified.

* Corresponding author. Mailing address: Department of Molecular Biology, Umeå University, S-90187 Umeå, Sweden. Phone: 46-90-7856731. Fax: 46-90-772630. E-mail: bernt.eric.uhlin{at}molbiol.umu.se.

Editor: V. J. DiRita

Infection and Immunity, October 2002, p. 5759-5769, Vol. 70, No. 10
0019-9567/02/$04.00+0     DOI: 10.1128/IAI.70.10.5759-5769.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.



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