In vitro demonstration of the invasive ability of Campylobacters

Adherence to and invasion of HeLa cells by Campylobacter spp. strains isolated from animals

ABSTRACT: The objective of this study was to evaluate the adherence to and invasion of HeLa cells by Campylobacter spp. strains (total n=63) isolated from chickens (n=4), dogs (n=4), non-human primates (n=16), pigs (n=9), calf feces (n=18), and bovine genital tracts (n=12). Thirty-two strains adhered to and 13 invaded HeLa cells. Invasive strains included 1 of 4 dog isolates, 4 of 16 non-human primate isolates (2 C. jejuni and 2 C. coli), 1 of 9 C. coli strains isolated from pigs, and 7 of 18 C. fetus subsp. fetus isolated from calf feces. Only 25% of chicken and dog isolates and 23% of pig isolates were able to adhere to HeLa cells, a property of 65% of strains obtained from calf feces and 83% of bovine genital tract-isolated strains. The adherent phenotype was observed in 5 of 19, 6 of 15, and 21 of 29 strains of C. jejuni, C. coli, and C. fetus subsp. fetus, respectively, whereas 3 of 19, 3 of 15, and 7 of 29 strains were additionally able to invade HeLa cells, respectively. C. jejuni, C. coli, and C. fetus subsp. fetus strains isolated from animal feces are able to adhere and invade HeLa cells, whereas C. fetus subsp. fetus strains isolated from the bovine genital tract were not invasive in HeLa cells. The present study showed that C. jejuni isolated from primates and dogs, C. coli isolated from non-human primates and pigs, and C. fetus subsp. fetus isolated from calf feces have the ability to adhere to and to invade HeLa cells. Moreover, the lack of invasive ability by C. fetus subsp. fetus strains isolated from the bovine genital tract could be important in the pathogenesis of the genital tract diseases caused by this bacterium.

Identification of hyperinvasive Campylobacter jejuni strains isolated from poultry and human clinical sources

Campylobacter jejuni causes gastroenteritis with a variety of symptoms in humans. In the absence of a suitable animal model, in vitro models have been used to study virulence traits such as invasion and toxin production. In this study, 113 C. jejuni isolates from poultry and poultry-related (n=74) environments as well as isolates from human cases (n=39) of campylobacteriosis and bacteraemia were tested for invasiveness using INT 407 cells. The method was sufficiently reproducible to observe a spectrum of invasiveness amongst strains. As a result, strains were classified as low, high and hyper-invasive. The majority of strains (poultry and human) were low invaders (82 % and 88 %, respectively). High invasion was found for 5 % of human strains and 11 % of poultry-related isolates. However, only 1 % of poultry strains were classified as hyperinvasive compared to 13 % of human isolates (P=0.0182). Of those isolates derived from the blood of bacteraemic patients, 20 % were hyperinvasive, though this correlation was not statistically significant. An attempt was made to correlate invasiveness with the presence of seven genes previously reported to be associated with virulence. Most of these genes did not correlate with invasiveness, but gene cj0486 was weakly over-represented, and a negative correlation was observed for the gene ciaB. This trend was stronger when the two genes were analysed together, thus ciaB(-) cj0486(+) was over-represented in high and hyperinvasive strains, with low invaders more commonly found to lack these genes (P=0.0064).

Lack of response of INT-407 cells to the presence of non-culturable Campylobacter jejuni

Many contradictory articles on the infectivity of non-culturable Campylobacter jejuni can be found. We studied the effect of non-culturable C. jejuni in an in vitro assay. To prevent the potential effect of a few culturable bacteria in the non-culturable suspension, INT-407 cells, which mimic the outer cell layer in the small intestines, were exposed to culturable C. jejuni suspensions with or without non-culturable C. jejuni. The number of bacteria adhering to and/or invading INT-407 cells and the IL-8 secretion were measured. No differences were found between bacterial suspensions with or without non-culturable C. jejuni added. These findings show that non-culturable C. jejuni do not adhere to or invade INT-407 cells and do not induce an immune response. As previous studies showed a correlation between the used in vitro assays and the effect in vivo, our study strongly suggests that culturability is a good indicator of the risk for C. jejuni infection.

