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

1H nuclear magnetic resonance-based metabolite profiling of guava leaf extract: an attempt to develop a prototype for standardization of plant extracts

Background

Herbal medicines are fast gaining popularity. However, their acceptability by modern practitioners is low which is often due to lack of standardization. Several approaches towards standardization of herbals have been employed. The current study attempted to recognize key peaks from ¹H NMR spectra which together would comprise of a spectral fingerprint relating to efficacy of Psidium guajava (guava) leaf extract as an antidiarrhoeal when a number of unidentified active principles are involved.

Methods

Ninety samples of guava leaves were collected from three locations over three seasons. Hydroalcoholic (water and ethanol, 50:50) extracts of these samples were prepared and their ¹H NMR spectra were acquired. Spectra were also obtained for quercetin, ferulic acid and gallic acid as standards. Eight bioassays reflecting different stages of diarrhoeal pathogenesis were undertaken and based on pre-decided cut-offs, the extracts were classified as ‘good’ or ‘poor’ extracts. The bioactivity data was then correlated with the ¹H NMR profiles using Regression or Orthogonal Partial Least Square-Discriminant Analysis (OPLS-DA).

Results

OPLS-DA showed seasonal and regional segregation of extracts. Significant models were established for seven bioassays, namely those for anti-bacterial activity against Shigella flexneri and Vibrio cholerae, adherence of E. coli, invasion of E. coli and S. flexneri and production and binding of toxin produced by V. cholerae. It was observed that none of the extracts were good or bad across all the bioassays. The spectral analysis showed multiple peaks correlating with a particular activity. Based on NMR and LC-MS/MS, it was noted that the extracts contained quercetin, ferulic acid and gallic acid. However, they did not correlate with the peaks that segregated extracts with good and poor activity.

Conclusions

The current study identified key peaks in ¹H NMR spectra contributing to the anti-diarrhoeal activity of guava leaf extracts. The approach of using spectral fingerprinting employed in the present study can thus be used as a prototype towards standardization of plant extracts with respect to efficacy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12906-021-03221-5.

Effect of Psidium guajava (guava) L. Leaf Decoction on Antibiotic-resistant Clinical Diarrhoeagenic Isolates of Shigella spp

Background: Although shigellosis is self-limiting, antibiotics are recommended to minimize the severity of symptoms and reduce mortality rates. However, due to the increasing reports of antibiotic resistance, alternative approaches are needed to combat shigellosis. Interest for research on medicinal plants has increased in recent years, and hence, they can be explored to treat this infectious diarrhoea. Objective: To study the effect of Psidium guajava L. (guava) leaf decoction (GLD) on the antibiotic-resistant clinical isolates of Shigella spp. Materials and Methods: A total of 43 isolated Shigella spp. from diarrhoeal patients were used in this study. The effect of GLD on the bacterial viability was initially assessed. The isolates were divided into two categories: sensitive and resistant to GLD. For sensitive isolates, antibacterial activity of GLD was evaluated while for resistant strains, the ability of GLD for reducing the bacterial invasion of the HEp-2 cell line underwent an investigation. Results: Among the 43 Shigella isolates, GLD affected the growth of 23 strains. The invasion of 9 strains from the 20 remaining resistant isolates was unaffected. Although the number of isolates was less, the data suggested that isolates belonging to S. flexneri serogroup were more sensitive to GLD in comparison with other spp (i.e., sonnei, boydii, and dysenteriae). Conclusion: The results of this study revealed the efficacy of GLD against drug-resistant Shigella spp. and thus could be considered for the treatment of diarrhoea. GLD can be a cost-effective alternative to antibiotics.

Evaluation of regulated delayed attenuation strategies for Salmonella enterica serovar Typhi vaccine vectors in neonatal and infant mice

