Staphylococcus aureus Overcomes Anaerobe-Derived Short-Chain Fatty Acid Stress via FadX and the CodY Regulon

Volatile biomarkers of Gram-positive bacteria of clinical relevance as a tool for infection diagnosis

AIM

Volatile organic compounds (VOCs) are being studied as potential biomarkers in many infections. Therefore, this study aimed to analyze the volatile profile of three Gram-positive bacteria of clinical relevance to identify potential volatile biomarkers that allow their differentiation.

METHODS AND RESULTS

L. monocytogenes, S. aureus, and E. faecalis clinical isolates were inoculated in a thioglycollate medium until grown. Then, VOCs were extracted by solid-phase microextraction, and the data obtained were subjected to multivariate analysis. According to our results, there was a high production of aldehydes in E. faecalis. In the case of alcohols, they only increased in L. monocytogenes, while ketones were produced significantly in all three bacteria, mainly due to acetoin. Acids were produced significantly in E. faecalis and L. monocytogenes.

CONCLUSIONS

Potential biomarkers of L. monocytogenes could be 1-butanol and 2-methylbutanoic acid. In the case of E. faecalis, the VOC most related to its presence was nonanal. Lastly, potential biomarkers of S. aureus could be isoamyl butanoate and methionol, although some pyrazines have also been associated with this bacterium.

SIGNIFICANCE AND IMPACT OF THE STUDY

The identification of potential biomarkers of these clinically relevant bacteria could open the way for the diagnosis of these infections through the analysis of volatile compounds.

Anaerobic bacteria in chronic wounds: Roles in disease, infection and treatment failure

Infection is among the most common factors that impede wound healing, yet standard treatments routinely fail to resolve chronic wound infections. The chronic wound environment is largely hypoxic/anoxic, and wounds are predominantly colonised by facultative and obligate anaerobic bacteria. Oxygen (O2) limitation is an underappreciated driver of microbiota composition and behaviour in chronic wounds. In this perspective article, we examine how anaerobic bacteria and their distinct physiologies support persistent, antibiotic-recalcitrant infections. We describe the anaerobic energy metabolisms bacteria rely on for long-term survival in the wound environment, and why many antibiotics become less effective under hypoxic conditions. We also discuss obligate anaerobes, which are among the most prevalent taxa to colonise chronic wounds, yet their potential roles in influencing the microbial community and wound healing have been overlooked. All of the most common obligate anaerobes found in chronic wounds are opportunistic pathogens. We consider how these organisms persist in the wound environment and interface with host physiology to hinder wound healing processes or promote chronic inflammation. Finally, we apply our understanding of anaerobic physiologies to evaluate current treatment practices and to propose new strategies for treating chronic wound infections.

Commensal-derived short-chain fatty acids disrupt lipid membrane homeostasis in Staphylococcus aureus

The role of commensal anaerobic bacteria in chronic respiratory infections is unclear, yet they can exist in abundances comparable to canonical pathogens in vivo. Their contributions to the metabolic landscape of the host environment may influence pathogen behavior by competing for nutrients and creating inhospitable conditions via toxic metabolites. Here, we reveal a mechanism by which the anaerobe-derived short chain fatty acids (SCFAs) propionate and butyrate negatively affect Staphylococcus aureus physiology by disrupting branched chain fatty acid (BCFA) metabolism. In turn, BCFA impairment results in impaired growth, diminished expression of the agr quorum sensing system, as well as increased sensitivity to membrane-targeting antimicrobials. Altered BCFA metabolism also reduces S. aureus fitness in competition with Pseudomonas aeruginosa, suggesting that airway microbiome composition and the metabolites they produce and exchange directly impact pathogen succession over time. The pleiotropic effects of these SCFAs on S. aureus fitness and their ubiquity as metabolites in animals also suggests that they may be effective as sensitizers to traditional antimicrobial agents when used in combination.

Post-irradiation dysbiosis in patients with nasopharyngeal carcinoma having received radiotherapy - A pilot study

OBJECTIVE

To compare the changes in the sinonasal mucosa microbiome in patients with nasopharyngeal carcinoma (NPC) before and after radiotherapy (RT), and to explore the pathogenesis of post-irradiation chronic rhinosinusitis (PI-CRS) and its association with dysbiosis.

