Instituto de Biología y Medicina Experimental, CONICET, 1428, Buenos Aires, Argentina.
J Dairy Sci. 2011 Jan;94(1):138-45. doi: 10.3168/jds.2010-3319.
Bovine mastitis is one of the most economically deleterious diseases affecting dairy herds and results from an infection of the udder by pathogenic microorganisms such as Staphylococcus aureus, Streptococcus uberis, and Escherichia coli. The mammary gland is capable of preventing and combating bacterial infection by means of a complex network of innate and adaptive immune mechanisms. Lactoferrin is an 86-kDa protein with antibacterial activity that plays a role in the mammary gland's defense against infection. β-Lactoglobulin (β-LG) is an 18-kDa protein that is present in most mammals but is notably absent in humans, rodents, and lagomorphs. Different genetic variants of this protein exist, with β-LG A and β-LG B being the most common. In spite of being well studied, the biological function of β-LG is not thoroughly understood, and most noticeably, no reports exist on the effects of the native protein on bacterial growth. Hence, the objective of this study was to assess the potential antibacterial activity of β-LG against mastitis agents. To do this, we purified β-LG from normal bovine milk using a mild, nondenaturing method and performed in vitro growth inhibition assays with Staph. aureus, E. coli, and Strep. uberis. β-Lactoglobulin inhibited the growth of Staph. aureus and Strep. uberis but had no effect on E. coli. The antimicrobial activity against Staph. aureus and Strep. uberis was concentration dependent and was elicited by the intact protein because Tricine-sodium dodecyl sulfate-PAGE and analytical gel filtration chromatography did not reveal the presence of short degradation peptides. Analysis of the genetic variants of β-LG showed that β-LG A has higher inhibitory activity against Staph. aureus and Strep. uberis than β-LG B. Coincubation of β-LG and lactoferrin resulted in an augmented antibacterial activity against Staph. aureus, suggesting an additive effect of the proteins. This result, along with the proteins' complementary spectrum of action, suggests that β-LG and lactoferrin may complement each other in the mammary gland's defenses against bacterial infection.
奶牛乳腺炎是影响奶牛群的最具经济危害性疾病之一，是由金黄色葡萄球菌、停乳链球菌和大肠杆菌等病原微生物感染乳房引起的。乳腺通过复杂的先天和适应性免疫机制网络来预防和对抗细菌感染。乳铁蛋白是一种具有抗菌活性的 86kDa 蛋白，在乳腺抗感染中发挥作用。β-乳球蛋白（β-LG）是一种存在于大多数哺乳动物中的 18kDa 蛋白，但在人类、啮齿动物和兔形目动物中明显不存在。该蛋白存在不同的遗传变异体，其中β-LG A 和β-LG B 最为常见。尽管已经进行了广泛的研究，但β-LG 的生物学功能仍未被完全理解，最明显的是，没有关于天然蛋白对细菌生长影响的报道。因此，本研究旨在评估β-LG 对乳腺炎病原体的潜在抗菌活性。为此，我们使用温和的非变性方法从正常牛乳中纯化β-LG，并进行了体外生长抑制试验，以评估其对金黄色葡萄球菌、大肠杆菌和停乳链球菌的作用。β-乳球蛋白抑制金黄色葡萄球菌和停乳链球菌的生长，但对大肠杆菌没有影响。抗菌活性对金黄色葡萄球菌和停乳链球菌具有浓度依赖性，并且是由完整蛋白引起的，因为三羟甲基氨基甲烷-十二烷基硫酸钠-聚丙烯酰胺凝胶电泳和分析凝胶过滤色谱法未显示存在短的降解肽。对β-LG 的遗传变异体进行分析表明，β-LG A 对金黄色葡萄球菌和停乳链球菌的抑制活性高于β-LG B。β-LG 和乳铁蛋白的共同孵育导致对金黄色葡萄球菌的抗菌活性增强，表明两种蛋白具有相加作用。这一结果以及两种蛋白作用谱的互补性表明，β-LG 和乳铁蛋白可能在乳腺防御细菌感染方面相互补充。