We developed regulated delayed attenuation strategies for Salmonella vaccine vectors. In this study, we evaluated the combination of these strategies in recombinant attenuated Salmonella enterica serovar Typhi and Salmonella enterica serovar Typhimurium vaccine vectors with similar genetic backgrounds in vitro and in vivo. Our goal is to develop a vaccine to prevent Streptococcus pneumoniae infection in newborns; thus, all strains delivered a pneumococcal antigen PspA and the impact of maternal antibodies was evaluated. The results showed that all strains with the regulated delayed attenuated phenotype (RDAP) displayed an invasive ability stronger than that of the S. Typhi vaccine strain, Ty21a, but weaker than that of their corresponding wild-type parental strains. The survival curves of different RDAP vaccine vectors in vitro and in vivo exhibited diverse regulated delayed attenuation kinetics, which was different from S. Typhi Ty21a and the wild-type parental strains. Under the influence of maternal antibody, the persistence of the S. Typhimurium RDAP strain displayed a regulated delayed attenuation trend in nasal lymphoid tissue (NALT), lung, and Peyer's patches, while the persistence of S. Typhi RDAP strains followed the curve only in NALT. The bacterial loads of S. Typhi RDAP strains were lower in NALT, lung, and Peyer's patches in mice born to immune mothers than in those born to naive mothers. In accordance with these results, RDAP vaccine strains induced high titers of IgG antibodies against PspA and against Salmonella lipopolysaccharides. Immunization of mothers with S. Typhi RDAP strains enhanced the level of vaginal mucosal IgA, gamma interferon (IFN-γ), and interleukin 4 (IL-4) and resulted in a higher level of protection against S. pneumoniae challenge.

Newer insights into the mechanism of action of Psidium guajava L. leaves in infectious diarrhoea

BACKGROUND

Psidium guajava L., Myrtaceae, is used widely in traditional medicine for the treatment of diarrhoea, dysentery, gastroenteritis, stomachaches, and indigestion. However, the effect of the leaf extract of P. guajava on the pathogenesis of infectious diarrhoea has not been studied. The present study evaluates the effect of a hot aqueous extract (decoction) of dried leaves of P. guajava on parameters associated with pathogenicity of infectious diarrhoea. The aim was to understand its possible mechanism(s) of action in controlling infectious diarrhoea and compare it with quercetin, one of the most reported active constituents of P. guajava with antidiarrhoeal activity.

METHODS

The crude decoction and quercetin were studied for their antibacterial activity and effect on virulence features of common diarrhoeal pathogens viz. colonization of epithelial cells and production and action of enterotoxins. Colonization as measured by adherence of enteropathogenic Escherichia coli (EPEC) and invasion of enteroinvasive E. coli (EIEC) and Shigella flexneri was assessed using HEp-2 cell line. The production of E. coli heat labile toxin (LT) and cholera toxin (CT) and their binding to ganglioside monosialic acid (GM1) were studied by GM1-ELISA whereas the production and action of E. coli heat stable toxin (ST) was assessed by suckling mouse assay.

RESULTS

The decoction of P. guajava showed antibacterial activity towards S. flexneri and Vibrio cholerae. It decreased production of both LT and CT and their binding to GM1. However, it had no effect on production and action of ST. The decoction also inhibited the adherence of EPEC and invasion by both EIEC and S. flexneri to HEp-2 cells. Quercetin, on the other hand, had no antibacterial activity at the concentrations used nor did it affect any of the enterotoxins. Although it did not affect adherence of EPEC, it inhibited the invasion of both EIEC and S. flexneri to HEp-2 cells.

CONCLUSION

Collectively, the results indicate that the decoction of P. guajava leaves is an effective antidiarrhoeal agent and that the entire spectrum of its antidiarrhoeal activity is not due to quercetin alone.

Studies on the antidiarrhoeal activity of Aegle marmelos unripe fruit: validating its traditional usage

Background

Aegle marmelos (L.) Correa has been widely used in indigenous systems of Indian medicine due to its various medicinal properties. However, despite its traditional usage as an anti-diarrhoeal there is limited information regarding its mode of action in infectious forms of diarrhoea. Hence, we evaluated the hot aqueous extract (decoction) of dried unripe fruit pulp of A. marmelos for its antimicrobial activity and effect on various aspects of pathogenicity of infectious diarrhoea.

Methods

The decoction was assessed for its antibacterial, antigiardial and antirotaviral activities. The effect of the decoction on adherence of enteropathogenic Escherichia coli and invasion of enteroinvasive E. coli and Shigella flexneri to HEp-2 cells were assessed as a measure of its effect on colonization. The effect of the decoction on production of E. coli heat labile toxin (LT) and cholera toxin (CT) and their binding to ganglioside monosialic acid receptor (GM1) were assessed by GM1-enzyme linked immuno sorbent assay whereas its effect on production and action of E. coli heat stable toxin (ST) was assessed by suckling mouse assay.

