The present study was carried out to evaluate the prevalence of the clonal subgroup O16:H5-ST131 and the H30 and H30-Rx subclones among E. coli isolates causing extraintestinal infections and to know their virulence potential. The ST131 clonal group accounted for 490 (16%) of the 2995 isolates obtained from clinical samples in five Spanish hospitals during the study period (2005-2012). Among those 490 ST131 isolates, 456 belonged to serotype O25b:H4, 27 to O16:H5 and seven were O-non-typeable:H4 (ONT:H4). All 27 O16:H5 isolates showed fimH41, whereas fimH30 and fimH22 alleles were the most frequently detected among O25b:H4 isolates. The majority (381/490; 78%) of ST131 isolates belonged to H30 subclone, and 302 of 381 (79%) H30 isolates belonged to the H30-Rx subclone. Of the 27 O16:H5 isolates, 48% produced CTX-M-14; however, none produced CTX-M-15. In contrast, 46% of O25b:H4 isolates produced CTX-M-15 while only 2% produced CTX-M-14. More than a half of the O16:H5 isolates (56%) showed the ExPEC status which was significantly more prevalent within O25b:H4 isolates (81%) (P<. 0.01), especially among H30-Rx (97%) isolates. In the present study, a modified virotype scheme was applied within which approximately half (52%) of the O16:H5 isolates showed the C1 specific virotype. Despite their low virulence-gene score (mean of virulence genes 6.4 versus 8.5 in O25b:H4 isolates), six out of the 10 O16:H5 isolates assayed showed high virulence in the mouse model of sepsis (killed 90-100% of mice challenged). Furthermore, four O16:H5 isolates of virotypes A and C1, carrying K2 variant of group II capsule, showed lethality at 24. h. Thus, certain O16:H5 fimH41 isolates show a similar in vivo virulence to that reported with the highly virulent O25b:H4 H30-Rx isolates (Mora et al., PLOS ONE 2014, e87025), supporting their potential virulence for humans.

This work was partially supported by the Red Española de Investigación en Patología Infecciosa (REIPI RD06/0008/1018-1016) and grants PI09/01273, PI10/01955 and PI11/01117 (Instituto de Salud Carlos III, Fondo de Investigación Sanitaria, Ministerio de Economía y Competitividad, Gobierno de España), AGL 2013-47852-R (Ministerio de Economía y Competitividad, Gobierno de España). FEDER-INNTERCONECTA-COLIVAC (CDTI, Ministerio de Economía y Competitividad, Gobierno de España; Consellería de Economía e Industria, Xunta de Galicia; The European Regional Development Fund, ERDF), CN2012/303 and EM2014/001 (Consellería de Cultura, Educación e Ordenación Universitaria, Xunta de Galicia and the ERDF), and PI-0034/2009 (Junta de Andalucía, Consejeria de Salud). Work in the FdlC laboratory was financed by the Spanish Ministry of Economy and Competitivity (BFU2011-26608) and the European Seventh Framework Program (289326/FP7-KBBE-2011-5 and 282004/FP7-HEALTH-2011-2.3.1-2). A.M. acknowledges the Ramón y Cajal programme from the Spanish Ministerio de Economía y Competitividad, Gobierno de España. Rosalia Mamani acknowledges the grant of Agencia Española de Cooperación Internacional (AECI) (Ministerio de Asuntos Exteriores y de Cooperación).

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