In 2015, the United States Department of Agriculture (USDA) reported that 1 in 6 Americans fall ill with a foodborne infection annually, resulting in more than 3000 fatalities and an estimated $15 billion in economic burden due to combined medical costs, productivity loss, and death. On a per-case basis, infections caused by the marine bacterium Vibrio vulnificus are the most burdensome foodborne illness at $3.3 million/case. V. vulnificus-associated fatality rates are reported to exceed 50 percent. Yet, the bacterium’s major virulence factor and its relationship to foodborne infection remain poorly understood. As infection incidence climbs in conjunction with rising sea surface temperature, studies elucidating pathogenic mechanisms of V. vulnificus are increasingly critical. This study investigates the pathogenic mechanisms of V. vulnificus as mediated by its primary virulence factor, the Multifunctional Autoprocessing Repeats-in-Toxins (MARTX) toxin. The MARTX toxin, product of the rtxA1 gene, has been identified as the dominant secreted virulence factor in the intragastric mouse model of V. vulnificus infection. MARTX toxins are classified as repeats-in-toxins (RTX) family members by virtue of characteristic amino acid repeats at the protein C-terminus. MARTX toxins are further defined as a unique sub-family of RTX proteins possessing: 1) tandem amino acid repeats at the N-terminus; 2) a cysteine protease domain (CPD) for autoprocessing; and 3) a section of effector domains situated between N-terminal repeats and CPD. Functional roles for each toxin region have been previously postulated but only recently experimentally investigated. This study employs a combination of bacterial genetic manipulation, in vitro assays, and in vivo intragastric mouse infection. We demonstrate that the same native MARTX toxin effector domain repertoire that is dispensable for toxin secretion, toxin delivery to host cells, and cell lysis in vitro is essential for induction of rapid intestinal epithelial barrier dysfunction, bacterial dissemination from the mouse intestine, and anti-phagocytosis activity against macrophages. Moreover, the MARTX toxin effector domain repertoire is essential for bacterial virulence potential. We also investigate roles for individual effector domains within the larger repertoire. Each of the five investigated MARTX effector domains exhibit functional redundancy in the ability to disrupt phagocytic activity and intestinal barrier integrity. However, individual domains confer different virulence potential. This is demonstrated by altered survival outcomes of mice infected with strains harboring deletions in discrete effector domains. Together our results support a model in which the MARTX toxin repeat regions and CPD together function as a delivery platform for diverse effector cargo that define toxin potency and directly impact V. vulnificus virulence potential in mammalian hosts.

Last modified

• 11/19/2019

Creator

• Hannah Gavin

DOI

• https://doi.org/10.21985/n2-zjsx-ne83

Subject

• Driskill Graduate Training Program in Life Sciences

Keyword

• bacteria
• pathogenesis
• vulnificus
• toxin
• Vibrio
• virulence

Date created

• 2018-01-01

Resource type

• Dissertation

Rights statement

• In Copyright