STUDY DESIGN

Prospective cohort study.

SETTING

Unicenter, Tertiary referral hospital.

METHODS

Included patients newly diagnosed with NPC. Samples of ostiomeatal complex mucosa were collected before and after RT. Microbiome analysis was conducted using 16S rRNA sequencing, and statistical analysis was performed. Subgroup analyses based on RT modality (proton therapy or photon therapy) RESULTS: Total of 18 patients were enrolled in the study, with 62.1% receiving intensity-modulated proton therapy (IMPT). Corynebacterium was the most dominant genus identified in both the pre- and post-RT groups, with a visible increase in Staphylococcus and a decrease in Fusobacterium genus in post-RT group. Alpha-diversity did not significantly differ between groups, although the beta-diversity analysis revealed a dispersed microbiota in the post-RT group. The functional prediction indicated a higher relative abundance of taxonomies associated with biofilm formation in the post-RT group. The subgroup analysis revealed the above changes to be more significant in patients who received photon therapy (Intensity modulated radiation therapy, IMRT).

CONCLUSIONS

This is the first study to analyze the microbiome of patients with NPC after IMPT. We identified similarities between the post-RT microenvironment and that reported in patients with CRS, with a more apparent change noted in patients treated with IMRT. Further investigation is required to further elucidate the pathogenesis of PI-CRS and its relationship to post-RT dysbiosis, particularly IMPT.

Efficacy and Safety of Xylitol Nasal Irrigation after Functional Endoscopic Sinus Surgery: A Randomized Controlled Study

Xylitol is considered a naturally occurring antibacterial agent. It is generally believed to enhance the body's own innate bactericidal mechanisms. It also provides anti-adhesive effects against both Streptococcus pneumoniae and Haemophilus influenza. This study was performed to evaluate the efficacy and safety of xylitol nasal irrigation in the postoperative care of functional endoscopic sinus surgery (FESS). Patients with chronic rhinosinusitis who received FESS were recruited and randomly assigned to two groups at one month post-surgery. Thirty-five patients in the xylitol group received 400 mL of 5% xylitol nasal irrigation daily for 2 months, while another 35 in the normal saline (NS) group received 400 mL of NS nasal irrigation daily for 2 months. Prior to FESS, as well as before and after nasal irrigation, sinonasal symptoms were assessed through the 22-item Sino-Nasal Outcome Test Questionnaire. The patients also underwent an endoscopic examination while undergoing nasal function tests, and a cytokine measurement of the nasal lavage and a bacterial culture from the middle meatus were performed. The safety of the nasal irrigation was assessed through any self-reported adverse events, the Eustachian Tube Dysfunction Patient Questionnaire and the eustachian tube function test. The endoscopic scores and olfactory threshold significantly decreased after xylitol irrigation when compared with those before irrigation. The prevalence of Staphylococcus aureus in the nasal secretions also decreased significantly after xylitol irrigation. The amounts of Interleukin-5 and Interleukin-17A were significantly increased in the nasal lavage after xylitol irrigation. No side effects, including those related to eustachian tube function, were seen after nasal irrigation in both groups. Our results showed that xylitol nasal irrigation was both beneficial and safe during the postoperative care of FESS.

Remodeling of Paranasal Sinuses Mucosa Functions in Response to Biofilm-Induced Inflammation

