Can fatty acids and oxytetracycline protect artificially raised larvae from developing European foulbrood?

摘要

A quantitative assay for the transmission of European foulbrood (EFB) in artificially raised larvae was developed. This assay was used to determine the concentration of oxytetracycline (OTC) required to prevent larvae from developing EFB and whether 8 fatty acids (undecanoic, lauric [dodecanoic], myristic, myristoleic, ricinoleic, ricinelaidic, homo-y-linolenic and 13,16,19-docosatrienoic acids) which had previously been demonstrated to inhibit the growth of Melissococcus plutonius cultures, could protect larvae from developing EFB. The larval assay involved grafting individual larva (less than 24 hours old) into a single well in a micro-titre plate. Each larva was fed 10 μL of basic larval diet (BLD) containing 500 000 M. plutonius organisms. After 3 days the larvae were also fed 60 000 Paenibacillus alvei spores (a common secondary invader associated with EFB) in 10 μL BLD. The combination of these two organisms was required to reliably produce symptoms typical of that seen in field cases of EFB. Most larvae infected using this protocol died from EFB. To determine the efficacy of OTC, EFB infected larvae were fed 0, 1, 2.5, 5 10 or 20 μg/mL of OTC. Treatment with 1 μg/mL lowered the mortality rate from 93.75% to 69.5%. Treatments with 2.5 μg/mL to 10 μg/mL reduced the mortality rate further whereas treatment with 20 μg/mL reduced the rate to the same as the negative control. Larvae fed 20 or 200 μg/mL of each of the eight fatty acids were not protected from developing EFB.