Identifying methicillin-resistant Staphylococcus aureus (MRSA) lung infections in mice via breath analysis using secondary electrospray ionization-mass spectrometry (SESI-MS)

Heather D Bean,Jane E Hill,Jackson C Sengle,Jiangjiang Zhu

doi:10.1088/1752-7155/8/4/041001

Abstract

Invasive methicillin-resistant Staphylococcus aureus (MRSA) infections are a serious health threat, causing an estimated 11 000 deaths per year in the United States. MRSA pneumonias account for 16% of invasive infections, and can be difficult to detect as the current state-of-the-art diagnostics require that bacterial DNA is recovered from the infection site. Because 60% of patients with invasive infections die within 7 d of culturing positive for MRSA, earlier detection of the pathogen may significantly reduce mortality. We aim to develop breath-based diagnostics that can detect Staphylococcal lung infections rapidly and non-invasively, and discriminate MRSA and methicillin-sensitive S. aureus (MSSA), in situ. Using a murine lung infection model, we have demonstrated that secondary electrospray ionization-mass spectrometry (SESI-MS) breathprinting can be used to robustly identify isogenic strains of MRSA and MSSA in the lung 24 h after bacterial inoculation. Principal components analysis (PCA) separates MRSA and MSSA breathprints using only the first component (p < 0.001). The predominant separation in the PCA is driven by shared peaks, low-abundance peaks, and rare peaks, supporting the use of biomarker panels to enhance the sensitivity and specificity of breath-based diagnostics.

Highlights

In 2013 the Centers for Disease Control and Prevention (CDC) listed methicillin-resistant Staphylococcus aureus (MRSA) as a serious antibiotic-resistant microbial threat in the United States, which is the second-highest threat level used by the CDC [1]
Evaluating the features of the breathprints that classify the infection groups in principal components analysis (PCA), we found that the peaks driving separation are just as likely to be shared by both MRSA and methicillinsensitive S. aureus (MSSA) infections as they are to be unique to one strain
At the time of breath collection, there was an average of 1.6×106 CFU/lung of MSSA and 3.5×105 CFU/lung of MRSA, and the host immune response was activated in both infections, in concordance with previous murine lung infections we have studied. [19, 26, 27] The breath samples were analyzed using secondary electrospray ionization-mass spectrometry (SESI-MS), producing a volatile fingerprint, a.k.a. breathprint, for each lung infection (Fig. 1)

Summary

Introduction

In 2013 the Centers for Disease Control and Prevention (CDC) listed methicillin-resistant Staphylococcus aureus (MRSA) as a serious antibiotic-resistant microbial threat in the United States, which is the second-highest threat level used by the CDC [1]. The driving force behind our work is to develop rapid and sensitive mass spectrometry-based diagnostics that can detect bacterial and host metabolites arising from lower respiratory tract infections, and exhaled on the patient's breath. By others, used gas chromatography-mass spectrometry (GC-MS) to demonstrate that non-isogenic MSSA and MRSA strains produce different suites of volatiles in vitro [21, 22]. Based on these in vitro results, and on our previous in vitro and in vivo SESI-MS analyses, we hypothesized that we would be able to discriminate MRSA and MSSA lung infections in vivo using SESI-MS breathprinting

Objectives

Methods

Results

Conclusion