[Presence of Yersinia enterocolitica in conditions of agro complex]

AIM

Detection of duration of existence of Yersinia enterocolitica in substrates ofagro complex and formation of biofilms by causative agent during artificial semination of forage and meat products.

MATERIALS AND METHODS

Y. enterocolitica 09 strain and its rifampicin-resistant (Rmr) mutant were used. Microbial landscape of samples was studied by seeding on selective media (HiMedia), biochemical properties of isolates were controlled on API test-systems (Bio-Merieux). The presence ofyopA gene localized on virulence plasmid pCad was determined in PCR. Vital staining of biofilms was carried out by Live/Dead stain (Invitrogen, USA). Visualization of the data was registered by using GMS-510 (USA) microscope with digital camera and Skope Photo software (USA). Formation ofyersinia bacterial biofilms was confirmed by using scanning electron microscope (SEM) JSM6380 (Japan).

RESULTS

Prolonged duration of existence of Y. enterocolitica in substrates of agro complex with conservation of pCad virulence plasmid by causative agent was detected. SEM demonstrated stages of biofilm formation during artificial semination of animal forage, meat products and materials of food equipment in a wide range of temperatures from 10 to 30 degrees C, and vital stain detected viable yersinia in mature biofilms.

CONCLUSION

Agro complexes are a variant oftechnogenic foci where ecological conditions for prolonged existence of sapronosis are formed.

Function and molecular architecture of the Yersinia injectisome tip complex

By quantitative immunoblot analyses and scanning transmission electron microscopy (STEM), we determined that the needle of the Yersinia enterocolitica E40 injectisome consists of 139 +/- 19 YscF subunits and that the tip complex is formed by three to five LcrV monomers. A pentamer represented the best fit for an atomic model of this complex. The N-terminal globular domain of LcrV forms the base of the tip complex, while the central globular domain forms the head. Hybrids between LcrV and its orthologues PcrV (Pseudomonas aeruginosa) or AcrV (Aeromonas salmonicida) were engineered and recombinant Y. enterocolitica expressing the different hybrids were tested for their capacity to form the translocation pore by a haemolysis assay. There was a good correlation between haemolysis, insertion of YopB into erythrocyte membranes and interaction between YopB and the N-terminal globular domain of the tip complex subunit. Hence, the base of the tip complex appears to be critical for the functional insertion of YopB into the host cell membrane.

The V-antigen of Yersinia forms a distinct structure at the tip of injectisome needles

Many pathogenic bacteria use injectisomes to deliver effector proteins into host cells through type III secretion. Injectisomes consist of a basal body embedded in the bacterial membranes and a needle. In Yersinia, translocation of effectors requires the YopB and YopD proteins, which form a pore in the target cell membrane, and the LcrV protein, which assists the assembly of the pore. Here we report that LcrV forms a distinct structure at the tip of the needle, the tip complex. This unique localization of LcrV may explain its crucial role in the translocation process and its efficacy as the main protective antigen against plague.

Genetic analysis of the formation of the Ysc-Yop translocation pore in macrophages by Yersinia enterocolitica: role of LcrV, YscF and YopN

