比較不同生物膜形成能力之魚類來源乳酸球菌在體內持續感染期間與體外抗吞噬能力之差異

Abstract

格氏乳酸球菌 (Lactococcus garvieae) 為重要的水產動物病原，其感染對象包含多種淡、海水魚宿主，在夏季高水溫期經常因為疾病爆發而造成嚴重經濟損失，臨床上對於發病魚隻雖然可以選擇有效的抗生素治療，但往往投藥成效有限，並且在疾病控制後又可能反覆發生。早期文獻指出許多細菌性病原可能藉由在體內形成生物膜，而增加對抗菌劑之抵抗力，導致投藥治療效果不佳。因此本實驗針對近年來臨床上分離之L. garvieae進行最佳生物膜的培養條件測定，評估其生物膜形成能力，分析比較不同生物膜形成能力菌株在生長曲線、藥物感受性以及對巨噬細胞之抗吞噬與清除能力，再分別挑選形成能力較強與較弱之菌株，以兔抗偵測生物膜與細菌懸浮型態之抗體，比較細菌與生物膜之表面抗原之差異，並偵測體內生物膜之分布與形成。結果顯示不同生物膜形成能力之菌株，在生長速度、抗藥性、抗吞噬能力與清除能力皆可見顯著性差異，並於臨床發病與不顯性感染之魚隻皆可偵測到體內生物膜之訊號，且不顯性感染之魚隻受到相當之環境壓力時又會重新發病，顯示體內生物膜之形成確實可能成為臨床上L. garvieae難以治療，又反覆發病造成持續性感染的原因。

Lactococcus garvieae is one of the important aquaculture pathogen in Taiwan. It causes illness including freshwater and seawater teleosts. It causes high mortality while the water temperature rising, and latent infection on effective antibiotic treatment. The recurrence of diseases usually could be seen in practice. Literature review shows many bacterial pathogens form biofilm to enhance their resistant against antibiotics, and resulted into a worse prognosis. In view of this, we isolated several L. garvieae strains from clinical cases, and we tried to find the best biofilm formation condition, then compared the characteristics between the strong and weak biofilm formation ability strains such as growth curve, drug susceptibility, anti-phagocytosis and cell surviving experiment. To detect the distribution of biofilm formation in vivo, we produced an antibody to detect biofilm and planktonic bacteria. The results showed a significant difference in growth curve, drug susceptibility, anti-phagocytosis and cell surviving experiment between strong and weak biofilm formation ability strains. Besides, we located the biofilm signal not only in clinical cases, but also in latent infection which caused illness recurrence while stress increasing. In our conclusion, the biofilm formation of L. garvieae in vivo is the reason of control difficultly, breaking out recurrently, and persistent infection.