LAB-SCALE PRODUCTION OF RHAMNOLIPID BY PSEUDOMONAS AERUGINOSA A3 AND STUDY ITS SYNERGISTIC EFFECT WITH CERTAIN ANTIBIOTICS AGAINST SOME PATHOGENIC BACTERIA

Abstract

This study was aimed to obtain the considerable amount of the biosurfactant (rhamnolipid) from local isolate of Pseudomonas aeruginosa on industrial-scale. A 7L laboratory bioreactor was appointed to accomplish this task and all conditions of production were set as previously by batch culture experiments. Bioreactor with 3.5 L working volume was conducted for 120 h to obtain 16 g/L at 30ºC and 6.5 pH. The supernatant of production medium was used to reduce the surface tension of water from 72 to 27 mN/m, and the emulsification index was reached to 67%. The product was extracted with a mixture of solvents, purified by silica gel using a column of glass chromatography (3.5 × 30cm), and characterized by TLC and FTIR where it turn out that the biosurfactant is composed of both mono- and di-rhamnolipid. Mono-RL was tested for its antibacterial activity against some clinical isolates of Gram-positive and Gram-negative bacteria to obtain the MIC, which was about 250µg/ml, also at same concentration, the toxicity against Rat embryonic fibroblast (REF) cell line was reached to 23%. The combination effect of Mono-RL with some antibiotics was studied against pathogenic clinical isolates revealed that there is a synergistic effect with ampicillin against S. aureus and Serratia marcescens, with cefotaxime against E. coli and Kelbsiella pneumoniae, same as with tetracycline.