Biology subjects

Sah, G. P.

Publications and source records attributed to Sah, G. P..

3 recordsLinked to original sources

bioRxiv2024

Experimental Phage Evolution Results in Expanded Host Ranges Against MDR and XDR Klebsiella pneumoniae Isolates

Resistance to antibiotics is approaching crisis levels for organisms such as the ESKAPEE pathogens (includes Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter spp., and Escherichia coli) that often are acquired in hospitals. These organisms sometimes have acquired plasmids that confer resistance to most if not all beta-lactam antibiotics such as those produced by Carbapenem Resistant Enterobacterales (CREs). We have been developing alternative means for dealing with antibiotic resistant microbes that cause infections in humans by developing viruses (bacteriophages) that attack and kill them. We have been working with one of the ESKAPEE pathogens, K. pneumoniae, that has one of the highest propensities for antimicrobial resistance, to develop phages that target and kill it. We identified a number of phages that have lytic capacity against only a few clinical isolates, and through experimental evolution over the course of 30 days, were able to vastly expand the host ranges of these phages to kill a broader range of clinical K. pneumoniae isolates including MDR (multi-drug resistant) and XDR (extensively-drug resistant) isolates. Most interestingly, they were capable of inhibiting growth of clinical isolates both on solid and in liquid medium over extended periods. That we were able to extend the host ranges of multiple naive MDR and XDR K. pneumoniae through experimental phage evolution suggests that such a technique may be applicable to other antibiotic-resistant organisms to help stem the tide of antibiotic resistance and offer further options for medical treatments. ImportanceBacterial pathogens are becoming greater threats given the rise in antibiotic resistance, where traditional therapies may no longer work to cure some infections. Chief amongst these multidrug resistant infections (MDR) and extensively drug-resistant infections (XDR) is Klebsiella pneumoniae, which is known to sometimes harbor genetic elements that render it incredibly difficult to treat with conventional antibiotics. Treatments like bacteriophages have not had much success against such pathogens because resistance to the phages used often develops rapidly. We adapted a co-evolutionary technique to develop K. pneumoniae phages to be highly active longitudinally against K. pneumoniae clinical isolates. In as few as 30 days, we were able to vastly expand the host ranges of K. pneumoniae phages against MDR and XDR clinical isolates and that maintain their infectivity over clinically relevant time periods. By adapting these established techniques to clinical MDR and XDR K. pneumoniae isolates, we believe we can establish similar techniques for expanding phage host ranges against most antibiotic-resistant bacteria. As such, phages can be viable alternatives to antibiotics when antibiotic resistance exists in hospitals and communities.

microbiology↗

bioRxiv2024

In-vitro resensitization of multidrug resistant clinical isolates of Enterococcus faecium and faecalis through phage-antibiotic synergy

Bacteriophages are an increasingly attractive option for the treatment of antibiotic resistant infections, but their efficacy is difficult to discern due to confounding effects of antibiotics. Phages are generally delivered in conjunction with antibiotics, and thus, when patients improve its unclear whether the phages, antibiotics or both are responsible. This question is particularly relevant for enterococcus infections, as limited data suggest phages might restore antibiotic efficacy against resistant strains. Enterococci can develop high-level resistance to vancomycin, a primary treatment. We assessed clinical and laboratory isolates of Enterococcus faecium and Enterococcus faecalis to determine whether we could observe synergistic interactions between phages and antibiotics. We identified synergy between multiple phages and antibiotics including linezolid, ampicillin, and vancomycin. Notably, antibiotic susceptibility did not predict synergistic interactions with phages. Vancomycin resistant isolates (n=6) were eradicated by the vancomycin-phage combination as effectively as vancomycin susceptible isolates (n=2). Transcriptome analysis revealed significant gene expression changes under antibiotic-phage conditions, especially for linezolid and vancomycin, with upregulated genes involved in nucleotide and protein biosynthesis and downregulated stress response and prophage-related genes. While our results do not conclusively determine the etiology of the observed synergistic interactions between antibiotics and phages, they do confirm and build upon previous research that observed these synergistic interactions. Our work highlights how using phages can restore the effectiveness of vancomycin against resistant isolates. This finding provides a promising, although unexpected, strategy for moving forward with phage treatments for Vancomycin Resistant Enterococcus infections.

microbiology↗

bioRxiv2021

Emergent myxobacterial behaviors arise from reversal suppression induced by kin contacts

A wide range of biological systems - from microbial swarms to bird flocks, display emergent behaviors driven by coordinated movement of individuals. To this end, individual organisms interact by recognizing their kin and adjusting their motility based on others around them. However, even in the best-studied systems, the mechanistic basis of the interplay between kin recognition and motility coordination is not understood. Here, using a combination of experiments and mathematical modeling, we uncover the mechanism of an emergent social behavior in Myxococcus xanthus. By overexpressing cell surface adhesins, TraA and TraB, involved in kin recognition, large numbers of cells adhere to one another and form organized macroscopic circular aggregates that spin clockwise or counterclockwise. Mechanistically, TraAB adhesion results in sustained cell-cell contacts that trigger cells to suppress cell reversals, and circular aggregates form as the result of cells ability to follow their own cellular slime trails. Furthermore, our in-silico simulations demonstrate a remarkable ability to predict self-organization patterns when phenotypically distinct strains are mixed. For example, defying naive expectations, both models and experiments found that strains engineered to overexpress different and incompatible traAB allelles nevertheless form mixed circular aggregates. Therefore, this work provides key mechanistic insights into M. xanthus social interactions and demonstrates how local cell contacts induce emergent collective behaviors by millions of cells. ImportanceIn many species, large populations exhibit emergent behaviors whereby all related individuals move in unison. For example, fish in schools can all dart in one direction simultaneously to avoid a predator. Currently, it is impossible to explain how such animals recognize kin through brain cognition and elicit such behaviors at a molecular level. However, microbes also recognize kin and exhibit emergent collective behaviors that are experimentally tractable. Here, using a model social bacterium, we engineer dispersed individuals to organize into synchronized collectives that create emergent patterns. With experimental and mathematical approaches we explain how this occurs at both molecular and population levels. The results demonstrate how the combination of local physical interactions triggers intracellular signaling, which in turn leads to emergent behavior on a population scale.

biophysics↗