Effect of Small Amounts of Aureomycin and Terramycin on Virus of Feline Pneumonitis

Discussion and conclusions

The purpose of these experiments was to find out whether the phenomenon of acquired resistance could be demonstrated in the case of a filterable virus to the newer antibiotics. The virus of feline pneumonitis was employed, and the two antibiotics were terramycin and aureomycin. These two were used in subcurative dosages in mice following intranasal inoculation in one series of experiments, and aureomycin was studied in 12 experiments in varying dosages in embryonated eggs. In order to enhance the likelihood of the emergence of a resistant mutant, large inocula of virus were employed. Under the conditions of our experiments no evidence whatsoever of resistance could be demonstrated, but an interesting phenomenon was observed. In both the mouse series and the egg series virus seemed to persist through several passages in the presence of antibiotic in diminished amounts. Then, with no increase in the dosage of antibiotic, it died out. The significance of this finding is obscure. That it might be due to an actual increase in sensitivity of the virus to antibiotic is conceivable, although such an hypothesis is not proven by the data presented here.