Results

The decoction showed cidal activity against Giardia and rotavirus whereas viability of none of the six bacterial strains tested was affected. It significantly reduced bacterial adherence to and invasion of HEp-2 cells. The extract also affected production of CT and binding of both LT and CT to GM1. However, it had no effect on ST.

Conclusion

The decoction of the unripe fruit pulp of A. marmelos, despite having limited antimicrobial activity, affected the bacterial colonization to gut epithelium and production and action of certain enterotoxins. These observations suggest the varied possible modes of action of A. marmelos in infectious forms of diarrhoea thereby validating its mention in the ancient Indian texts and continued use by local communities for the treatment of diarrhoeal diseases.

Studies on Pongamia pinnata (L.) Pierre leaves: understanding the mechanism(s) of action in infectious diarrhea

While data are available on the effect of medicinal plants on intestinal motility and their antibacterial action, there is a paucity of information on their mode of action on various aspects of diarrheal pathogenicity, namely colonization to intestinal epithelial cells and production/action of enterotoxins. Crude decoction of dried leaves of Pongamia pinnata was evaluated for its antimicrobial (antibacterial, antigiardial and antirotaviral) effect; and its effect on production and action of enterotoxins (cholera toxin, CT; Escherichia coli labile toxin, LT; and E. coli stable toxin, ST); and adherence of enteropathogenic E. coli and invasion of enteroinvasive E. coli and Shigella flexneri to epithelial cells. The decoction had no antibacterial, antigiardial and antirotaviral activity, but reduced production of CT and bacterial invasion to epithelial cells. The observed results indicated that the crude decoction of P. pinnata has selective antidiarrheal action with efficacy against cholera and enteroinvasive bacterial strains causing bloody diarrheal episodes.

Effects of Listeria monocytogenes and Yersinia enterocolitica on cytokine gene expression and release from human polymorphonuclear granulocytes and epithelial (HEp-2) cells

The gene expression and cytokine release of the proinflammatory cytokines interleukin-1 beta (IL-1 beta), IL-6, and tumor necrosis factor alpha (TNF-alpha) after infection of human epithelial cells (HEp-2 cells) and polymorphonuclear granulocytes (PMNs) were investigated by using isogenic pairs of Listeria monocytogenes and Yersinia enterocolitica strains. By polymerase chain reaction-assisted mRNA amplification and RNA dot blot analysis, we showed that PMNs and HEp-2 cells expressed enhanced levels of mRNA encoding IL-1 beta, IL-6, and TNF-alpha after bacterial infection. Concomitant with the enhanced mRNA level, an increased secretion rate of IL-1 beta, IL-6, and TNF-alpha from PMNs as assessed by enzyme-linked immunosorbent assay was observed. HEp-2 cells after infection also released IL-6 and TNF-alpha into the cell supernatant, while no IL-1 beta release was detected. Cellular coincubation experiments were carried out with Transwell chambers. Our studies revealed that the coculture of PMNs and HEp-2 cells led to an increased IL-1 beta and IL-6 release. In contrast, after infection with the invasive bacteria, reduced levels of TNF-alpha were measured. Our data show that PMNs secrete the proinflammatory cytokines IL-1 beta, IL-6, and TNF-alpha within some hours after infection with L. monocytogenes and Y. enterocolitica and that cellular interactions with epithelial cells alone via soluble mediators influence the net amount of released proinflammatory cytokines.

Comparative study of histopathological alterations during intestinal infection of mice with pathogenic and non-pathogenic strains of Yersinia enterocolitica serotype O:8

Yersinia enterocolitica is an invasive pathogen capable of causing a wide spectrum of gastrointestinal diseases in man. While there is a considerable body of data on the invasiveness of Y. enterocolitica in vitro, little is known about the events in vivo leading to the translocation of the bacteria from the intestinal lumen into the ileal tissue. There is no detailed ultrastructural information describing the course of infection of pathogenic Y. enterocolitica in comparison with an avirulent strain. We compared a virulent plasmid-bearing strain and an isogenic avirulent plasmid-free derivative strain of Y. enterocolitica serotype O:8 at the ultrastructural level, in the established model of murine yersiniosis. At 12 h post-inoculation we found no indications of an active invasion of the intestinal epithelium, although microcolonies of the pathogenic strain were detectable closely under the follicle-associated epithelium of the Peyer's patches. The plasmid-bearing strain of Y. enterocolitica affected the gut-associated lymphoid tissue which was destroyed 36 h post-infection. Unlike the pathogenic strain of Y. enterocolitica, the nonpathogenic plasmid-free strain caused no detectable morphological alterations in the ileal tissue by this time. Morphological evidence is provided that Yersinia does not invade the ileal epithelium in an active manner, as has been observed in vitro, but appears to be transported across the epithelial barrier by M-cells.

