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Evaluation of a new chromogenic medium SaSelect for identification of Staphylococcus aureus

Abstract number: 1733_1100

Daurel C., Leclercq R.

Objectives: The objectives were to compare the sensitivities and specificities of SaSelect, a new chromogenic medium, and Mannitol salt agar medium (MSA, Chapman) associated with a slide coagulase test, for rapid and direct identification of Staphylococcus aureus from cultures of various clinical samples.

Methods: 322 clinical specimens of various natures were studied: suppurations (n = 126), upper and lower respiratory tract secretions (n = 54), faecal samples (n = 31), blood cultures with mixed Gram strains (n = 30), nasal samples (n = 41), urines (n = 20), catheters (n = 8) and others (n = 12). All samples were isolated on SaSelect (incubation 24 h) and MSA (incubation time: 24 and 48 h). The identification of pink colonies on SaSelect and colonies with a yellow halo on MSA was confirmed by a slide coagulase test.

Results: Most clinical samples were polymicrobial. 152 samples contained S. aureus with SaSelect (24 h of incubation) and 144 with MSA (48 h of incubation). 153 S. aureus were isolated on either medium. Specificity and sensitivity were calculated, considering that a sample was positive if any of the two tested media showed the presence of S. aureus. When only the pink colour of the colonies at 24 h of incubation on SaSelect was taken as a criterion of identification for S. aureus, the specificity (100%) was similar to that obtained on MSA combined with coagulase test at 24 and 48 h of incubation (99.4%). The sensitivity values were different. At 24 h, the sensitivity was 90.8% for MSA and 98% for SaSelect. At 48 h incubation time, the sensitivity determined on MSA increased to 94.7%.

Conclusion: The sensitivity and specificity of the SaSelect medium were close to 100% in our study. This medium can be used in routine for the identification of S. aureus on the basis of the pink colour of the colonies without requiring a complementary coagulase test for confirmation. SaSelect makes it possible to reduce the cost of the test and the working time.

Session Details

Date: 31/03/2007
Time: 00:00-00:00
Session name: European Society of Clinical Microbiology and Infectious Diseases
Subject:
Location: ICC, Munich, Germany
Presentation type:
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