The Ysc-Yop type III secretion (TTS) system allows extracellular Yersinia bacteria, adhering to eukaryotic target cells, to inject Yop effector proteins in the cytosol of these cells. The secretion apparatus, called the injectisome, ends up with a needle-like structure made of YscF. YopN, one of the proteins secreted by the injectisome is thought to act as a plug. YopB, YopD and LcrV, three other proteins secreted by the injectisome and called 'translocators' form a pore allowing translocation of the Yop effectors across the target cell plasma membrane. Here, we tested the role of LcrV, YscF and YopN in the formation of this pore in macrophages by monitoring the release of the low-molecular-weight fluorescent dye BCECF (2',7'-bis-(2-carboxyethyl)-5-(and-6)-carboxyfluorescein, acetoxymethyl ester, 623Da) and of the high-molecular-weight lactate dehydrogenase (LDH, 135 kDa). BCECF is released through the translocation pore itself provided no Yop effector is trafficking through the channel. In contrast, LDH is released by the osmotic lysis of the target cell that occurs after pore formation. This release is reduced by the GAP activity of YopE. In order to study the role of LcrV, one has to circumvent the regulatory effect of LcrV on the synthesis of YopB and YopD. We observed here that this regulatory role of LcrV is lost in a yopQ mutant and hence we studied the role of LcrV in a yopQ mutant background. A lcrV, yopQ double mutant was deficient in pore formation while able to produce YopB and YopD. Pore formation was restored by the introduction of lcrV(+) but not yopQ(+) confirming that LcrV itself is directly required for pore formation. Bacteria secreting only YopB, YopD and LcrV could form pores, showing that YopB, YopD and LcrV are sufficient for pore formation provided they are secreted by the same bacterium. LcrV is not involved in secretion of YopB and YopD as suggested previously. Bacteria producing normal Ysc injectisomes, including the YscF needle but no translocators did not form pores, indicating that the needle is not sufficient by itself for pore formation, as was also suggested. yopN mutant bacteria formed needles and released BCECF even if they secreted the effectors. This observation suggests that many translocation pores are not filled in the absence of YopN and thus that YopN might form a link between the needle and the pore, guiding the effectors.

The Needle Length of Bacterial Injectisomes Is Determined by a Molecular Ruler

Size determination represents a fundamental requirement for multicomponent biological structures. Some pathogenic bacteria possess a weapon derived from the flagellum. Like the flagellum, this type-III secretion apparatus, called the injectisome, has a transmembrane basal body, but the external component is a needle-like structure instead of a hook and a filament. Here, we provide evidence that the length of this needle is determined by the size of a protein, YscP, acting as a molecular ruler.

Experimental mixed infection of rabbits with Yersinia enterocolitica and Listeria monocytogenes

Experimental mixed infection was reproduced in rabbits after per os infection with Yersinia enterocolitica serotype 0:3 cells. Four days later some of animals were re-infected orally with Listeria monocytogenes serotype 4b cells. A third group of healthy rabbits was also infected per os with Listeria monocytogenes. The infectious process was followed dynamically from days 1-28. The experimental animals were examined for clinical, paraclinical and morphological findings. Augmentation of body temperature and alveolar macrophage number, a decreased number of peritoneal macrophages, leucopenia as well as purulent meningoencephalitis, catarrhal pneumonia, lienitis, lymphadenitis and enteritis were detected after experimental mixed infection. Both types of macrophages demonstrated a weak bactericidal activity against Yersinia enterocolitica and a highly expressed killing effect against Listeria monocytogenes. Yersinia and Listeria cells were isolated from the viscera and brain. Both species of bacteria were established intracellularly in the macrophages by electron-microscopic examination. The data received showed that mixed Yersinia enterocolitica 0:3 and Listeria monocytogenes 4b infection of rabbits runs with transitory hyperthermia as a generalized infection and is similar to the Listeria mono-infection. The immunosuppressive effect induced by oral Yersinia enterocolitica infection of rabbits promotes the expression of listerious agents.

