Undergraduate Honors Theses

An Analysis of Outer Inflammatory Protein A in cag Pathogenicity Island Negative and Positive Strains of Helicobacter pylori

Danielle N. Horridge, College of William and MaryFollow

Date Thesis Awarded

4-2017

Access Type

Honors Thesis -- Access Restricted On-Campus Only

Degree Name

Bachelors of Science (BS)

Department

Biology

Advisor

Mark H. Forsyth

Committee Members

Lisa Landino

Oliver Kerscher

Kurt Williamson

Abstract

Outer inflammatory protein A (OipA) is an outer membrane protein virulence factor of the bacterial gastric pathogen, Helicobacter pylori. oipA gene expression is regulated by phase variation at a CT dinucleotide repeat located within the 5’ end of the gene, such that the gene is alternatively in-frame (phase on) or out-of-frame (phase off). OipA has been shown to play a role in inflammation and as an adhesin that assists in the attachment of H. pylori to host cells. H. pylori isolates lacking the cag Pathogenicity Island (cagPAI negative), the primary virulence determinant of H. pylori, induce less host inflammation and almost uniformly possess an oipA allele that is phase off. Meanwhile, cagPAI positive H. pylori isolates almost always possess phase on oipA alleles. The cagPAI encodes a type IV secretion system (T4SS) that elicits the secretion of the pro-inflammatory cytokine, Interleukin 8 (IL-8), by infected gastric epithelial cells. The present study investigates the role of OipA in cagPAI positive and negative H. pylori infection of human gastric adenocarcinoma (AGS) cells. Experimentally turning oipA phase off in a cagPAI positive strain of H. pylori resulted in a decrease in oipA transcript levels compared to the wild type. The novel phase on oipA mutant of a cagPAI negative strain resulted in an increase in oipA transcription, and western blots revealed expression at the whole cell level. AGS attachment assays revealed that H. pylori adherence was significantly increased in both the cagPAI positive and negative strain when oipA was phase on compared to isogenic oipA phase off strains. Quantification of IL-8 by enzyme-linked immunosorbent assay showed that this variation in H. pylori attachment was only linked to changes in IL-8 production by AGS cells when infected by the cagPAI positive strain, not cagPAI negative. Based on the current study, we hypothesize that the highly conserved, albeit apparently non-expressed, oipA in cagPAI negative strains can affect the adherence character of these isolates of reduced virulence when altered to a phase on status; however OipA’s role in inflammation may be dependent upon the presence of the cagPAI.

Recommended Citation

Horridge, Danielle N., "An Analysis of Outer Inflammatory Protein A in cag Pathogenicity Island Negative and Positive Strains of Helicobacter pylori" (2017). Undergraduate Honors Theses. William & Mary. Paper 1126.
https://scholarworks.wm.edu/honorstheses/1126