Biology subjects

Savva, G. M.

Publications and source records attributed to Savva, G. M..

6 recordsLinked to original sources

bioRxiv2026

The effects of bacteriophage cocktail treatment on healthy gut microbiota: an in vitro human colon model study

The human gut microbiome is a complex community that plays an important role in health, where perturbations can result in dysbiosis and disease. Bacteriophages (phages) can provide treatment for bacterial gastrointestinal disease, and commercial preparations such as the Intesti bacteriophage cocktail can be taken orally to target bacterial pathogens. However, interactions between these phages and the native gut microbiota are understudied. To investigate the impact of phage treatment, we used simulated gut models seeded with healthy donor microbiota from three individuals, sequenced the DNA, and analysed the bacterial and viral portion from samples obtained over time. Each donor had a unique bacterial composition which diverged with time. When comparing phage treated to control samples, we observed that Escherichia coli abundance accounted for the largest portion of bacterial community variance and was more associated with the controls. The lower abundance in phage treated samples may have resulted from the lytic action of phages from the cocktail. Additionally, our analyses of the viral portion revealed a phage bloom exclusive to phage treated samples. A highly abundant phage in this bloom was matched with the Intesti bacteriophage cocktail, showed similarity to Enterobacteria phage phi92, and provided evidence of productive infection within the model. While we did observe fluctuations in relative abundance of additional viral sequences in the presence of the phage cocktail, these changes were often transient. Furthermore, we detected only slight differences to typical members of the virome, and low numbers of active prophages. Our experiments suggest that the phage cocktail had minimal interruption to the native gut microbiota within the model. Impact statementBacteriophages are increasingly investigated and tested for their efficacy in treating infections and are a key component in fight against antimicrobial resistant bacterial infections. Because of their specificity, it has become almost a dogma to state that they do not alter the gut microbiome. We have now tested this in an in vitro study using a commercially available cocktail and real human faecal microbiota. We show minimal effects on the composition of the healthy microbiota with an individual-specific effect on Escherichia coli caused by productive infection of one phage in the cocktail.

microbiology↗

bioRxiv2025

Environmental context as a key driver of Pseudomonas biocontrol activity against Salmonella.

Salmonella poses a significant threat to food security, with frequent outbreaks reported worldwide. A large percentage of these outbreaks are associated with fresh produce intended for raw consumption. Plant microbiomes harbour diverse microbial communities, including commensal microbes such as Pseudomonas that sometimes exhibit biocontrol activity against plant pathogens. However, little is known about whether Pseudomonas strains can effectively suppress foodborne pathogens and the mechanisms they employ. In this study, we identified and characterised food derived Pseudomonas isolates capable of inhibiting Salmonella growth in vitro and in planta. The identified isolates were active against a range of Salmonella serovars, and additionally E. coli isolates derived from food. We demonstrated that dynamics of the interaction between Pseudomonas and Salmonella are environment and application dependant. To uncover the mechanisms Pseudomonas employs to suppress Salmonella, we used transcriptomics coupled with pathway analysis in the two different settings. We showed that Pseudomonas metabolism undergoes significant environment-specific changes in the presence of Salmonella, implicating different pathways responsible for the control of the pathogen in the two different settings. Our results highlight the plasticity of Pseudomonas metabolism in response to Salmonella in two distinct environments and provide evidence that Pseudomonas biocontrol activity is multifactorial and environment dependent.

microbiology↗

bioRxiv2022

Development of a high-throughput starch digestibility assay reveals wide variation among the A. E. Watkins wheat landrace collection

Breeding for less digestible starch in wheat can improve the health impact of bread and other wheat foods. Based on an established in vitro starch digestibility assay by Edwards et al. (2019) we developed a high-throughput assay to measure starch digestibility in hydrothermally processed samples for use in forward genetic approaches. Digestibility of purified starch from maize and wheat was measured using both methods and produced comparable results. Using the high-throughput assay, we estimated starch digestibility of 118 wheat landraces from the core Watkins collection and found wide variation across lines and elite UK varieties, (20% to 40% and 31% to 44% starch digested after 90 minutes respectively). Sieved flour fractions and purified starch for selected lines showed altered starch digestibility profiles compared with wholemeal flour, suggesting that matrix properties of flour rather than intrinsic properties of starch granules conferred the low starch digestibility observed.

