Identification of phlebotomine sand flies using one MALDI-TOF MS reference database and two mass spectrometer systems
Abstract
Rapid, accurate and high-throughput identification of vectors is of paramount importance in surveillance programmes. Protein profiling by MALDI-TOF fulfils the requirements for identification.
We established and validated a reference database containing 20 phlebotomine sand fly species by using specimens from colonies or field-collections stored for various periods of time. Identical mass patterns were obtained with colony-or field-derived specimens of the same species.
In the validation study, high quality spectra were obtained with all fresh insects from colonies, and with 55/59 insects deep-frozen (liquid nitrogen/-80 degrees C) for up to 25 years. In contrast, only 36/52 specimens stored in ethanol could be identified.
This resulted in an overall sensitivity of 87 %; specificity was 100 %. Duration of storage impaired data counts in the high mass range, and thus cluster analyses of closely related specimens might reflect their storage conditions.
A major drawback of MALDI-TOF MS is the restricted availability of databases and the fact that mass spectrometers from 2 companies (Bruker, Shimadzu) are widely being used. We have analysed fingerprints of sand flies obtained by automatic procedure on a Bruker instrument by using database and software established on a Shimadzu system.
The sensitivity with 312 specimens from 8 species from laboratory colonies when evaluating only high quality spectra was 98.3 %; the specificity was 100 %. The corresponding diagnostic values with 55 field-collected specimens from 4 species were 94.7 % and 97.4 %.
A centralized database created by expert taxonomists that is easily amenable to customer-oriented identification services is a highly desirable resource. As shown in the present work, spectra obtained from different specimens with different instruments can be analysed using a centralized database, which should be available in the near future via an online platform in a cost-efficient manner.