Acknowledgements
We wish to thank: E. Carretto (Arcispedale of Santa Maria Nuova, Reggio Emilia), F. Luzzaro (Hospital Alessandro Manzoni, Lecco), F. Campanile and S. Stefani (Microbiology, University of Catania, Catania), P. Frascaria, G. Bruno, R. Tomei and S. Falasca (Hospital San Salvatore, L’Aquila) for their cooperation in the collection of clinical isolates.