Planta Med 2007; 73 - P_136
DOI: 10.1055/s-2007-986917

Development of a suitable culture medium for TLC-bioautography. Application to the detection of antibacterial compounds from Cordia gilletii extracts

PN Okusa 1, M Devleeschouwer 2, P Duez 1
  • 1Université Libre de Bruxelles, Institut de Pharmacie, Laboratoire de Pharmacognosie, de Bromatologie et de Nutrition Humaine, CP 205/9, Bd du Triomphe, 1050 Bruxelles, Belgique
  • 2Université Libre de Bruxelles, Institut de Pharmacie, Laboratoire de Microbiologie Pharmaceutique et Hygiène, CP 205/2, Bd du Triomphe, 1050 Bruxelles, Belgique

TLC-bioautography is a convenient and simple way of testing plant extracts and pure substances for their effects on pathogenic microorganisms, allowing an easy detection of active fractions [1]. Its application requires a medium fluid enough to cast microorganism suspensions but viscous enough to stick to the TLC plate and maintain sufficient humidity for bacterial growth. Mueller-Hinton (MH) agar is often used for this purpose, the microorganism suspension being prepared in molten MH agar at about 50°C and distributed over the plate; upon solidification at ambient temperature, the plate is then incubated at 37°C [2]. A MH broth is also frquently used, TLC plates being dipped in the broth containing the microorganisms, air dried and incubated in humidified chambers [3]. These two techniques, however, each present a major drawback; hot molten agar can induce heat shock to microorganisms [4] and broth does not conveniently adhere to the TLC plate or dies too fast. To overcome these problems, we investigated the combination of MH broth and MH agar in different proportions (95:5, 90:10, 85:15, 80:20, 75:25, 70:30, 60:60 and 50:50) to determine a medium fluid enough to prepare bacterial suspensions at 37°C (temperature for optimum growth of many pathogenic bacteria) and which gets solid at ambient temperature to adhere to the TLC plate. The 90:10 mixture of MH broth: MH agar fulfilled both these requirements; higher MH agar proportions were solid at 37°C, and lower MH agar didn't adhere conveniently to the TLC plate.

The proportion 90:10 was applied to detect antimicrobial compounds of a Congolese medicinal plant, Cordia gilletii [5], affording superior chromatographic resolutions compared to MH agar alone or MH broth alone.

Acknowledgement: M. Faes and O. Vaillant (Laboratoire de Pharmacognosie, ULB, Brussels).

References: [1] Rios, JL et al. (1988) J of Ethnopharmacol 23: 127–149. [2] Ahmad, I and Beg, A.Z (2001) J of Ethnopharmacol 74: 113–123. [3] Horvath, G et al. (2002) Acta Biol Szeged 46: 145–146. [4] Stamm, L.V et al. (1991) Infect Immun 59 (4): 1572–1575. [5] Okusa, P.N et al. (2007) J. Ethnopharmacology, in press.