Identification of Haemophilus influenzae Type b Isolates by Use of Matrix-Assisted Laser Desorption Ionization-Time of Flight Mass Spectrometry.
Haemophilus influenzae type b (Hib) is, in contrast to non-type b H. influenzae, associated with severe invasive disease, such as meningitis and epiglottitis, in small children. To date, accurate H. influenzae capsule typing requires PCR, a time-consuming and cumbersome method. Matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS) provides rapid bacterial diagnostics and is increasingly used in clinical microbiology laboratories. Here, MALDI-TOF MS was evaluated as a novel approach to separate Hib from other H. influenzae. PCR-verified Hib and non-Hib reference isolates were selected based on genetic and spectral characteristics. Mass spectra of reference isolates were acquired and used to generate different classification algorithms for Hib/non-Hib differentiation using both ClinProTools and the MALDI Biotyper software. A test series of mass spectra from 33 Hib and 77 non-Hib isolates, all characterized by PCR, was used to evaluate the algorithms. Several algorithms yielded good results, but the two best were a ClinProTools model based on 22 separating peaks and subtyping main spectra (MSPs) using MALDI Biotyper. The ClinProTools model had a sensitivity of 100% and a specificity of 99%, and the results were 98% reproducible using a different MALDI-TOF MS instrument. The Biotyper subtyping MSPs had a sensitivity of 97%, a specificity of 100%, and 93% reproducibility. Our results suggest that it is possible to use MALDI-TOF MS to differentiate Hib from other H. influenzae. This is a promising method for rapidly identifying Hib in unvaccinated populations and for the screening and surveillance of Hib carriage in vaccinated populations.
Clinical Microbiology, Department of Translational Medicine, Lund University, Lund, Sweden.
Viktor
V
Månsson
Clinical Microbiology, Department of Translational Medicine, Lund University, Lund, Sweden fredrik.resman@med.lu.se.
Fredrik
F
Resman
Bruker Daltonics, Bremen, Germany.
Markus
M
Kostrzewa
Clinical Microbiology, Labmedicin, Region Skåne, Sweden Division of Medical Microbiology, Department of Laboratory Medicine, Lund University, Lund, Sweden.
Bo
B
Nilson
Clinical Microbiology, Department of Translational Medicine, Lund University, Lund, Sweden.
Kristian
K
Riesbeck
D001431:Bacteriological Techniques / Q000379:methods*; D002675:Child, Preschool; D006192:Haemophilus Infections / Q000175:diagnosis* / Q000382:microbiology; D019741:Haemophilus influenzae type b / Q000737:chemistry / Q000145:classification* / Q000302:isolation & purification; D006801:Humans; D012680:Sensitivity and Specificity; D012984:Software; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*