Takamatsu Daisuke, Sato Masumi, Yoshiyama Mikio
Bacterial and Parasitic Diseases Research Division, National Institute of Animal Health, National Agriculture and Food Research Organization, 3-1-5 Kannondai, Tsukuba, Ibaraki 305-0856, Japan.
J Vet Med Sci. 2016 Jan;78(1):29-34. doi: 10.1292/jvms.15-0405. Epub 2015 Aug 8.
Melissococcus plutonius is an important pathogen that causes European foulbrood (EFB) in honeybee larvae. Recently, we discovered a group of M. plutonius strains that are phenotypically and genetically distinct from other strains. These strains belong to clonal complex (CC) 12, as determined by multilocus sequence typing analysis, and show atypical cultural and biochemical characteristics in vitro compared with strains of other CCs tested. Although EFB is considered to be a purely intestinal infection according to early studies, it is unknown whether the recently found CC12 strains cause EFB by the same pathomechanism. In this study, to obtain a better understanding of EFB, we infected European honeybee (Apis mellifera) larvae per os with a well-characterized CC12 strain, DAT561, and analyzed the larvae histopathologically. Ingested DAT561 was mainly localized in the midgut lumen surrounded by the peritrophic matrix (PM) in the larvae. In badly affected larvae, the PM and midgut epithelial cells degenerated, and some bacterial cells were detected outside of the midgut. However, they did not proliferate in the deep tissues actively. By immunohistochemical analysis, the PM was stained with anti-M. plutonius serum in most of the DAT561-infected larvae. In some larvae, luminal surfaces of the PM were more strongly stained than the inside. These results suggest that infection of CC12 strain in honeybee larvae is essentially confined to the intestine. Moreover, our results imply the presence of M. plutonius-derived substances diffusing into the larval tissues in the course of infection.
蜂房蜜蜂球菌是一种重要的病原体，可导致蜜蜂幼虫患欧洲幼虫腐臭病（EFB）。最近，我们发现了一组在表型和基因上与其他菌株不同的蜂房蜜蜂球菌菌株。通过多位点序列分型分析确定，这些菌株属于克隆复合体（CC）12，并且与测试的其他CC菌株相比，在体外表现出非典型的培养和生化特征。尽管根据早期研究，EFB被认为是一种纯粹的肠道感染，但尚不清楚最近发现的CC12菌株是否通过相同的致病机制导致EFB。在本研究中，为了更好地了解EFB，我们用特征明确的CC12菌株DAT561经口感染欧洲蜜蜂（意大利蜜蜂）幼虫，并对幼虫进行组织病理学分析。摄入的DAT561主要定位于幼虫中肠腔内，被围食膜（PM）包围。在受严重影响的幼虫中，PM和中肠上皮细胞退化，并且在中肠外检测到一些细菌细胞。然而，它们并没有在深部组织中积极增殖。通过免疫组织化学分析，在大多数感染DAT561的幼虫中，PM被抗蜂房蜜蜂球菌血清染色。在一些幼虫中，PM的腔表面比内部染色更强。这些结果表明，CC12菌株在蜜蜂幼虫中的感染基本上局限于肠道。此外，我们的结果暗示在感染过程中存在从蜂房蜜蜂球菌扩散到幼虫组织中的物质。