Interaction of Yersinia enterocolitica and Y. pseudotuberculosis with platelets

Yersinia enterocolitica is a bacterium capable of growth at 4 degrees C in donated blood and has been responsible for many deaths following transfusion. Interaction of Y. enterocolitica with blood cells is of interest in understanding the mechanisms of survival and growth in blood. The closely related organism Y. pseudotuberculosis is known to invade platelets and cause platelet aggregation by a mechanism that involves expression of the chromosomal inv gene. Yersinia isolates were made to express green fluorescent protein (GFP) and their interaction with platelets was studied by flow cytometry, enterocolitica did not cause platelet aggregation or activation, not even when grown at 22 degrees C to maximise inv expression. Attachment of Y. enterocolitica O:9 to platelets occurred with virulence plasmid-bearing (pYV+) strains grown at 37 degrees C but not with pYV- strains nor with strains grown at 22 degrees C. Y. pseudotuberculosis containing inv did cause platelet activation and aggregation when grown at 22 degrees C, as has been shown before, but also showed enhanced attachment to platelets when grown at 37 degrees C. Electron microscopy studies confirmed that inv-expressing Y. pseudotuberculosis invaded platelets but Y. enterocolitica attached only to the outer surface of platelets. Interaction of Y. enterocolitica O:9 with platelets provided a modest protection against bacterial killing by human serum. Interaction of Y. enterocolitica O:9 with platelets does not lead to platelet invasion or activation, and is mediated through plasmid-coded factors, not inv.

Infection of synovial fibroblasts in culture by Yersinia enterocolitica and Salmonella enterica serovar Enteritidis: ultrastructural investigation with respect to the pathogenesis of reactive arthritis

Synovial fibroblasts were infected with Yersinia enterocolitica or Salmonella enterica serovar Enteritidis and analyzed by electron microscopy and fluorescence in situ hybridization. Intracellular bacterial replication was followed by degradation leading to "ghosts" possessing lipopolysaccharides but not DNA. However, single bacteria survived for more than 2 weeks. Therefore, transient intra-articular infection might be the missing link between initial intestinal infection and late synovial inflammation in the pathogenesis of reactive arthritis.

Polymerization of a single protein of the pathogen Yersinia enterocolitica into needles punctures eukaryotic cells

A number of pathogenic, Gram-negative bacteria are able to secrete specific proteins across three membranes: the inner and outer bacterial membrane and the eukaryotic plasma membrane. In the pathogen Yersinia enterocolitica, the primary structure of the secreted proteins as well as of the components of the secretion machinery, both plasmid-encoded, is known. However, the mechanism of protein translocation is largely unknown. Here we show that Y. enterocolitica polymerizes a 6-kDa protein of the secretion machinery into needles that are able to puncture the eukaryotic plasma membrane. These needles form a conduit for the transport of specific proteins from the bacterial to the eukaryotic cytoplasm, where they exert their cytotoxic activity. In negatively stained electron micrographs, the isolated needles were 60-80 nm long and 6-7 nm wide and contained a hollow center of about 2 nm. Our data indicate that it is the polymerization of the 6-kDa protein into these needles that provides the force to perforate the eukaryotic plasma membrane.

Structure and sequence analysis of Yersinia YadA and Moraxella UspAs reveal a novel class of adhesins

The non-fimbrial adhesins, YadA of enteropathogenic Yersinia species, and UspA1 and UspA2 of Moraxella catarrhalis, are established pathogenicity factors. In electron micrographs, both surface proteins appear as distinct 'lollipop'-shaped structures forming a novel type of surface projection on the outer membranes. These structures, amino acid sequence analysis of these molecules and yadA gene manipulation suggest a tripartite organization: an N-terminal oval head domain is followed by a putative coiled-coil rod and terminated by a C-terminal membrane anchor domain. In YadA, the head domain is involved in autoagglutination and binding to host cells and collagen. Analysis of the coiled-coil segment of YadA revealed unusual pentadecad repeats with a periodicity of 3.75, which differs significantly from the 3.5 periodicity found in the Moraxella UspAs and other canonical coiled coils. These findings predict that the surface projections are formed by oligomers containing right- (Yersinia) or left-handed (Moraxella) coiled coils. Strikingly, sequence comparison revealed that related proteins are found in many proteobacteria, both human pathogenic and environmental species, suggesting a common role in adaptation to specific ecological niches.

