Utilization of Indigenous Microbial Isolates and their Mutants in the Biodegradation of Cellulosic Medical Waste

Abstract

This study was designed to evaluate the ability of Pseudomonas fluorescens, Aspergillus fumigatus and Aspergillus niger to degrade cellulosic medical waste. Biodegradation was carried out in bioreactors and the ability to degrade or utilize cellulose was established on the basis of bacterial growth on cellulose medium (filter paper) as sole carbon source and indirectly by the amount of CO₂ produced when substrate was seeded with isolates. Total viable counts of the microbial populations from study sites ranged from 3.9 x10⁶ to 7.3 x 10⁶ cfu/ml for P. fluorescens, 5.4 x 10⁶ to 8.8 x 10⁶ cfu/1ml for A.fumigatus and 2.8 x 10⁶ to 4.4 x 10⁶ cfu/ml for A. niger. After 28 days incubation, cellulose utilization by P. fluorescens, A. fumigatus and A. niger ranged from 26 – 58%, 22 - 46% and 16 - 25% respectively. Mixed cultures of the isolates were found to degrade cellulose better than axenic cultures. The total amount of CO₂ produced by 50g dry weight (gdwt) of axenic cultures of P. fluorescens using untreated cellulose substrate ranged from 13.2mg to 41.7mg, while the same weight of axenic cultures of A. fumigatus produced between 16.8mg and 44.3mg CO₂ and A .niger produced 14.1mg to 40.2mg of CO₂. The amount of CO₂ produced by mutant strains (50 gdwt) over the same period ranged from 16.1mg to 59.3mg by P. fluorescens, 23.4mg to 67.4mg by A. fumigatus and 18.0mg to 38.8mg by A. niger. Mixed cultures of P .fluorescens and A. fumigatus produced the highest amount of CO₂ (168.1mg to 312.8mg). These microorganisms, with cellulose-degrading potential, could be cultivated and used as inoculants for field studies.

Key words: cellulosic medical waste, microbial biodegradation, carbondioxide

Journal of Medical Laboratory Science Vol.13(1) 2004: 48 - 53