Expansion of a subset within C2 clade of Escherichia coli sequence type 131 (ST131) is driving the increasing rates of Aminoglycoside resistance: a molecular epidemiology report from Iran

The most important lineage of Escherichia coli, named sequence type 131 (ST131) is a pandemic clone which drives the increasing rates of antibiotic resistance. While the pervasiveness of ST131 clade C, especially subclades C2 and C1-M27 has been demonstrated in numerous global surveys, no report about the ST131 clades and its virotypes has been published from Iran, so far. So, in this study we investigated and compared the virotypes, antibiotic susceptibility patterns, resistance/ virulence determinants and clonality of ST131 clades collected during one-year surveillance study. Most of isolates belonged to clade C2 (34/76 [44.7%]), with the highest virulence factor (VF) scores and resistance rates. The distinctive profiles of clade C2 virulence genes were revealed by 9principle coordinates analysis9 (PcoA) test. The distribution of hlyA/cnf1virulence genes among clade C2 was not uniform, so that positive strains showed significantly higher rates of resistance markers (blaCTX-M-15, blaOXA-1, aac6Ib/Ib-cr and aac3IIa) and ampicillin-sulbactam/gentamicin/tobramycin resistance. Virotype C as the most common virotype (48.7%) was predominant among clade C1 population, while almost all of virotypes E and F [(22/23), 95.6%] strains belonged to clade C2, with the highest VF scores and aminoglycoside resistance rates. 9Multi locus variable Number tandem repeats analysis9 (MLVA) clustered clades C1 and C2 together, while clades A and B strains were mostly identified as singletons. Appearance of virotypes E and F among clade C2 strains with higher rates of aminoglycoside resistance/virulence genes content demonstrate the shifting dynamics of this pandemic clone in response to antibiotic selection pressure by establishing the newly-emerged subsets.