In vitro Inactivation of Newcastle Disease Virus by Penicillin Preparations

Abstract

Summary

1. When Newcastle disease virus is mixed with penicillin, inactivation of the virus takes place. The extent of the inactivation depends both on the concentration of penicillin and the time of incubation of the mixture. Incubation of the virus in vitro for 3 hours with more than 5000 units per ml of crystalline penicillin G results in at least a 100-fold reduction of the infectivity of the virus and up to 2 million ELD₅₀ of the virus may be completely inactivated. 2. The virus inactivating property of penicillin may be destroyed by acid or alkali treatment but is not affected by heating. Penicillinase also inactivates the antiviral properties of fresh and heated penicillin. However, this effect is apparently not due to enzymic action. Virus previously inactivated by fresh or heated penicillin cannot be restored to its original potency when penicillin is neutralized by penicillinase. 3. Injection of 50000 units of penicillin mixed with the virus protects chick embryos and 10-day-old chicks against as many as 4000 ELD₅₀ of the virus. At this concentration, however, penicillin has no prophylactic or therapeutic activity.