Eleven-day-old chicken embryos were used to compare the relative virulence of minimally passaged human isolates of Campylobacter jejuni and Campylobacter coli. Graded doses of bacteria were inoculated onto the chorioallantoic membrane, and 50% lethal doses were calculated at 72 h postinfection. Strains varied markedly in their ability to invade the chorioallantoic membrane and kill the embryos. The 50% lethal doses varied by about 6 logs for 25 strains of C. jejuni, and by 2 logs for 5 strains of C. coli. Although both outbred and inbred embryos were employed in the study, the latter were found to be more susceptible to infection with most strains. All isolates were screened for plasmid DNA, but there was no apparent relationship between plasmid content and virulence of strains for the embryos. Neither could virulence be associated with the production of siderophores by the strains. The ability of selected strains of C. jejuni to invade the liver of embryos was also studied. The number of campylobacters culturable from the liver was found to be inversely related to the 50% lethal dose of the strain. By inoculating 11-day-old embryos intravenously, it was possible to demonstrate that a strain of C. jejuni which was poorly virulent after chorioallantoic inoculation was relatively noninvasive. Invasiveness alone, however, could not fully account for the lethality of two highly virulent strains of C. jejuni administered by the intravenous route. Finally, there was no correlation between motility and virulence in this model system.
Neonatal mice (2.3 to 2.8 g) were inoculated intragastrically with different human isolates of Campylobacter fetus subsp. jejuni. At weekly intervals thereafter, mice were sacrificed and dilution plate counts were performed on segments of the gastrointestinal tract. Mice were uniformly colonized by some strains for 2 weeks, whereas other strains were being cleared at that time. One strain (BO216) persisted in some mice for 3 weeks. The greatest number of organisms (107) was
SUMMARY. Adult female mice were given drinking water containing tobramycin 0.05 mg/ml for a week. After a further day without antibiotic they were inoculated intragastrically with one of three strains of Campylo hac t er . jejun i. Co 1 on i sat i o n of the gas t r o i n tes t i nal tract was judged by culturing faecal pellets. Tobramycin-treated mice differed from untreated animals in that many more of them discharged infected pellets, and their pellets contained 5-> 300 times more campylobacters. Colonisation could be prevented by inoculating the tobramycin-treated animals intragastrically, 24 h before the administration of C. jejuni, with a bacterial suspension prepared from normal faecal pellets. Coliforms, lactobacilli, the two in combination, and anaerobes grown from faecal pellets were not effective in preventing colonisation. Most of the C. jejuni were found in the large intestine of the tobramycin-fed mice. The persistence of colonisation of six dams nursing C. jejuni-infected offspring ranged from 10 to at least 29 weeks.
Summary. The virulence of Campylobacter jejuni for 1 1 -day-old chick embryos is associated with the ability to invade the chorio-allantoic membrane, to resist phagocytosis and to survive and proliferate in vim. The pathogenicity of a well characterised avirulent C. jejuni strain was enhanced by passaging it intravenously and chorio-allantoically through chick embryos. The resulting isogenic variants had greatly increased ability to survive in vim. In this study, the morphological and cell-surface characteristics of the avirulent parental strain were compared with those of the more virulent variants to determine whether pathogenicity was associated with one or more cell-surface constituents. Changes associated with the increased virulence of the two variants included alterations in cultural and cellular morphology, loss of flagella, expression of a new outer-membrane protein, alterations in cell-surface carbohydrates and decreases in cell-surface hydrophobicity.
The 11-day-old chicken embryo has been shown to be a useful animal model for comparing the virulence of human isolates of Campylobacter jejuni. Virulence in this system is associated with the ability to invade the chorioallantoic membrane and to survive and proliferate in vivo. In this study, the survival and multiplication of C. jejuni in the embryonic host was investigated. It was possible to enhance the virulence of a relatively avirulent C. jejuni strain by passaging it intravenously through the embryos. The resulting isogenic variants demonstrated enhanced abilities to survive in vivo but were still unable to invade when inoculated onto the chorioallantoic membrane. The bloodstream clearance of C. jejuni was studied, and virulent, but not avirulent, strains persisted and multiplied both in the bloodstream and in embryonic liver. Virulent strains also were cleared significantly more slowly from the bloodstream of adult BALB/c mice after intravenous challenge than were avirulent strains. C. jejuni strains which were cleared slowly in vivo were also ingested slowly in vitro by mouse peritoneal macrophages. Clearance studies in mice pretreated with cobra venom factor demonstrated that opsonization by serum complement was not a prerequisite for clearance of campylobacters from the murine bloodstream.
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