Several factors affect the composition of species that inhabit our intestinal tract, including mode of delivery, genetics and nutrition. Antimicrobial peptides and proteins secreted in the gastrointestinal tract are powerful tools against bacteria. Lactoferrin (LF) inhibits the growth of several bacterial species, such as Enterobacteriaceae, but may stimulate probiotic bacteria. Activity of LF against gut symbiotic species of the Bacteroides genus could give us insights on how these species colonize the gut. We investigated the effects of the antimicrobial protein lactoferrin and its derived peptide, lactoferricin B on two species of strict anaerobes, opportunistic pathogens that cause diseases in both adults and children, commonly found in the microbiota of the human gastrointestinal tract, Bacteroides fragilis and B. thetaiotaomicron., In vitro biofilm formation and binding to laminin were strongly inhibited by a low concentration of lactoferrin (12.5 μg/ml). Conversely, the growth of the strains in a micro-dilution assay in minimal media with different iron sources was not affected by physiological concentrations (2 mg/ml) of apo-lactoferrin or holo-lactoferrin. The combination of lactoferrin with antibiotics in synergism assays was also negative. The lactoferricin B fragment was also unable to inhibit growth in a similar test with concentrations of up to 32 μg/ml. Resistance to lactoferrin could confer an advantage to these species, even when high amount of this protein is present in the gastrointestinal tract. However, colonization is hampered by the binding and biofilm inhibitiory effect of lactoferrin, which may explain the low prevalence of Bacteroides in healthy babies. Resistance to this antimicrobial protein may help understand the success of these opportunistic pathogens during infection in the peritoneum.

几个因素会影响我们肠道的物种组成，包括分娩方式，遗传和营养。胃肠道分泌的抗菌肽和蛋白质是抵抗细菌的强大工具。乳铁蛋白（LF）抑制几种细菌的生长，例如肠杆菌科，但可能会刺激益生菌。LF对拟杆菌属的肠道共生物种的活性可能使我们对这些物种如何在肠道中定居有所了解。我们研究了抗菌蛋白乳铁蛋白及其衍生肽乳铁蛋白B对两种严格厌氧菌的影响，这两种厌氧菌是引起成年人和儿童疾病的机会病原体，通常在人类胃肠道微生物区系中发现，脆弱的拟杆菌和B. thetaiotaomicron。，体外低浓度的乳铁蛋白（12.5μg/ ml）强烈抑制生物膜的形成和与层粘连蛋白的结合。相反，在微量稀释法中，在具有不同铁源的基本培养基中，菌株的生长不受脱脂乳铁蛋白或全乳铁蛋白的生理浓度（2 mg / ml）的影响。协同测定中乳铁蛋白与抗生素的结合也为阴性。浓度高达32μg/ ml的类似测试中，乳铁蛋白B片段也无法抑制生长。即使在胃肠道中存在大量这种蛋白，对乳铁蛋白的抗性也可以赋予这些菌种以优势。然而，乳铁蛋白的结合和生物膜抑制作用阻碍了定植，这可能解释了拟杆菌属的低流行在健康的婴儿中。对这种抗菌蛋白的耐药性可能有助于了解这些机会病原体在腹膜感染过程中的成功。