Open Access Highly Accessed Research article

Large screening of CA-MRSA among Staphylococcus aureus colonizing healthy young children living in two areas (urban and rural) of Portugal

Débora A Tavares1, Raquel Sá-Leão12, Maria Miragaia1 and Hermínia de Lencastre13*

Author Affiliations

1 Laboratory of Molecular Genetics, Instituto de Tecnologia Química e Biológica (ITQB), Universidade Nova de Lisboa (UNL), Oeiras, Portugal

2 Centro de Matemática e Aplicações Fundamentais (CMAF), Universidade de Lisboa, Lisboa, Portugal

3 Laboratory of Microbiology, The Rockefeller University, New York, NY, USA

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BMC Infectious Diseases 2010, 10:110  doi:10.1186/1471-2334-10-110

Published: 3 May 2010



The incidence of pediatric infections due to community-associated methicillin-resistant Staphylococcus aureus (CA-MRSA), including children with no identifiable risk factors, has increased worldwide in the last decade. This suggests that healthy children may constitute a reservoir of MRSA in the community. In this study, nested within a larger one on nasopharyngeal ecology, we aimed to: (i) evaluate the prevalence of MRSA colonizing young children in Portugal; and (ii) compare results with those obtained in a study conducted a decade ago, when this prevalence was <0.5%.


In the years 2006, 2007, and 2009, nasopharyngeal samples were obtained from 2,100 children aged up to 6 years attending day-care centers. S. aureus were isolated by routine procedures and strains were tested for susceptibility against a panel of 12 antimicrobial agents. MRSA isolates were further characterized by SmaI-PFGE profiling, MLST, spa typing, SCCmec typing, and presence of virulence factors.


Seventeen percent of the children carried S. aureus. Among the 365 isolates, non-susceptibility rates were 88% to penicillin, 14% to erythromycin, 6% to clindamycin, 2% to tetracycline, and <1% to oxacillin, rifampicin, ciprofloxacin, and SXT. Three MRSA strains were isolated. These had properties of CA-MRSA, such as low-level resistance to oxacillin and limited resistance to non-beta-lactams. Two CA-MRSA were related to USA700 (ST72-IV): one was ST72-IVc, spa type t148; the other was ST939-IVa (ST939 is a single locus variant (SLV) of ST72), spa type t324. The third strain was related to USA300 (ST8-IV) being characterized by ST931 (SLV of ST8)-VI, spa type t008. The three MRSA strains were PVL-negative, but all carried LukE-LukD leukocidin, hemolysins gamma, gamma variant and beta, and staphylococcal enterotoxin sel.


Our results, based on analysis of S. aureus isolated from nasopharyngeal samples, suggest that in Portugal the prevalence of CA-MRSA carriage in healthy young children remains extremely low favoring the exclusion of this group as a reservoir of such isolates.