HOST-RANGE SUSCEPTIBILITY OF ENTEROCOCCUS SP. STRAINS ISOLATED FROM DISEASED TURBOT - POSSIBLE ROUTES OF INFECTION

Experiments were conducted to assess the pathogenicity of Enterococcus sp, strains isolated from diseased turbot for several fish species (t urbot, salmon, trout, and seabream), as well as for mice. The intraper itoneal injection assays indicated that the tested strains showed host specificity for turbot, with a high degree of virulence (50% lethal d ose of 10(4) cells per g of fish). The Spanish Enterococcus sp, isolat es were nonpathogenic for the other fish species studied and for mice, The possible routes of infection were determined by bath exposure (wi th and without prior abrasion of the skin) and by intragastric inocula tions with food and feces contaminated with the pathogen, The bath cha llenges indicated that the Enterococcus isolates were able to overcome the defense mechanisms present on the surface of the turbot only if t he skin was abraded prior to the exposure, The antibacterial activitie s of components of a glycoprotein nature present in the turbot skin mu cus are probably responsible in part for the resistance in noninjured fish to infection, On the other hand, we demonstrated the capacity of this pathogen to overcome adverse conditions in the stomachs of fish w hen associated with food or fecal material, since it is able to establ ish an infective state and to produce mortalities after 16 to 20 days postingestion. From all of these findings, we can conclude that horizo ntal transmissions through water and the fecal-oral route are the main avenues of infection of turbot streptococcosis.