Estudo das infecções por Streptococcus agalactiae em modelo murino de diabetes induzida

Abstract

Streptococcus agalactiae, also known as Group B Streptococcus (GBS), is the most common cause of bacterial infections in newborns and imunnocompromised adults, and it is classified in ten different GBS capsular types (Ia, Ib, II-IX). Severe GBS infections can also afflict nonpregnant adults, particularly in the elderly and individuals compromised by underlying medical conditions, like diabetes, cardiovascular diseases or cancer. The main reasons for increased incidence of GBS disease is not well understood. Among all diseases associated with GBS infections, diabetes is one of the most common. The insulin resistance is associated with increase susceptibility of invasive bacterial infections. The aim of the present study was to investigate the mechanisms of GBS pathogenesis using streptozotocin-induced diabetic models in mice. In addition, we analyzed seven virulence genes (lmb, gbs2018 [ST-17], PI-1, PI-2a, PI-2b, fbsA, fbsB e hylB) as genomic biomarkers in GBS90356. Six-week-old male and female Swiss webster mice were divided in four groups: 1. control; 2. infected control; 3. diabetic; 4. infected diabetic. Three days later, the mice were infected intranasal with hipervirulent GBS90356 strain. After three and five weeks, mice were euthanized and lungs and heart were collected. Lungs fragments were fixed with paraformaldehyde 4% for histopathological analysis and for determining colony-forming units per milliliter (CFU/mL) on blood agar base containing 5 % sheep defibrinated blood. Heart fragments were only submitted to CFU/mL count. Only heart tissues presented higher bacterial growth on diabetic mice (~103 CFU/mL) when compared to control. A higher number of inflammatory cells were observed (mostly macrophages) in groups 2 and 4. Group 4 presented less tick and ruptured alveolar septa and hemorrhagic points. Diabetic groups presented more collagen and elastic fibers expression. The GBS90356 strain presented all the virulence genes, except PI-2a, justifying the invasive potential of the strain studied. The results showed that intranasal GBS infection in mice was successful and suggest that individuals with diabetes can develop severe GBS infections, activate intense immune response and be more susceptible to recurrent lung infections.