# Anthocyanin-Incorporated Chromogenic Agar for Rapid, Selective Detection of Streptococcus pneumoniae via Hydrogen Peroxide-Mediated Oxidation

## TL;DR

A new agar using anthocyanin pigment can quickly detect Streptococcus pneumoniae by turning gray when the bacteria produce hydrogen peroxide.

## Contribution

A novel chromogenic agar using anthocyanin enables rapid, selective detection of S. pneumoniae through H2O2-mediated oxidation.

## Key findings

- Gray zones appear within 7 hours for 1000 CFU/mL S. pneumoniae.
- The agar shows high selectivity against other pathogens.
- Digital image processing enhances objective detection of color changes.

## Abstract

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.