Antibiotic tolerance in a drug naïve methicillin sensitive S. aureus (MSSA) strain FDA209P from pre-antibiotic era.

<strong>SCHOOL OF ENVIRONMENTAL SCIENCES JAWAHARLAL NEHRU UNIVERSITY </strong> a talk on <strong>Antibiotic tolerance in a drug naïve methicillin sensitive S. aureus (MSSA) strain FDA209P from pre-antibiotic era.</strong> Speaker: <strong>Dr. Madhuri Singh</strong>, Department of Bacteriology, School of Medicine, Juntendo University, Hongo Campus, Bunkyo-Ku, Tokyo, Japan Date: <strong>9th September 2015 </strong> <strong>Abstract:</strong> The bacterial strategies to overcome antibiotics fall into two categories i.e., Resistance and Tolerance. In case of resistance bacteria grow in the presence of constant antibiotic pressure, whereas tolerance allowsthe bacteria to survive in the presence of antibiotic even at very high concentration. Although both adaptation strategies are responsible for the failure of the antibiotic, tolerance is less understood than resistance. The mechanism of resistance for each antibiotic has been well established, which make the resistant variants to be easily identified and cured in patients. However, the characteristics of antibiotic tolerant strains are generalized and not yet clear for a specific antibiotic exposure, thus, making their isolation and elimination very difficult. Here, we studied the adaptive responses of a drug naive Rosenbach1884 Staphylococcus aureus strain FDA209P, which was collected before antibiotic era, to vancomycin and Imipenem exposures. Of various mechanisms, slow growth and delayed lag phase was the typical characteristics of tolerant variants, irrespective of antibiotic type. Using whole genome sequencing, the vancomycin selected tolerant mutants independently showed five mutations (Single nucleotide polymorphisms)in genes i.e.; pp2C (pp2C protein phosphatase), div IVA (Cell division initiation protein), ribA(riboflavin biosynthesis protein), ileS(isoleucyl-tRNAsynthetase) and SA1386 (Endonuclease IV). And Imiepenem selected strains showed a mutation in parC (Topoisomerase IV) gene. The mutations in some of these genes for instance pp2Cand ileS have already been implicated in antibiotic resistance, however, rest are the newly identified mutations related to antibiotic tolerance. This study will enhance our knowledge of vancomycin tolerance, thus it may bring improvement in diagnosis of the recurrent infections and their treatments.