Date of Graduation

12-2012

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Poultry Science (PhD)

Degree Level

Graduate

Department

Poultry Science

Advisor/Mentor

Slavik, Michael F.

Committee Member

Marcy, John A.

Second Committee Member

Rath, Narayan C.

Third Committee Member

Hettiarachchy, Navam S.

Keywords

Biological sciences; Adhesion; Antibiotic sensitivity; Campylobacter jejuni; Invasion; Stress-adaptation

Abstract

The foodborne pathogen Campylobacter jejuni is one of the leading causes of human gastroenteritis. This bacterium is not a robust organism compared with many other foodborne pathogens and requires special conditions in the laboratory for its growth. In nature, however, this organism is able to survive in very diverse and hostile environments and produce disease in humans. The different mechanisms by which C. jejuni survives stressful conditions in the environment remain unclear. Adhesion and invasion are thought to be important factors for the colonization of C. jejuni in the intestinal tracts of hosts. Previous research in our laboratory showed that C. jejuni has the ability to induce an adaptive tolerance response to stresses like acid and aerobic conditions. The objectives of this research were to determine the influence of acid-adaptation on the virulence and antibiotic profiles of Campylobacter jejuni. In experiment 1, the effect of acid-adaptation on virulence was studied by determining the adhesion and invasion of human intestinal cells by different strains of Campylobacter jejuni. Different human and poultry isolates of C. jejuni were exposed to an acid stress (pH 5.5) and further subjected to different secondary stresses such as an acid pH of 4.5, starvation, and salt (3%). After exposure to the secondary stress, the adhesion and invasion abilities of the isolates were evaluated in vitro using an INT 407 cell line. Acid-adapted C. jejunishowed an increase in adhesion and invasion when exposed to the secondary stresses of acid, starvation and salt. The degree of adhesion and invasion varied with strains of C. jejuni, the time of adaptation to acid, as well as exposure time to the second stress. These data indicate that some stresses may increase the virulence of C. jejuni. In experiment 2, the effect of acid adaptation on the antibiotic sensitivity of different strains of C. jejuni were studied. The antibiotic profiles of C. jejuni after stress-adaptation were compared with antibiotic profiles of non-stressed C. jejuni using the Kirby Bauer agar disc diffusion assay. The antibiotic profiles of C. jejuni were found to change when the acid-adapted bacteria were subjected to further stresses such as a lethal acidic pH of 4.5, aerobic atmosphere and starvation. In the majority of the cases antibiotic-resistant C. jejuni strains were found to become sensitive to antibiotics after stress-adaptation, but in a few cases C. jejuni showed increased resistance. These results indicate that increasing various stresses in C. jejuni may, in some cases, reduce antibiotic resistance.

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