Anthocyanin-Incorporated Chromogenic Agar for Rapid, Selective Detection of Streptococcus pneumoniae via Hydrogen...

The rapid and cost-effective identification of Streptococcus pneumoniae (S. pneumoniae) is crucial for the prompt treatment of pneumonia and meningitis. However, conventional culture methods are time-consuming and molecular techniques are prohibitively expensive in resource-limited settings. To address this challenge, we developed a novel anthocyanin chromogenic agar as a diagnostic tool for the selective and rapid detection of S. pneumoniae. Unlike traditional pH-based indicators, this method exploits the unique oxidative capability of S. pneumoniae, which releases excessive amounts of hydrogen peroxide (H₂O₂). This results in the oxidative degradation of the blue anthocyanin pigment to a colorless form, creating distinct gray zones. The detection efficiency was evaluated as a function of bacterial concentration and incubation time. Upon inoculation at concentrations ranging from 1 to 1000 CFU/mL, color changes were monitored visually over 24 h. Notably, an inoculum of 1000 CFU/mL produced visible gray spots within just 7 h of incubation. The anthocyanin chromogenic agar demonstrated high selectivity against common coexisting pathogens, which caused a pH-dependent color change from blue to pink, whereas only S. pneumoniae induced the specific gray signal. Furthermore, colorimetric results were analyzed using digital image processing for objective detection and differentiation. In conclusion, anthocyanin chromogenic agar presents a clinically applicable alternative that significantly reduces both incubation time and cost compared to other chromogenic agars. While the standardization of natural anthocyanin stability remains a consideration for commercial upscaling, this method offers a promising perspective for decentralized testing in resource-limited settings.