MALDI-TOF Mass Spectrometry Detection of Pathogens in Vectors: The Borrelia crocidurae/ Ornithodoros sonrai Paradigm

Abstract

Background

In Africa, relapsing fever borreliae are neglected vector-borne pathogens that cause mild to deadly septicemia and miscarriage. Screening vectors for the presence of borreliae currently requires technically demanding, time- and resource-consuming molecular methods. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) has recently emerged as a tool for the rapid identification of vectors and the identification of cultured borreliae. We investigated whether MALDI-TOF-MS could detect relapsing fever borreliae directly in ticks.

Methodology/Principal Findings

As a first step, a Borrelia MALDI-TOF-MS database was created to house the newly determined Mean Spectrum Projections for four Lyme disease group and ten relapsing fever group reference borreliae. MALDI-TOF-MS yielded a unique protein profile for each of the 14 tested Borrelia species, with 100% reproducibility over 12 repeats. In a second proof-of-concept step, the Borrelia database and a custom software program that subtracts the uninfected O. sonrai profile were used to detect Borrelia crocidurae in 20 Ornithodoros sonrai ticks, including eight ticks that tested positive for B. crocidurae by PCR-sequencing. A B. crocidurae-specific pattern consisting of 3405, 5071, 5898, 7041, 8580 and 9757-m/z peaks was found in all B. crocidurae-infected ticks and not found in any of the un-infected ticks. In a final blind validation step, MALDI-TOF-MS exhibited 88.9% sensitivity and 93.75% specificity for the detection of B. crocidurae in 50 O. sonrai ticks, including 18 that tested positive for B. crocidurae by PCR-sequencing. MALDI-TOF-MS took 45 minutes to be completed.

Conclusions/Significance

After the development of an appropriate database, MALDI-TOF-MS can be used to identify tick species and the presence of relapsing fever borreliae in a single assay. This work paves the way for the use of MALDI-TOF-MS for the dual identification of vectors and vectorized pathogens.

Author Summary

In Africa, relapsing fever borreliae are neglected vector-borne infections that cause mild to deadly septicemia and miscarriage. The causative relapsing fever borreliae are transmitted by the bite of soft ticks, except for Borrelia recurrentis which is transmitted by body lice. Screening vectors for these relapsing fever borreliae currently relies on time- and resource-consuming methods such as polymerase chain reaction-based method. Here, we applied matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) to the rapid detection of borreliae in ticks. As a first step, we created a Borrelia MALDI-TOF-MS database and we detected B. crocidurae in Ornithodoros sonrai ticks. As a blind validation step, the 45-minute MALDI-TOF-MS exhibited a 88.9% sensitivity and a 93.75% specificity for the detection of B. crocidurae in 50 O. sonrai ticks including 18 ticks detected positive for B. crocidurae by PCR-sequencing. These findings provide the proof-of-concept that MALDI-TOF-MS can be used to identify tick species and the presence of relapsing fever borreliae. This technique could be translated for field applications.