Abstract
Chlorpyrifos (CP) is the most commonly used pesticide throughout the world. Its widespread use in agriculture and its potential toxicity to humans from ingestion of CP contaminated food have raised concerns about its risk to health. Human intestinal microflora has the ability to degrade pesticides, but the exact mechanisms involved and the metabolite end-products formed are not well understood. The primary objective of this work was to analyse the in vitro degradation of CP by five model intestinal bacteria namely Lactobacillus lactis, L. fermentum, L. plantarum, Escherichia coli and Enterococcus faecalis. Plate assay results revealed that L. lactis, E. coli and L. fermentum could grow with high concentrations of CP (>1,400 μg/mL), whereas E. faecalis and L. plantarum could grow with concentrations as low as 400 and 100 μg/mL, respectively. The best three CP degraders were therefore used in further experiments. The degradation of CP-induced organophosphorous phosphatase (OPP) production and that OPP concentration were higher in the supernatant (extracellular) rather than inside the cells by factor of up to 28. L. fermentum degraded 70 % CP with 3,5,6-trichloro-2-pyridinol (TCP) detected as the end product. L.lactis degraded up to 61 % CP with chlorpyrifos oxon detected as the end product, whereas E.coli degraded a lesser concentration (16 %) to chlorpyrifos-oxon and diethylphosphate.