Biology subjects

Ramsey, M. M.

Publications and source records attributed to Ramsey, M. M..

4 recordsLinked to original sources

bioRxiv2026

Whats SUPP, developing an in vitro model for healthy oral biofilms

Summary/Abstract (this is copy paste of abstract)Human supragingival plaque (SUPP) is a polymicrobial biofilm whose contents undergo dysbiotic transitions during multiple oral diseases. The study of healthy SUPP may lead to future pro or prebiotic therapies, to help prevent or revert dysbiosis during disease. However, many oral plaque models focus on the cultivation of oral pathogens and do not well cultivate commensal SUPP populations. Here, we use a 16S microbiome guided iterative approach to develop a low-cost high sample number SUPP model. Our model demonstrates several findings including a surprisingly minimal impact on salivary preparation methods on model microbiota and the ability to test microbial interactions with added oral strains to assess their fitness. This model provides a reductionist system for the study of healthy oral commensals in a complex polymicrobial framework in the absence of host immune responses.

microbiology↗

bioRxiv2024

Essential genes for Haemophilus parainfluenzae survival and biofilm growth

Haemophilus parainfluenzae (Hp) is a Gram-negative, pleomorphic rod, highly prevalent and abundant as a commensal in the human oral cavity, and an infrequent extraoral opportunistic pathogen. Hp occupies multiple niches in the oral cavity, including the tongue dorsum, keratinized gingiva, and the supragingival plaque biofilm. As a member of the HACEK group, Hp is also known to cause infective endocarditis. Additionally, case reports have identified Hp as the causative agent of meningitis, septic arthritis, chronic osteomyelitis, septicemia, and a variety of other infectious diseases. Little is known about how Hp interacts with its neighbors in the healthy biofilm nor about its mechanisms of pathogenesis as an extraoral opportunistic pathogen. To address these unknowns, we identified the essential genomes of two Hp strains and the conditionally essential genes for their growth in in vitro biofilms aerobically and anaerobically. Using transposon insertion sequencing (TnSeq) with a highly saturated mariner transposon library in two strains, the ATCC33392 type-strain (Hp 392) and a commensal oral isolate EL1 (Hp EL1), we show that the essential genome of Hp 392 and Hp EL1 is composed of 395 and 384 genes, respectively. The core essential genome, consisting of 341 essential genes conserved between both strains, was composed of genes associated with genetic information processing, carbohydrate, protein, and energy metabolism. We also identified conditionally essential genes for aerobic and anaerobic biofilm growth, which were associated with carbohydrate and energy metabolism in both strains of Hp. Additionally, RNAseq analysis determined that most genes upregulated during anaerobic growth are not essential for Hp 392 anaerobic biofilm survival. The completion of this library and analysis under these conditions gives us a foundational insight into the basic biology of H. parainfluenzae in differing oxygen conditions, similar to its in vivo oral habitat. Further, the creation of this library presents a valuable tool for further investigation into conditionally essential genes for an organism that lives in close contact with many microbial species in the human oral habitat.

microbiology↗

bioRxiv2022

Corynebacterium matruchotii fitness enhancement of adjacent streptococci by multiple mechanisms

Polymicrobial biofilms are present in many environments particularly in the human oral cavity where they can prevent or facilitate the onset of disease. While recent advances have provided a clear picture of both the constituents and their biogeographical arrangement, it is still unclear what mechanisms of interaction occur between individual species in close proximity within these communities. In this study we investigated two mechanisms of interaction between the highly abundant supragingival plaque (SUPP) commensal Corynebacterium matruchotii and Streptococcus mitis which are directly adjacent in vivo. We discovered that C. matruchotii enhanced the fitness of streptococci dependent on its ability to detoxify streptococcal-produced hydrogen peroxide and its ability to oxidize lactate also produced by streptococci. We demonstrate that the fitness of adjacent streptococci was linked to that of C. matruchotii and that these mechanisms support the previously described "corncob" arrangement between these species but that this is favorable only in aerobic conditions. Further we utilized scanning electrochemical microscopy (SECM) to quantify lactate production and consumption between individual bacterial cells for the 1st time, revealing that lactate oxidation provides a fitness benefit to S. mitis and not pH mitigation. This study describes mechanistic interactions between two highly abundant human commensals that can explain their observed in vivo spatial arrangements and suggest a way by which they may help preserve a healthy oral bacterial community.

microbiology↗

bioRxiv2020

Mechanisms underlying proximity between oral commensal bacteria

Complex polymicrobial biofilm communities are abundant in nature particularly in the human oral cavity where their composition and fitness can affect health. While the study of these communities during disease is essential and prevalent, little is known about interactions within the healthy plaque community. Here we describe interactions between two of the most abundant species in this healthy microbiome, Haemophilus parainfluenzae and Streptococcus mitis. We discovered that H. parainfluenzae typically exists adjacent to Mitis group streptococci in vivo with which it also positively correlated based on microbiome data. By comparing in vitro coculture data to ex vivo microscopy we revealed that this co-occurrence is density dependent and further influenced by H2O2 production. We discovered that H. parainfluenzae has a more redundant, multifactorial response to H2O2 than related organisms and that the integrity of this system enhances streptococcal fitness. We also show that Mitis group streptococci can act as an in vivo source of NAD for H. parainfluenzae and that streptococci in vitro evoke patterns of carbon utilization from H. parainfluenzae that are similar to those observed in vivo. Our findings describe mechanistic interactions between two of the most abundant and prevalent members of healthy supragingival plaque that contribute to their survival in vivo.

microbiology↗