Rubén Jurado

Staphylococcus aureus is one of the main etiological agents of acute mastitis during lactation, and its ability to persist in biofilms can compromise conventional antimicrobial treatments. Lactic acid bacteria (LAB) have emerged as promising probiotic candidates for mastitis management, but the molecular mechanisms underlying their interaction with S. aureus remain poorly understood. This study aimed to evaluate the ability of three LAB strains ( Limosilactobacillus fermentum I7, Limosilactobacillus reuteri 7SNG3–30 and Ligilactobacillus salivarius 22SNG3-30) to interfere with mature biofilms formed by two mastitis-associated S. aureus strains, SA4 and SA55, and to characterize the associated transcriptional responses. The LAB strains were able to colonize preformed 24-h S. aureus biofilms, eventually dominating the mixed-species communities and reducing the attached staphylococcal population. RT-qPCR showed limited transcriptional changes after 4 h of LAB exposure, followed by a broader 16-h response characterized by induction of the stress/adaptation marker uspA and repression of genes related to quorum sensing, virulence, biofilm matrix production and iron acquisition. RNA-seq analysis of SA4 biofilms exposed to LAB for 16 h confirmed extensive transcriptional remodeling in S. aureus and revealed a conserved response across the three LAB treatments, including activation of stress, proteostasis, energy metabolism and arginine catabolism functions, together with repression of surface-associated, matrix-related, metal acquisition and virulence-associated pathways. In contrast, LAB transcriptomic responses were more moderate and strain-dependent, suggesting different metabolic, nutrient-acquisition and envelope-adaptation strategies during biofilm-associated interactions. Overall, these findings suggest that these LAB strains can displace mastitis-associated S. aureus from mature biofilms and promote a coordinated transcriptional shift toward stress adaptation and attenuation of virulence- and persistence-associated functions.

Allogeneic hematopoietic stem cell transplantation (HSCT) is a medical procedure to treat hematologic malignancies and restore bone marrow function. However, this approach may lead to graft-versus-host disease (GvHD), a major cause of mortality and morbidity after allogeneic HSCT. Some studies have suggested the involvement of gut microbiota in the development and prognosis of GvHD. In this context, the main objective of this study was to compare the fecal microbiome composition and short-chain profile of pediatric patients who underwent successful HSCT, developed GvHD or died. The bacterial composition was analyzed using 16S rRNA gene sequencing, while short-chain fatty acids (SCFAs) were quantified by gas chromatography. Fecal samples at engraftment were mainly characterized by a loss of bacterial diversity, a depletion of sequences belonging to the genus Blautia and significantly lower concentrations of fecal butyrate and acetate compared with those obtained before HSCT and 100 days after HSCT. Our findings confirm that children experiencing GvHD after HSCT have distinct gut microbiota and SCFA profiles, which might contribute to developing new microbiota-targeted strategies for GvHD prevention during HSCT procedures.

Acute mastitis is a common infection during lactation, primarily caused by Staphylococcus aureus , a bacterium known for its ability to form biofilms within mammary ducts and develop antibiotic resistance. This study aimed to genomically characterize S. aureus strains isolated from women with acute mastitis and healthy asymptomatic women to better understand how S. aureus strains transition from harmless components of the human milk microbiota to pathogenic agents responsible for mastitis. Whole-genome sequencing was performed on nine S . aureus strains—six from women with mastitis and three from healthy women—followed by in silico analyses of core and accessory genes, resistome, virulome, mobilome, and secondary metabolite synthesis to identify genes related to virulence, antibiotic resistance, biofilm formation, and mobile genetic elements such as plasmids, bacteriophages, and pathogenicity islands. Antimicrobial resistance profiles were evaluated using Sensititre EUST2 plates, antimicrobial activity by an agar diffusion method, biofilm formation in 96-well plates, and siderophore production with the Chrome Azurol S assay. Results showed that complete bacteriophage genomes were only present in S. aureus strains isolated from mastitis cases. Some virulence genes, including fnbB and cna , were absent in strains from healthy women. Both types of S. aureus strains exhibited biofilm formation capacity, with mastitis-associated strains SA4 and SA5 being the highest biofilm producers. Similarly, although all strains secreted siderophores, SA4 and SA55 exhibited the strongest siderophore production, indicating a link between this trait and virulence in mastitis-associated strains. The analysis of key genomic features, including virulence factors, resistance genes, and biofilm-forming capabilities, revealed some mechanisms by which S. aureus contributes to the pathogenesis of mastitis. IMPORTANCE: Acute mastitis is a widespread infection in lactating women, and its main cause, Staphylococcus aureus , has developed resistance to antibiotics, making treatment challenging. The ability of this bacterium to form biofilms complicates its eradication from the mammary glands. Understanding the genomic and phenotypic characteristics of S. aureus strains associated with mastitis, compared to those isolated from asymtomatic women, is critical for developing better treatment strategies. This study provides new insights into the genetic features, such as virulence factors, antibiotic resistance profiles, and presence of bacteriophages, that make S. aureus strains pathogenic in mastitis. It also highlights the potential of biofilm formation and siderophore production as key factors in mastitis progression. These findings could guide the development of novel therapeutic approaches, such as targeted therapies or probiotics, which can more effectively treat mastitis and reduce reliance on antibiotics, ultimately improving maternal and infant health.

Phelan–McDermid syndrome (PMS) is a neurodevelopmental disorder characterized by a developmental delay and autism spectrum disorder (ASD)-like behaviors. Emerging research suggests a link between gut microbiota and neuropsychiatric conditions, including PMS. This study aimed to investigate the fecal microbiota and immune profiles of children with PMS compared to healthy controls. Fecal samples were collected from children diagnosed with PMS and age-matched healthy controls. The bacterial composition was analyzed using 16S rRNA gene sequencing, while short-chain fatty acids (SCFAs) were quantified through gas chromatography. Immunological profiling was conducted using a multiplex cytokine assay. Significant differences were observed in the gut microbiota composition between PMS patients and controls, including a lower abundance of key bacterial genera such as Faecalibacterium and Agathobacter in PMS patients. SCFA levels were also reduced in PMS patients. Immunological analysis revealed higher levels of several pro-inflammatory cytokines in the PMS group, although these differences were not statistically significant. The findings indicate that children with PMS have distinct gut microbiota and SCFA profiles, which may contribute to the gastrointestinal and neurodevelopmental symptoms observed in this syndrome. These results suggest potential avenues for microbiota-targeted therapies in PMS.

The interplay between enterohepatic circulation and the gut microbiota is the main driver determining systemic levels of estrogens and their metabolites. Nevertheless, the role of potentially probiotic microorganisms in estrogen metabolism has not been investigated so far. In this work, we have explored the ability of six Ligilactobacillus salivarius strains isolated from human milk and vaginal samples to degrade and/or conjugate parental estrogens in vitro and under aerobic conditions. The quantification of estrogens and their derivatives was carried out in cell-free supernatants by LC-QQQ-MS. All the tested L. salivarius strains achieved an average degradation rate of estrone and estriol of 98% and 55%, respectively, whereas 17β-estradiol was preferentially conjugated (up to 40%). The presence of seven out of ten genes encoding enzymes relevant for estrogen metabolism was further confirmed by PCR, highlighting their genetic potential for degrading, conjugating and/or deconjugating estrogens. The tested L. salivarius strains may be considered potential probiotics affecting the fate of endogenous estrogens. Clinical trials targeting populations with estrogen-dependent conditions will be required to elucidate the true potential of these strains for the restoration and maintenance of a healthy host estrobolome.