Infection of human enterocyte-like cells with rotavirus enhances invasiveness of Yersinia enterocolitica and Y. pseudotuberculosis

Mixed infection with rotavirus and either Yersinia enterocolitica or Y. pseudotuberculosis was analysed in Caco-2 cells, an enterocyte-like cell line highly susceptible to these pathogens. Results showed an increase of bacterial adhesion and internalisation in rotavirus-infected cells. Increased internalisation was also seen with Escherichia coli strain HB101 (pRI203), harbouring the inv gene from Y. pseudotuberculosis, which is involved in the invasion process of host cells. In contrast, the superinfection with bacteria of Caco-2 cells pre-infected with rotavirus resulted in decreased viral antigen synthesis. Transmission electron microscopy confirmed the dual infection of enterocytes. These data suggest that rotavirus infection enhances the early interaction between host cell surfaces and enteroinvasive Yersinia spp.

The Yersinia enterocolitica motility master regulatory operon, flhDC, is required for flagellin production, swimming motility, and swarming motility

The ability to move over and colonize surface substrata has been linked to the formation of biofilms and to the virulence of some bacterial pathogens. Results from this study show that the gastrointestinal pathogen Yersinia enterocolitica can migrate over and colonize surfaces by swarming motility, a form of cooperative multicellular behavior. Immunoblot analysis and electron microscopy indicated that swarming motility is dependent on the same flagellum organelle that is required for swimming motility, which occurs in fluid environments. Furthermore, motility genes such as flgEF, flgMN, flhBA, and fliA, known to be required for the production of flagella, are essential for swarming motility. To begin to investigate how environmental signals are processed and integrated by Y. enterocolitica to stimulate the production of flagella and regulate these two forms of cell migration, the motility master regulatory operon, flhDC, was cloned. Mutations within flhDC completely abolished swimming motility, swarming motility, and flagellin production. DNA sequence analysis revealed that this locus is similar to motility master regulatory operons of other gram-negative bacteria. Genetic complementation and functional analysis of flhDC indicated that it is required for the production of flagella. When flhDC was expressed from an inducible ptac promoter, flagellin production was shown to be dependent on levels of flhDC expression. Phenotypically, induction of the ptac-flhDC fusion also corresponded to increased levels of both swimming and swarming motility.

Flagellar flhA, flhB and flhE genes, organized in an operon, cluster upstream from the inv locus in Yersinia enterocolitica

The inv gene of Yersinia enterocolitica codes for invasin, a member of the invasin/intimin-like protein family, which mediates the internalization of the bacterium into cultured epithelial cells. The putative inclusion of inv into a pathogenicity island was tested by investigating its flanking sequences. Indeed, the enteropathogenic Escherichia coli (EPEC) intimin, a member of the same family of proteins, is encoded by eaeA, a gene which belongs to a pathogenicity island. An ORF located upstream from inv was of particular interest since it appeared homologous both to the flagellar flhA gene and to sepA, an EPEC gene lying inside the same pathogenicity island as eaeA. A mutant in this ORF was non-motile and non-flagellated while its invasion phenotype remained unaffected. These data indicated that the ORF corresponded to the flhA gene of Y. enterocolitica. Subsequently, the flhB and flhE genes, located respectively upstream and downstream from flhA, were identified. The three flh genes appear to be transcribed from a single operon called flhB, according to the nomenclature used for Salmonella typhimurium. Intergenic sequence between flhE and inv includes a grey hole, with no recognizable function. Downstream from inv, we have detected the flagellar flgM operon as already reported. Finally, the incongruous localization of inv amidst the flagellar cluster is discussed; while transposition could explain this phenomenon, no trace of such an event was detected.

