Probiotics are nonpathogenic microorganisms that confer a health benefit on the host when administered in adequate amounts. Ample evidence is documented to support the potential application of probiotics for the prevention and treatment of infections. Health benefits of probiotics include prevention of diarrhea, including antibiotic-associated diarrhea and traveler's diarrhea, atopic eczema, dental carries, colorectal cancers, and treatment of inflammatory bowel disease. The cumulative body of scientific evidence that demonstrates the beneficial effects of probiotics on health and disease prevention has made probiotics increasingly important as a part of human nutrition and led to a surge in the demand for probiotics in clinical applications and as functional foods.

The ability of probiotics to promote health is attributed to the various beneficial effects exerted by these microorganisms on the host. These include lactose metabolism and food digestion, production of antimicrobial peptides and control of enteric infections, anticarcinogenic properties, immunologic enhancement, enhancement of short-chain fatty acid production, antiatherogenic and cholesterol-lowering attributes, regulatory role in allergy, protection against vaginal or urinary tract infections, increased nutritional value, maintenance of epithelial integrity and barrier, stimulation of repair mechanism in cells, and maintenance and reestablishment of well-balanced indigenous intestinal and respiratory microbial communities. Most of these attributes primarily focus on the effect of probiotic supplementation on the host. Hence, in most cases, it can be concluded that the ability of a probiotic to protect the host from infection is an indirect result of promoting overall health and well-being. However, probiotics also exert a direct effect on invading microorganisms.

The direct modes of action resulting in the elimination of pathogens include inhibition of pathogen replication by producing antimicrobial substances like bacteriocins, competition for limiting resources in the host, antitoxin effect, inhibition of virulence, antiadhesive and antiinvasive effects, and competitive exclusion by competition for binding sites or stimulation of epithelial barrier function. Although much has been documented about the ability of probiotics to promote host health, there is limited discussion on the above mentioned effects of probiotics on pathogens. Being in an era of antibiotic resistance, a better understanding of this complex probiotic–pathogen interaction is critical for development of effective strategies to control infections. Therefore, this chapter will focus on the ability of probiotics to directly modulate the infectious nature of pathogens and the underlying mechanisms that mediate these effects.

益生菌是非致病性微生物，当以足够的量给药时，可以赋予宿主健康。有足够的证据证明支持益生菌在预防和治疗感染中的潜在应用。益生菌的健康益处包括预防腹泻，包括与抗生素有关的腹泻和旅行者腹泻，特应性湿疹，牙结石，结直肠癌以及炎症性肠病的治疗。累积的科学证据证明了益生菌对健康和健康的有益作用 疾病预防使益生菌作为人类营养的一部分变得越来越重要，并导致对临床应用和功能性食品中益生菌的需求激增。

益生菌促进健康的能力归因于这些微生物对宿主产生的各种有益作用。这些包括乳糖代谢和食物消化，抗菌肽的生产和肠道感染的控制，抗癌性，免疫学增强，短链脂肪酸产生的增强，抗动脉粥样硬化和降低胆固醇的特性，在过敏中的调节作用，防止阴道或尿液感染，增加营养价值，维持上皮完整性和屏障，刺激细胞修复机制以及维持和重建平衡良好的本地肠道和呼吸道微生物群落。这些属性中的大多数主要集中在益生菌补充剂对宿主的影响上。因此，在大多数情况下，可以得出结论，益生菌保护宿主免受感染的能力是促进整体健康和福祉的间接结果。但是，益生菌也对入侵的微生物具有直接作用。

导致病原体消除的直接作用方式包括通过产生抗细菌物质（如细菌素）来抑制病原体复制，竞争限制宿主中的资源，抗毒素作用，抑制毒力，抗粘附和抗侵袭作用以及通过竞争竞争而排斥结合上皮屏障功能的部位或刺激。尽管关于益生菌促进宿主健康的能力的文献很多，但是关于益生菌对病原体的上述影响的讨论很少。处于抗生素抗性时代，对这种复杂的益生菌-病原体相互作用的更好理解对于制定控制感染的有效策略至关重要。所以，