Studies on the interaction between different O-serotypes of Yersinia enterocolitica and HeLa cells

Common themes in microbial pathogenicity

A bacterial pathogen is a highly adapted microorganism which has the capacity to cause disease. The mechanisms used by pathogenic bacteria to cause infection and disease usually include an interactive group of virulence determinants, sometimes coregulated, which are suited for the interaction of a particular microorganism with a specific host. Because pathogens must overcome similar host barriers, common themes in microbial pathogenesis have evolved. However, these mechanisms are diverse between species and not necessarily conserved; instead, convergent evolution has developed several different mechanisms to overcome host barriers. The success of a bacterial pathogen can be measured by the degree with which it replicates after entering the host and reaching its specific niche. Successful microbial infection reflects persistence within a host and avoidance or neutralization of the specific and nonspecific defense mechanisms of the host. The degree of success of a pathogen is dependent upon the status of the host. As pathogens pass through a host, they are exposed to new environments. Highly adapted pathogenic organisms have developed biochemical sensors exquisitely designed to measure and respond to such environmental stimuli and accordingly to regulate a cascade of virulence determinants essential for life within the host. The pathogenic state is the product of dynamic selective pressures on microbial populations.

Penetration of Salmonella through a polarized Madin-Darby canine kidney epithelial cell monolayer

Many intracellular parasites are capable of penetrating host epithelial barriers. To study this process in more detail we examined the interactions between the pathogenic bacteria Salmonella choleraesuis and polarized epithelial monolayers of Madin-Darby canine kidney (MDCK) cells grown on membrane filters. Association of bacteria with the MDCK cell apical surface was an active event, requiring bacterial RNA and protein synthesis, and was blocked by low temperatures. Salmonella were internalized within a membrane-bound vacuole and exhibited penetration through, but not between MDCK cells. A maximum of 14 Salmonella per MDCK cell crossed the monolayer per hour to the basolateral surface yet the monolayer remained viable and impermeable to Escherichia coli. Apical S. choleraesuis infection resulted in an increase in paracellular permeability but the MDCK intercellular contacts were not significantly disrupted. Basolateral S. choleraesuis infection was inefficient, and only small numbers of S. choleraesuis penetrated to the apical medium.

Comparison of the ability of enteroinvasive Escherichia coli, Salmonella typhimurium, Yersinia pseudotuberculosis, and Yersinia enterocolitica to enter and replicate within HEp-2 cells

Salmonella typhimurium, enteroinvasive Escherichia coli, Yersinia pseudotuberculosis, and Yersinia enterocolitica possess the ability to enter intestinal epithelial cells. We used a quantitative tissue culture model employing HEp-2 cells to compare the abilities of these bacteria to enter epithelial cells. S. typhimurium and Yersinia species were highly infective for HEp-2 cells but were unable to replicate extensively intracellularly. Enteroinvasive E. coli exhibited low infectivity but replicated extensively intracellularly. The growth of enteroinvasive E. coli led to destruction of the HEp-2 monolayer, whereas Yersinia spp. and S. typhimurium were maintained intracellularly for prolonged periods without damage to the monolayer. The ability of enteroinvasive E. coli to enter HEp-2 cells required prior growth at 37 degrees C; neither S. typhimurium nor Yersinia spp. exhibited this temperature dependence for cell entry. An E. coli K-12 derivative containing a 230-kilobase plasmid from enteroinvasive E. coli was constructed. This derivative shared all the invasive characteristics of the parental enteroinvasive strain, suggesting that determinants required for cell entry and intracellular multiplication were at least partially plasmid encoded. An HB101 derivative containing a cloned invasion determinant from Y. pseudotuberculosis was constructed in our laboratory. HEp-2 monolayers were coinfected with these two K-12 derivatives to compare invasion determinants from enteroinvasive E. coli with those of Y. pseudotuberculosis in a common genetic background. Results from these experiments suggest that these organisms reside within separate intracellular compartments.

