sequence type 131 (ST131) of E. coli 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.
A collection of 73 consecutive ST131 isolates from extraintestinal specimens were investigated for determination of virotypes, antibiotic susceptibility patterns, resistance/ virulence determinants and clades subsets.
Most of isolates belonged to subclade C2 (33/73 [45.2%]) with the highest virulence factor (VF) scores and resistance rates, followed by C1-M27 [18, (24.6%)], C1-non-M27 [14, (19.1%)] and A [8, (10.9%)]. The distinctive profiles of subclade C2 virulence genes were revealed by “principle coordinates analysis” (PcoA) test. The distribution of hlyA virulence gene among subclade C2 was not uniform, so that positive strains [21 (63.6%)] showed significantly higher rates of resistance (blaCTX-M-15, blaOXA-1, aac(6')-Ib-cr, aac(6')-Ib , aac(3)-IIa) and virulence (hra, tia/hek, K5, cnf, papGII, papC) markers, and gentamicin/tobramycin resistance. Virotype C as the most common virotype [34, (46.5%)] was predominant among subclade C1 population, while virotypes E and F [21, (28.7%)] were detected among subclade C2, with the highest VF scores and aminoglycoside resistance rates.
Appearance of virotypes E and F among subclade C2 strains with higher rates of aminoglycoside resistance/virulence genes content shows the shifting dynamics of this pandemic clone in response to antibiotic selection pressure by establishing subsets with higher survival potential.