The integrin-binding domain of invasin is sufficient to allow bacterial entry into mammalian cells

Yersinia pseudotuberculosis is able to enter normally nonphagocytic host cells by multiple pathways, the most efficient of which is mediated by invasin, a 986-amino-acid bacterial outer membrane protein. It has previously been shown that the C-terminal 192 amino acids of invasin are sufficient to bind mammalian cells. To determine if additional regions of the invasin protein are necessary to promote entry, we developed a novel assay that tests the ability of various invasin derivatives to confer on Staphylococcus aureus the ability to enter animal cells. We determined that the 192-amino-acid cell-binding region of invasin, when used to coat the bacterial cell surface, was also sufficient to promote cellular penetration. These results suggest that the simple binding of invasin to its receptors is sufficient to mediate entry and that the bacterium plays a largely passive role in the entry process.

Relevance of inoculation route to virulence of three Salmonella spp. strains in mice

The virulence of three Salmonella species strains was compared by the i.p. and i.v. routes in BALB/c mice. Salmonella choleraesuis, SL2824 (serogroup C1, O-6,7), was more virulent by the i.v. than i.p. route. A strain of S. typhimurium, SL1260 (serogroup B; O-1,4,12) was more virulent i.p. than i.v. while another strain, SL3201 (O-4,5,12) was equally virulent i.p. or i.v. The LD50 of each strain by either route correlated with the number of bacteria in the liver and spleen on day one after inoculation and thus seems determined mainly by initial bactericidal mechanisms. The rate of bacterial growth in the liver and spleen was independent of inoculation route but differed between the three strains. Salmonella choleraesuis multiplied faster than either strain of S. typhimurium. Non-virulent aromatic-dependent (aro) derivatives of these strains were tested, instead of their virulent ancestors, for survival within peritoneal macrophages in vitro. Salmonella choleraesuis SL 2824 aro and S. typhimurium SL1260 aro were much more readily killed intracellularly than S. typhimurium SL3201 aro. The data indicate that the survival and multiplication of different Salmonella serotypes or strains in vivo may depend on different critical properties or mechanisms to overcome host defenses.

Interaction of chlamydiae and host cells in vitro

The obligately intracellular bacteria of the genus Chlamydia, which is only remotely related to other eubacterial genera, cause many diseases of humans, nonhuman mammals, and birds. Interaction of chlamydiae with host cells in vitro has been studied as a model of infection in natural hosts and as an example of the adaptation of an organism to an unusual environment, the inside of another living cell. Among the novel adaptations made by chlamydiae have been the substitution of disulfide-bond-cross-linked polypeptides for peptidoglycans and the use of host-generated nucleotide triphosphates as sources of metabolic energy. The effect of contact between chlamydiae and host cells in culture varies from no effect at all to rapid destruction of either chlamydiae or host cells. When successful infection occurs, it is usually followed by production of large numbers of progeny and destruction of host cells. However, host cells containing chlamydiae sometimes continue to divide, with or without overt signs of infection, and chlamydiae may persist indefinitely in cell cultures. Some of the many factors that influence the outcome of chlamydia-host cell interaction are kind of chlamydiae, kind of host cells, mode of chlamydial entry, nutritional adequacy of the culture medium, presence of antimicrobial agents, and presence of immune cells and soluble immune factors. General characteristics of chlamydial multiplication in cells of their natural hosts are reproduced in established cell lines, but reproduction in vitro of the subtle differences in chlamydial behavior responsible for the individuality of the different chlamydial diseases will require better in vitro models.

