USE OF ANTIBIOTICS IN THE PREPARATION OF CANINE KIDNEY TISSUE CULTURE VACCINES TO ELIMINATE LEPTOSPIRAL INFECTION HAZARDS.
The potential leptospiral infection hazard in the use of vaccines prepared from canine kidney monolayer cultures was studied. Cell cultures were prepared from kidneys of dogs experimentally infected with Leptospira serotype canicola. Viable leptospires were found in kidney cell suspensions at the time of seeding, surviving trypsinization either at room temperature for approximately 2 hr or overnight at 4 C, even in the presence of antibiotics. In tissue cultures maintained without antibiotics, leptospires were cultured up to the time of involution of cells at 25 to 34 days of incubation. Cytopathogenic effects of leptospires on cultured kidney cells were not noted; neither was growth of leptospires remarkable. Generally, the leptospire culture titer decreased to 10(-4) or 10(-5) at the 4th hr or 1st day of incubation to 10(-1) or negative by the 30th or 34th day of incubation. The addition of either a combination of penicillin (100 units per ml) plus streptomycin (100 mug/ml) or polymyxin B (50 units per ml) plus dihydrostreptomycin (100 mug/ml) to seeding cell suspensions resulted in the elimination of viable leptospires by the 4th hr of incubation. From cell cultures treated with neomycin (100 mug/ml) or chloramphenicol (100 mug/ml), leptospires were recovered, respectively, after 24 and 48 hr, but not thereafter. It was apparent that antibiotics, particularly the combination of polymyxin B and dihydrostreptomycin, could be effectively used to eliminate leptospires in tissue culture. Other antibiotics with known antileptospiral activities probably would be effective also. If antibiotics are not used in canine kidney tissue culture employed for viral vaccine preparations, rigid testing for the presence of leptospires in donor dogs and tissue-culture vaccine is indicated.