Virulence properties of Campylobacter jejuni isolates of poultry and human origin

Campylobacter jejuni is one of the leading causes of food-borne gastroenteritis. Because of the high prevalence of C. jejuni in poultry, poultry meat is considered a major source of C. jejuni infections for humans. However, it is not known whether all poultry-associated C. jejuni strains are capable of causing disease in humans. Four different virulence properties of C. jejuni strains were compared between 20 poultry isolates and 24 human isolates. Strains were chosen based on their PFGE pattern to represent a heterogeneous population. The isolates were compared for their ability to invade and induce interleukin-8 (IL-8) production in T84 cells, their production of functional cytolethal distending toxin (CDT) using HEp-2 cells, and their sodium deoxycholate resistance. All four virulence factors were present among strains of human and poultry origin, with strong differences observed among strains. For invasion and IL-8 induction, no difference was observed between the two populations. However, on average, human isolates arrested more HEp-2 cells in their cell cycle than did the poultry isolates (P=0.041), suggesting higher CDT production by the former. The ability to survive 16 000 mug sodium deoxycholate ml(-1) was significantly more pronounced (P=0.006) among human isolates than poultry isolates, although all strains possessed the cmeABC operon. These data suggest that all four virulence properties are widespread among C. jejuni isolates, but that a higher degree of bile-salt resistance and more pronounced CDT production are associated with strains causing enteritis in humans.

Campylobacter jejuni adhere to and invade chicken intestinal epithelial cells in vitro

Campylobacter jejuni is a common cause of serious diarrhoeal disease in humans, in contrast to the avian population, where exposure results in prolonged colonization at high density without disease. Colonized poultry present a significant source of infection to humans worldwide. The aim of this work was to compare the interaction of Campylobacter with primary intestinal cells from humans and poultry to identify factors that account for the divergent outcome following Campylobacter exposure. A primary intestinal cell model of Campylobacter infection was developed using cells grown from human and chicken intestinal biopsies. The cultured cells were infected with a number of strains of Campylobacter. Invasion by C. jejuni and the influence of intestinal mucus on Campylobacter internalization were studied by fluorescence microscopy and gentamicin protection assays. C. jejuni invaded primary human intestinal cells in a microtubule-, microfilament- and caveolin-dependent manner. Entry of C. jejuni into primary chicken intestinal cells also occurred. Chicken mucus, but not intestinal mucus of human origin, significantly reduced infection of primary human intestinal cells. Avian mucus appears to inhibit Campylobacter from interacting with epithelial cell surfaces.

Invasion of human epithelial cells by Campylobacter upsaliensis

Few data exist on the interaction of Campylobacter upsaliensis with host cells, and the potential for this emerging enteropathogen to invade epithelial cells has not been explored. We have characterized the ability of C. upsaliensis to invade both cultured epithelial cell lines and primary human small intestinal cells. Epithelial cell lines of intestinal origin appeared to be more susceptible to invasion than non-intestinal-derived cells. Of three bacterial isolates studied, a human clinical isolate, CU1887, entered cells most efficiently. Although there was a trend towards more efficient invasion of Caco-2 cells by C. upsaliensis CU1887 at lower initial inocula, actual numbers of intracellular organisms increased with increasing multiplicity of infection and with prolonged incubation period. Confocal microscopy revealed C. upsaliensis within primary human small intestinal cells. Both Caco-2 and primary cells in non-confluent areas of the infected monolayers were substantially more susceptible to infection than confluent cells. The specific cytoskeletal inhibitors cytochalasin B, cytochalasin D and vinblastine attenuated invasion of Caco-2 cells in a concentration-dependent manner, providing evidence for both microtubule- and microfilament-dependent uptake of C. upsaliensis. Electron microscopy revealed the presence of organisms within Caco-2 cell cytoplasmic vacuoles. C. upsaliensis is capable of invading epithelial cells and appears to interact with host cell cytoskeletal structures in order to gain entry to the intracellular environment. Entry into cultured primary intestinal cells ex vivo provides strong support for the role of host cell invasion during human enteric C. upsaliensis infection.

Comparison of Campylobacter isolates from poultry and humans: association between in vitro virulence properties, biotypes, and pulsed-field gel electrophoresis clusters

The in vitro virulence properties of 197 temporally and geographically related Campylobacter isolates from chicken broilers and humans were compared. Comparisons of the virulence properties associated with genotypes and biotypes were made. All isolates adhered to, and 63% invaded, INT-407 cells, whereas 13% were cytotoxic for CHO cells. CHO cell-cytotoxic extracts were also cytotoxic for INT-407 cells, but the sensitivity for Vero cells was variable. The proportion of isolates demonstrating a high invasiveness potential (>1,000 CFU ml(-1)) or Vero cell cytotoxicity was significantly higher for human than for poultry isolates. Invasiveness was associated with Campylobacter jejuni isolates of biotypes 1 and 2, whereas CHO and INT-407 cell cytotoxicity was associated with C. jejuni isolates of biotypes 3 and 4. Cytotoxic isolates were also clustered according to pulsed-field gel electrophoresis profiles.