Penetration of M cells and destruction of Peyer's patches by Yersinia enterocolitica: an ultrastructural and histological study

Yersinia enterocolitica is enteropathogenic for man and rodents. Previous studies provided evidence that Y. enterocolitica invades the lymphoid follicles of the Peyer's patches (PP) of the small intestine. In this study Y. enterocolitica-induced tissue alterations of the follicle-associated epithelium (FAE) and the underlying PP tissue were analysed by scanning (SEM) and transmission electron microscopy (TEM) as well as by conventional histological examination. For this purpose, an experimental mouse infection model including orogastric infections as well as ileal loop experiments were used. A rapid and selective colonisation of the FAE after orogastric yersinia infection was observed by SEM. TEM studies confirmed that Y. enterocolitica adhered closely to the FAE including M cells and enterocytes. Histological studies and TEM revealed that Y. enterocolitica selectively invaded the PP via M cells but not via other cells of the FAE. One day after Y. enterocolitica infection the FAE was altered and small micro-abscesses comprising yersiniae expressing the major outer-membrane protein YadA were observed immediately beneath the FAE. Adjacent villi were dilated from lymphangiectasis and transmigrating polymorphonuclear leucocytes (PMNL) were found within the epithelium. At 5-7 days after infection the FAE and parts of PP were destroyed. Profound alterations of the cyto-architecture of the PP were due to the enormous recruitment of PMNL. By day 5 after infection, abscesses were found in the mesenteric lymph nodes. However, TEM studies revealed evidence that Y. enterocolitica may disseminate from the PP not only via the lymphatics but also by invasion of blood vessels. Taken together, the results of this study demonstrate that the FAE is the primary site of host-pathogen interaction in Y. enterocolitica infection and that this pathogen penetrates M cells and subsequently induces destruction of the PP.

Temperature-dependent regulation of Yersinia enterocolitica Class III flagellar genes

Temperature is a key environmental cue for Yersinia enterocolitica as well as for the two other closely related pathogens, Yersinia pestis and Yersinia pseudotuberculosis. Between the range of 30 degrees C and 37 degrees C, Y. enterocolitica phase-varies between motility and plasmid-encoded virulence gene expression. To determine how temperature regulates Y. enterocolitica motility, we have been dissecting the flagellar regulatory hierarchy to determine at which level motility is blocked by elevated temperature (37 degrees C). Here we report the cloning, DNA sequences, and regulation of the two main regulators of Class III flagellar genes, fliA (sigma F) and flgM (anti-sigma F), and a third gene, flgN, which we show is required for filament assembly. Identification of the Y. enterocolitica fliA and flgM genes was accomplished by functional complementation of both S. typhimurium and Y. enterocolitica mutations and by DNA sequence analysis. The Y. enterocolitica fliA gene, encoding the flagellar-specific sigma-factor, sigma F, maps immediately downstream of the three flagellin structural genes. The flgM and flgN genes, encoding anti-sigma F and a gene product required for filament assembly, respectively, map downstream of the invasin (inv) gene but are transcribed in the opposite (convergent) direction. By using Northern blot analyses we show that transcription of both fliA and flgM is immediately arrested when cells are exposed to 37 degrees C, coincident with the timing of virulence gene induction. Unlike S. typhimurium flgM mutants, Y. enterocolitica flgM mutants are fully virulent.

Interactions of Yersinia enterocolitica with polarized human intestinal Caco-2 cells

The in vitro interactions of Yersinia enterocolitica, Salmonella typhimurium and Escherichia coli with polarized human colonic carcinoma (Caco-2) cells are described. Invasion of a confluent Caco-2 cell monolayer by Yersinia and Salmonella took place within 4 h after contact, which was in marked contrast to E. coli which did not invade Caco-2 cells. Cytoplasmic extrusions developed on the apical membrane and indicated the site of entrance of bacteria into the Caco-2 cells. Intracellular Yersinia and Salmonella were surrounded by a vacuolar membrane. Single as well as multiple bacteria were enclosed within a single vacuole. At 6 h after contact some of the intracellular yersiniae were found free in the cytoplasm. Furthermore, morphological signs of degeneration of Caco-2 cells such as vacuolization and autophagy were observed. Caco-2 cells infected with Salmonella also showed degenerative changes but the salmonellae resided within membrane-bound vacuoles in contrast to Yersinia. These observations are in contrast to those described for the invasion of other cells lines (not derived from intestinal epithelium) by Yersinia and may reflect more closely the interactions between Yersinia and the intestinal epithelium during gastrointestinal infection.

