Oxytetracycline resistance of Melissococcus plutonius strains in Japan

AbstractEuropean foulbrood caused by the Gram-positive lanceolate coccus, Melissococcus plutonius, is a major bacterial infection of honey bee brood. Oxytetracycline (OTC) has been used to combat this disease in some countries. Although OTC resistance was not previously reported despite its long-term use, the first case was finally detected in an M. plutonius strain isolated in Canada in 2019. In Japan, OTC has not been approved for use in the control of any honey bee diseases. However, after testing 77 M. plutonius strains isolated in Japan between the 1980s and 2010s, we identified four OTC-resistant strains with a minimum inhibitory concentration of OTC on agar medium of 16 µg/ml. The four strains were isolated in 2008 (1 strain), 2013 (1 strain), and 2015 (2 strains); i.e., before the Canadian OTC-resistant isolate. These results provide insights into the mechanisms underlying the development of OTC-resistant M. plutonius.Keywords: European foulbroodMelissococcus plutoniusoxytetracyclineantibiotic resistanceJapan AcknowledgmentsThe present study was conducted under regulatory research projects for food safety, animal health, and plant protection (JPJ008617.17935699) funded by the Ministry of Agriculture, Forestry and Fisheries of Japan. We thank Sota Kobayashi for his helpful suggestions regarding statistical analyses.Disclosure statementThe authors declare no conflicts of interest.