單核細胞增多性李斯特菌生物膜細胞暴露於乳酸鏈球菌素的生理反應

Abstract

單核細胞增多性李斯特菌 (Listeria monocytogenes) 是一種常見於即食食品中的食源性病原菌。由於李斯特菌病 (listeriosis) 在所有食源性疾病中具有相對較高的致死率，因此特別受到關注。乳酸鏈球菌素 (nisin) 是一種被認證為「公認安全」 (Generally recognized as safe, GRAS) 的細菌素，廣泛用作食品防腐劑。然而，研究表示 L. monocytogenes 在生物膜中可能因暴露於亞致死濃度的乳酸鏈球菌素與生物膜形成過程中的生理變化，而表現出敏感性下降的現象。為提升乳酸鏈球菌素於存在生物膜的食品加工環境中的抑菌效能，亟需進一步釐清生物膜所引發之耐受性與抗藥性機制。本研究探討三種 L. monocytogenes 細胞型態之間的生理差異與其對乳酸鏈球菌素的敏感性，分別為：隔夜培養之浮游細胞、培養三天之浮游細胞，以及自培養三天之生物膜中分離出的貼附細胞。結果顯示，貼附細胞的生長遲滯期較長（5.71 ± 0.60 小時），明顯高於隔夜培養之浮游細胞（3.58 ± 0.83 小時）與培養三天之浮游細胞（3.60 ± 0.31 小時）；惟三者在運動能力與表面疏水性方面並無顯著差異。貼附細胞需長時間（約 29 分鐘）暴露於高濃度乳酸鏈球菌素下，才能達到與其他細胞型態（約 4 至 6 分鐘）相當之菌數下降，顯示其對乳酸鏈球菌素具較低的敏感性。本研究亦比較了經乳酸鏈球菌素處理後浮游態、貼附態及生物膜形式 L. monocytogenes 的細菌存活比，結果發現生物膜形式具有最高的存活比。這些發現顯示，細胞型態的轉變與生物膜基質的存在皆導致 L. monocytogenes 對乳酸鏈球菌素敏感性下降。本研究凸顯了進一步探討乳酸鏈球菌素作用下生物膜結構動態及貼附細胞敏感性下降機制的重要性，期能改善生物膜的控制策略。

Listeria monocytogenes is a foodborne pathogen commonly found in ready-to-eat foods. It is a highly concerning pathogen due to a relatively high mortality rate of listeriosis among foodborne illnesses. Nisin, a bacteriocin recognized as Generally Recognized as Safe (GRAS), is widely used as a food preservative. However, studies have shown that L. monocytogenes may exhibit reduced susceptibility to nisin in biofilms due to sub-lethal exposure and physiological changes during biofilm formation. Further studies are essential to uncover the mechanisms of biofilm-induced tolerance and resistance, in order to enhance the efficacy of nisin in food-processing environments where biofilms are prevalent. We aimed to investigate the physiological differences and nisin susceptibility among three L. monocytogenes populations: overnight-cultured planktonic cells, long-term planktonic cells incubated for 3 days, and sessile cells harvested from 3-day-old biofilms. Results demonstrated that sessile cells exhibited a significantly longer lag phase (5.71 ± 0.60 h) compared to overnight-cultured planktonic cells (3.58 ± 0.83 h) and 3-day-old planktonic cells (3.60 ± 0.31 h), while no significant differences were observed among the three groups in motility or surface hydrophobicity. Sessile cells require prolonged exposure (approximately 29 minutes) to high concentrations of nisin to achieve equivalent levels of bacterial reduction comparable to those of other cell types (approximately 4–6 minutes), indicating reduced susceptibility to nisin. We also compared the bacterial survival ratios of planktonic, sessile, and biofilm forms of L. monocytogenes after nisin treatment, and found that the biofilm form exhibited the highest survival ratio. These findings suggest that both the transition in cell types and the presence of the biofilm matrix lead to the reduced susceptibility of L. monocytogenes to nisin. It highlights the necessity for further investigation into biofilm structural dynamics and the mechanisms of reduced susceptibility in sessile cells under nisin exposure to improve biofilm control strategies.