Rapid detection of Staphylococcus aureus and Streptococcus pneumoniae by real-time analysis of volatile metabolites

Abstract

Rapid detection of pathogenic bacteria is needed for rapid diagnostics allowing adequate and timely treatment. In this study, we aimed to evaluate the technical feasibility of Secondary Electro-Spray Ionization-High Resolution Mass Spectrometry (SESI-HRMS) as a diagnostic tool for rapid detection of bacterial infections and compare its performance with the current standard of diagnostics. We compared the time required to confirm growth of the pathogenic bacteria Staphylococcus aureus and Streptococcus pneumoniae by conventional detection by culture and MAL-DI-TOF vs. detection of specific volatile organic compounds (VOCs) produced by these human pathobionts. SESI-HRMS could consistently detect VOCs produced by S. aureus or S. pneumoniae on blood agar plates within minutes, allowing to positively identify bacteria within hours. Unique S. aureus and S. pneumoniae features were detected already at bacterial densities as low as [~]103 colony forming units. Rich mass spectral fingerprints allowed for the distinction of these two bacteria on a species and even strain level. To give an incentive towards clinical application of this technology, further analyzed 17 clinical samples previously diagnosed by conventional methods. We predominantly obtained a separation of samples which showed growth (i.e. presence of living bacteria) compared to samples with no bacterial growth (i.e. presence of dead bacteria). We conclude that SESI-HRMS allows rapid identification of unique bacterial features. Further development of real-time analysis of clinical samples by SESI-HRMS will shorten the time required for microbiological diagnosis with a high level of confidence and sensitivity and should help to improve patients tailored treatment. IMPORTANCEA timely identification of a pathogenic bacteria causing the infection is of pivotal importance for the initiation of an adequate antimicrobial therapy. In this regard, different technologies have been developed with the aim to achieve a highly reliable, specific, and overall fast identification of pathogenic bacteria. However, conventional diagnostic techniques still require long preprocessing times (hours to days) to acquire enough biological material for an accurate identification of the pathogen. Therefore, in this work, we aimed to further shorten the detection time of current gold standards for microbiological diagnostics by providing a system capable of a fast, sensitive and specific discrimination of different pathogenic bacteria. This system relies on the real-time mass spectrometric detection of volatile organic compounds (VOCs) produced by a given organism during its growth, potentially leading to a significant shortening of the time required to obtain a positive reliable diagnostic.