Inhibitory Effect of Shikimic Acid on Biofilm Formation and the Expression of Critical Biofilm-associated Genes in Streptococcus agalactiae

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Background Streptococcus agalactiae is well-known for causing adverse pregnancy outcomes, such as stillbirths and miscarriages, as well as being a major cause of newborn sepsis and meningitis. Aims This study sought to investigate how shikimic acid influences the expression of genes involved in the synthesis of biofilms. Methods A total of 181 specimens were obtained from pregnant women. Twenty-two isolates were bacteriologically recognized as S. agalactiae from these specimens. They were gathered from hospitals in the Al-Anbar province. These twenty-two isolates were identified as Group B streptococcus (GBS) based on their cultural and microscopical properties, as well as automated (VITEK-2 system) and molecular identification based on the atr gene, which is an essential gene expressed in all S. agalactiae isolates. Results GBS produced varying amounts of biofilm (weak, moderate, and strong). Shikimic acid (SA) was tested for its antibacterial effect against biofilm. Shikimic acid was incubated at various doses, and its effects on biofilm growth and formation were evaluated by MTT and crystal violet assay. SA greatly reduced the GBS inhibitory effects on GBS biofilms in pregnant women. Furthermore, it demonstrated a potent initial cell attachment, but it had less inhibitory effects on biofilms that had already been developed on polystyrene surfaces after eight hours. However, the Checkerboard approach produced a synergistic interaction between erythromycin and shikimic acid. Polymerase Chain Reaction (PCR) was used to verify the presence of pilA and PilB genes in the GBS strain. We detected these genes by PCR. The results revealed that pilA was found only in three isolates (13.63%), but pilB was found in all isolates (22/22;100%). Conclusion Quantitative real-time PCR was used to determine the effect of shikimic acid on the expression of genes (sag1407 and sag1408), and the results showed down-regulation of the expression of biofilm synthesis genes sag1407 and sag1408 when treated with Sub-MIC of shikimic acid.