Evidence for bacteria-independent hatching of Trichuris muris eggs.

Hatching of infective larvae from embryonated eggs in the intestine is an essential first step in Trichuris infections. There are three isolates of the murine parasitic nematode Trichuris muris: E, E-J (the E isolate maintained in Japan), and S. Incubation of T. muris embryonated eggs with the intestinal bacteria Escherichia coli and Staphylococcus aureus induced in vitro hatching of the eggs, but Enterococcus faecalis failed to induce hatching. Bacteria-induced in vitro hatching of embryonated eggs occurred in the E and E-J isolates, whereas the S isolate was unresponsive to bacteria. T. muris worms recovered from infected mice showed no significant difference between the E-J and S isolates in their infectivity to susceptible B10.BR mice (P>0.05). In vivo hatching of embryonated eggs occurred at 30 min post-infection in the upper and lower halves of the small intestine of ddY mice infected with the E-J or S isolates, and on average, 65% of embryonated eggs recovered from the upper half of the small intestine were hatched in both the E-J and S isolates. In comparison with Enterococcus, the bacteria E. coli and S. aureus represent relatively minor components of the flora of the upper half of the small intestine of mice. These observations point to the possibility that bacteria-independent hatching might also occur in vivo, at least for the S isolate, and imply the existence of a very different system of induction of hatching in vivo.