Role of capsular modified heptose in the virulence of Campylobacter jejuni

Abstract

SummaryThe Campylobacter jejuni capsular polysaccharide is important for virulence and often contains a modified heptose. In strain ATCC 700819 (a.k.a. NCTC 11168), the modified heptose branches off from the capsular backbone and is directly exposed to the environment. We reported previously that the enzymes encoded by wcaG, mlghB and mlghC are involved in heptose modification. Here, we show that inactivation of any of these genes leads to production of capsule lacking modified heptose and alters the transcription of other capsule modification genes differentially. Inactivation of mlghB or mlghC, but not of wcaG, decreased susceptibility to bile salts and abrogated invasion of intestinal cells. All mutants showed increased sensitivity to serum killing, especially wcaG::cat, and had defects in colonization and persistence in chicken intestine, but did not show significant differences in adhesion, phagocytosis and intracellular survival in murine macrophages. Together, our findings suggest that the capsular heptose modification pathway contributes to bacterial resistance against gastrointestinal host defenses and supports bacterial persistence via its role in serum resistance and invasion of intestinal cells. Our data further suggest a dynamic regulation of expression of this pathway in the gastrointestinal tract.

Key Role of Capsular Polysaccharide in the Induction of Systemic Infection and Abortion by Hypervirulent Campylobacter jejuni

“…4B). This notion is supported by findings from previous studies in which the capsule of C. jejuni was shown to play an important role in adhesion to/invasion of intestinal epithelial cells in vitro, colonization of chickens and mice, and induction of diarrhea in ferrets (29,31,(40)(41)(42). The lack of capsule in C. jejuni was also associated with increased cytokine production by murine dendritic cells in vitro (43) and by lamina propria CD4 T cells from mouse intestine (31), which play an important role in the innate immune response to enteric bacterial pathogens (44,45), suggesting the involvement of capsule in protection against the induction of immune responses in the gut.…”

“…However, bacterial factors involved in the pathogenesis of extraintestinal infections due to C. jejuni are understudied. Even though the capsule of C. jejuni was presumed to play a crucial role in systemic disease due to its involvement in resistance to serum killing and phagocytosis as determined by in vitro studies (22,32,40), direct in vivo evidence for its contribution to the induction of bacteremia and systemic infection had not been demonstrated prior to this study. Here, we provide compelling evidence demonstrating that capsule is a key virulence determinant in a highly pathogenic C. jejuni clone (clone SA) using two different animal models, i.e., mouse bacteremia and guinea pig abortion.…”

Phase-Variable Changes in the Position of O -Methyl Phosphoramidate Modifications on the Polysaccharide Capsule of Campylobacter jejuni Modulate Serum Resistance

“…Capsules are a major factor in resistance to complement-mediated killing and, in the case of C. jejuni 81-176 (HS23/36), decoration of the CPS with MeOPN is essential for complement resistance. Thus, mutants of 81-176 expressing a CPS lacking MeOPN were as sensitive to complement-mediated killing as a mutant lacking CPS (23,24,28). CPS of two serotypes, HS2 and HS23/36, have also been shown to have immunomodulatory effects in vitro (23,27), and the immunomodulatory effects for the 81-176 CPS have been confirmed in vivo in a mouse model (29).…”

“…The CJJ1420::aph3 mutant was complemented with a repaired allele as follows. The wild-type CJJ1420 gene was PCR amplified using primers pg12.29 and pg12.30, which introduced BamHI and EcoR1 sites, respectively, and the resulting amplicon was cloned into BamHI and EcoRI digested pCPE108, which contains the 28 promoter from flaA cloned between the XbaI and BamHI sites of pBluescript (44). The phase-variable G9 tract within CJJ1420 was repaired by QuikChange (Life Technologies) mutagenesis such that the G9 was changed to GGAGGAGGA using the primers pg12.37 and pg12.38.…”

“…jejuni CPS have been shown to be important for pathogenesis. Nonencapsulated mutants were attenuated in a ferret model of diarrheal disease and were reduced in their ability to colonize chickens, mice, and piglets (21)(22)(23)(24)(25), although there are conflicting reports on the role of MeOPN in pathogenesis of a Galleria mellonella model of disease (26,27) and in the invasion of intestinal epithelial cells in vitro (24,28). Capsules are a major factor in resistance to complement-mediated killing and, in the case of C. jejuni 81-176 (HS23/36), decoration of the CPS with MeOPN is essential for complement resistance.…”