Penetration and intracellular growth of Brucella abortus in nonphagocytic cells in vitro

In pregnant ruminants, Brucella abortus localizes and replicates within the rough endoplasmic reticulum of trophoblastic epithelial cells. In this study, Vero cells were exposed to B. abortus to investigate its internalization and intracellular growth in nonphagocytic cells. A new double-fluorescence staining procedure to discriminate between extracellular and intracellular bacteria was developed. Studies with the double-fluorescence staining procedure and quantitative bacteriologic culture of disrupted host cells showed that various B. abortus strains replicated within Vero cells, including smooth virulent (strains 2308S and 544), smooth attenuated (strain 19), and rough (strains 45/20 and 2308R) strains. Rough brucellae were more adherent and entered a greater number of Vero cells. Intracellular replication occurred in a larger percentage of cells with smooth virulent (2308S and 544) strains than with smooth attenuated (19) or rough (45/20 and 2308R) strains. Differences in adhesiveness and invasiveness were correlated to hydrophobicity of the organism, as measured by hydrocarbon adherence. Ultrastructurally, intracellular smooth (2308S) and rough (45/20) brucellae were consistently found within cisternae of the rough endoplasmic reticulum and nuclear envelope. The results suggest that transfer to the rough endoplasmic reticulum is the limiting step in the infection of nonphagocytic cells by B. abortus.

Nucleotide sequence of the Yersinia enterocolitica ail gene and characterization of the Ail protein product

The ability to enter (invade) eucaryotic cells is a property common to many pathogenic bacteria. Yersinia enterocolitica is a facultative intracellular pathogen whose primary site of multiplication is the reticuloendothelial system. In an effort to understand how Y. enterocolitica crosses the intestinal epithelial cell layer, we previously reported the cloning of two loci from Y. enterocolitica that individually conferred an invasive phenotype to the normally noninvasive Escherichia coli HB101. One of these loci, ail, is encoded by a region of DNA that is less than 650 base pairs. We have identified the ail gene product in maxicells as a 17-kilodalton membrane-associated protein. The Ail protein has been purified, and its N-terminal sequence has been determined. The nucleotide sequence of the ail gene revealed a single unique open reading frame of 178 amino acids. Comparison of amino acid sequences deduced from the gene and obtained by analysis of the purified protein identified the first 23 amino acids as a signal sequence. The site(s) at which transcription initiates on the ail gene was identified by primer extension analysis and shown to be identical in E. coli and Y. enterocolitica. Two small open reading frames downstream of ail were found and shown to exhibit considerable identity to the proposed IS3 transposase.

Cloning and molecular characterization of genes whose products allow Salmonella typhimurium to penetrate tissue culture cells

Invasion of the intestinal epithelium is thought to be an important step in the pathogenesis of Salmonella infections. Using an in vitro system, we have isolated a genetic locus, inv, that confers to a noninvasive strain of Salmonella typhimurium the ability to penetrate tissue culture cells. Highly virulent S. typhimurium strains carrying inv mutations were defective for entry into Henle-407 cells while remaining unaffected in their ability to attach to cultured cells. When administered perorally to BALB/c mice, inv mutants of S. typhimurium had higher 50% lethal doses (LD50) than their wild-type parent strains. To the contrary, there were no differences in the observed LD50 when strains were administered intraperitoneally. In addition, inv mutants presented decreased ability to colonize the Peyer's patches, the small intestinal wall, and the spleen when administered perorally, although when administered intraperitoneally, they showed no difference in their ability to colonize the spleen compared to the wild-type parent strain.

Cellular events and intracellular survival of Campylobacter jejuni during infection of HEp-2 cells

Invasion and intracellular survival of Campylobacter jejuni in HEp-2 cells were analyzed by transmission electron microscopy and by viable counts after killing of extracellular bacteria by gentamicin. During the first 30 min after challenge, no bacteria were seen in association with the host cell. After 1 h, campylobacters apparently attached to the cell membrane, with areas of close appositions. In these areas, an intracellular network of actin-like filaments was seen beneath the plasma membrane. Other bacteria were included into endocytic vacuoles. After 3 h, an intense lysosomal response was observed in the host cells, as determined by the presence of myelinic forms and acid phosphatase activity. After 9 h, bacteria still contained in vacuoles showed signs of degradation with a change from spiral to coccal forms. Morphological evidence of phagosome-lysosome fusion was also seen, and these observations by transmission electron microscopy correlated well with a decrease in bacteria viability 9 h after challenge, as determined from separate kinetics studies. Inhibitors of phagocytosis were observed to reduce markedly the entry of C. jejuni into the cells at concentrations which apparently did not affect bacterial viability. These results suggest that the campylobacters were successively attached to the HEp-2 cell membrane, internalized by a phagocytic-like mechanism, and digested after phagosome-lysosome fusion.

