Real-time detection of volatile metabolites enabling species-level discrimination of bacterial biofilms associated with wound infection

Volatile organic compounds (VOCs) detection for the identification of bacterial infections in clinical wound samples

Early detection of wound infections is critical for timely intervention and prevention of possible complications since prompt treatment can help lower pathogen spread and enhance faster healing. Early detection also helps reduce the risk of serious infections requiring extensive medical interventions or life-threatening diseases such as sepsis. Culture-based approaches currently used for bacterial identification have limited sensitivity and specificity. At the same time, they are time-consuming, resulting in delays in therapy and, therefore, having a negative impact on the treatment outcomes. Quantifying the volatile organic compounds (VOCs) released by bacteria residing in wounds is a promising, non-invasive option for detecting infections at early stages. This method allows for continuous monitoring without requiring invasive procedures, thereby reducing patient discomfort and the risk of further complications. Spectroscopy methods and sensors are the primary VOC detection and quantification approaches, but sensors are more rapid, cost-effective, non-invasive, and precise. This review highlights the significance of the early detection of wound infection to enable timely intervention and prevent complications, emphasizing the limitations of culture-based approaches. It also explores the potential of quantifying VOCs using different methods and discusses the correlation between their levels and the rate of bacterial infections in wounds. Additionally, the review evaluates current VOC-based monitoring methods for wound management, identifies gaps in the field, and advocates for further research to advance wound care and enhance patient outcomes.

Bacterial Communities and Their Role in Bacterial Infections

Since infections associated with microbial communities threaten human health, research is increasingly focusing on the development of biofilms and strategies to combat them. Bacterial communities may include bacteria of one or several species. Therefore, examining all the microbes and identifying individual community bacteria responsible for the infectious process is important. Rapid and accurate detection of bacterial pathogens is paramount in healthcare, food safety, and environmental monitoring. Here, we analyze biofilm composition and describe the main groups of pathogens whose presence in a microbial community leads to infection (Staphylococcus aureus, Enterococcus spp., Cutibacterium spp., bacteria of the HACEK, etc.). Particular attention is paid to bacterial communities that can lead to the development of device-associated infections, damage, and disruption of the normal functioning of medical devices, such as cardiovascular implants, biliary stents, neurological, orthopedic, urological and penile implants, etc. Special consideration is given to tissue-located bacterial biofilms in the oral cavity, lungs and lower respiratory tract, upper respiratory tract, middle ear, cardiovascular system, skeletal system, wound surface, and urogenital system. We also describe methods used to analyze the bacterial composition in biofilms, such as microbiologically testing, staining, microcolony formation, cellular and extracellular biofilm components, and other methods. Finally, we present ways to reduce the incidence of biofilm-caused infections.

New-generation biofilm effective antimicrobial peptides and a real-time anti-biofilm activity assay: CoMIC

Nowadays, it is very important to produce new-generation drugs with antimicrobial properties that will target biofilm-induced infections. The first target for combating these microorganisms, which are the source itself. Antimicrobial peptides, which are more effective than antibiotics due to their ability to kill microorganisms and use a different metabolic pathway, are among the new options today. The aim of this study is to develop new-generation antibiotics that inhibit both biofilm-producing bacteria and the biofilm itself. For this purpose, we designed four different peptides by combining two amino acid forms (D- and L-) with the same sequence having alpha helix structures. It was found that the combined use of these two forms can increase antimicrobial efficacy more than 30-fold. These results are supported by molecular modeling and scanning electron microscopy (SEM), at the same time cytotoxicity (IC50) and hemotoxicity (HC50) values remained within the safe range. Furthermore, antibiofilm activities of these peptides were investigated. Since the existing biofilm inhibition methods in the literature do not technically simulate the exact situation, in this study, we have developed a real-time observable biofilm model and a new detection method based on it, which we call the CoMIC method. Findings have shown that the NET1 peptide with D-leucine amino acid in its structure and the NET3 peptide with D-arginine amino acid in its structure are effective in inhibiting biofilm. As a conclusion, our peptides can be considered as potential next-generation broad-spectrum antibiotic molecule/drug candidates that might be used in biofilm and clinical important bacteria. KEY POINTS: • Antimicrobial peptides were developed to inhibit both biofilms producing bacteria and the biofilm itself. • CoMIC will fill a very crucial gap in understanding biofilms and conducting the necessary quantitative studies. • Molecular modelling studies, NET1 peptide molecules tends to move towards and adhere to the membrane within nanoseconds.