Growth of food-borne pathogenic bacteria in oil-in-water emulsions: I--Methods for investigating the form of growth

Methods are presented for investigating the site and form of growth of bacteria in model oil-in-water emulsions and in dairy cream. Following growth of the bacteria, the continuous aqueous phase is gelled using agarose and the oil phase removed using a mixture of chloroform and methanol. Using this method, the authors have found that Listeria monocytogenes, Salmonella typhimurium and Yersinia enterocolitica grow in the form of colonies in concentrated oil-in-water emulsions. Colonies of L. monocytogenes and Y. enterocolitica also form in artificially-inoculated fresh and tinned dairy cream. If information about the precise site of growth is not required, the authors have discovered that intact colonies can be liberated from the model emulsions by dissolving away the oil phase with chloroform:methanol.

Thermoregulation in Yersinia enterocolitica is coincident with changes in DNA supercoiling

Yersinia enterocolitica is a facultative intracellular parasite, displaying the ability to grow saprophytically or invade and persist intracellularly in the mammalian reticuloendothelial system. The transition between such diverse environments requires the co-ordinated regulation of specific sets of genes on both the chromosome and virulence plasmid. Temperature has a profound pleiotropic effect on gene expression and phenotypically promotes alterations in cell morphology, outer-membrane protein synthesis, urease production, lipopolysaccharide synthesis, motility, and synthesis of genes involved in invasion of eukaryotic host cells. By examining thermoregulated flagella biosynthesis, we have determined that motility is repressed at 25 degrees C (permissive temperature) with subinhibitory concentrations of novobiocin. These conditions also induce virulence gene expression suggesting novobiocin addition simulates, at least partially, a high-temperature environment. Furthermore, temperature-shift experiments, using Y. enterocolitica containing pACYC184 as a reporter plasmid, indicate that thermo-induced alterations of DNA supercoiling coincide with temperature-induced phenotypic changes. A class of putative DNA gyrase mutant (novobiocin resistant) likewise demonstrates the 37 degrees C phenotype when cultured at 25 degrees C; it is non-motile, urease negative, calcium growth dependent, and positive for Yop expression. These results support a model implicating DNA topology as a contributing factor of Y. enterocolitica thermoregulation.

Deposition of bismuth by Yersinia enterocolitica

Yersinia enterocolitica 8081c cultures in exponential growth were incubated for 1 h in 0.1% microcrystalline bismuth subsalicylate (BSS) suspensions. Scanning electron microscopy (SEM) revealed microcrystals directly bound to BSS-treated bacteria. Energy dispersive spectroscopy (EDS) X-ray microanalysis of the attached microcrystals confirmed that the crystals were the microcrystalline BSS. X-ray spectra positive for bismuth were also obtained by SEM-EDS X-ray microanalysis of whole bacteria, suggesting metal incorporation into the bacteria in regions absent of bound microcrystals. Transmission electron microscopy of thin sections of embedded preparations of BSS-treated exponential-growth-phase bacteria showed electron-dense deposits in the periphery of the bacteria. Y. enterocolitica cultures that were in stationary phase at the time of incubation with microcrystalline BSS showed no evidence of the electron-dense deposits and EDS spectra were negative for bismuth. Bacteria incubated in the absence of microcrystalline BSS also lacked electron-dense deposits. Scanning transmission electron microscopy used in conjunction with EDS X-ray microanalysis to view and analyze semi-thick sections (250-300 nm) of embedded preparations of BSS-treated bacteria in exponential growth confirmed that the electron-dense deposits at the periphery of the bacteria are the sites of bismuth depositions.