Rhinosinusitis (RS) is an acute (ARS) or chronic (CRS) inflammatory disease of the nasal and paranasal sinus mucosa. CRS is a heterogeneous condition characterized by distinct inflammatory patterns (endotypes) and phenotypes associated with the presence (CRSwNP) or absence (CRSsNP) of nasal polyps. Mucosal barrier and mucociliary clearance dysfunction, inflammatory cell infiltration, mucus hypersecretion, and tissue remodeling are the hallmarks of CRS. However, the underlying factors, their priority, and the mechanisms of inflammatory responses remain unclear. Several hypotheses have been proposed that link CRS etiology and pathogenesis with host (eg, "immune barrier") and exogenous factors (eg, bacterial/fungal pathogens, dysbiotic microbiota/biofilms, or staphylococcal superantigens). The abnormal interplay between these factors is likely central to the pathophysiology of CRS by triggering compensatory immune responses. Here, we discuss the role of the sinonasal microbiota in CRS and its biofilms in the context of mucosal zinc (Zn) deficiency, serving as a possible unifying link between five host and "bacterial" hypotheses of CRS that lead to sinus mucosa remodeling. To date, no clear correlation between sinonasal microbiota and CRS has been established. However, the predominance of Corynebacteria and Staphylococci and their interspecies relationships likely play a vital role in the formation of the CRS-associated microbiota. Zn-mediated "nutritional immunity", exerted via calprotectin, alongside the dysregulation of Zn-dependent cellular processes, could be a crucial microbiota-shaping factor in CRS. Similar to cystic fibrosis (CF), the role of SPLUNC1-mediated regulation of mucus volume and pH in CRS has been considered. We complement the biofilms' "mechanistic" and "mucin" hypotheses behind CRS pathogenesis with the "structural" one - associated with bacterial "corncob" structures. Finally, microbiota restoration approaches for CRS prevention and treatment are reviewed, including pre- and probiotics, as well as Nasal Microbiota Transplantation (NMT).

A cross talk between microbial metabolites and host immunity: Its relevance for allergic diseases

BACKGROUND

Allergic diseases, including respiratory and food allergies, as well as allergic skin conditions have surged in prevalence in recent decades. In allergic diseases, the gut microbiome is dysbiotic, with reduced diversity of beneficial bacteria and increased abundance of potential pathogens. Research findings suggest that the microbiome, which is highly influenced by environmental and dietary factors, plays a central role in the development, progression, and severity of allergic diseases. The microbiome generates metabolites, which can regulate many of the host's cellular metabolic processes and host immune responses.

AIMS AND METHODS

Our goal is to provide a narrative and comprehensive literature review of the mechanisms through which microbial metabolites regulate host immune function and immune metabolism both in homeostasis and in the context of allergic diseases.

RESULTS AND DISCUSSION

We describe key microbial metabolites such as short-chain fatty acids, amino acids, bile acids and polyamines, elucidating their mechanisms of action, cellular targets and their roles in regulating metabolism within innate and adaptive immune cells. Furthermore, we characterize the role of bacterial metabolites in the pathogenesis of allergic diseases including allergic asthma, atopic dermatitis and food allergy.

CONCLUSION

Future research efforts should focus on investigating the physiological functions of microbiota-derived metabolites to help develop new diagnostic and therapeutic interventions for allergic diseases.

QingXiaoWuWei decoction alleviates methicillin-resistant Staphylococcus aureus-induced pneumonia in mice by regulating metabolic remodeling and macrophage gene expression network via the microbiota-short-chain fatty acids axis

IMPORTANCE

Methicillin-resistant Staphylococcus aureus (MRSA) colonizes the upper respiratory airways and is resistant to antibiotics. MRSA is a frequently acquired infection in hospital and community settings, including cases of MRSA-induced pneumonia. Multidrug-resistant Staphylococcus aureus and the limited efficacy of antibiotics necessitate alternative strategies for preventing or treating the infection. QingXiaoWuWei decoction (QXWWD) protects against both gut microbiota dysbiosis and MRSA-induced pneumonia. Furthermore, the QXWWD-regulated metabolic remodeling and macrophage gene expression network contribute to its protective effects through the microbiota-short-chain fatty acid axis. The results of this study suggest that QXWWD and its pharmacodynamic compounds might have the potential to prevent and treat pulmonary infections, especially those caused by multidrug-resistant organisms. Our study provides a theoretical basis for the future treatment of pulmonary infectious diseases by manipulating gut microbiota and their metabolites via traditional Chinese medicine.

