False-negative test results in the Slidex Staph Plus (bioMérieux) agglutination test are mainly caused by spa-type t001 and t001-related strains

• Published in: European journal of clinical microbiology & infectious diseases 2011-02, Vol.30 (2), p.201-208
• Main Authors: Szabados, F, Woloszyn, J, Kaase, M, Gatermann, S. G
• Format: Article
• Language: English
• Subjects: Agglutination Tests - methods; Automation; Bacterial Typing Techniques; Bacteriological Techniques - methods; Biological and medical sciences; Biomedical and Life Sciences; Biomedicine; Diagnostic Errors; False Negative Reactions; Humans; Identification systems; Infectious diseases; Internal Medicine; Mass spectrometry; Medical Microbiology; Medical sciences; Molecular Typing; Scientific imaging; Sensitivity and Specificity; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization; Staphylococcal Infections - diagnosis; Staphylococcus aureus - isolation & purification
• ISSN: 0934-9723; 1435-4373
• DOI: 10.1007/s10096-010-1070-4

The relative sensitivity of commercial agglutination kits for fast identification of S. aureus is usually given to be about 98%. This reported sensitivity has sometimes been questioned. In this study, three collections of molecularly defined, single-copy strains of S. aureus were used to compare the sensitivities of agglutination-based identification and the MALDI-TOF mass spectrometry-based identification using the Biotyper 2.0 database to a molecularly defined reference method. Clinical isolates (n = 363) of methicillin-susceptible S. aureus (MSSA) and 240 clinical isolates of methicillin-resistant S. aureus (MRSA) were included. In order to rule out a predominance of local MRSA-strains, a collection of 104 pulsed-field-gel electrophoresis divergent MRSA strains were also tested. MALDI-TOF MS using Biotyper database (Bruker) identified all isolates, whereas the Slidex Staph Plus (bioMérieux) detected only 98.0% of the MSSA, 94.5% of the MRSA and only 70.1% of the MRSA of the molecularly divergent strain collection. Interestingly, strains with a false-negative test result in the agglutination methods were mostly spa-type t001 and t001 related. The MALDI-TOF MS based identification can thus be used as an alternative identification method for suspected false-negative results from the agglutination tests, especially if the local prevalence of t001 and t001 related strains is high.