Association with HeLa cells of Campylobacter jejuni and Campylobacter coli isolated from human feces

We developed a rapid in vitro test for determining the association of Campylobacter jejuni and C. coli with HeLa cells. Association was expressed as a weighted mean of the number of bacteria associated with one cell in an association index (AI). The reproducibility of the AI was checked by repeating the test six times, using four strains chosen at random. Means and standard deviations of the means were 7.3 +/- 1.2, 6.8 +/- 0.9, 1.8 +/- 1.2, and 0.1 +/- 0.2. The experimental conditions for which the results are reliable have been standardized. Among 42 strains from human feces, two groups appeared: for 22 nonassociative strains (52%), AI values ranged from 0.0 to 2.1 (mean +/- SD, 0.5 +/- 0.6); for 20 associative strains (48%), AI values ranged from 3.5 to 8.3 (mean +/- SD, 6.2 +/- 1.4). Of these 42 strains, 17 were clinically documented. Diarrhea occurred more frequently in patients infected with associative strains than in those infected with noninvasive strains (7/7 versus 3/10, P = 0.01). Fever also occurred more frequently in patients infected with associative strains (6/7 versus 2/10, P = 0.03). Transmission electron microscopy and viable counts made after killing of extracellular bacteria by gentamicin support the fact that associated Campylobacter spp. are adherent to the cell membrane and are internalized into cytoplasmic vacuoles. The described test seems to be a convenient and rapid method for estimating the pathogenicity of a given strain.

Pathogenicity of Campylobacter jejuni isolates from animals and humans

Fourteen isolates of Campylobacter jejuni of different serotypes and one Campylobacter coli isolate, from various human and animal sources, were tested for potential pathogenic mechanisms. Enterotoxin production was not detected in the infant mouse test or by calf and piglet ligated intestinal loop studies. Isolates were not invasive by the Sereny test. All isolates associated with and penetrated HeLa cells, although both actions occurred generally in a minor way under the conditions of our study. The C. coli isolate showed extensive HeLa cell association, but three other C. coli isolated tested did not. None of the 15 isolates produced diarrhea or death in 3-day-old chickens inoculated orally and observed for 3 days, nor did they consistently produce diarrhea and death in 9- to 10-day-old infant mice over a 3-day period after oral inoculation. Diarrheal disease and mortality were not observed when 3-day-old gnotobiotic chickens were infected with one of five isolates and observed over a 2-week period.

Enhancement of invasiveness of Yersinia enterocolitica and Escherichia coli in HEp-2 cells by centrifugation

Centrifugation enhanced the infectivity of invasive Escherichia coli and Yersinia enterocolitica for HEp-2 cells. Noninvasive bacteria were not endocytosed after centrifugation. The centrifugation procedure may increase the sensitivity of testing for bacterial invasiveness in cell culture without causing false-positive results.

Relationship of HeLa cell infectivity to biochemical, serological, and virulence characteristics of Yersinia enterocolitica

Examination of 69 strains of Yersinia enterocolitica which represented 20 serotypes and nontypable isolates for HeLa cell infectivity by a roller tube technique that provided a quantitative index of infection showed that infectivity (index, greater than 3.50) was confined to strains of serotypes O:8, O:3, O:5, 27, O:9, O:1, O:1,2,3, O:2,3, O:4,32, and O:21. All strains that were HeLa positive were sucrose positive and negative for salicin, esculin, rhamnose, raffinose, melibiose, alpha-methylglucoside, and citrate. All HeLa-negative strains were either sucrose and salicin positive or were sucrose negative. Twenty-one strains were examined for virulence by the ability to produce guinea pig conjunctivitis and diarrhea in mice. Positive strains were limited to those that were HeLa positive and were autoagglutination positive and calcium dependent at 35 degrees C. There was no association between virulence and the ability to produce enterotoxin measured by the infant mouse assay. Loss of autoagglutinability and calcium dependency was accompanied by loss of virulence, but HeLa cell infectivity was unchanged. The results suggest that at least two properties are necessary for virulence: the presence of the V and W antigens, mediated by the same plasmid as autoagglutination and calcium dependency, and an invasive factor demonstrated in vitro by HeLa cell infectivity. These virulence properties are found in only certain biotypes of Y. enterocolitica.

