ACTIN ENHANCES THE HEMOLYTIC-ACTIVITY OF ESCHERICHIA-COLI

Actin is a major cytoskeletal protein of mammalian muscle and non-musc le cells. Exposure of cells to soluble factors that damage cell membra nes results in the release of actin into the extracellular spaces. The alpha-haemolysin (HlyA) of Escherichia coli is the prototype RTX (rep eat in toxin) toxin and is thought to be important in virulence becaus e of its ability to lyse cells by formation of pores in the cell membr ane. These studies were conducted to determine if actin influences gro wth and haemolytic activity of E. coli. Growth of E. coli in the prese nce of actin resulted in culture supernatant haemolytic activity that was 2.4; 2.7- and 3.3-fold greater than that of E. coli grown in mediu m containing BSA, non-supplemented medium, or medium containing heat-d enatured actin, respectively. The enhanced haemolytic activity occurre d only when actin was present during the growth phase and there was no effect when actin was added to culture supernatants containing haemol ysin. The increased haemolytic activity by actin was concentration-dep endent, detectable in early-exponential-phase growth, and associated w ith increased concentrations of secreted HlyA by Western blotting. Act in induced a 2.9-fold increase in alkaline phosphatase activity in E. coli CC118 with a TnphoA insertion in the hlyB determinant of the reco mbinant haemolysin plasmid pWAM04. These results indicate that extrace llular actin enhances haemolysin production by E. con and may have imp lications in the pathogenesis of E. coli infections.