The ability of bacterial pathogens to form biofilms is an important virulence mechanism in relation to its pathogenesis and transmission. Biofilms play a crucial role in survival in unfavourable environmental conditions, act as reservoirs of microbial contamination and antibiotic resistance. For intestinal pathogen Campylobacter jejuni, biofilms are considered to be a contributing factor in transmission through the food chain and currently, there are no known methods for intervention. Here we present an unconventional approach to reducing biofilm formation by C. jejuni by the application of D-amino acids (DAs), and L-amino acids (LAs). We found that DAs and not LAs, except L-alanine, reduced biofilm formation by up to 70%. The treatment of C. jejuni cells with DAs changed the biofilm architecture and reduced the appearance of amyloid-like fibrils. In addition, a mixture of DAs enhanced antimicrobial efficacy of D-Cycloserine (DCS) up to 32% as compared with DCS treatment alone. Unexpectedly, D-alanine was able to reverse the inhibitory effect of other DAs as well as that of DCS. Furthermore, L-alanine and D-tryptophan decreased transcript levels of peptidoglycan biosynthesis enzymes alanine racemase (alr) and D-alanine-D-alanine ligase (ddlA) while D-serine was only able to decrease the transcript levels of alr. Our findings suggest that a combination of DAs could reduce biofilm formation, viability and persistence of C. jejuni through dysregulation of alr and ddlA.

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D-氨基酸对空肠弯曲菌生物膜形成的抑制作用

细菌病原体形成生物膜的能力是与其发病机制和传播有关的重要毒力机制。生物膜在不利的环境条件下的生存中起着至关重要的作用，是微生物污染和抗生素耐药性的储存库。对于空肠弯曲菌来说，生物膜被认为是通过食物链传播的重要因素，目前尚无已知的干预方法。在这里，我们介绍了一种非常规方法，可通过应用D-氨基酸（DAs）和L-氨基酸（LAs）来减少空肠弯曲杆菌生物膜的形成。我们发现，除L-丙氨酸外，DAs而非LAs最多可减少70％的生物膜形成。用DAs处理空肠弯曲杆菌细胞改变了生物膜的结构并减少了淀粉样蛋白原纤维的出现。此外，与单独的DCS治疗相比，DAs混合物可增强D-环丝氨酸（DCS）的抗菌功效，最高可达32％。出乎意料的是，D-丙氨酸能够逆转其他DA和DCS的抑制作用。此外，L-丙氨酸和D-色氨酸降低了肽聚糖生物合成酶丙氨酸消旋酶（alr）和D-丙氨酸-D-丙氨酸连接酶（ddlA）的转录水平，而D-丝氨酸只能降低alr的转录水平。我们的研究结果表明，DAs的组合可通过alr和ddlA的失调减少空肠弯曲杆菌的生物膜形成，活力和持久性。D-丙氨酸能够逆转其他DA和DCS的抑制作用。此外，L-丙氨酸和D-色氨酸降低了肽聚糖生物合成酶丙氨酸消旋酶（alr）和D-丙氨酸-D-丙氨酸连接酶（ddlA）的转录水平，而D-丝氨酸只能降低alr的转录水平。我们的研究结果表明，DAs的组合可通过alr和ddlA的失调减少空肠弯曲杆菌的生物膜形成，活力和持久性。D-丙氨酸能够逆转其他DA和DCS的抑制作用。此外，L-丙氨酸和D-色氨酸降低了肽聚糖生物合成酶丙氨酸消旋酶（alr）和D-丙氨酸-D-丙氨酸连接酶（ddlA）的转录水平，而D-丝氨酸只能降低alr的转录水平。我们的研究结果表明，DAs的组合可通过alr和ddlA的失调减少空肠弯曲杆菌的生物膜形成，活力和持久性。