PATHOGENICITY AND VIRULENCE OF RHODOCOCCUS-EQUI IN FOALS FOLLOWING INTRATRACHEAL CHALLENGE

Twelve foals, between 27 and 83 days old, were infected with 2 strains of Rhodococcus equi by intratracheal administration. Ten of the 12 fo als were inoculated with 10(4)-10(10) colony forming units (cfu) of AT CC 33701 strain, The other 2 foals were inoculated with 10(9) cfu of a plasmid-cured derivative of the ATCC 33701 strain (ATCC 33701P(-)). A ll of the 10 foals challenged with the ATCC 33701 strain showed clinic al signs of pulmonary disease within 5-13 days, such as gross lesions associated with acute bronchopneumonia and microscopic lesions associa ted with granulomatous pneumonia. The two foals challenged with the AT CC 33701P(-) strain showed neither clinical signs of disease nor gross lesions, Apparently, when lacking plasmid, the virulent Rhodococcus e qui lost its pathogenicity. (C) 1997 Elsevier Science B.V.