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Journal of Venomous Animals and Toxins including Tropical Diseases

On-line version ISSN 1678-9199

J. Venom. Anim. Toxins incl. Trop. Dis vol.14 no.3 Botucatu  2008 



Evalution of methods for the detection of MRSA in patients of Botucatu Medical School Hospital, São Paulo, Brazil



Correspondence to



Thesis: Andre Martins submitted this dissertation for his Masters in Tropical Diseases at Botucatu Medical School, São Paulo State University, UNESP, Botucatu, Sao Paulo State, Brazil, 2008.

Advisor: Professor Maria de Lourdes Ribeiro de Souza da Cunha


Oxacillin is the main drug of choice for the treatment of S. aureus infections. However, S. aureus resistance to oxacillin has become a major problem in the recent decades. The study aimed assess the rates of oxacillin resistance in S. aureus samples obtained at the Botucatu Medical School Hospital, UNESP, and to compare phenotypic techniques for the detection of MRSA against the gold standard method (mecA gene detection) in these samples. A total of 102 samples, previously isolated between 2002 and 2006, and kept at the Culture Collection of the Department of Microbiology and Immunology, in the Botucatu Biosciences Institute, UNESP, were included. Oxacillin resistance was assessed by oxacillin and cefoxitin disk diffusion and agar dilution tests, screening tests using Mueller-Hinton agar with 6 µg/mL of oxacillin and 4% NaCl, E-test, and mecA gene detection. Of the samples analyzed, 46 (45.1%) were mecA-positive. Oxacillin disk sensitivity and specificity were 86.9% and 91.1%, respectively. Cefoxitin disk sensitivity and specificity were respectively 91.3% and 91.1%. The screening test with the cefoxitin disk showed almost the same level of sensitivity (91.3%) and specificity (91.1%). With E-test strips, sensitivity was higher (97.8%) and specificity was comparable to that found with the other methods (91.1%). Ninety-three percent of the samples produced β-lactamase and five of them were mecA-negative. There was a gradual increase in the number of oxacillin-resistant S. aureus samples between 2002 and 2004. However, from 2004 to 2006, the number of resistant samples dropped from 55% of MRSA in 2004, to 45% in 2005 and 34.6% in 2006. The data obtained reveal that, among phenotypic methods, the E-test yielded the best results, with higher sensitivity levels when compared to the other methods. The decreased resistance rate observed over the most recent years may be explained by the rational use of antimicrobial agents associated with good practices in the control of hospital infection, or may be related to the diminished use of oxacillin as a treatment option.

Key Words: oxacillin, mecA, MRSA, Staphylococcus aureus.



Correspondence to:
Maria de Lourdes Ribeiro de Souza da Cunha
Departamento de Microbiologia e Imunologia, Instituto de Biociências, Universidade Estadual de São Paulo, UNESP
Distrito de Rubião Junior, s/n
18618-000, Botucatu, SP, Brasil
Phone: 55 14 3811 6058

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