Carvacrol, a natural antimicrobial compound present in the essential oil fraction of oregano and thyme, is bactericidal towards Bacillus cereus. A decrease of the sensitivity of B. cereus towards carvacrol was observed after growth in the presence of non-lethal carvacrol concentrations. A decrease of the melting temperature (Tm) of membranes from 20.5 degrees C to 12.6 degrees C was the immediate effect of the addition of carvacrol. Cells adapted to 0.4 mM carvacrol showed a lower membrane fluidity than nonadapted cells. Adaptation of 0.4 mM carvacrol increased the Tm from 20.5 degrees C to 28.3 degrees C. The addition of carvacrol to cell suspensions of adapted B. cereus cells decreased Tm again to 19.5 degrees C, approximately the same value as for the non-adapted cells in the absence of carvacrol. During adaptation, changes in the fatty acid composition were observed. The relative amount of iso-C13:0, C14:0, and iso-C15:0 increased and cis-C16:1 and C18:0 decreased. The head-group composition also changed, two additional phospholipids were formed and one phospholipid was lacking in the adapted cells. It could be concluded that B. cereus adapts to carvacrol when present at non-lethal concentrations in the growth medium by lowering its membrane fluidity by changing the fatty acid and headgroup composition.

译文

香芹酚是一种天然抗菌化合物,存在于牛至和百里香的精油部分中,对蜡样芽孢杆菌具有杀菌作用。在非致命香芹酚浓度存在下生长后,观察到蜡状芽孢杆菌对香芹酚的敏感性降低。膜的熔化温度 (Tm) 从20.5 ℃ 降低到12.6 ℃ 是添加香芹酚的直接效果。与不适应的细胞相比,适应于0.4 mM香芹酚的细胞显示出更低的膜流动性。0.4 mM香芹酚的适应将Tm从20.5 ℃ 提高到28.3 ℃。向适应的蜡状芽孢杆菌细胞的细胞悬液中添加香芹酚再次将Tm降低至19.5 ℃,与不存在香芹酚的非适应细胞的值大致相同。在适应过程中,观察到脂肪酸组成的变化。iso-C13:0、C14:0和iso-C15:0的相对量增加,cis-C16:1和C18:0降低。头基组成也发生了变化,形成了两种额外的磷脂,并且在适应的细胞中缺少一种磷脂。可以得出结论,蜡状芽孢杆菌在生长培养基中以非致命浓度存在时,通过改变脂肪酸和头基组成来降低其膜流动性,从而适应香芹酚。

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