Plasmids in Yersinia enterocolitica serotypes O:3 and O:9: correlation with epithelial cell adherence in vitro

Human isolates of Yersinia enterocolitica serotypes O:3 (biotype 4) and O:9 (biotype 3) harbored plasmids sized approximately 47 and 44 megadaltons, respectively. No such plasmids were found in "apathogenic" strains of Y. enterocolitica belonging to biotype 1. There was a positive correlation among the presence of plasmid, autoagglutination, and adherence to and toxicity for HEp-2 cell cultures; all of these properties were lost by culturing at 37 degrees C in the absence of calcium. Strains of Y. enterocolitica O:3 and O:9 cured of the plasmids showed increased invasiveness in the HEp-2 cell culture model, but no invasiveness in guinea pig eye. It is suggested that the plasmids of Y. enterocolitica primarily determine epithelial cell adherence, but may also be associated with other pathogenic properties.

Yersiniosis in children

40 cases of bacteriologically proved Yersinia enterocolitica infections in children under 15 years were reviewed. Most children presented with abdominal symptoms, and diarrhoea was present in 80% of them. In half of those with diarrhoea the stools were mucoid and gross blood was often present. Faecal leucocytes were found in 4 out of the 5 children studied. The clinical findings are consistent with the enteroinvasive pathogenic mechanism proposed for Y. enterocolitica. 29 of 30 faecal isolates of Y. enterocolitica were found invasive for human epithelial cells in vitro. Nine strains produced an enterotoxin demonstrable in newborn mouse assay. Toxin production may be an additional pathogenic mechanism in human yersiniosis.

Experimental Yersinia enterocolitica enteritis in rabbits

Young rabbits weighing 500 to 800 g were inoculated orogastrically with clinical isolates of Yersinia enterocolitica (serotype O:3; enterotoxigenic; HeLa cell invasive) at a dose of 1.4 X 10(10) bacteria suspended in 10% sodium bicarbonate solution. Diarrhea developed in 41 (87%) of 47 rabbits, with a mean +/- standard deviation onset at 5.4 +/- 2.4 days. The attack rate and onset of diarrhea were correlated with inoculum size. The 50% infectious dose was 2.9 X 10(8) bacteria. Bacterial colonization occurred in almost all rabbits, regardless of inoculum size. Seroconversion was demonstrated in 30 (71%) of 42 rabbits with or without diarrhea. Histopathological alterations were present in the jejuna, ilea, and colons of rabbits with diarrhea; the most pronounced changes were generally noted in the ilea. Crypt abscesses localized at the depth of the intestinal glands were observed consistently and were composed of a bacterial nidus admixed with and enveloped by inflammatory cells comprised of eosinophils, neutrophils, and mononuclear cells. Rabbits inoculated with a raw fish isolate of Y. enterocolitica (serotype O:6,30; non-enterotoxigenic; HeLa cell noninvasive) did not exhibit infection clinically, bacteriologically, or pathologically.

Pathogenic properties of Yersinia enterocolitica

A total of 88 isolates of Yersinia enterocolitica was examined for heat-stable enterotoxin production and ability to penetrate HeLa cells and evoke keratoconjunctivitis in guinea pigs (Séreny test) as potential pathogenic properties. All 49 isolates belonging to serotypes O:3, O:8, O:9, and O:5,27 and only 5 of 39 strains of other serotypes were HeLa positive. Séreny-positive strains were found only in serotype O:8. Heat-stable enterotoxin production was almost ubiquitous in all serotypes. Y. enterocolitica strains were classified into five groups with regard to their potential pathogenic properties.

Two modified selenite media for the recovery of Yersinia enterocolitica from meats

Yersinia enterocolitica is one of the few human pathogens that grows at the proper food refrigeration temperatures of 0 to 5 degrees C. Although the isolation of environmental biotypes of Y. enterocolitica from many types of food and water has been reported in the literature, the recovery of the sensitive strains inoculated into foods has been slow and uncertain. Rapid recovery of several clinical strains inoculated into meats was accomplished by using two modified selenite broths without added nutrients. It was critical to restrict the sample size of the blended meat suspension at the 0.2-g/100 ml level, thereby restricting the growth of the total bacterial population in the selenite enrichment media. Otherwise, the slower growing Y. enterocolitica would be overwhelmed by the faster growing normal bacterial flora from the meat. Both the resistant serotype O:3 and the sensitive O:8 clinical isolates of Y. enterocolitica were recovered from the modified selenite enrichment media after 2 and 3 days of incubation at 22 degrees C.