**6. Acknowledgments**

This work was supported in part by grants from the University of Buenos Aires, Buenos Aires, Argentina, and Agencia Nacional de Promoción Científica y Tecnológica (Buenos Aires, Argentina; PICT 1634) to MM. MM and LB are members of "Carrera del Investigador", CONICET, Argentina.

The authors thank clinical microbiologists for providing isolates and clinical data. In particular, Martha von Spetch and Mabel Regueira; as well as Alejandra Corso for providing the pediatric clone isolate.
