Screening alternative antibiotics against oxytetracycline-susceptible and -resistant Paenibacillus larvae

Abstract

Since resistance of the causative organism of American foulbrood, Paenibacillus larvae subsp. larvae, to oxytetracycline (OTC) is becoming widespread in the United States, we began a scarch for effective alternative antibiotics. We investigated the sensitivity of P. l. larvae to 27 antibiotics, which were primarily ones already registered with the US Food and Drug Administration for agricultural uses. Bacterial resistance to OTC also conferred resistance to other tetracyclines, although the level of resistance varied. The most active antibiotics screened that are currently used in agriculture were erythromycin, lincomycin, monensin, and tylosin. Rifampicin was by far the most active antibiotic tested, but since it is used against tuberculosis, registration of this material for agricultural use is unlikely.