Abstract
Encapsulated Haemophilus influenzae strains belong to type-specific genetic lineages. Reliable capsule typing requires PCR, but a more efficient method would be useful. We evaluated capsule typing by using matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry. Isolates of all capsule types (a−f and nontypeable; n = 258) and isogenic capsule transformants (types a−d) were investigated. Principal component and biomarker analyses of mass spectra showed clustering, and mass peaks correlated with capsule type-specific genetic lineages. We used 31 selected isolates to construct a capsule typing database. Validation with the remaining isolates (n = 227) showed 100% sensitivity and 92.2% specificity for encapsulated strains (a−f; n = 61). Blinded validation of a supplemented database (n = 50) using clinical isolates (n = 126) showed 100% sensitivity and 100% specificity for encapsulated strains (b, e, and f; n = 28). MALDI-TOF mass spectrometry is an accurate method for capsule typing of H. influenzae.
Highlights
Encapsulated Haemophilus influenzae strains belong to type-specific genetic lineages
Genetic Lineages of Encapsulated H. influenzae in the Evaluation Set To construct a clinically useful reference database for capsule typing by MALDI-TOF mass spectrometry, we aimed to identify and collect isolates from all known lineages of encapsulated H. influenzae (Figure 2; online Technical Appendix Table)
In this study, we have shown that encapsulated H. influenzae have different MALDI-TOF mass spectra that correlate with genetic lineages representing different capsule types
Summary
Encapsulated Haemophilus influenzae strains belong to type-specific genetic lineages. Matrix-assisted laser desorption/ionization time-offlight (MALDI-TOF) mass spectrometry is commonly used to identify bacterial and fungal species, including H. influenzae, by analyzing the composition of ribosomal proteins in a sample It is a rapid and convenient method and has a low cost per sample [28]. We examined the capacity of MALDI-TOF mass spectrometry to perform full capsule typing of H. influenzae This method would be valuable for first-line diagnostics of H. influenzae to identify patients at risk for immunodeficiency or anatomic cerebrospinal fluid space defect, and to detect rapidly outbreaks caused by specific capsule types. It would increase time and cost effectiveness of surveillance of H. influenzae epidemiology and Hib vaccination efficacy
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