IgG and IgA antibody responses against porins in Yersinia-triggered reactive arthritis

Using an enzyme immunoassay, the development and persistence of serum IgG and IgA class antibody responses against porins, a class of the major outer membrane proteins, were compared between patients who developed reactive arthritis and subjects who did not after Yersinia infection. A significant difference was seen between the two patient groups in the beginning of the disease: those with reactive arthritis had higher levels of IgG and IgA class antibodies against the porins. A similar difference in the IgA class antibodies was also seen at follow-up. This supports the hypothesis of persistence of the pathogen within the arthritic host.

Yersinia enterocolitica in the synovial membrane of patients with Yersinia-induced arthritis

Using a monospecific rabbit antibody against Yersinia enterocolitica outer membrane protein 1, we examined synovial biopsy specimens from 7 patients with Yersinia-induced arthritis. Yersinia were demonstrated in the synovial membrane by indirect immunofluorescence in 4 patients with Yersinia-induced arthritis, but not in 6 control patients with Salmonella-induced arthritis or with rheumatoid arthritis. These findings suggest the persistence of Yersinia in the joints of patients with Yersinia-induced arthritis.

Immunohistochemical and electron microscopic study of interaction of Yersinia enterocolitica serotype O8 with intestinal mucosa during experimental enteritis

The experimental infection of mice with Yersinia enterocolitica serotype O8 was investigated in a quantitative and histological study. The course of bacterial penetration and spreading was precisely determined by immunohistochemical staining. After oral administration, the bacteria passed the epithelial barrier of the ileum and spread into the lamina propria. By preference they entered Peyer's patches, which were about 1,000 times more heavily colonized than the surrounding epithelium of a comparable surface area. The bacteria proliferated in the follicles, from which they spread into the lamina propria of the villi. At either site most of the bacteria multiplied extracellularly, with only a small percentage observed to be present within the phagocytes. The bacteria did not appear to be able to pass the intact basement membrane; hence, the integrity of the basement membrane is likely to play a role in determining the route of entry and limit of spread of Y. enterocolitica infection.

The growth of potential food poisoning organisms on chicken and pork muscle surfaces

Muscle surfaces of pork were inoculated with a mixture of Yersinia enterocolitica and Staphylococcus aureus, and chicken muscle with Campylobacter jejuni or a mixture of Salmonella typhimurium and Staph. aureus. The surface growth at 20 degrees C was followed microscopically. Organisms grew as discrete colonies bound together by a glycocalyx which differed between bacterial species. On prolonged incubation colonies spread peripherally and tended to coalesce, while still retaining their colony structure. Staphylococcus aureus colonies were very small and remained so. The glycocalyx was considered critical in maintaining the dense populations of bacteria on the meat surfaces.

[Isolation and ultrastructure of Yersinia spheroplasts and protoplasts]

The conditions suitable for the cultivation of Yersinia and the inhibition of their cell-wall synthesis have been selected with the aim of obtaining spheroplasts and protoplasts of these microorganisms. Penicillin, streptomycin and lithium chloride have proved to be not very suitable for this purpose as they induce essential changes in the structure of the cytoplasmic membrane in altered Yersinia forms. The addition of 1% of glycine (for Y. pseudotuberculosis), 1-1.5% of methionine in combination with growth stimulators has made it possible to obtain Yersinia spheroplasts and protoplasts with the intact cytoplasmic membrane, thus permitting the isolation and purification of the cytoplasmic membrane fraction.

[Invasiveness and cytotoxicity as criteria in assessing Yersinia attenuation]

