The RTX haemolysins ApxI and ApxII are major virulence factors of the swine pathogenActinobacillus pleuropneumoniae:evidence from mutational analysis

Abstract

Summary The involvement of the RTX haemolysins (Apxl and ApxII) of the swine pathogen Actinobacillus pleuropneumoniae in virulence was investigated using haemolysin‐deficient mutants constructed by a mini‐Tn10 mutagenesis procedure. Two types of haemolysin mutant with single insertions of the transposon were obtained from a serotype 1 strain producing both ApxI and ApxII. One presented a complete loss of haemolytic activity because of the absence of ApxI and ApxII production. The other displayed weaker haemolysis than the wild type and produced only ApxII. The chromosomal regions flanking mini‐Tn10 were cloned and sequenced. In the non‐haemolytic mutant, the transposon had inserted in apxIB, a gene involved in the exportation of ApxI and ApxII toxins. The weakly haemolytic mutant resulted from the disruption of the structural gene for ApxI. Both mutations In the apxI operon were associated with a significant loss of virulence for mice and pigs, demonstrating that haemolysins are involved in A. pleuropneumoniae pathogenicity. The non‐haemolytic mutant was apathogenic and the weakly haemolytic mutant retained some virulence for pigs, suggesting that both ApxI and ApxII are needed for full virulence.

Actinobacillus pleuropneumoniaeIron Transport and Urease Activity: Effects on Bacterial Virulence and Host Immune Response

“…To date, conclusive evidence obtained by challenge experiments has been presented to confirm the role of Apx toxins and capsular material. A spontaneous Apx toxin-negative A. pleuropneumoniae strain was shown to be avirulent (14), and this result was supported later by using transposon mutagenesis (36) as well as by an isogenic A. pleuropneumoniae apxC insertion mutant (29). Also, capsule-deficient A. pleuropneumoniae strains obtained by chemical mutagenesis were shown to be attenuated (22), and this result was confirmed by reconstituting virulence properties and capsule formation upon transformation with a recombinant plasmid (39).…”

Cytotoxic Activities of Leptospira interrogans Hemolysin SphH as a Pore-Forming Protein on Mammalian Cells

“…S. aureus alpha-toxin (40) and E. coli hemolysin (Hly) (9) produce thromboxane-mediated vasoconstriction and edema formation in the isolated and perfused rabbit lungs and thus are implicated in the development of septic lung failure. In addition, two RTX family hemolysins of the gram-negative bacterium Actinobacillus pleuropneumoniae were shown to be important virulence factors in production of hemorrhagic and necrotic lung infections in swine (44).…”

The N-Terminal Domain of RTX Toxin ApxI of Actinobacillus pleuropneumoniae Elicits Protective Immunity in Mice

“…To date, 15 serotypes have been described which variously secrete four different cytotoxins belonging to the RTX toxin family: ApxI, ApxII, ApxIII, and ApxIV (4,31). The virulence of A. pleuropneumoniae is multifactorial (7, 10, 11, 13, 16-19, 21, 29); however, studies indicate that virulence is strongly correlated with the production of Apx exotoxins (20,22,23,29,33), with serovars producing ApxI, together with ApxII, being the most virulent (13,14,24). Apx toxins are strongly immunogenic and have been studied as a potential vaccine against porcine pleuropneumonia.…”