Preparation of natural indicator incorporated media and its logical use as a colorimetric biosensor for rapid and sensitive detection of Methicillin-resistant Staphylococcus aureus.

Herein, we report a rational design in preparation of natural indicator incorporated media used as a rapid, selective, sensitive and economic colorimetric biosensor for detection of Methicillin-resistant Staphylococcus aureus (MRSA). Anthocyanins obtained from red cabbage (Brassica oleracea) extract (RCE) are major components and acted as pH responsive indicators in the RCE media. The RCE media was tested for eight gram-positive, four gram-negative bacterial and one model fungal pathogens. We experimentally revealed how salt concentration and antibiotic (cefoxitin) in the RCE media influence the growth of pathogens and especially MRSA. Benefiting pH dependent color change function of anthocyanins is indispensable point of the RCE media in sensing of MRSA growth. The potential MRSA colorimetric sensing mechanism of anthocyanins relies on both protonation and decrease in electron density on structures of anthocyanins by acidic organic volatile compounds produced during growth of MRSA. The protonated anthocyanins with low electron density changed original purple color of the RCE media to pink color. We demonstrated that detection of MRSA was achieved by spectrophotometrically (one single cell) and visually with naked eyes (100 cells) in 2nd hrs and 6th hrs of incubation, respectively. We optimized concentrations of cefoxitin (from 1 μg/mL to 20 μg/mL) against MRSA and Methicillin-sensitive Staphylococcus aureus (MSSA) bacterial cell (3 McFarland) suspensions, then growth of MRSA was visually and clearly detected in the presence of 4 μg/mL cefoxitin between 90 min and 3 h. We persistently offer that the proposed RCE media can be a well alternative to currently used phenotypic methods in clinics owing to its much rapid, sensitive, selective and economic properties.