Preparation of nature inspired indicator based agar for detection and identification of MRSA and MRSE

Natural indicator, red cabbage extract (RCE) incorporated agars were developed, for the first time, as colorimetric sensors for identification of MRSA and MRSE. These strains were differentiated in RCE media with addition of plasma due to coagulase positive property of MRSA, they were differentiated by manipulating NaCl and introducing gelatin in RCE agar. RCE agar was examined based on concentration of NaCl and MRSA concentrations and incubation time for detection of MRSA. RCE agar was prepared mixing 10g peptone, 1g beef extract, NaCl, 15 mg/mL agar and 25% RCE in distilled water and sterilized in autoclave at 121°C for 15 min. 4 μg/mL cefoxitin was added to mixture based on experiment. The color of RCE agar including 50 mg/mL NaCl was turned to pink dependent upon growth of MRSA, MRSE and MSSA, growth of E. coli was inhibited due to its salt intolerance property. Introducing 4 μg/mL cefoxitin, growth of MRSA was not observed. 1 CFU/mL, 10 CFU/mL, 100 CFU/mL and 1000 CFU/mL of MRSA inoculated on the RCE agar showed growth and led color change in 24 hrs. Additionally, slight pink spots on RCE agar and pale pink color on whole RCE agar were appeared in 8th hrs and 11th hrs of inoculation, respectively when 1000 CFU/mL of MRSA used. The RCE agar was successfully used for detection of MRSA and differentiation of them. Finally, the RCE agar can be implemented in clinics and may alleviate incubation time and cost compared to the chromogenic agars.

Keywords: (MRSE); Agar; Colorimetric sensor; Detection; MRSA; Methicillin-resistant Staphylococcus aureus; Methicillin-resistant Staphylococcus epidermidis; Natural indicator.