CYTOTOXIN PRODUCTION IN 100 STRAINS OF HAEMOPHILUS-DUCREYI FROM DIFFERENT GEOGRAPHIC LOCATIONS

One-hundred strains of Haemophilus ducreyi, representing isolates from different parts of the world, including the reference strains, were o btained from different collections and characterized with special refe rence to cytotoxin production in vitro. The cytotoxic activity on cult ured epithelial cells (HEp-2) was examined with two methods. The activ ity in bacterial sonicates was tested an freshly trypsinated cells and strains manifesting little or no cytotoxic activity in sonicates were investigated using attached living bacteria on HEp-2 cell-monolayers. Sonicates from the majority of the H. ducreyi strains (89%) produced significant cytotoxic effects on HEp-2 cells. The reciprocal cytotoxic titers of the sonicates ranged from 2.4 x 10(2) to 5.3 x 10(5). Sonic ates of 11 strains had low cytotoxic titers (less than or equal to 1:3 to 1:81), eight of those originating from Asia and three from Africa. These II strains caused no damage to the cell monolayer, indicating t hat the 11 strains produce little or no cytotoxic activity in vitro. I n summary, the majority of H. ducreyi isolates produce cytotoxic activ ity, which support the hypothesis that the cytotoxin may be an importa nt virulence factor of this species.