Identification of trans-genus biomarkers for early diagnosis of intestinal schistosomiasis and progression of gut pathology in a mouse model using metabolomics

Schistosomiasis is one of the most devastating human diseases worldwide. The disease is caused by six species of Schistosoma blood fluke; five of which cause intestinal granulomatous inflammation and bleeding. The current diagnostic method is inaccurate and delayed, hence, biomarker identification using metabolomics has been applied. However, previous studies only investigated infection caused by one Schistosoma spp., leaving a gap in the use of biomarkers for other species. No study focused on understanding the progression of intestinal disease. Therefore, we aimed to identify early gut biomarkers of infection with three Schistosoma spp. and progression of intestinal pathology. We infected 3 groups of mice, 3 mice each, with Schistosoma mansoni, Schistosoma japonicum or Schistosoma mekongi and collected their feces before and 1, 2, 4 and 8 weeks after infection. Metabolites in feces were extracted and identified using mass spectrometer-based metabolomics. Metabolites were annotated and analyzed with XCMS bioinformatics tool and Metaboanalyst platform. From >36,000 features in all conditions, multivariate analysis found a distinct pattern at each time point for all species. Pathway analysis reported alteration of several lipid metabolism pathways as infection progressed. Disturbance of the glycosaminoglycan degradation pathway was found with the presence of parasite eggs, indicating involvement of this pathway in disease progression. Biomarkers were discovered using a combination of variable importance for projection score cut-off and receiver operating characteristic curve analysis. Five molecules met our criteria and were present in all three species: 25-hydroxyvitamin D2, 1α-hydroxy-2β-(3-hydroxypropoxy) vitamin D3, Ganoderic acid Md, unidentified feature with m/z 455.3483, and unidentified feature with m/z 456.3516. These molecules were proposed as trans-genus biomarkers of early schistosomiasis. Our findings provide evidence for disease progression in intestinal schistosomiasis and potential biomarkers, which could be beneficial for early detection of this disease.

The Effect of Mesenchymal Stem Cells on the Wound Infection

Wound infection often requires a long period of care and an onerous treatment process. Also, the rich environment makes the wound an ideal niche for microbial growth. Stable structures, like biofilm, and drug-resistant strains cause a delay in the healing process, which has become one of the important challenges in wound treatment. Many studies have focused on alternative methods to deal the wound infections. One of the novel and highly potential ways is mesenchymal stromal cells (MSCs). MSCs are mesoderm-derived pluripotent adult stem cells with the capacity for self-renewal, multidirectional differentiation, and immunological control. Also, MSCs have anti-inflammatory and antiapoptotic effects. MScs, as pluripotent stromal cells, differentiate into many mature cells. Also, MSCs produce antimicrobial compounds, such as antimicrobial peptides (AMP), as well as secrete immune modulators, which are two basic features considered in wound healing. Despite the advantages, preserving the structure and activity of MSCs is considered one of the most important points in the treatment. MSCs' antimicrobial effects on microorganisms involved in wound infection have been confirmed in various studies. In this review, we aimed to discuss the antimicrobial and therapeutic applications of MSCs in the infected wound healing processes.

Volatilomes of human infection

The human volatilome comprises a vast mixture of volatile emissions produced by the human body and its microbiomes. Following infection, the human volatilome undergoes significant shifts, and presents a unique medium for non-invasive biomarker discovery. In this review, we examine how the onset of infection impacts the production of volatile metabolites that reflects dysbiosis by pathogenic microbes. We describe key analytical workflows applied across both microbial and clinical volatilomics and emphasize the value in linking microbial studies to clinical investigations to robustly elucidate the metabolic species and pathways leading to the observed volatile signatures. We review the current state of the art across microbial and clinical volatilomics, outlining common objectives and successes of microbial-clinical volatilomic workflows. Finally, we propose key challenges, as well as our perspectives on emerging opportunities for developing clinically useful and targeted workflows that could significantly enhance and expedite current practices in infection diagnosis and monitoring.

A growing battlefield in the war against biofilm-induced antimicrobial resistance: insights from reviews on antibiotic resistance

Biofilms are a common survival strategy employed by bacteria in healthcare settings, which enhances their resistance to antimicrobial and biocidal agents making infections difficult to treat. Mechanisms of biofilm-induced antimicrobial resistance involve reduced penetration of antimicrobial agents, increased expression of efflux pumps, altered microbial physiology, and genetic changes in the bacterial population. Factors contributing to the formation of biofilms include nutrient availability, temperature, pH, surface properties, and microbial interactions. Biofilm-associated infections can have serious consequences for patient outcomes, and standard antimicrobial therapies are often ineffective against biofilm-associated bacteria, making diagnosis and treatment challenging. Novel strategies, including antibiotics combination therapies (such as daptomycin and vancomycin, colistin and azithromycin), biofilm-targeted agents (such as small molecules (LP3134, LP3145, LP4010, LP1062) target c-di-GMP), and immunomodulatory therapies (such as the anti-PcrV IgY antibodies which target Type IIIsecretion system), are being developed to combat biofilm-induced antimicrobial resistance. A multifaceted approach to diagnosis, treatment, and prevention is necessary to address this emerging problem in healthcare settings.