biochemistry↗

bioRxiv2022

Impact of storage on starch digestibility and texture of a high-amylose wheat bread

Staling is a complex process that determines the shelf-life of baked products like bread. Breads made using high-amylose flour may elicit a lower glycaemic response, with benefits for health, however the impact of storage on novel high-amylose wheat foods structure are not known. We investigated the staling behaviour of high-amylose bread made from a starch branching enzyme II (sbeII) wheat mutant compared to a wild-type (WT) control, by measuring starch digestibility (susceptibility to amylolysis) and bread texture over time in different storage conditions. Breads prepared from sbeII and WT control wheat flours were subjected to fresh, refrigerated and frozen storage, and starch digestibility and crumb texture were measured up to three days. Starch from sbeII flour was characterised by a larger proportion of long chains resulting in increased amylose content, typical of sbeII mutant wheat. Starch in sbeII bread was less susceptible to amylolysis when freshly baked (~17% difference of starch digested at 90 min, C90) and after storage (26%-28% C90 difference, depending on the storage condition), compared to the WT control. Texture of freshly baked sbeII bread was similar to the WT control; storage conditions affected the progression of crumb firming and resilience to touch for both breads, but changes in crumb texture were less pronounced in sbeII bread. Overall, sbeII bread was less prone to staling than conventional WT bread during the first three days of storage, particularly when stored in the fridge or at room temperature.

biochemistry↗

bioRxiv2020

Multiple Holins Contribute to Extracellular DNA Release in Pseudomonas aeruginosa Biofilms

Bacterial biofilms are comprised of aggregates of cells encased within a matrix of extracellular polymeric substances (EPS). One key EPS component is extracellular DNA (eDNA), which acts as a glue, facilitating cell-cell and cell-substratum interactions. We have previously demonstrated that eDNA is produced in Pseudomonas aeruginosa biofilms via explosive cell lysis. This phenomenon involves a subset of the bacterial population explosively lysing, due to peptidoglycan degradation by the endolysin Lys. Here we demonstrate that in P. aeruginosa three holins, AlpB, CidA and Hol, are involved in Lys-mediated eDNA release within both submerged (hydrated) and interstitial (actively expanding) biofilms, albeit to different extents, depending upon the type of biofilm and the stage of biofilm development. We also demonstrate that eDNA release events determine the sites at which cells begin to cluster to initiate microcolony formation during the early stages of submerged biofilm development. Furthermore, our results show that sustained release of eDNA is required for cell cluster consolidation and subsequent microcolony development in submerged biofilms. Overall, this study adds to our understanding of how eDNA release is controlled temporally and spatially within P. aeruginosa biofilms.

microbiology↗

bioRxiv2019

Antibiotics select for novel pathways of resistance in biofilms

Most bacteria in nature exist in aggregated communities known as biofilms. Bacteria within biofilms are inherently highly resistant to antibiotics. Current understanding of the evolution and mechanisms of antibiotic resistance is largely derived from work from cells in liquid culture and it is unclear whether biofilms adapt and evolve in response to sub-inhibitory concentrations of drugs. Here we used a biofilm evolution model to show that biofilms of a model food borne pathogen, Salmonella Typhimurium rapidly evolve in response to exposure to three clinically important antibiotics. Whilst the model strongly selected for improved biofilm formation in the absence of any drug, once antibiotics were introduced the need to adapt to the drug was more important than the selection for improved biofilm formation. Adaptation to antibiotic stress imposed a marked cost in biofilm formation, particularly evident for populations exposed to cefotaxime and azithromycin. We identified distinct resistance phenotypes in biofilms compared to corresponding planktonic control cultures and characterised new mechanisms of resistance to cefotaxime and azithromycin. Novel substitutions within the multidrug efflux transporter, AcrB were identified and validated as impacting drug export as well as changes in regulators of this efflux system. There were clear fitness costs identified and associated with different evolutionary trajectories. Our results demonstrate that biofilms adapt rapidly to low concentrations of antibiotics and the mechanisms of adaptation are novel. This work will be a starting point for studies to further examine biofilm specific pathways of adaptation which inform future antibiotic use.

microbiology↗