No abstract

Comparison of hemolytic activity and chromate-releasing activity of partially purified preparations of staphylococcal a-toxin indicated the presence of a lytic factor other than a-toxin. This lytic release factor (RF) was isolated from the preparations and was shown to be active against both lipid spherules and erythrocytes. Heat-purified a-toxin (HP a-toxin) disrupted spherules, with the formation of fragments which always showed the presence of ring structures similar in dimensions (ca. 90 A) to pure a 12S-toxin. The interaction of HP a-toxin with spherules was accompanied by loss of hemolytic activity and adsorption of toxic protein. The a 12S-toxin, although only weakly hemolytic, was shown to be lytic for spherules. An a 12S-free toxin rapidly disrupted spherules, with formation of fragments with attached rings similar in dimensions to the a 12S molecule. Lipid monolayer experiments showed that HP a-toxin could penetrate lipid monolayers by virtue of a hydrophobic interaction. Effects of HP a-toxin on rabbit and human erythrocyte ghosts were similar to its effects on spherules, in that rings appeared on membrane fragments. Toxin-lysed rabbit erythrocytes showed similar rings on the resulting membrane fragments. However, rings were not seen on toxin-treated rabbit erythrocytes in the prelytic lag phase; this result and the fact that human erythrocytes are largely insensitive to a-toxin were interpreted as evidence against a lytic mechanism involving ring formation as the primary event. Rings were interpreted as toxin polymers similar to a 12S molecules, formed from specifically orientated active toxin molecules at the surface of lipid structures. Possible mechanisms for toxin lysis of spherules and erythrocytes are discussed.

Three broad-host-range plasmids (pRK290, pSa4 and pKT230) and one native Pasteurella haemolytica plasmid (pPH33) were used in transformation experiments with P. haemolytica strains T179 (serotype A1), Y216 (serotype A2) and its capsular-deficient variant Y216/NS1. No transformants were detected with either heat-shock or freeze-thaw techniques. However, by electroporation, all P. haemolytica strains were transformed by pPH33 but not by pRK290 or pSa4. The highest frequency obtained was 91 x 10(4) transformants per microgram of pPH33 DNA with P. haemolytica strain Y216/NS1. Although pPH33 itself was non-transmissible by conjugation, it could be mobilized from Escherichia coli, using the transfer function of the IncP plasmid pRK2013, into P. haemolytica at a frequency of 0.3-2.2 x 10(-3) per recipient cell.

No abstract