Repurposing blood glucose test strips for identification of the antimicrobial colistin

The presence and fate of antimicrobial residues in the environment is a subject of growing concern. Previous researchers have demonstrated the persistence of residues in soil and water. Additionally, antimicrobial resistance is a growing concern, particularly to public health, animal health and economic development. In this study, a low cost, commercial blood glucose meter was explored as the basis for detecting antimicrobial residues in conjunction with a microorganism sensitive to this residue. A microbial bioassay was developed based on the metabolic response of Geobacillus stearothermophilus, a sensitive bacteria used in the determination of antimicrobial residues in food products, by measuring changes in glucose as a result of metabolic activity. After optimizing experimental conditions, this sensing strategy was tested using bacterial cultures in the presence of colistin, a last-resort antibiotic used for human and animal health. Growth of G. stearothermophilus was measurable as a change in glucose concentration after 2–4 h incubation at 60 °C, when LB media was supplemented with 100 mg/dL of glucose. The lowest measured colistin concentration that resulted in inhibition of growth was 1 mg/L colistin and an increase in lag phase resulted at 100 µg/L colistin. To increase the sensitivity of the assay, we then added a sub-inhibitory concentration of chloramphenicol to the media and found that growth inhibition could be achieve at a lower colistin concentration of 8 µg /L. These results provide a promising basis for a future low-cost sensor to identify antimicrobial residues from environmental samples in the field.