The fadXDEBA locus of Staphylococcus aureus is required for metabolism of exogenous palmitic acid and in vivo growth

In Staphylococcus aureus, genes that should confer the capacity to metabolize fatty acids by β-oxidation occur in the fadXDEBA locus, but their function has not been elucidated. Previously, incorporation into phospholipid through the fatty acid kinase FakA pathway was thought to be the only option available for S. aureus to metabolize exogenous saturated fatty acids. We now find that in S. aureus USA300, a fadX::lux reporter was repressed by glucose and induced by palmitic acid but not stearic acid, while in USA300ΔfakA basal expression was significantly elevated, and enhanced in response to both fatty acids. When cultures were supplemented with palmitic acid, palmitoyl-CoA representing the first metabolite in the β-oxidation pathway was detected in USA300, but not in a fadXDEBA deletion mutant USA300Δfad, which relative to USA300 exhibited increased incorporation of palmitic acid into phospholipid accompanied by a rapid loss of viability. USA300Δfad also exhibited significantly reduced viability in a murine tissue abscess infection model. Our data are consistent with FakA-mediated incorporation of fatty acids into phospholipid as a preferred pathway for metabolism of exogenous fatty acids, while the fad locus is critical for metabolism of palmitic acid, which is the most abundant free fatty acid in human plasma.

The Short-chain Fatty Acid Propionic Acid Activates the Rcs Stress Response System Partially through Inhibition of d-Alanine Racemase

The Enterobacterial Rcs stress response system reacts to envelope stresses through a complex two-component phosphorelay system to regulate a variety of environmental response genes, such as capsular polysaccharide and flagella biosynthesis genes. However, beyond Escherichia coli, the stresses that activate Rcs are not well-understood. In this study, we used a Rcs system-dependent luminescent transcriptional reporter to screen a library of over 240 antimicrobial compounds for those that activated the Rcs system in Serratia marcescens, a Yersiniaceae family bacterium. Using an isogenic rcsB mutant to establish specificity, both new and expected activators were identified, including the short-chain fatty acid propionic acid, which is found at millimolar levels in the human gut. Propionic acid did not reduce the bacterial intracellular pH, as was hypothesized for its antibacterial mechanism. Instead, data suggest that the Rcs-activation by propionic acid is due, in part, to an inactivation of alanine racemase. This enzyme is responsible for the biosynthesis of d-alanine, which is an amino-acid that is required for the generation of bacterial cell walls. Consistent with what was observed in S. marcescens, in E. coli, alanine racemase mutants demonstrated elevated expression of the Rcs-reporter in a d-alanine-dependent and RcsB-dependent manner. These results suggest that host gut short-chain fatty acids can influence bacterial behavior via the activation of the Rcs stress response system. IMPORTANCE The Rcs bacterial stress response system responds to envelope stresses by globally altering gene expression to profoundly impact host-pathogen interactions, virulence, and antibiotic tolerance. In this study, a luminescent Rcs-reporter plasmid was used to screen a library of compounds for activators of Rcs. Among the strongest inducers was the short-chain fatty acid propionic acid, which is found at high concentrations in the human gut. This study suggests that gut short-chain fatty acids can affect both bacterial virulence and antibiotic tolerance via the induction of the Rcs system.

Targeting the Achilles' Heel of Multidrug-Resistant Staphylococcus aureus by the Endocannabinoid Anandamide

Antibiotic-resistant Staphylococcus aureus is a major health issue that requires new therapeutic approaches. Accumulating data suggest that it is possible to sensitize these bacteria to antibiotics by combining them with inhibitors targeting efflux pumps, the low-affinity penicillin-binding protein PBP2a, cell wall teichoic acid, or the cell division protein FtsZ. We have previously shown that the endocannabinoid Anandamide (N-arachidonoylethanolamine; AEA) could sensitize drug-resistant S. aureus to a variety of antibiotics, among others, through growth arrest and inhibition of drug efflux. Here, we looked at biochemical alterations caused by AEA. We observed that AEA increased the intracellular drug concentration of a fluorescent penicillin and augmented its binding to membrane proteins with concomitant altered membrane distribution of these proteins. AEA also prevented the secretion of exopolysaccharides (EPS) and reduced the cell wall teichoic acid content, both processes known to require transporter proteins. Notably, AEA was found to inhibit membrane ATPase activity that is necessary for transmembrane transport. AEA did not affect the membrane GTPase activity, and the GTPase cell division protein FtsZ formed the Z-ring of the divisome normally in the presence of AEA. Rather, AEA caused a reduction in murein hydrolase activities involved in daughter cell separation. Altogether, this study shows that AEA affects several biochemical processes that culminate in the sensitization of the drug-resistant bacteria to antibiotics.