Use of the fluorescent in situ hybridization technique for the rapid identification of staphylococcus aureus in blood cultures

Abstract

Background: The technique of reference for the detection of bacteriemia is the blood culture. One of the most frequent bacteria responsible of bacteriemia is Staphylococcus aureus (SAU). The presence of Gram positive cocci (CGPR), in blood culture give the suspicious of bacteriemia, although the relevance of the finding depends on the correct identification of the microorganism. The definitive typification it demands from 24 to 48 hours. The technique of fluorescent in situ hybridization (FISH), is a rapid method for the identification of bacteria in blood culture. Aims: The aims of this work was to establish the FISH technique directed to the 16S RNA of SAU in samples of blood cultures with CGPR to the Gram staining, to determine the concordance with the method of reference, and to evaluate the possibility to use as standard method in the laboratory of microbiology. Material and Methods: The blood cultures analyzed in the Laboratory of Microbiology of the Hospital Privado Cordoba from 01.01.2009 to 31.12.09 were included in this study. To each positive blood culture which showed CGPR was applied simultaneously biochemical identification and FISH. Results: From 496 positive samples, 32 showed CGPR, 24 of them were identified as SAU. A concordance of 100% (IC95% 99 to 100) between both methods of diagnosis, with a value of k<0.01 was observed. Discussion: The excellent concordance opens the prospect for a study in order to determine the predictive value of FISH, its sensibility and specificity. Furthermore, it will be possible to evaluate its clinical impact being incorporated in a laboratory of clinical bacteriology.