The Potential of Fecal Volatile Organic Compound Analysis for the Early Diagnosis of Late-Onset Sepsis in Preterm Infants: A Narrative Review

Abstract

Early diagnosis and treatment of late-onset sepsis (LOS) is crucial for survival, but challenging. Intestinal microbiota and metabolome alterations precede the clinical onset of LOS, and the preterm gut is considered an important source of bacterial pathogens. Fecal volatile organic compounds (VOCs), formed by physiologic and pathophysiologic metabolic processes in the preterm gut, reflect a complex interplay between the human host, the environment, and microbiota. Disease-associated fecal VOCs can be detected with an array of devices with various potential for the development of a point-of-care test (POCT) for preclinical LOS detection. While characteristic VOCs for common LOS pathogens have been described, their VOC profiles often overlap with other pathogens due to similarities in metabolic pathways, hampering the construction of species-specific profiles. Clinical studies have, however, successfully discriminated LOS patients from healthy individuals using fecal VOC analysis with the highest predictive value for Gram-negative pathogens. This review discusses the current advancements in the development of a non-invasive fecal VOC-based POCT for early diagnosis of LOS, which may potentially provide opportunities for early intervention and targeted treatment and could improve clinical neonatal outcomes. Identification of confounding variables impacting VOC synthesis, selection of an optimal detection device, and development of standardized sampling protocols will allow for the development of a novel POCT in the near future.

Keywords: biomarker; detection; electronic nose; intestinal microbiota; late-onset sepsis; neonatology; non-invasive diagnostics; preterm infants; volatile organic compounds.

Figure 1

Simplified overview of analytical techniques used for volatile organic compound analyses of preterm infants with late-onset sepsis with their advantages and disadvantages. Diagnosis of late-onset sepsis (LOS) in a preterm infant requires adequate assessment of clinical symptoms, laboratory findings, including C-reactive protein and hematological parameters, and blood culture results. Recognition of LOS remains challenging, resulting in unnecessary antibiotic treatment or delayed initiation of targeted therapy. Identification and characterization of fecal volatile organic compounds (VOCs) may aid in early diagnosis of LOS in preterm infants and guide the initiation of targeted antibiotic treatment or gut microbiota modulation (e.g., fecal microbiota transplant, probiotics). Fecal VOC profiles can be assessed using an electronic nose, ion mobility spectrometry, and/or gas chromatography–mass spectrometry. These approaches require different detection techniques, and have different advantages, and disadvantages, as summarized in Figure 1. Figure created with Biorender.com. Accessed on 20 March 2024. Abbreviations: VOCs, volatile organic compounds; GC, gas chromatography.

Figure 2

Overview of volatile organic compounds produced by clinical isolates of common late-onset sepsis pathogens Escherichia coli, Staphylococcus aureus, Klebsiella spp. and Pseudomonas aeruginosa. Depicted are four common LOS pathogens (orange) connected to the volatiles they produce. Only the VOCs that have been described in two unrelated research experiments focusing on the same pathogen have been included in this overview. The metabolites in blue represent the VOCs that are uniquely produced by one pathogen, and the metabolites in green are produced by two or more of the pathogens included in this overview. The width of the lines indicates the number of studies that have designated that specific metabolite as discriminatory for the pathogen: a thicker line indicates more studies. To note, only the in vitro studies that have utilized clinical isolates, ex vivo studies, and in vivo studies are displayed. References can be found in Supplementary Table S2. Figure created with Biorender.com. Accessed on 20 March 2024.

Figure 3

Proposed mechanism of volatile organic compound detection in stool samples of preterm infants with late-onset sepsis. (A) In healthy preterm infants, the fecal volatile organic compound (VOC) profile results from physiologic microbial and host metabolic processes. (B) In the days prior to the clinical onset of late-onset sepsis, alterations in microbial composition result in detectable alterations in fecal VOC profile. (C) Upon diagnosis of late-onset sepsis, increasing amounts of pathogenic bacteria have translocated across the compromised gut barrier, resulting in a systemic response. Alterations in VOC profiles due to human inflammatory processes as well as microbial VOCs can be detected in stool samples as well as in blood samples. Figure created with Biorender.com. Accessed on 20 March 2024. Abbreviations: E. coli, Escherichia coli; VOCs, volatile organic compounds.

Figure 4

Flowchart guiding the development of a fecal point-of-care test for the early detection of late-onset sepsis in preterm infants. Figure created with Biorender.com. Accessed on 20 March 2024. Abbreviations: LOS, late-onset sepsis; E. coli, Escherichia coli; NEC, necrotizing enterocolitis; VOC, volatile organic compounds; eNose, electronic nose; POCT, point-of-care test.