INTRACELLULAR GROWTH AND CYTOTOXICITY OF MYCOBACTERIUM-HAEMOPHILUM INA HUMAN EPITHELIAL-CELL LINE (HEC-1-B)

We developed an in vitro model to study the temperature-regulated cyto toxicity and intracellular growth of Mycobacterium haemophilum in cult ured human epithelial and endothelial cells. M, haemophilum associated with human epithelial and endothelial cells at similar rates when inc ubated at 33 and 37 degrees C, but only the epithelial cell line suppo rted the multiplication of this organism, M, Haemophilum grew equally well with epithelial cells at both temperatures, The aminoglycoside an tibiotic amikacin was used to study the intracellular growth of M, hae mophilum in the epithelial cells at 33 and 37 degrees C, Although an a pproximately equal number of bacteria were found within cells after 2 days of incubation at both temperatures, intracellular replication of M, haemophilum was 1,000-fold greater at 33 than at 37 degrees C. This intracellular multiplication was associated with destruction of the m onolayers at 33 but not at 37 degrees C, and only culture filtrates fr om infected monolayers incubated at 33 degrees C were cytotoxic to fre sh epithelial cell monolayers, This strain of M, haemophilum also prod uced contact-dependent hemolysis of sheep erythrocytes, demonstrating the possible presence of a cytolysin, These studies suggest that M, ha emophilum has a preference for growth with cultured human epithelial c ells, In addition, intracellular growth is best at 33 degrees C in epi thelial cells, and this correlated with cytotoxicity at this temperatu re. This phenotype may be caused by induction of a soluble cytotoxic c omponent, possibly a hemolytic cytolysin.