microbiology, Vol 144, 291-298, Copyright © 1998 by Society for General Microbiology

ARTICLES

Inactivation of two haemolytic toxin genes in Aeromonas hydrophila attenuates virulence in a suckling mouse model

CY Wong, MW Heuzenroeder and RL Flower
School of Pharmacy and Medical Sciences, University of South Australia, Adelaide, Australia. cwong@microb.adelaide.edu.au

The contribution of two unrelated Aeromonas hydrophila beta-haemolytic toxins to virulence was assessed in a suckling mouse model. The first haemolysin gene, isolated from an A. hydrophila A6 cosmid bank, encoded a potential gene product of 621 amino acids and a predicted molecular size of 69.0 kDa. The inferred amino acid sequence showed 89% identity to the AHH1 haemolysin of A. hydrophila ATCC 7966, and 51% identity to the HlyA haemolysin of Vibrio cholerae EI Tor strain O17. The second haemolysin gene (designated aerA), which encodes aerolysin, a pore- forming toxin, was partially cloned by PCR for the purpose of mutant construction. This PCR product was a 1040 bp fragment from the C- terminal region of aerA. It is proposed that the 69.0 kDa V. cholerae- HlyA-like haemolysin gene be termed hlyA to contrast with the aerA terminology for the aerolysin. A suicide vector was used to inactivate both the hlyA and aerA genes in A. hydrophila A6. When assessed in the suckling mouse model, only the hlyA aerA double mutant showed a statistically significant reduction in virulence--a 20-fold change in LD50 (Scheffe test, P < 0.05). Cytotoxicity to buffalo green monkey kidney cell monolayers and haemolysis on horse blood agar were eliminated only in the hlyA aerA double mutants. This is the first report of cloning and mutagenesis of two unrelated haemolytic toxin genes in the same strain of a mesophilic aeromonad. For A. hydrophila, a two-toxin model provides a more complete explanation of virulence.

This article has been cited by other articles:

				H. B. Yu, Y. L. Zhang, Y. L. Lau, F. Yao, S. Vilches, S. Merino, J. M. Tomas, S. P. Howard, and K. Y. Leung Identification and Characterization of Putative Virulence Genes and Gene Clusters in Aeromonas hydrophila PPD134/91 Appl. Envir. Microbiol., August 1, 2005; 71(8): 4469 - 4477. [Abstract] [Full Text] [PDF]

				H. B. Yu, P. S. S. Rao, H. C. Lee, S. Vilches, S. Merino, J. M. Tomas, and K. Y. Leung A Type III Secretion System Is Required for Aeromonas hydrophila AH-1 Pathogenesis Infect. Immun., March 1, 2004; 72(3): 1248 - 1256. [Abstract] [Full Text] [PDF]

				M. R. Chacon, L. Soler, E. A. Groisman, J. Guarro, and M. J. Figueras Type III Secretion System Genes in Clinical Aeromonas Isolates J. Clin. Microbiol., March 1, 2004; 42(3): 1285 - 1287. [Abstract] [Full Text] [PDF]

				G. Wang, C. G. Clark, C. Liu, C. Pucknell, C. K. Munro, T. M. A. C. Kruk, R. Caldeira, D. L. Woodward, and F. G. Rodgers Detection and Characterization of the Hemolysin Genes in Aeromonas hydrophila and Aeromonas sobria by Multiplex PCR J. Clin. Microbiol., March 1, 2003; 41(3): 1048 - 1054. [Abstract] [Full Text] [PDF]

				R. Olson and E. Gouaux Vibrio cholerae cytolysin is composed of an {alpha}-hemolysin-like core Protein Sci., February 1, 2003; 12(2): 379 - 383. [Abstract] [Full Text] [PDF]

				Y. L. Zhang, C. T. Ong, and K. Y. Leung Molecular analysis of genetic differences between virulent and avirulent strains of Aeromonas hydrophila isolated from diseased fish Microbiology, April 1, 2000; 146(4): 999 - 1009. [Abstract] [Full Text]

				G. Filler, J. H. H. Ehrich, E. Strauch, and L. Beutin Acute Renal Failure in an Infant Associated with Cytotoxic Aeromonas sobria Isolated from Patient's Stool and from Aquarium Water as Suspected Source of Infection J. Clin. Microbiol., January 1, 2000; 38(1): 469 - 470. [Full Text]

				J. A. Santos, C. J. González, A. Otero, and M.-L. García-López Hemolytic Activity and Siderophore Production in Different Aeromonas Species Isolated from Fish Appl. Envir. Microbiol., December 1, 1999; 65(12): 5612 - 5614. [Abstract] [Full Text]

				S. Swift, M. J. Lynch, L. Fish, D. F. Kirke, J. M. Tomas, G. S. A. B. Stewart, and P. Williams Quorum Sensing-Dependent Regulation and Blockade of Exoprotease Production in Aeromonas hydrophila Infect. Immun., October 1, 1999; 67(10): 5192 - 5199. [Abstract] [Full Text] [PDF]