Analysis of insertion elements in Staphylococcus aureus mutants selected after antibiotic treatment using whole genome sequencing.

DI GREGORIO SABRINA; HAIM MARÍA SOL; HERRERA MELINA; FAMIGLIETTI ANGELA; CARDONA ST; DI CONZA JOSÉ; MOLLERACH MARTA

New Orleans

Congreso; ASM MICROBE 2017; 2017

American Society for Microbiology

Background:In S. aureus antibiotic pressure during prolonged periods of treatment could generate diverse genetic rearrangements. Previously we reported the increase in IS256 transposition after antibiotic treatment in S. aureus strains belonging to diverse lineages. In this study we aim to characterize the full genome sequences of such isogenic strains in order to unravel chromosomal changes associated to mobile elements after antibiotic treatmentMethods: Whole genome sequencing (WGS) using Illumina MiSeq platform was performed on S. aureus strains recovered before and after antibiotic selective pressure with vancomycin (ST100) and tigecycline (ST5, ST239). Genomes were assembled using SPAdes and annotated with PROKKA. ISseeker software was used to explore the genome in order to detect differences in insertion sequence (IS) content between parental and mutant strains, and also to annotate the flanking edges of IS elements in draft genomesResults:The assembled draft genomes yielded the following average results for ST100, ST5 and ST239 respectively: total genome length of 2792075, 2790669 and 2886951 bp; GC content of 32.85, 32.84 and 32.81%; 40, 49 and 73 contigs > 1kb in length; and N50 of 241419, 169268 and 93903 bp. PROKKA annotated an average of 2595 (ST100), 2578 (ST5) and 2742 (ST239) coding sequences.Increase in IS256 copy number was observed in mutant strains belonging to ST5, ST100 and ST239 by ISseeker analysis as already reported. By contrast, there was no change in the copy number of other staphylococcal IS elements. Preliminary results regarding relevant IS256 insertion sites displayed that the global regulators sarX and araC are flanked by IS256 in ST100 parental strain but are absent in ST100 derived mutants suggesting a potential deletion of this region.New IS256 insertion sites identified in mutant strains included the agrB gene, the intergenic region between clfA and coa1 genes (ST100); a region upstream of the walR gene (ST5); and a region downstream of a putative heme peroxidase (ST239).No changes were observed in sigB and rsbU genes, known global regulators of IS256 transpositionConclusions: Comparative genomic analysis of paired S. aureus strains showed evidence of genetic rearrangements after antibiotic treatment mediated by the transposition of IS256 and not by other staphylococcal IS. Such rearrangements might impact in the virulence (agrB, clfA, coa1) and antibiotic resistance (walR) of this pathogen. More studies are ongoing to determine mutational changes associated with antibiotic pressure in these strains Acknowledgments/ References:SPAdes: doi:10.1089/cmb.2012.0021PROKKA: doi:10.1093/bioinformatics/btu153ISseeker: DOI: 10.1099/mgen.0.000062. http://github.com/JCVI-VIRIFX/ISseeker.MSH, SDiG, JDC and MM are also members of CONICET.STC is also professor at the Department of Medical Microbiology and Infectious disease, University of Manitoba, Canada.