IBMC - Instituto de Biologia Molecular e Celular, Rua do Campo Alegre 83, Porto, Portugal.
ICBAS - Instituto de Ciências Biomédicas de Abel Salazar, Largo do Professor Abel Salazar 2, 4099-003 Porto, Portugal.
J Med Microbiol. 2011 Dec;60(Pt 12):1717-1724. doi: 10.1099/jmm.0.031922-0. Epub 2011 Jul 28.
Staphylococcus epidermidis is an opportunistic pathogen and, due to its ability to establish biofilms, is a leading causative agent of indwelling medical device-associated infection. The presence of high amounts of dormant bacteria is a hallmark of biofilms, making them more tolerant to antimicrobials and to the host immune response. We observed that S. epidermidis biofilms grown in excess glucose accumulated high amounts of viable but non-culturable (VBNC) bacteria, as assessed by their low ratio of culturable bacteria over the number of viable bacteria. This effect, which was a consequence of the accumulation of acidic compounds due to glucose metabolism, was counteracted by high extracellular levels of calcium and magnesium added to the culture medium allowing modulation of the proportions of VBNC bacteria within S. epidermidis biofilms. Using bacterial inocula obtained from biofilms with high and low proportions of VBNC bacteria, their stimulatory effect on murine macrophages was evaluated in vitro and in vivo. The inoculum enriched in VBNC bacteria induced in vitro a lower production of tumour necrosis factor alpha, interleukin-1 and interleukin-6 by bone-marrow-derived murine macrophages and, in vivo, a lower stimulatory effect on peritoneal macrophages, assessed by increased surface expression of Gr1 and major histocompatibility complex class II molecules. Overall, these results show that environmental conditions, such as pH and extracellular levels of calcium and magnesium, can induce dormancy in S. epidermidis biofilms. Moreover, they show that bacterial suspensions enriched in dormant cells are less inflammatory, suggesting that dormancy can contribute to the immune evasion of biofilms.
表皮葡萄球菌是一种机会性病原体，由于其形成生物膜的能力，是导致留置医疗设备相关感染的主要病原体。休眠细菌的大量存在是生物膜的一个标志，使它们更能耐受抗生素和宿主免疫反应。我们观察到，在过量葡萄糖中生长的表皮葡萄球菌生物膜积累了大量的存活但非可培养（VBNC）细菌，这可以通过可培养细菌与活细菌数量的低比例来评估。这种效应是由于葡萄糖代谢产生的酸性化合物积累所致，通过向培养基中添加高浓度的细胞外钙和镁来对抗，从而允许调节表皮葡萄球菌生物膜中 VBNC 细菌的比例。使用从 VBNC 细菌比例高和低的生物膜中获得的细菌接种物，评估了它们对体外和体内鼠巨噬细胞的刺激作用。富含 VBNC 细菌的接种物在体外诱导骨髓来源的鼠巨噬细胞产生较低水平的肿瘤坏死因子-α、白细胞介素-1 和白细胞介素-6，并且在体内通过增加 Gr1 和主要组织相容性复合体 II 分子的表面表达，对腹腔巨噬细胞产生较低的刺激作用。总之，这些结果表明，环境条件（如 pH 值以及细胞外钙和镁的水平）可以诱导表皮葡萄球菌生物膜进入休眠状态。此外，它们表明富含休眠细胞的细菌悬浮液的炎症反应性较低，这表明休眠状态可能有助于生物膜的免疫逃避。
