Biology subjects

Salvadori, G.

Publications and source records attributed to Salvadori, G..

4 recordsLinked to original sources

bioRxiv2026

Genetic and functional characterization of the natural transformation system in Streptococcus constellatus

Streptococcus constellatus is an opportunistic pathogen frequently associated with abscess formation in various body sites. While the species has been shown to acquire exogenous DNA through natural transformation, functional analyses of its underlying mechanisms and optimized genetic editing protocols remain limited. Thus, our aim was to characterize the natural transformation system in S. constellatus and investigate environmental factors regulating its natural transformation system. In addition, we sought to develop an optimized protocol for genome editing. Genomic analysis revealed that 73% of analyzed strains possess orthologs for essential competence regulon genes, with 55% harboring both a complete ComCDE-based operon and the necessary transformation machinery. While all complete genomes harbored three copies of the master regulator sigX, the accessory regulator comW was seemingly absent. Lacking the peptide exporter comAB, we demonstrated that S. constellatus utilizes the bacteriocin transporter silED for competence-stimulating peptide export. Gene expression assays indicated system activation at peptide concentrations as low as 4 nM, with peak sigX expression obtained over 60 nM. With the goal of optimizing gene editing strategies, we developed a protocol utilizing rich media supplemented with bovine serum albumin and calcium chloride, substantially increasing transformation frequencies. Furthermore, we observed that environmental stressors can upregulate the system, including hydrogen peroxide and subinhibitory concentrations of the antibiotics erythromycin, chloramphenicol, and ampicillin. Given the increasing clinical relevance of the anginosus group, elucidating horizontal gene transfer mechanisms can provide critical insights into the evolutionary success and pathogenic potential of these species.

microbiology↗

bioRxiv2026

Mapping antibiotic resistance determinants in oral streptococci

BackgroundAntibiotic resistance is a global priority in healthcare. Leveraging thousands of whole-genome sequences, here we reveal the core resistance determinants of oral streptococci, focusing on assessing pattern variability and gene exchange across commensals and pathogens. MethodsGenomic information was obtained from the National Center for Biotechnology Information. Determinants of antibiotic resistance were identified using AMRFinderPlus and CARD. ICEscreen was employed for calling of integrative and conjugative elements. Variability and recombination in penicillin-binding protein sequences were assessed with MMseqs2 and fastGEAR. ResultsA total of 2,087 genomes from 15 species were included with members from the mitis, mutans, anginosus, salivarius, and bovis groups. We observed 3,576 hits from 55 unique resistance genes conferring resistance to 11 antibiotic classes. The species with most resistance determinants per genome were identified as Streptococcus mitis (2.7), Streptococcus oralis (2.5), Streptococcus parasanguinis (1.9), Streptococcus gallolyticus (1.3), and Streptococcus anginosus (1.2). The two latter species also presented the most diverse composition of determinants. Over 1,800 integrative and conjugative elements were shown across all genomes, with nearly 18% of them carrying at least one antibiotic resistance gene. Penicillin-binding protein variation analyses showed a high diversity in the mitis group. Even though S. mitis and S. oralis composed less than 4% of the genomes included in the analyses, they were recognized as sources of DNA for over a third of recombination events in pbp1a and nearly half for both pbp2b and pbp2x in resistant isolates of Streptococcus pneumoniae. ConclusionsWe show that tetracycline and macrolide resistance were highly abundant and tightly connected to integrative and conjugative elements. Further, recent recombination data show frequent genetic exchange from oral streptococci to beta-lactam-resistant S. pneumoniae. Finally, assessing the dynamics of genetic exchange across species is central for the development of strategies to mitigate the impact of antibiotic resistance.

microbiology↗

bioRxiv2025

Large-scale global molecular epidemiology of antibiotic resistance determinants in Streptococcus pneumoniae

BackgroundStreptococcus pneumoniae is a leading pathogen in terms of deaths attributable to or associated with antimicrobial resistance globally. Thus, monitoring antibiotic resistance determinants constitutes a key aspect of surveillance efforts. AimLeveraging on publicly available whole-genome sequencing data, we aimed to investigate the presence and distribution patterns of antibiotic resistance in S. pneumoniae with a focus on multi-drug resistance and serotype distribution. MethodsMetadata and genomes were obtained from the National Center for Biotechnology Information Pathogen Detection database. Curation and harmonization were performed in R and SPSS. Data on resistance patterns was defined according to AMRFinderPlus and a combination of prediction tools were employed for in silico serotyping. ResultsAnalyses involved 75,161 genomes totaling 122,673 gene/allele counts from 14 antibiotic classes. Multi-drug resistance was observed in 16.7% of isolates with the highest increasing rates in Asia and South America. Within antibiotic classes, increase in macrolide resistance genes was highlighted, particularly in the proportion of genomes presenting mefA/msrD. Over a third of isolates with serotypes 19F, 23F, 15A, 6B, and 19A showed multi-drug resistance. We further observed the highest significant increases in the presence of resistance in 33F, 22F, 10A, and 23A. Serotype 13, not included in any vaccine formulation, presented high multi-drug resistance rates with a strong increasing trend. ConclusionsThe findings of this study highlight variations in resistance determinants globally and across serotypes over time. Collectively these data underscore the added value of utilizing public whole-genome sequencing data to investigate the effectiveness and repercussions of treatment and vaccination strategies on managing antibiotic resistance.

microbiology↗

bioRxiv2023

Unravelling the landscape of antibiotic resistance determinants in the nasopharynx and the impact of antibiotics: a longitudinal study of preterm infants

Respiratory pathogens, commonly colonizing nasopharynx, are among the leading causes of death due to antimicrobial resistance. Yet, antibiotic resistance determinants within nasopharyngeal microbial communities remain poorly understood. Utilizing shotgun metagenomics, we investigated the nasopharynx resistome development in preterm infants, assessed early antibiotic impact on its trajectory, and explored its association with clinical covariates. Our findings revealed widespread nasopharyngeal carriage of antibiotic resistance genes (ARGs) with resistomes undergoing transient changes, including increased ARG diversity, abundance, and composition alterations due to early antibiotic exposure. ARGs associated with the critical nosocomial pathogen Serratia marcescens persisted up to 8-10 months of age, representing a long-lasting hospitalization signature. The nasopharyngeal resistome strongly correlated with microbiome composition, with inter-individual differences and postnatal age explaining most of the variation. Our report on the collateral effects of antibiotics and prolonged hospitalization underscores the urgency of further studies focused on this relatively unexplored reservoir of pathogens and ARGs.

microbiology↗