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Journal of Clinical Microbiology, October 2009, p. 3246-3254, Vol. 47, No. 10
0095-1137/09/$08.00+0     doi:10.1128/JCM.00624-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Molecular Surveillance and Population Structure Analysis of Methicillin-Susceptible and Methicillin-Resistant Staphylococcus aureus in High-Risk Wards{triangledown} ,{dagger}

Simona Sergi,1 Francesca Donnarumma,1 Giorgio Mastromei,1 Emanuele Goti,1 Pierluigi Nicoletti,2 Patrizia Pecile,2 Daniela Cecconi,2 Roberta Mannino,2 Rosa Fanci,3 Alberto Bosi,3 Benedetta Bartolozzi,3 and Enrico Casalone1*

CIBIACI and Department of Evolutionary Biology, University of Florence,1 Laboratory of Microbiology, Careggi Hospital,2 Stem Cell Transplantation Unit, Department of Haematology, Careggi Hospital, University of Florence, Florence, Italy3

Received 27 March 2009/ Returned for modification 21 May 2009/ Accepted 23 July 2009

In this study we report the results of analysis of 253 isolates of Staphylococcus aureus (132 methicillin [meticillin]-resistant S. aureus [MRSA] isolates and 121 methicillin-susceptible S. aureus [MSSA] isolates) from 209 patients admitted to 18 high-risk wards of six hospitals located in Florence, Italy, over an 8-month period during which a program of epidemiological surveillance of hospital-acquired infections was conducted. The majority (69%) of the 87 reported S. aureus infections were caused by MRSA. No outbreak events have been reported. All the isolates were typed by amplified fragment length polymorphism (AFLP), and AFLP profiles were analyzed in order to define similarity groups. The discriminatory power of AFLP is very high with MSSA (Simpson index of diversity [D], 95.9%), whereas its resolution capability with MRSA (D, 44.7%) is hampered by the well-known high clonality of these populations (the main MRSA group accounted for 74% of the MRSA isolates). Combining AFLP, improved by visual inspection of polymorphisms, with multiplex PCR greatly increases MRSA resolution (D, 85.5%), resolving the MRSA population to a level that is one of the highest reported in the literature. Widespread and sporadic clones of MSSA and MRSA were identified, and their diffusion in the different hospitals and wards over the surveillance period was studied. The understanding of MSSA and MRSA population structures should be the starting point for the design of a more rational surveillance program for S. aureus species, maximizing benefits and reducing the cost of infection control strategies.

* Corresponding author. Mailing address: Department of Evolutionary Biology, Via Romana 17/19, 50125 Florence, Italy. Phone: 0039 0552288245. Fax: 0039 0552288250. E-mail: enrico.casalone{at}unifi.it

{triangledown} Published ahead of print on 5 August 2009.

{dagger} Supplemental material for this article may be found at http://jcm.asm.org/.

Journal of Clinical Microbiology, October 2009, p. 3246-3254, Vol. 47, No. 10
0095-1137/09/$08.00+0     doi:10.1128/JCM.00624-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.





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