Current Limitations of Staph Infection Diagnostics, and the Role for VOCs in Achieving Culture-Independent Detection

Staphylococci are broadly adaptable and their ability to grow in unique environments has been widely established, but the most common and clinically relevant staphylococcal niche is the skin and mucous membranes of mammals and birds. S. aureus causes severe infections in mammalian tissues and organs, with high morbidities, mortalities, and treatment costs. S. epidermidis is an important human commensal but is also capable of deadly infections. Gold-standard diagnostic methods for staph infections currently rely upon retrieval and characterization of the infectious agent through various culture-based methods. Yet, obtaining a viable bacterial sample for in vitro identification of infection etiology remains a significant barrier in clinical diagnostics. The development of volatile organic compound (VOC) profiles for the detection and identification of pathogens is an area of intensive research, with significant efforts toward establishing breath tests for infections. This review describes the limitations of existing infection diagnostics, reviews the principles and advantages of VOC-based diagnostics, summarizes the analytical tools for VOC discovery and clinical detection, and highlights examples of how VOC biomarkers have been applied to diagnosing human and animal staph infections.

A Host-Directed Approach to the Detection of Infection in Hard-to-Heal Wounds

Wound infection is traditionally defined primarily by visual clinical signs, and secondarily by microbiological analysis of wound samples. However, these approaches have serious limitations in determining wound infection status, particularly in early phases or complex, chronic, hard-to-heal wounds. Early or predictive patient-derived biomarkers of wound infection would enable more timely and appropriate intervention. The observation that immune activation is one of the earliest responses to pathogen activity suggests that immune markers may indicate wound infection earlier and more reliably than by investigating potential pathogens themselves. One of the earliest immune responses is that of the innate immune cells (neutrophils) that are recruited to sites of infection by signals associated with cell damage. During acute infection, the neutrophils produce oxygen radicals and enzymes that either directly or indirectly destroy invading pathogens. These granular enzymes vary with cell type but include elastase, myeloperoxidase, lysozyme, and cathepsin G. Various clinical studies have demonstrated that collectively, these enzymes, are sensitive and reliable markers of both early-onset phases and established infections. The detection of innate immune cell enzymes in hard-to-heal wounds at point of care offers a new, simple, and effective approach to determining wound infection status and may offer significant advantages over uncertainties associated with clinical judgement, and the questionable value of wound microbiology. Additionally, by facilitating the detection of early wound infection, prompt, local wound hygiene interventions will likely enhance infection resolution and wound healing, reduce the requirement for systemic antibiotic therapy, and support antimicrobial stewardship initiatives in wound care.

Multi-Strain and -Species Investigation of Volatile Metabolites Emitted from Planktonic and Biofilm Candida Cultures

Candida parapsiliosis is a prevalent neonatal pathogen that attains its virulence through its strain-specific ability to form biofilms. The use of volatilomics, the profiling of volatile metabolites from microbes is a non-invasive, simple way to identify and classify microbes; it has shown great potential for pathogen identification. Although C. parapsiliosis is one of the most common clinical fungal pathogens, its volatilome has never been characterised. In this study, planktonic volatilomes of ten clinical strains of C. parapsilosis were analysed, along with a single strain of Candida albicans. Headspace-solid-phase microextraction coupled with gas chromatography-mass spectrometry were employed to analyse the samples. Species-, strain-, and media- influences on the fungal volatilomes were investigated. Twenty-four unique metabolites from the examined Candida spp. (22 from C. albicans; 18 from C. parapsilosis) were included in this study. Chemical classes detected across the samples included alcohols, fatty acid esters, acetates, thiols, sesquiterpenes, and nitrogen-containing compounds. C. albicans volatilomes were most clearly discriminated from C. parapsilosis based on the detection of unique sesquiterpene compounds. The effect of biofilm formation on the C. parapsilosis volatilomes was investigated for the first time by comparing volatilomes of a biofilm-positive strain and a biofilm-negative strain over time (0–48 h) using a novel sampling approach. Volatilomic shifts in the profiles of alcohols, ketones, acids, and acetates were observed specifically in the biofilm-forming samples and attributed to biofilm maturation. This study highlights species-specificity of Candida volatilomes, and also marks the clinical potential for volatilomics for non-invasively detecting fungal pathogens. Additionally, the range of biofilm-specificity across microbial volatilomes is potentially far-reaching, and therefore characterising these volatilomic changes in pathogenic fungal and bacterial biofilms could lead to novel opportunities for detecting severe infections early.