ACTINOBACILLUS-PLEUROPNEUMONIAE RTX-TOXINS - UNIFORM DESIGNATION OF HEMOLYSINS, CYTOLYSINS, PLEUROTOXIN AND THEIR GENES

The three different pore-forming RTX-toxins of Actinobacillus pleuropn eumoniae are reviewed, and new and uniform designations for these toxi ns and their genes are proposed. The designation ApxI (for Actinobacil lus pleuropneumoniae RTX-toxin I) is proposed for the RTX-toxin produc ed by the reference strains for serotypes 1, 5a, 5b, 9, 10 and 11, whi ch was previously named haemolysin I (HlyI) or cytolysin I (ClyI). Thi s protein is strongly haemolytic and shows strong cytotoxic activity t owards pig alveolar macrophages and neutrophils; it has an apparent mo lecular mass in the range 105 to 110 kDa. The genes of the apxI operon will have the designations apxIC, apxIA, apxIB, and apxID for the act ivator, 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 pre viously named App, HlyII, ClyII or Cyt. This protein is weakly haemoly tic and moderately cytotoxic and has an apparent molecular mass betwee n 103 and 105 kDa. The genes of the apxII operon will have the designa tions apxIIC for the activator gene and apxIIA for the structural toxi n gene. In the apxII operon, no genes for secretion proteins have been found. Secretion of ApxII seems to occur via the products of the secr etion genes apxIB and apxID of the apxI 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 III (ClyIII), pleurotoxin (Ptx), or macrophage toxin (Mat). This prote in is strongly cytotoxic and has an apparent molecular mass of 120 kDa . The genes of the apxIII operon have the designations apxIIIC, apxIII A, apxIIIB and apxIIID for the activator gene, the structural gene and the two secretion genes respectively.