Modified MacConkey agar: a simple selective medium for isolation of Burkholderia pseudomallei from soil

Abstract

Background and objectives:A selective medium is required for isolation of Burkholderia pseudomallei from soil. The present study aimed to develop an easy to prepare selective media by modifying MacConkey agar medium for improved isolation of B. pseudomallei from soil. Materials and methods: The media was prepared by using commercially available MacConkey agar as the basal medium and incorporating it with 4% glycerol and four antimicrobials namely vancomycin, amphotericin B, gentamicin and colistin at a concentration of 2.5 mg/L, 1 mg/L, 5 mg/L and 10 mg/L respectively. The media was initially optimized for growth of B. pseudomallei by addition of 100 organisms/plate of B. pseudomallei and ATCC strains of Gram negative and Gram positive bacteria. Sterile and unsterile soils were spiked with graded concentration (1x106 to 1x101 CFU/gm of soil) of B. pseudomallei and other clinical and saprophytic Gram negative organisms and cultured on MacConkey, Ashdown and modified MacConkey media after enrichment in Ashdown broth. Growth of B. pseudomallei in the three media was compared. The newly devised media was termed as - Modified MacConkey agar for Burkholderia (MMB media). Results: Culture of supernatant from spiked sterile soil after enrichment showed equivalent isolation of B. pseudomallei on MMB and Ashdown’s media and there was 100% inhibition of Klebsiella pneumoniae, Escherichia coli and Pseudomonas aeruginosa on MMB medium. Almost similar inhibition of Comamonas testosteroni, Aeromonas salmonicida and Burkholderia cepacia was observed on both MMB and Ashdown’s media. Culture of sterile soil seeded with different concentrations of P. aeruginosa showed no growth in MMB media. But there was growth of P. aeruginosa when sterile soil samples spiked with 1x106 to 1x103 CFU of P. aeruginosa were cultured in Ashdown media. When unsterile soil was seeded with graded concentration of B. pseudomallei, the colony count of this bacterium gradually declined in all three medium with decreased spiking concentrations. Growth of other soil organisms was less in MMB media compared to other two media. Conclusion: The newly devised MMB media is selective and easy to prepare for the detection of B. pseudomallei from soil. IMC J Med Sci. 2024; 18(1):011. DOI: https://doi.org/10.55010/imcjms.18.011 *Correspondence:Md. Shariful Alam Jilani, Department of Microbiology, Ibrahim Medical College, 1/A Ibrahim Sarani, Segun Bagicha, Dhaka-1000, Bangladesh. Email: jilanimsa@gmail.com