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- All Subjects: Staphylococcus aureus
Description
The viscous lung mucus of cystic fibrosis (CF) patients is characterized by oxygen gradients, which creates a unique niche for bacterial growth. Pseudomonas aeruginosa and Staphylococcus aureus, two predominant microorganisms chronically infecting the airways of CF patients, typically localize in hypoxic regions of the mucus. While interspecies interactions between P. aeruginosa and S. aureus have been reported, little is known about the role of low oxygen in regulating these interactions. Studying interspecies interactions in CF lung disease is important as evidence suggests that microbial community composition governs disease progression. In this study, P. aeruginosa lab strain PAO1 and two primary clinical isolates from hypoxic tissues were cultured alone, or in combination, with methicillin resistant S. aureus (MRSA) strain N315 under hypoxic or normoxic conditions. Herein, it is shown for the first time that low oxygen conditions relevant to the CF lung affect the competitive behavior between P. aeruginosa and S. aureus. Specifically, S. aureus was able to better survive competition in hypoxic versus normoxic conditions. Competition data from different oxygen concentrations were consistent using PAO1 and clinical isolates even though differences in the level of competition were observed. PAO1 strains carrying mutations in virulence factors known to contribute to S. aureus competition (pyocyanin/phzS, elastase/lasA and lasI quorum sensing/lasI) were used to determine which genes play a role in the differential growth inhibition. The lasA and lasI mutants competed less effectively with S. aureus regardless of the oxygen level present in the culture compared to the isogenic wild type strain. These results are consistent with previous findings that elastase and lasI quorum sensing play a role in competitive behavior of P. aeruginosa and S. aureus. Interestingly, the phzS mutant competed less effectively in hypoxic conditions suggesting that pyocyanin may be important in microaerophilic conditions. This study demonstrates that oxygen plays a role in competition between P. aeruginosa and S. aureus and contributes to understanding CF environmental factors that may regulate microbial community dynamics important for disease progression with potential for development of therapeutic avenues.
ContributorsLedesma Barrera, Maria Alexandra (Author) / Nickerson, Cheryl A. (Thesis advisor) / Reyes del Valle, Jorge (Committee member) / Clark-Curtiss, Josephine (Committee member) / Stout, Valerie (Committee member) / Ott, C M (Committee member) / Arizona State University (Publisher)
Created2014
Description
First-semester student retention is a constant priority for undergraduate institutions. The transition to the collegiate level, and to a new scholastic program and format, is frequently challenging academically and socially—for this reason, many first-semester course schedules for incoming freshman undergraduates feature an introductory seminar to ease transition to an undergraduate lifestyle. Arizona State University features a required “Careers in the Life Sciences” course for its first-semester School of Life Sciences students, which has had tractable results in first semester student retention and academic success. Here, we evaluate a component of the seminar, the peer-mentorship program, for its efficacy in students’ first semester experience. Analysis of self-reports from 168 first-semester “mentees” and their 25 mentors indicates frequency of mentee-mentor contact was the best indicator of a higher first semester GPA, comfort with academic resources and study habits, and desire to engage in extracurricular activities and internships. These data indicate that access to a mentor who actively engages and verbally connects with their mentees is a valuable component of first-semester student academic integration and retention.
ContributorsMathews, Ian T. (Author) / Capco, David (Thesis director) / Clark-Curtiss, Josephine (Committee member) / Harrell, Carita (Committee member) / Barrett, The Honors College (Contributor) / School of Life Sciences (Contributor)
Created2014-05