Streptococcus suis (S. suis) and Actinobacillus pleuropneumoniae (A. pleuropneumoniae) are primary swine pathogens that have been frequently co-isolated from pigs suffering from severe respiratory disease. The purpose of this study was to investigate the biological impacts of the interactions between S. suis and A. pleuropneumoniae. A single- and dual-species culture model was established in vitro via S. suis HA9801 (serotype 2) and A. pleuropneumoniae CVCC265 (serotype 1). The single or mixed biofilms were imaged by confocal laser scanning microscopy. The biomass and viable cells in biofilms were quantified by crystal violet staining and determination of colony-forming units. The antibiotic susceptibility was determined by a microdilution broth method. The differences in gene transcription in pure- or mixed-species biofilms of S. suis and A. pleuropneumoniae was evaluated by quantitative PCR. S. suis and A. pleuropneumoniae formed two-species biofilms when co-cultured in vitro. When co-cultured with S. suis, biofilm formation by A. pleuropneumoniae was significantly increased with the absence of NAD that is necessary for the growth of A. pleuropneumoniae. Moreover, compared with monocultures, the antibiotic resistance of S. suis and A. pleuropneumoniae was both enhanced in the co-culture model. When grown in dual-species biofilms, for A. pleuropneumoniae, genes associated with virulence factors, including exotoxins and adhesins, were significantly upregulated. For S. suis, virulence factor-related genes cps2, gdh, mrp, and sly were highly induced. These results suggest that the interspecies interactions between S. suis and A. pleuropneumoniae may be cooperative under specific conditions and may play an important role in the disease progression and persistent infection.

中文翻译：

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猪链球菌和胸膜肺炎放线杆菌的体外混合生物膜影响抗生素敏感性并调节毒力因子基因表达。

猪链球菌（S. suis）和胸膜肺炎放线杆菌（A. pleuropneumoniae）是主要的猪病原体，通常与患有严重呼吸道疾病的猪共分离。这项研究的目的是调查猪链球菌和胸膜肺炎链球菌之间相互作用的生物学影响。通过猪链球菌HA9801（血清型2）和胸膜肺炎链球菌CVCC265（血清型1）在体外建立了单物种和双物种培养模型。通过共聚焦激光扫描显微镜对单个或混合生物膜成像。通过结晶紫染色和确定菌落形成单位来定量生物膜中的生物量和活细胞。通过微量稀释肉汤法测定抗生素敏感性。猪链球菌和猪链球菌纯种或混合种生物膜中基因转录的差异。通过定量PCR评估胸膜肺炎。猪链球菌和胸膜肺炎链球菌在体外共培养时会形成两种生物膜。当与猪链球菌共培养时，胸膜肺炎链球菌的生物膜形成显着增加，而没有NAD，胸膜肺炎链球菌的生长是必需的。此外，与单一培养相比，在共培养模型中猪链球菌和胸膜肺炎链球菌的抗药性均得到增强。当在双物种生物膜中生长时，胸膜肺炎链球菌与毒力因子（包括外毒素和粘附素）相关的基因被显着上调。对于猪链球菌，高度诱导了与毒力因子相关的基因cps2，gdh，mrp和sly。这些结果表明猪链球菌和猪链球菌之间的种间相互作用。