Reduced growth of Blastocrithidia culicis and Crithidia oncopelti freed of intracellular symbiotes by chloramphenicol.

The intracellular symbiotes of Blastocrithidia culicis and Crithidia oncopelti can be eliminated from cultures of the flagellates by a single chloramphenicol (CAP) treatment. Effective dosages were determined to be 0.01-0.08 per cent (w/v) CAP after a treatment for 2 weeks or more for B. culicis and 0.08 per cent (w/v) after 1 month for C. oncopelti in most cases. Ineffective dosages only lowered the numbers of symbiote-bearing flagellates. Growth of both species of flagellates in the presence of CAP was reduced in proportion to the drug concentration. Repeated subcultures at effectie dosages yielded symbiote-free flagellates, which maintained a low level of growth rate. After repeated subcultures at ineffective dosages, the growth rate rose and the symbiote-bearing cells, initially very few, increases in number. The lowest effective dosages proved to be marginal, often producing symbiote-free cultures, but occasionally cultures with a few symbiote-bearing cells. After repeated subcultures at these drug concentrations, symbiote-containing cultures grew faster than the symbiote-free cultures. Hence, the symbiotic bacteria benefit the growth of their hosts, perhaps by supplying essential factors that are adequate even in a rich blood medium.