JAC Advance Access originally published online on April 17, 2007
Journal of Antimicrobial Chemotherapy 2007 59(6):1109-1113; doi:10.1093/jac/dkm098
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Comparative evaluation of VITEK 2® for antimicrobial susceptibility testing of group B Streptococcus
1 Groupe Hospitalier Cochin-Saint Vincent de Paul, Service de Bactériologie, Assistance Publique-Hôpitaux de Paris, 27 rue du Faubourg Saint Jacques, 75679 Paris, France 2 French National Reference Centre for Streptococci, Groupe Hospitalier Cochin-Saint Vincent de Paul, Assistance Publique-Hôpitaux de Paris, 27 rue du Faubourg Saint Jacques, 75679 Paris, France 3 Institut Cochin Department of Infectious Diseases-INSERM U567-UMR CNRS 810, Faculté de Médecine Descartes, Université Paris Descartes, 24 rue du Faubourg Saint Jacques, 75014 Paris, France 4 Unité de Biologie des Bactéries Pathogènes à Gram-positif, URA CNRS 2172, Institut Pasteur, 75724 Paris, France
Received 28 January 2007; returned 1 March 2007; revised 10 March 2007; accepted 12 March 2007
* Correspondence address. Service de Bactériologie, Centre National de Référence des Streptocoques, Institut Cochin, INSERM567, Faculté de Médecine Descartes, 27 rue du Faubourg Saint Jacques, 75014 Paris, France. Tel: +33-1-58-41-15-60; Fax: +33-1-58-41-15-48; E-mail: claire.poyart{at}cch.aphp.fr
Objectives: Intrapartum antibiotic prophylaxis is recommended to prevent neonatal group B streptococcal (GBS) disease in colonized women, and penicillin or aminopenicillin constitute the first-line antibiotics. Most isolates are resistant to tetracycline, and resistance to macrolide–lincosamide–streptogramin (MLS) antibiotics is increasing. Therefore, laboratory testing for MLS resistance in GBS is now recommended for penicillin-allergic patients. The aim of this study was to compare the antimicrobial susceptibility of GBS as determined by the VITEK 2 system (bioMérieux, Marcy l'Étoile, France), agar diffusion methods and PCR-genotypic detection of resistance genes.
Methods: One hundred and ten unrelated selected GBS clinical isolates were studied. The antibiotics tested (VITEK 2 and agar diffusion method) were benzylpenicillin, ampicillin, erythromycin, clindamycin, co-trimoxazole, tetracycline, kanamycin, streptomycin and vancomycin. A standardized double-disc (DD) diffusion test was performed for MLS antibiotics. Genotypic characterization of tetracycline, MLS and aminoglycoside resistance genes was performed by PCR.
Results: All strains were susceptible to benzylpenicillin, ampicillin and vancomycin [category agreement (CA) between VITEK 2 and the diffusion method was 100%]. Ninety-five (86%) strains were resistant to tetracycline (CA was 98.9%). Eighty-one strains (73.6%) harboured an MLS resistance phenotype; 50 (61.8%) an MLSB-constitutive phenotype, 25 (30.8%) an MLSB-inducible phenotype and 6 (7.4%) an M phenotype. The agreement between data of VITEK 2 and the DD diffusion test for the detection of MLSB-constitutive, MLSB-inducible and M phenotype isolates was 76%, 36% and 100%, respectively. Almost all discrepancies were due to failure to detect erythromycin resistance by VITEK 2.
Conclusions: VITEK 2 allows accurate determination of GBS susceptibility for the majority of antibiotics, but has to be improved for erythromycin. Thus, the DD diffusion test remains the most simple and reliable method for macrolide resistance detection among this streptococcal species.
Keywords: Streptococcus agalactiae , antibiotics , macrolides–lincosamides–streptogramins , PCR
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