Solar disinfection of MODS mycobacterial cultures in resource-poor settings

Abstract

Introduction. Safe disposal of TB culture material in which the infectious burden of clinical samples has been greatly amplified is an important challenge in resource-limited settings. The bactericidal capacity of solar cookers has been demonstrated previously for conventional bacteria and contaminated clinical waste. We investigated the use of a simple solar cooker for the sterilization of mycobacterial broth cultures from the microscopic observation drug susceptibility assay (MODS). Methods. Simulated TB culture materials were prepared by inoculating 24-well MODS plates with 500 μL of a known concentration of Mycobacterium bovis BCG. In a series of experiments, samples were simultaneously placed inside a box-type solar cooker and control box and removed at timepoints between 15 minutes ind 6 hours. Quantitative cultures were performed using retrieved samples to determine sterilization effect. Results. All cultures from the control box were positive at or within 1-4 logs of inoculation concentration. Simulated culture plates at concentrations from 1.03 colony-forming-units (CFU)/ml to 107 CFU/ml were completely sterilized after only one hour of cooker exposure, at temperatures between 50-102°C. At 109 CFU/ml (far in excess of diagnostic cultures), it was only possible to recover mycobacterial growth in plates removed after 15 minutes. By 30 minutes all plates were effectively sterilized. Discussion. Solar disinfection provides a very effective, safe and low-cost alternative to conventional equipment used for disposal of mycobacterial culture material. Effect of climatic conditions and optimal operating procedure remain to be defined. © 2007 Nathavitharana et al.