Interação de Streptococcus agalactiae com modelo murino de diabetes induzida: formação de biofilme, expressão de espécies reativas de oxigênio e de citocinas pró-inflamatórias

Abstract

Streptococcus agalactiae, also known as Group B Streptococcus (GBS), is a pathogen recognized as one of the main causes of severe infections in pregnant women and neonates. In the past few years, the number of immunocompromised adults and elderly presenting diseases caused by S. agalactiae significantly increased, and this became a huge concern to immunosuppressive patients, especially with diabetes. Diabetic individuals present higher susceptibility to bacterial infections and consequently to the development of associated diseases such as pneumonia and cardiovascular problems. According to the literature, there is a correlation between S. agalactiae, diabetes and lung/heart diseases that is still not very elucidated. In addition to the ability to adhere and invade host cells, some Gram-positive microorganisms present a secretion system in response to the cellular microenvironment, being able to evade the immune system and become more virulent. Therefore, the aim of this study was to understand the action of hypervirulent S. agalactiae strains in a murine model of induced diabetes, how they develop diseases such as sepsis, pneumonia and endocarditis, the inflammatory response of the host and the presence of a secretion system acting as a virulence mecanism in S. agalactiae strains. In this study, four different infection routes were performed, involving CD-1 and C57Bl/6 mice inoculated with different virulent strains of S. agalactiae. Murine tissues were used to produce histological slides, confirming the potential of tissue damage after S. agalactie infection; in addition to a higher number of colony-forming units in different diabetic animals and quantification of the reactive oxygen species expression that was also significantly higher in diabetic infected animals. Cellular markers of immune cells were also analyzed by flow cytometry and RT-qPCR, showing a high number of macrophages in diabetic infected animals. Proinflammatory cytokines such as IL-1β and KC protein were quantified and indicated a hyper-inflamed environment in lungs and hearts of diabetic infected animals. After the construction of the essC mutant, we performed tail vain and vaginal inoculations in murine models that showed the reduction in virulent potential when the gene responsible for activating the type 7 secretion system was deleted. Thus, the results obtained in this work demonstrated that hypervirulent S. agalactiae strains were able to disseminate, develop severe manifestations in multiple organs and promote an exacerbated pro-inflammatory microenvironment in infected diabetic animals, enhancing the cellular fragility and toxicity caused by diabetes. Furthermore, confirmation of the presence of essC gene showed that the activity of this secretion system is an advantage to evade the immune system and survive in the host for long periods of time.