Cytotoxic activity of clinical Stenotrophomonas maltophilia

To determine the potential virulence factors produced by culture supernatants of clinical isolates of Stenotrophomonas maltophilia. Culture supernatants of clinical isolates of S. maltophilia were assayed for haemolytic, enzymatic (lipase, protease and phospholipase) and cytotoxic activity. Cytotoxic activity was assayed in Vero (African green monkey), HeLa (human cervix) and HEp-2 (human larynx epidermoid carcinoma) cells. Microscopic analyses revealed intensive rounding, loss of intercellular junctions and membrane alterations (blebbing) followed by death of HEp-2 cells. In Vero and HeLa cells, the cytotoxic effects were characterized by vigorous endocytosis and cell aggregation. The viability of cultured mammalian cells was determined with neutral red and demonstrated that the sensitivity among the cells was different. This activity was inactivated by heating at 56°C for 15 min and protease inhibitors did not inhibit cytotoxic activity. The clinical S. maltophilia presented a cell-free haemolytic activity similar to the 'hot-cold' haemolysins. S. maltophilia culture supernatants caused vigorous endocytosis and cell aggregation in HeLa and Vero cells, produced haemolytic and enzymatic activities. This work revealed the presence of putative virulence factors that could be associated with human infections involving Stenotrophomonas maltophilia strains.