The ail locus is found uniquely in Yersinia enterocolitica serotypes commonly associated with disease

Yersinia enterocolitica is a heterogeneous group of organisms with more than 50 serotypes and several biotypes. Only a few of these serotypes cause gastrointestinal disease in otherwise healthy hosts; these serotypes are the pathogenic serotypes. Although Y. enterocolitica requires a high-molecular-weight plasmid to cause disease, chromosome-encoded determinants are required for the full expression of virulence. The ability of Yersinia spp. to invade eucaryotic cells is thought to be a virulence factor, because nonpathogenic serotypes are noninvasive in animals and in tissue culture cell models. Current evidence indicates that invasion ability is chromosome encoded. We recently reported cloning two loci, inv and ail, from Y. enterocolitica O8 strain 8081c that allow Escherichia coli to invade tissue culture cells. We investigated the link between invasion in an in vitro tissue culture invasion (TCI) model and hybridization to probes derived from the two invasion loci, inv and ail. We examined 177 Yersinia strains. Strains of serotypes and species associated with disease were TCI+, whereas strains of serotypes and species not associated with disease were TCI-. Only TCI+ strains had DNA homologous to probes derived from ail. All strains (TCI+ and TCI-) had DNA homologous to probes derived from inv, but there were certain restriction fragment-linked polymorphisms that were associated primarily with TCI+ strains. These observations held true for strains epidemiologically associated with disease. Both the inv and ail loci were found to be clearly located on the chromosome. No other genera, including other invasive organisms, had DNA homologous to inv or ail. These data support the hypothesis that the ail locus encodes a Y. enterocolitica invasion factor that may be involved in pathogenesis.

Effect of mucin on Campylobacter jejuni association and invasion on HEp-2 cells

We report the development of an in vitro assay using HEp-2 cell monolayers in which cell association of five C. jejuni strains and E. coli K12 C600 were tested under different experimental conditions. Both total cell associated colony forming units (CFU) and the CFU protected from gentamicin killing (i.e. internalized bacteria) were determined. Pretreatment of HEp-2 cells with mucin (100 micrograms/ml) enhanced internalization of four fresh isolates of C. jejuni by 3.2 to 20.7-fold, depending on the strain, but not internalization of C. jejuni K105 (a stock culture) or E. coli C600. Mucin also increased the total number of cell associated C. jejuni fresh isolates by 2 to 3.4-fold, the four strains yielding similar results. We conclude from these studies that mucin, which has been shown to be a prerequisite of intestinal colonization by C. jejuni, also promotes infectivity.

Virulence of Yersinia pseudotuberculosis isolated from pork and from the throats of swine

Yersinia pseudotuberculosis was isolated from retail pork and from healthy swine throats. These wild-type strains and their representative cured isogenic strains were tested for the presence of plasmids and several virulence factors, and these characteristics were compared with those of virulent strains from humans. Two pork isolates (serotype IVB) and four swine isolates (serotypes IIB, IIC, III, and IVB) harbored a 42- to 48-megadalton plasmid which had similar fragmentation patterns resulting from digestion with restriction endonuclease. These six strains were lethal for mice via oral challenge and were positive in autoagglutination and calcium dependency tests. They also invaded HeLa cells and induced cytotoxicity. Histopathological examination and indirect fluorescent-antibody staining provided definite evidence of the pathogenicity of these strains when tissue sections from orally infected mice were used. The virulence factors of wild-type pork and swine isolates with the 42- to 48-megadalton plasmid were identical to those of two human isolates (serotypes IVB and VB). Hence, these pork and swine isolates should be considered potentially pathogenic for humans. The finding suggests that retail pork and swine may play an important role in the epidemiology of human infections caused by Y. pseudotuberculosis.

