Journal of General Microbiology (1993), 139, 1723-1728. Printed in Great Britain 1723 Actinobacillus pleuropneumoniae RTX-toxins : uniform designation of haemolysins, cytolysins, pleurotoxin and their genes J. FREY,'" J. T. BOSSE,~ Y.-F. CHANG,3 J. M. CULLEN,4 B. FENWICK,' G. F. GERLACH,'~ D. GYGI,~ F. HAESEBROUCK,7 T. J. INZZANA,~ R. JANSEN,9 E. M. KAMP,9 J. MACDONALDP M. A. SMITS,9 E. STENBAEK,13 D. K. STRUCK,14 J. F. VAN DEN BOSCH,~~ P. J. WILLSON" and R. YOUNG14 J. I. MACINNES,~ K. R. MITTAL,'~ J. NICOLET,' A. N. RYCROFT,~~ R. P. A. M. SEGERS,'~ Institute for Veterinary Bacteriology, University of Berne, Langgass-Strasse 122, CH-3012 Berne, Switzerland 'University of Guelph, Guelph, Ontario, Canada 'College of Veterinary Medicine, Cornell University, Ithaca, N Y, USA 4Department of Veterinary Pathology, University of Glasgow, Glasgow, UK 'Department of Pathology and Microbiology, Kansas State University, Manhattan, KS, USA 6Departrnent of Pathology, Cambridge University, Cambridge, UK 'Faculty of Veterinary Medicine, University of Gent, Gent, Belgium 'Central Veterinary Institute, Lelystad, The Netherlands "Facultk de mkdkcine vktkrinaire, Universitk de Montrkal, St-Hyacinthe, Qukbec, Canada 121ntervet International BV, A A Boxmeer, The Netherlands 13Statens Veterinaere Serumlaboratorium, Kobenhavn, Denmark 14TexasA&M University, College Station, TX, USA 15Veterinary Infectious Disease Organization, University of Saskatchewan, Saskatoon, Saskatchewan, Canada 161nstitute for Microbiology and Infectious Diseases, Veterinary School, Hanover, Germany Virginia Polytechnic, Blacksburg, V A , U S A Royal Veterinary College, UCL, London, UK (Received 13 April 1993; accepted 23 April 1993) The three different pore-forming RTX-toxins of Actinobacillus pleuropneumoniae are reviewed, and new and uniform designations for these toxins and their genes are proposed. The designation ApxI (for &tinobacillus pZeuropneumoniae RTX-toxin I) is proposed for the RTX-toxin produced by the reference strains for serotypes 1, 5a, 5b, 9,lO and 11, which was previously named haemolysin I (HlyI) or cytolysin I (ClyI). This protein is strongly haemolytic and shows strong cytotoxic activity towards pig alveolar macrophages and neutrophils; it has an apparent molecular mass in the range 105 to 110 kDa. The genes of the apxZ operon will have the designations apxZC, apxZA, apxZB, and apxZD for the activator, the structural gene and the two secretion genes respectively. The designation ApxII is proposed for the RTX-toxin which is produced by all serotype reference strains except serotype 10 and which was previously named App, HlyII, ClyII or Cyt. This protein is weakly haemolytic and moderately cytotoxic and has an apparent molecular m a s between 103 and 105 kDa. The genes of the apxZZ operon will have the designations apxZZC for the activator gene and apxZZA for the structural toxin gene. In the apxZZ operon, no genes for secretion proteins have been found. Secretion of ApxII seems to occur via the products of the secretion genes apxZB and apxZD of the apxZ operon. The designation ApxIII is proposed for the non- haemolytic RTX-toxin of the reference strains for serotypes 2, 3, 4, 6 and 8, which was previously named cytolysin 111 (ClyIII), pleurotoxin (Ptx), or macrophage toxin (Mat). This protein is strongly cytotoxic and has an apparent molecular mass of 120 kDa. The genes of the apxZZZ operon have the designations apxZZZC, apxZZZA, apxZZZB and apxZZZD for the activator gene, the structural gene and the two secretion genes respectively. * Author for correspondence. Tel. + 41 3 1 63 1 2484; fax + 41 3 1 63 1 2634; e-mail JFREY @VBI . UNIBE . CH. 0001-8285 0 1993 SGM