Biology subjects

Hristova, K. R.

Publications and source records attributed to Hristova, K. R..

3 recordsLinked to original sources

bioRxiv2025

Acinetobacter spp. with lower susceptibility to quaternary ammonium compounds enriched in microbial communities of frequently used sinks

Sanitary environments that undergo frequent cleaning and disinfection may harbor microbial communities with potential health risks. While biofilms in healthcare settings are well studied, comparatively less is known about sink microbiomes in public and educational buildings, where hundreds of people may interact with shared sink fixtures. This study characterized the spatial and temporal heterogeneity of sink drain biofilm microbiomes in academic buildings. We sampled 16 sinks from two buildings (four floors each, with sinks closest and furthest to the bathroom entrance), which are cleaned daily with quaternary ammonium compound (QAC) disinfectants, during periods of low and high student traffic (during and after academic breaks, respectively) across winter, spring, and summer. We observed significant spatial and temporal variations in microbial assemblages. Individual sinks accounted for 43% (PERMANOVA, p < 0.0001) of the variation in microbial communities. Microbiomes in each building were dominated by two genera, which together accounted for 30% of the community composition: Acinetobacter and Enhydrobacter (also classified as Moraxella) in the newer building, and Sphingomonas and Mycobacterium in the older building. Acinetobacter abundance varied seasonally and showed higher relative abundance during periods of high traffic. Metagenomic analysis of selected sinks revealed a high prevalence of qac genes and metagenome-assembled genomes (MAGs) harboring antimicrobial resistance genes (ARGs) including A. parvus. Notably, 34-53% of qac genes were co-localized on contigs associated with mobile genetic elements. These findings suggest that disinfected sink drains serve as persistent reservoirs of diverse microorganisms and potentially mobile resistance elements. IMPORTANCESink drains are recognized environmental reservoirs for multidrug-resistant bacteria and have been linked to healthcare-associated outbreaks. In public and educational buildings, these microbiomes are shaped by frequent human activity, making them potential sources of exposure and contributors to the environmental dissemination of antibiotic resistance genes. Quaternary ammonium compound (QAC) disinfectants are widely used on surfaces; however, they can select for resistant taxa and co-select for antibiotic resistance. In this study, despite routine cleaning with QACs, public restroom drains remain colonized by resilient biofilms, posing a potential risk to multiple users. Additionally, factors such as human traffic and seasonal variation may influence drain usage and microbial community composition. Elucidating how seasonal dynamics and human activity shape sink biofilms is essential for understanding their role in the environmental transmission of antimicrobial resistance and informing mitigation strategies in nonclinical settings.

microbiology↗

bioRxiv2023

Bacillus subtilis maintains antibiofilm activity against Staphylococcus aureus following adaptive laboratory evolution

Quorum sensing interference has been touted as an ideal mechanism for the development of new anti-virulence therapies. Recent work has established Bacillus subtilis 6D1, a Gram-positive spore forming bacterium with probiotic qualities, produces metabolites that inhibit Staphylococcus aureus virulence and biofilm formation via quorum sensing interference. However, it remains unknown how long-term exposure to these molecules drive S. aureus adaptation and evolution. S. aureus planktonic cells and biofilms were propagated in the presence of B. subtilis 6D1 cell free extracts (CFE) for [~]73 generations. Fitness, virulence, and antibiotic resistance assays of the ancestor and all evolved lineages revealed the emergence of treatment and lifestyle associated ecological traits. Compared to the ancestor and media-evolved lineages, S. aureus lineages evolved in the presence of B. subtilis 6D1 CFE were less competitive in a biofilm and exhibited increased phenotypic sensitivity to multiple antibiotics. Notably, B. subtilis 6D1 CFE maintained its ability to inhibit S. aureus biofilm growth and disassemble mature biofilm in all evolved lineages. S. aureus populations propagated in the presence of CFE acquired missense mutations in genes associated with plasmid-borne efflux systems and RNA polymerase. Furthermore, CFE-evolved lineages did not develop mutations in both competence and drug resistance pathways found in similarly evolved control lineages. Our data suggest long-term exposure to biofilm inhibitory molecules, like those produced by B. subtilis 6D1, can reduce S. aureus fitness in a biofilm and increase sensitivity to multiple antibiotics. ImportanceQuorum sensing interference (QSI) has been touted as an ideal mechanism to diminish bacterial virulence and improve antibiotic killing, however few studies investigate the genetic and phenotypic adaptations that occur after long-term exposure to QSI therapies. Recent studies revealed Bacillus subtilis reduces biofilm formation and virulence via signaling interference with the S. aureus Agr QS system; however, it remains unclear how long-term exposure to these compounds drives S. aureus adaptation and evolution. This study helps to address these gaps by investigating whether QSI strategies deployed by probiotic bacteria are viable approaches to increase antibiotic efficacy without increasing antibiotic resistance evolution.

microbiology↗

bioRxiv2023

Bacillus subtilis derived lipopeptides disrupt quorum sensing and biofilm assembly in Staphylococcus aureus

Multidrug-resistant Staphylococcus aureus is one of the most clinically important pathogens in the world with infections leading to high rates of morbidity and mortality in both humans and animals. S. aureus ability to form biofilm protects individual cells from antibiotics and promotes the transfer of antibiotic resistance genes. Therefore, new strategies aimed to inhibit biofilm growth and disassemble mature biofilms are urgently needed. Probiotic species, namely Bacillus subtilis, are gaining interest as a potential therapeutic against S. aureus for their ability to reduce S. aureus colonization and virulence. Here, we collected and screened 1123 Bacillus strains obtained from a variety of agricultural environments in search of isolates with strong antibiofilm activity against clinical multi-drug resistant S. aureus. We selected a single strain, B. subtilis 6D1, based on its ability to inhibit biofilm growth, disassemble mature biofilm, and improve antibiotic sensitivity of S. aureus biofilms through an Agr quorum sensing interference mechanism. Biochemical and molecular networking analysis of an active organic fraction revealed multiple surfactin isoforms and an uncharacterized compound were both driving this antibiofilm activity. Furthermore, when compared against commercial HPLC grade surfactin obtained from B. subtilis, this active fraction inhibited biofilm formation against all four S. aureus Agr backgrounds and prevented S. aureus-induced cytotoxicity when applied to HT29 human intestinal cell lines better than the commercial standard. Our results demonstrate the mixture of compounds produced by B. subtilis 6D1 can mitigate S. aureus virulence through multiple mechanisms. Contribution to the FieldThe biofilm formation capability of bacterial pathogens, such as Staphylococcus aureus, increases these microorganisms virulence potential and decreases the efficacy of common antibiotic regiments. Probiotics possess a variety of strain-specific strategies to reduce biofilm formation in competing organisms, however, the mechanisms and compounds responsible for these phenomena often go uncharacterized. In this study, we identified a mixture of small probiotic-derived peptides capable of Agr quorum sensing interference as one of the mechanisms driving antibiofilm activity against S. aureus. This collection of peptides also improved antibiotic killing and protected human gut epithelial cells from S. aureus-induced toxicity by stimulating an adaptive immune response. We conclude that purposeful strain screening and selection efforts can be used to identify unique probiotic strains that possess specially desired mechanisms of action. This information can be used to further improve our understanding of the ways in which probiotic and probiotic-derived compounds can be applied to prevent bacterial infections in clinical and agricultural settings.

microbiology↗