Preliminary investigations into possible resistance to oxytetracycline in Melissococcus plutonius,a pathogen of honeybee larvae

AIMS: To investigate the occurrence of oxytetracycline (OTC) resistance in Melissococcus plutonius, which causes European foulbrood in honeybee colonies. METHODS AND RESULTS: Strains of M. plutonius were isolated from diseased colonies in England and Wales and tested for resistance to OTC. The minimum inhibitory concentration (MIC) of OTC was also determined for selected isolates. No resistance to the antibiotic was found in any isolate and the average MIC was found to be 3.9 microg ml-1. Melissococcus plutonius was found to be susceptible to both chlortetracycline and tetracycline. CONCLUSIONS: No resistance to OTC was found in M. plutonius. SIGNIFICANCE AND IMPACT OF THE STUDY: This study demonstrated that OTC can continue to be used to treat European foulbrood and that resistance may not explain why some treatments fail.