No abstract

Campylobacter jejuni is a zoonotic pathogen, and a hypervirulent clone, named clone SA, has recently emerged as the predominant cause of ovine abortion in the United States. To induce abortion, orally ingested Campylobacter must translocate across the intestinal epithelium, spread systemically in the circulation, and reach the fetoplacental tissue. Bacterial factors involved in these steps are not well understood. C. jejuni is known to produce capsular polysaccharide (CPS), but the specific role that CPS plays in systemic infection and particularly abortion in animals remains to be determined. In this study, we evaluated the role of CPS in bacteremia using a mouse model and in abortion using a pregnant guinea pig model following oral challenge. Compared with C. jejuni NCTC 11168 and 81-176, a clone SA isolate (IA3902) resulted in significantly higher bacterial counts and a significantly longer duration of bacteremia in mice. The loss of capsule production via gene-specific mutagenesis in IA3902 led to the complete abolishment of bacteremia in mice and abortion in pregnant guinea pigs, while complementation of capsule expression almost fully restored these phenotypes. The capsule mutant strain was also impaired for survival in guinea pig sera and sheep blood. Sequence-based analyses revealed that clone SA possesses a unique CPS locus with a mosaic structure, which has been stably maintained in all clone SA isolates derived from various hosts and times. These findings establish CPS as a key virulence factor for the induction of systemic infection and abortion in pregnant animals and provide a viable candidate for the development of vaccines against hypervirulent C. jejuni. KEYWORDS Campylobacter, capsule, systemic infection, abortion, sheep, bacteremiaA s a zoonotic pathogen, Campylobacter is a leading cause of bacterial foodborne gastroenteritis in humans (1). In addition, Campylobacter species have been recognized as one of the most common causes of ovine abortion in the United States and worldwide, with an overall abortion rate of 5 to 50% in affected flocks (2). As a consequence, Campylobacter poses a significant economic burden on sheep producers and greatly impacts sheep health and welfare. A national study, NAHMS Sheep 2001, conducted by the USDA/APHIS/Veterinary Services in collaboration with the American Sheep Industry Association revealed that Campylobacter species ranked first among all infectious causes of abortion within the last 3 years of the study, with 53.7% of the reported cases being confirmed by a veterinarian or diagnostic laboratory (3).Historically, Campylobacter fetus subsp. fetus accounted for the majority of the Campylobacter spp. associated with ovine abortion; however, we recently discovered a remarkable shift in the etiology of the disease (4, 5). Specifically, a highly virulent

Campylobacter jejuni clone SA has emerged as the predominant cause of Campylobacter-associated ovine abortion in the U.S., and this clone is highly pathogenic in pregnant sheep and guinea pigs. To induce abortion, orally ingested Campylobacter must be able to translocate across the intestinal epithelium and spread systemically. To understand the pathogenic mechanisms and immune protection of C. jejuni-induced abortion, it is necessary to develop a cost-effective animal model to evaluate systemic infection induced by this pathogenic clone. In this study, two different breeds of female mice (BALB/c and CD-1) were orally inoculated with C. jejuni IA3902, a clinical clone SA isolate whose complete genome sequence has been determined, to evaluate the induction of bacteremia and hepatic infection. Our results revealed that CD-1 mice were more susceptible than BALB/c mice to infection by IA3902. In CD-1 mice, C. jejuni IA3902 induced bacteremia and hepatic infection within 1 hour after oral inoculation, and bacteremia peaked at 8 and/or 12 hours after inoculation. Compared with IA3902, the magnitude and duration of bacteremia and hepatic infection induced by C. jejuni strains NCTC 11168 and 81-176 were significantly less prominent, indicating that IA3902 is more virulent than the other strains tested with regard to systemic spread. Mutagenesis in IA3902 showed that the loss of the capsule (ΔkpsS) completely prevented the organism from causing bacteremia and hepatic infection, while the loss of pVir plasmid did not affect systemic spread. These findings indicate that the CD-1 mouse model is suitable for examining critical steps of Campylobacter pathogenesis and identify the capsule as a key virulence factor of this pathogenic organism to induce bacteremia.