Effect of lactic acid bacterial extract on the elimination of antibiotic resistance of some clinical bacterial isolates

Background & objectives: Multiple drug resistance (MDR) is a serious health problem and major challenge to global drug discovery programmes. Most of the genetic determinants that confer resistance to antibiotics are located on plasmids in bacteria. The present investigation was undertaken to investigate the ability of the extra- and intra-cellular extract of lactic acid bacteria (LAB) to cure plasmid acquiring resistance in certain clinical antibiotic- resistant bacterial isolates (pseudomonas aeruginosa, staphylococcus areus, klebsiella penuomonia and shigella sp). Methods: Transformation experiments were carried out using clinical isolates as plasmid donor and Escherichia coli strain HB101 (sensitive to the tested antibiotic), as recipient. Minimal inhibitory concentration (MIC) of LAB extracts was determined using the microtiter plate method. Plasmid curing activity of LAB extracts was determined by evaluating the inability of bacterial colonies (pre treated with LAB extract for 18h) to grow in the presence of antibiotics. The physical loss of plasmid DNA in the cured derivatives was further confirmed by agarose gel electrophoresis. Results: The presence of plasmid in transformants was confirmed through electrophoresis and the transformants were also tested for each antibiotic resistance already recorded for the donor isolates. Both extracts (extra – & intra-cellular extracts) inhibited the growth of the clinical isolates. Extracellular extracts exceeded 90% inhibition on some isolates. The LAB extract mediated plasmid curing resulted in the subsequent loss of antibiotic (Chl, Dox, Ery, Gm, Kaf, Lin, and Pen) resistance encoded in the plasmids as revealed by antibiotic resistance profile of cured strains. Conclusions: The extracellular extract of LAB may be a source of anti-plasmid (plasmid borne multiple antibiotic resistance) agents of natural origin.