Hemolysin supports survival but not entry of the intracellular bacterium Listeria monocytogenes

The gram-positive bacterium Listeria monocytogenes is a facultative intracellular pathogen. The only known property of L. monocytogenes which has been shown to be involved in virulence is a hemolysin, listeriolysin (J. L. Gaillard, P. Berche, and P. Sansonetti, Infect. Immun. 52:50-55, 1986; S. Kathariou, P. Metz, H. Hof, and W. Goebel, J. Bacteriol. 169:1291-1297, 1987). Using our previously obtained transposon Tn916-induced hemolysin-negative mutants of L. monocytogenes Sv1/2a (Mackaness strain), we demonstrated that the loss of hemolysin reduced significantly the rate of survival of the bacteria in mouse peritoneal macrophages but did not reduce their uptake. It was further shown that virulent L. monocytogenes strains could invade the mouse embryo fibroblast 3T6 cell line, i.e., mammalian cells which are nonprofessional phagocytes. This uptake was inhibited by cytochalasin B and hence seems to be accomplished by parasite-induced endocytosis. Hemolysin was not essential for this step. Strains of other Listeria species could not efficiently penetrate the 3T6 cells.

Virulence associated ingestion of Legionella pneumophila by HeLa cells

Invasion of HeLa cell monolayers by Legionella pneumophila was studied. Virulent L. pneumophila strains efficiently entered cultured HeLa cells whereas isogenic avirulent isolates were nearly 1000-fold less efficient at cellular entry. Animal passage of avirulent strains, which restored bacterial virulence, coincided with a return to the virulent parental level of HeLa cell invasion. Diminished HeLa cell invasion by avirulent strains was not a function of reduced bacterial association with the cell monolayer. These data suggest that ingestion of L. pneumophila by non-professional phagocytes is a virulence directed property.

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.

Immune function in patients with previous yersinia arthritis: lymphocyte responses to PHA and Staphylococcus aureus strain Cowan I

Evidence has accumulated that, first, polymorphonuclear leukocytes (PMN) and humoral factors such as fragments of complement components may regulate immune response, and second, PMN function is enhanced in HLA-B27-positive subjects. We therefore used a whole-blood culture technique to study lymphocyte proliferation in response to phytohaemagglutinin-P (PHA) in blood samples obtained from patients with previous yersinia arthritis and from healthy subjects with or without HLA-B27. In another series of experiments, mononuclear cells were separated from peripheral blood and lymphocyte responses to Staphylococcus aureus strain Cowan I, a B-cell mitogen in fetal calf serum, and to PHA in pooled normal human serum were determined. The patients and the control subjects were always tested simultaneously. The results showed no significant differences between the subject groups. This suggests that humoral factors and enhanced neutrophil function do not exert remarkable effects on in vitro lymphocyte responses to mitogens in HLA-B27-positive subjects.

A single genetic locus encoded by Yersinia pseudotuberculosis permits invasion of cultured animal cells by Escherichia coli K-12

For many species of pathogenic bacteria, invasion and survival within animal cells is central to establishing a successful host-parasite relationship. Localization within host cells protects the microorganism from host defences, or permits it to cross epithelial barriers and subsequently become systemically distributed. The precise mechanisms that permit entry of bacteria into host tissues are unclear, therefore we have been studying the invasion of epithelial cells by Yersinia pseudotuberculosis. As a first step towards identifying the factors required for this process, we report here the identification of a single genetic locus from this organism that is sufficient to convert the innocuous Escherichia coli K-12 strain into an organism capable of invading cultured animal cells.

Adherence and toxicity of Yersinia enterocolitica 0:3 and 0:9 containing virulence-associated plasmids for various cultured cells

Plasmid (47 and 44 Mdal, respectively) containing strains of Yersinia enterocolitica 0:3 and 0:9 adhered to and were toxic for HEp-2 human epithelial and Y-1 adrenal cells in vitro, At 37 degrees C, but not at room temperature, the adhesion of the bacteria lead to rounding and partial detachment of the cultured cells. UV-inactivated plasmid-positive Y. enterocolitica were neither adherent nor toxic for the cells but were readily endocytosed by HEp-2 cells. The adherence of plasmid-positive Y. enterocolitica 0:3 and 0:9 on epithelial cells may be pathogenetically important as an initial step for intestinal colonization, and possibly in Y. enterocolitica-induced diarrhoea. Plasmid-positive Y. enterocolitica also adhered to the surface of cultured human macrophages and were apparently not phagocytosed as effectively as the plasmid-negative derivatives of the same bacteria. Thus resistance to phagocytosis may form an additional plasmid-dependent virulence property of Y. enterocolitica 0:3 and 0:9.