522 Methicillin-Resistant Staphylococcus aureus (MRSA) Genomic Pattern: Temporal Changes in an Endemic Hospital Environment

Saturday, March 20, 2010
Grand Hall (Hyatt Regency Atlanta)
Gleice Cristina Leite, MD , Faculdade de Ciências Médicas, Universidade Estadual de Campinas, Campinas, Brazil
Maria Clara Padoveze, RN, MD, PhD , Escola de Enfermagem, Universidade de Sao Paulo, Sao Paulo, Brazil
Maria Luiza Moretti, MD, PhD , Faculdade de Ciências Médicas, Universidade Estadual de Campinas, Campinas, Brazil
Background: MRSA has long been recognized as an important nosocomial pathogen causing a variety of infections. MRSA is able to produce a specific penicillin-binding protein (PBP) called PBP2a or PBP2’ encoded by the mecA gene, which is carried by a mobile genetic element, called staphylococcal cassette chromosome mec (SCCmec) integrated in the MRSA chromosome. This protein possesses reduced affinities for binding to β-lactam antibiotics. SCCmec type III strains are usually hospital-acquired, while SCCmec type IV strains are associated with community acquisition.
Objective: to identify the DNA genomic profile and SCCmec type in a set of samples of MRSA obtained from patients seeking assistance at a university hospital in Campinas, Brazil, and to describe its geographic and temporal distribution.
Methods: a total of 99 MRSA isolates obtained from 89 patients in the period from January 1999 to February 2004 were analyzed and their respective medical records were reviewed. MRSA strains were identified from blood and central venous catheter tip cultures collected for clinical reasons. SCCmec profile was obtained using the polymerase chain reaction (PCR-multiplex) and the genomic profile was defined by means of pulsed-field gel electrophoresis (PFGE) using SmaI enzyme restriction. The Dice coefficient was used to determine similarity.
Results: the analysis of genomic DNA by PFGE showed 26 different profiles, whose distribution revealed a temporal pattern. The PFGE profile predominance changed over the studied period. Only one strain showed to be present during the whole period although without numerical relevance. No geographic pattern of strain distribution among the hospital units could be observed. SCCmec type IIIA were identified in 92.9% (n=92) of the strains, and SCCmec type IV were identified in 7.1% (n=7) of the strains. SCCmec type IV strains showed resistance against all antimicrobials except vancomicin. Reviewal of the patient’s medical record did not suggest community acquisition in any of the cases. SCCmec type IV strains showed several different PFGE profiles and were not clustered in time or space.

Conclusions: genomic MRSA profile predominance changed over time at the same institution. SCCmec type IV strains were probably hospital-acquired.