Disruption of cytoplasmic membrane-associated functions in Staphylococcus aureus by epicatechin gallate

金黄色葡萄球菌通常是皮肤和粘膜的定植者，但当细菌有机会进入体内时，会引起一系列感染。它还产生一系列导致食物中毒的毒素：如果食品工人携带细菌，它可以进入食物链，即使在咸的食物中也能存活，因为它有耐盐的能力。葡萄球菌通过获得耐药机制显示出显著的抵抗常用抗生素作用的能力。特别是，它们可以获得mecA基因，其产物青霉素结合蛋白（PBP）2a使其能够在高浓度青霉素（如甲氧西林和苯唑西林）存在下存活。这种耐甲氧西林的S.金黄色葡萄球菌（MRSA）对进入医院的患者是一种威胁，特别是对于大手术，并且在社区中越来越多地获得。这些感染一度仅限于人类，但近年来在伴侣动物中遇到，特别是狗和猫;这些细菌很可能最初是从人类获得的。动物和人类MRSA感染难以治疗，迫切需要新的治疗和控制方法，特别是那些降低耐药性出现率的方法。我们已经确定，绿色茶的主要成分之一，一种相对不稳定的物质，称为表儿茶素没食子酸酯，或ECG，改变了S。金黄色葡萄球菌的方式，应该是有益的动物和人类。虽然心电图对MRSA的生长速度没有影响，但它可以将其对青霉素的耐药性降低500倍，这增加了它可以与传统抗生素一起用于治疗感染的可能性。由于ECG修饰而不是杀死目标细菌，因此它不会像目前使用的“杀菌”药物那样施加相同程度的极端选择压力，并且可能会减缓对治疗组合的耐药性的出现。此外，我们还发现，心电图可以防止毒素和酶的分泌，这些毒素和酶使生物体能够引起组织损伤和感染，并导致食物中毒的症状。心电图还可以防止生物膜的形成：这些复杂的细菌聚集体在界面处形成，并且是在组织侵入之前宿主表面和器械（如导管和假体）定殖的必要先决条件。不幸的是，由于其不稳定的性质和中等的活性，天然存在的化学物质对于治疗目的并不理想，我们正在制造具有更有吸引力的特征的ECG衍生物。这些尝试受到阻碍的心电图如何发挥其抗葡萄球菌活动的不完全理解。我们开始了解到它具有如此广泛的特性，因为它插入细菌膜，这是一种具有许多基本酶细胞功能的结构。我们知道，这种化合物改变了膜的性质，从而影响了嵌入其中的蛋白质。例如，青霉素耐药性是由于两种PBP 2和2a之间的合作，使细菌能够在药物存在的情况下继续制造细胞壁。我们将确定ECG是否在细胞分裂的位点破坏这种复合物，或者它是否只是以一种允许在“错误”位点继续合成的方式分离复合物。越来越明显的是，细胞分裂区域的脂质环境的细节对于确定有效的细菌复制是至关重要的;我们将研究心电图改变这一参数的方式。最后，ECG增加葡萄球菌盐敏感性的能力意味着它可以成为保存食物和防止食物中毒相关毒素产生的有效试剂。细菌使用膜定位蛋白泵出钠离子，我们将检查ECG损害这种机制的能力。

Staphylococcus aureus is commonly encountered as a coloniser of skin and mucosa but gives rise to a range of infections when there is an opportunity for the bacteria to enter the body. It also makes a range of toxins that are responsible for food poisoning: if food workers carry the bacterium, it can enter the food chain and will survive even in salty foods due to its ability to tolerate salt. Staphylococci show a remarkable capacity to resist the action of commonly used antibiotics through the acquisition of resistance mechanisms. In particular, they can acquire the mecA gene, whose product penicillin binding protein (PBP) 2a allows it to survive in the presence of high concentrations of penicillins such as methicillin and oxacillin. Such methicillin-resistant S. aureus (MRSA) are a threat to patients entering hospitals, particularly for major surgery, and are increasingly acquired in the community. At one time these infections were confined to humans but in recent years have been encountered in companion animals, especially dogs and cats; in all likelihood the bacteria were initially acquired from humans. Animal and human MRSA infections are difficult to treat and new approaches to therapy and control are urgently needed, in particular those that reduce the rate of emergence of drug resistance. We have established that one of the major components of green tea, a relatively labile substance termed epicatechin gallate, or ECg, alters the properties of S. aureus in a way that should be beneficial to animals and humans. Although ECg has no effect on the growth rate of MRSA, it reduces their resistance to penicillins by a much as five hundredfold, raising the possibility that it can be used alongside conventional antibiotics to treat infections. As ECg modifies rather than kills the target bacteria, it will not apply the same degree of extreme selective pressure as currently used 'bactericidal' drugs and may slow the emergence of resistance to therapeutic combinations. Additionally, we have discovered that ECg prevents the secretion of toxins and enzymes that enable the organism to cause tissue damage and infection and that are responsible for the symptoms of food poisoning. ECg also prevents the formation of biofilms: these complex assemblages of bacteria form at interfaces and are a necessary prerequisite for colonisation of host surfaces and devices such as catheters and prostheses prior to tissue invasion. Unfortunately, the naturally occurring chemical is not ideal for therapeutic purposes due to its labile nature and moderate activity and we are making derivatives of ECg with a more attractive profile. These attempts are hampered by an incomplete understanding of how ECg exerts its anti-staphylococcal activities. We are beginning to learn that it possesses such wide-ranging properties because i inserts into the bacterial membrane, a structure that is home to many essential enzymatic cellular functions. We know that the compound changes the properties of the membrane in a way that will affect the proteins embedded in it. For example, penicillin resistance is due to cooperation between two PBPs, 2 and 2a, enabling the bacteria to continue to make cell wall in the presence of the drug. We will determine if ECg disrupts this complex at the site of cell division or if it simply detaches the complex in a way that allows continued synthesis at 'wrong' sites. It is becoming apparent that the fine detail of the lipid environment in the region of cell division is critical to the determination of efficient bacterial replication; we will examine the way in which ECg alters this parameter. Finally, the capacity of ECg to increase salt sensitivity of staphylococci means that it could become an effective agent for preserving food and preventing the elaboration of toxins associated with food poisoning. The bacteria pump out sodium ions using membrane-located proteins and we will examine the capacity of ECg to compromise this mechanism.