Biology subjects

Mediati, D. G.

Publications and source records attributed to Mediati, D. G..

4 recordsLinked to original sources

bioRxiv2025

Molecular evolution of silver nanoparticle resistance in a bacterial pathogen and a unique adaptation response to ionic silver

This research explores the adaptive defense mechanisms of a nanosilver-resistant pathogen (NAgR) to protect and fight off the complex antimicrobial targeting of silver nanoparticles. The Gram-negative bacterium Acinetobacter baumannii upregulated expression of outer membrane proteins for cell surface defense, as well as membrane and capsule synthesis genes. Increased abundance of surface-attached biofilm colonies in NAgR was linked to the phenotypically indicated increase in membrane integrity, with the bacterium also forming more EPS, the biopolymer matrix that protects the residing colony. In response to the known reactive oxygen species (ROS) toxicity characteristics of the nanoparticle, NAgR upregulated its oxidative stress management system, specifically involving ROS scavenger enzymes and opportunistic metal efflux pumps. Many of these evolved defense mechanisms only manifested in the resistant bacterium, while they were absent in the wild-type strain. This study also details the unique defenses of an ionic silver-adapted A. baumannii variant, having evolved from the same wild-type parental strain as NAgR. Despite similarities in cell surface and biofilm defense trends, the slower-to-kill tolerant strain (AgT) exclusively upregulated multidrug efflux systems and respiratory chain enzymes, thought to maintain enhanced respiration activity, a known tolerant characteristic. Identification of these stable defense mechanisms can recommend strategies for molecular targeting to overcome the adaptation phenomena.

microbiology↗

bioRxiv2023

Genetic requirements for uropathogenic E. coli proliferation in the bladder cell infection cycle

Uropathogenic Escherichia coli (UPEC) requires an adaptable physiology to survive the wide range of environments experienced in the host, including gut and urinary tract surfaces. To identify UPEC genes required during intracellular infection, we developed a transposon-directed insertion-site sequencing (TraDIS) approach for cellular infection models and searched for genes in a library of [~]20,000 E. coli UTI89 transposon-insertion mutants that are specifically required for growth in M9-glycerol minimal medium, and at the distinct stages of infection of cultured bladder epithelial cells. Some of the functional requirements apparent for growth in M9-glycerol overlapped with those for the intracellular stage of infection, notably nutrient utilization, polysaccharide and macromolecule precursor biosynthesis, and cell envelope stress tolerance. Two genes implicated in both conditions were confirmed through independent gene deletion studies: neuC (sialic acid capsule biosynthesis) and hisF (histidine biosynthesis). Distinct sets of UPEC genes were also implicated in bacterial dispersal, where UPEC erupt from bladder cells in highly filamentous or motile forms upon exposure to human urine, and during recovery from infection in rich (LB) medium. Genes linked to septal peptidoglycan processes, ytfB and dedD, appeared to play roles in dispersal and may help stabilize cell division or the envelope during envelope stress created during infection. Our findings support a view that the host intracellular environment and infection cycle are multi-nutrient limited and create stress that demand an array of biosynthetic, cell envelope integrity and biofilm-related functions of UPEC. IMPORTANCEUrinary tract infections (UTIs) are one of the most frequent infections worldwide. Uropathogenic Escherichia coli (UPEC), which accounts for [~]80 % of UTIs, must rapidly adapt to highly variable host environments, such as the gut, bladder sub-surface and urine. In this study, we searched for UPEC genes required for bacterial growth and survival throughout the cellular infection cycle. Genes required for de novo synthesis of biomolecules and cell envelope integrity appeared to be important, and other genes were also implicated in bacterial dispersal and recovery from infection of cultured bladder cells. With further studies of individual gene function, their potential as therapeutic targets may be realized. This study expands knowledge of the UTI infection cycle and establishes an approach to genome-wide functional analyses of stage-resolved microbial infections.

microbiology↗

bioRxiv2023

The functional small RNA interactome of vancomycin tolerant Staphylococcus aureus

RNA-RNA interactome profiling techniques have expanded our understanding of sRNA-mRNA interactions in bacteria. However, determining the function of these interactions for hundreds of sRNA-mRNA pairs is a major challenge. At steady-state, protein and mRNA abundances are often highly correlated and lower than expected protein abundance may indicate translational repression of an mRNA. To specifically identify sRNA-mRNA interactions that regulate mRNA translation, we examined the correlation between gene transcript abundance, ribosome occupancy, and protein levels. We used SOMS to cluster genes with similar transcription and translation patterns and identified a cluster of mRNAs that appeared to be post-transcriptionally repressed. By integrating this clustering analysis with sRNA-mRNA interactome data generated in vancomycin tolerant S. aureus by RNase III-CLASH, we identified sRNAs that may be mediating this translational repression. We have confirmed sRNA-dependant post-transcriptional repression of several mRNAs in this cluster. Two of these interactions are mediated by RsaOI, a sRNA that is highly upregulated by vancomycin treatment. While RsaOI is not essential for vancomycin tolerance, we demonstrate regulation of the phosphocarrier protein HPr and the cell-wall autolysin Atl. These findings suggest that RsaOI may serve as a regulator of carbon metabolism and cell wall turnover during cell wall stress exerted by vancomycin.

microbiology↗

bioRxiv2023

The 3'UTR of vigR is required for virulence in Staphylococcus aureus and has expanded through STAR sequence repeat insertions

Staphylococcus aureus is an adaptable human pathogen causing life-threatening endocarditis and bacteraemia. Methicillin-resistant S. aureus (MRSA) is alarmingly common, and treatment is confined to last-line antibiotics. Vancomycin is the treatment of choice for MRSA bacteraemia and vancomycin treatment failure is often associated with vancomycin-intermediate S. aureus strains termed VISA. The regulatory 3 UTR of vigR mRNA contributes to vancomycin tolerance in the clinical VISA isolate JKD6008 and upregulates the lytic transglycosylase IsaA. Using MS2-affinity purification coupled with RNA sequencing (MAPS), we find that the vigR 3 UTR also interacts with mRNAs involved in carbon metabolism, amino acid biogenesis, cell wall biogenesis, and virulence. The vigR 3 UTR was found to repress dapE, a succinyl-diaminopimelate desuccinylase required for lysine and cell wall peptidoglycan synthesis, suggesting a broader role in controlling cell wall metabolism and vancomycin tolerance. Deletion of the vigR 3 UTR increased VISA virulence in a wax moth larvae model, and we find that an isaA mutant is completely attenuated in the larvae model. Sequence and structural analysis of the vigR 3 UTR indicates that the UTR has expanded through the acquisition of Staphylococcus aureus repeat insertions (STAR repeats) that partly contribute sequence for the isaA interaction seed and may functionalise the 3 UTR. Our findings reveal an extended regulatory network for vigR, uncovering a novel mechanism of regulation of cell wall metabolism and virulence in a clinical S. aureus isolate.

microbiology↗