Campylobacter fetus adheres to and enters INT 407 cells

Campylobacter fetus is a Gram-negative bacterial pathogen of humans and ungulates and is normally transmitted via ingestion of contaminated food or water with infection resulting in mild to severe enteritis. However, despite clinical evidence that C. fetus infection often involves transient bacteremic states from which systemic infection may develop and the frequent isolation of C. fetus from extra-intestinal sites, this organism displays very poor invasiveness in in vitro models of infection. In this study, immunofluorescence microscopy and gentamicin protection assays were used to investigate the ability of six clinical isolates and one reference strain of C. fetus to adhere to and invade the human intestinal epithelial cell line, INT 407. During an initial 4-h infection period, all C. fetus strains were detected intracellularly using both techniques, though adherence and internalization levels were very low when determined from gentamicin protection assays. Microscopy results indicated that during a 4-h infection period, four of the five clinical strains tested were adherent to 41.3-87.3% of INT 407 cells observed and that 25.2-34.6% of INT 407 cells contained intracellular C. fetus. The C. fetus reference strain displayed the lowest levels of adherence and internalization. A modified infection assay revealed that C. fetus adherence did not necessarily culminate in internalization. Despite the large percentage of INT 407 cells with adherent bacteria, the percentage of INT 407 cells with intracellular bacteria remained unchanged when incubation was extended from 4 h to 20 h. However, microscopy of INT 407 cells 24 h postinfection (p.i.) revealed that infected host cells contained clusters of densely packed C. fetus cells. Gentamicin protection assays revealed that intracellular C. fetus cells were not only viable 24 h p.i. but also that C. fetus had increased in number approximately three- to fourfold between 4 and 24 h p.i., indicative of intracellular replication. Investigation of the role of the host cell cytoskeleton revealed that pretreatment of host cells with cytochalasin D, colchicine, vinblastine, taxol, or dimethyl sulfoxide (DMSO) did not impact upon C. fetus adherence or internalization of INT 407 cells. Microscopy indicated neither rearrangement nor colocalization of either microtubules or microfilaments in INT 407 cells in response to C. fetus adherence or internalization. Together, these data indicate that clinical isolates of C. fetus are capable of adhering, entering, and surviving within the nonphagocytic epithelial cell line, INT 407.

Involvement of a plasmid in virulence of Campylobacter jejuni 81-176

Campylobacter jejuni strain 81-176 contains two, previously undescribed plasmids, each of which is approximately 35 kb in size. Although one of the plasmids, termed pTet, carries a tetO gene, conjugative transfer of tetracycline resistance to another strain of C. jejuni could not be demonstrated. Partial sequence analysis of the second plasmid, pVir, revealed the presence of four open reading frames which encode proteins with significant sequence similarity to Helicobacter pylori proteins, including one encoded by the cag pathogenicity island. All four of these plasmid-encoded proteins show some level of homology to components of type IV secretion systems. Mutation of one of these plasmid genes, comB3, reduced both adherence to and invasion of INT407 cells to approximately one-third that seen with wild-type strain 81-176. Mutation of comB3 also reduced the natural transformation frequency. A mutation in a second plasmid gene, a virB11 homolog, resulted in a 6-fold reduction in adherence and an 11-fold reduction in invasion compared to the wild type. The isogenic virB11 mutant of strain 81-176 also demonstrated significantly reduced virulence in the ferret diarrheal disease model. The virB11 homolog was detected on plasmids in 6 out of 58 fresh clinical isolates of C. jejuni, suggesting that plasmids are involved in the virulence of a subset of C. jejuni pathogens.

Campylobacter-host cell interactions

The enteric pathogens Campylobacter jejuni and Campylobacter coli are a major cause of infectious diarrhoea. Their ability to adhere to human epithelial cells is ubiquitous and their propensity to invade cells is also well documented and requires motility and de novo protein synthesis, as well as several host factors. The molecular basis of the interaction between campylobacters and host cells is only beginning to be elucidate. The characteristics of this interaction promise to be interesting and may provide new insights into host-pathogen interactions in other enteric diseases.