Bacterial biofilms are an important virulence factor with a vital role in evasion from the host immune system, colonization and infection. The aim of the present study was to evaluate in vitro the effects of three environmental factors (H⁺, glucose and human plasma) in biofilm formation, by carrier and invasive Streptococcus agalactiae strains of ST17 and ST19 sequence types, including DNase producers and non-producers. Bacteria ability to assemble biofilms was classified based on crystal violet assay. Biofilm formation was also monitored by scanning electron microscopy. Depending on the growth medium used, each bacterial isolate could fit in different biofilm production categories. Our data showed that optimal conditions for S. agalactiae biofilm assembly were reached after 48 h incubation at pH 7.6 in the presence of glucose and inactivated human plasma. In the presence of inactivated human plasma, the biofilm biomass of ST19 strains experienced a higher increase than ST17 strains. The composition of the extracellular polymeric matrix of the three strongest biofilm producers (all from ST17) was accessed by enzymatic digestion of mature biofilms and proteins were shown to be the predominant component. The detailed identification of the extracellular protein components should contribute to the development of new therapeutic strategies to fight S. agalactiae infections.

细菌生物膜是重要的毒力因子，在逃避宿主免疫系统，定植和感染中起着至关重要的作用。本研究的目的是通过ST17和ST19序列类型的携带者和侵入性无乳链球菌菌株（包括DNase产生者和非DNase产生者）在体外评估三种环境因素（H ⁺，葡萄糖和人血浆）对生物膜形成的影响。生产者。细菌组装生物膜的能力根据结晶紫分析法进行分类。还通过扫描电子显微镜监测生物膜的形成。根据所用生长培养基的不同，每种细菌分离株可能适合不同的生物膜生产类别。我们的数据表明无乳链球菌的最佳条件在葡萄糖和灭活的人类血浆中，在pH 7.6下孵育48小时后，达到了生物膜组装。在失活的人血浆存在下，ST19菌株的生物膜生物量比ST17菌株具有更高的增加。通过酶消化成熟的生物膜获得了三个最强的生物膜生产者（均来自ST17）的细胞外聚合物基质的组成，并且蛋白质是主要成分。细胞外蛋白成分的详细鉴定应有助于对抗无乳链球菌感染的新治疗策略的发展。