Impact of different culture media and culture conditions on the growth and survival of Melissococcus plutonius, the causative agent of European foulbrood

Melissococcus plutonius, the causative agent of European foulbrood, is an increasingly important and intensively studied honey bee pathogen. M. plutonius strains are classified into several groups, including clonal complex (CC) 3, CC12, and CC13, according to genotypes, and strains with different genetic backgrounds have different characteristics, including their virulence. Several types of culture media are used to isolate and culture M. plutonius, and growth and viability on each medium may vary among strains with different genetic backgrounds. We, therefore, evaluated the proliferation and survival of representative strains of different CCs in the Basal medium, which has been used in many studies, and the KSBHI medium, which is gaining more frequent use. The growth dynamics and survival of M. plutonius varied widely among strains and media, but similarities were observed among strains belonging to the same CC. M. plutonius generally grew faster in Basal containing L-cysteine than in KSBHI, but the bacteria survived longer in KSBHI than in Basal. The difference in survival between the two media was particularly pronounced for CC12 strains, which grew rapidly in Basal but then died rapidly in it. The rapid growth and subsequent death of CC12 strains in Basal was partially attributed to the presence of L-cysteine. These findings highlight the significant influence that media and cultural conditions have on study results. Thus, in the study of M. plutonius, it is important to know the strain growth dynamics and viability under the test conditions in advance to obtain accurate experimental results and correctly interpret them.