The electron microscopic study of cells HEp-2 and the complex microbiological and morphological study of tissues and organs of guinea pigs and mice infected with the isogenic pairs of Yersinia strains (Y. pseudotuberculosis I and Y. enterocolitica 09) differing in the presence of the calcium-dependence plasmid, as well as Y. pseudotuberculosis mutants resistant to rifampicin, nalidixic acid or crystal violet without this plasmid, have revealed that the invasiveness and cytotoxicity of the infective agents are not directly related to the presence of the above-mentioned plasmid in these bacteria. The use of the quantitative characteristics of virulence, such as penetration ability, intracellular multiplication, dissemination and the formation of degenerative changes, has made it possible to find out that the mutants of Y. pseudotuberculosis I, yielding the negative result in the keratoconjunctivitis test and resistant to the above-mentioned antimicrobial substances, can be arranged in the following order according to the degree of attenuation: rifr mutants--nalr mutants--kvlr mutants. In contrast to Y. pseudotuberculosis I, the loss of the calcium-dependence plasmid by Y. enterocolitica 09 is accompanied by an essential decrease in their invasive and cytotoxic properties, but this relationship is indirect and unstable. The proposed criteria intended for use in the evaluation of the degree of the manifestation of the invasive and cytotoxic properties of bacteria can be useful for the selection of optimally attenuated Yersinia strains showing promise as vaccine strains.

Factors contributing to the reduced invasiveness of chlorine-injured Yersinia enterocolitica

The invasion of epithelial cells in vitro and in vivo by chlorine-injured Yersinia enterocolitica was assessed by direct microscopic observations. These experiments showed that injury by chlorine inhibited invasiveness of virulent Y. enterocolitica. Two requirements appeared to be necessary for invasiveness: the organism must be viable and metabolically active, and the organism must have certain surface components to initiate engulfment. Inhibition of RNA synthesis by rifampin and protein synthesis by chloramphenicol, tetracycline, and spectinomycin inhibited the invasiveness but not the attachment of Y. enterocolitica to epithelial cells. Membrane preparations from untreated and antimicrobial-agent-treated Y. enterocolitica blocked the invasiveness of virulent Y. enterocolitica, whereas membranes from chlorinated cells were unable to block invasiveness. Chlorine did not change the hydrophobicity or surface charge of injured Y. enterocolitica. The results indicate that invasion was more than simple association of the bacterium with the epithelial cell and involved a specific trigger to stimulate engulfment.

Immunocytochemical localization of enterobacterial common antigen in Escherichia coli and Yersinia enterocolitica cells

Enterobacterial common antigen (ECA) was localized on Lowicryl K4M sections and on ultrathin cryosections by using either a mouse monoclonal antibody or an absorbed rabbit polyclonal immune serum with the corresponding gold-labeled secondary antibodies. Comparable results were obtained with both monoclonal antibody and polyclonal immune serum. Controls with two ECA-negative mutants revealed the ECA specificity of both labeling systems. On Lowicryl K4M sections, good labeling of the outer membrane and of membrane-associated areas in the cytoplasm was obtained. Unexpectedly, however, the ribosome-containing areas of the cytoplasm also showed significant labeling. On ultrathin cryosections, labeling of the cytoplasmic areas was much weaker, although the density of label in the outer membrane was comparable to that obtained with the Lowicryl K4M sections. With the techniques used, it cannot be completely excluded that the appearance of ECA in the cytoplasm is due to displacement of ECA-reactive sites during the preparation procedure.

Studies on the serology of flagellar antigens of Yersinia enterocolitica and related Yersinia species

A total of 1242 strains of Y. enterocolitica, 104 strains of Y. frederiksenii, 95 strains of Y. kristensenii and 85 strains of Y. intermedia were serotyped with antisera against 56 O antigens and 19 H antigens according to the extended antigenic scheme of Wauters, and with additional antisera against 4 somatic and 19 flagellar antigens not previously described. H antigens of Y. frederiksenii, Y. kristensenii, and Y. intermedia turned out to be rather homogeneous without distinct subfactors. In these species the scope of identified serovars was narrow. Flagellar antigens of Y. enterocolitica were mostly composed of several subfactors, leading to a total of 117 serovars identified in the species. A number of cross-reactions between Yersinia H antigens were observed which could be avoided by absorption without significant lowering of the titre. Flagellar antigens of Yersinia were monophasic, and species specific. The antigens remained stable after storage in agar stabs and repeated subcultures. The epidemiological value of serotyping is demonstrated by strains from three different sources. It is suggested serotyping of Yersinia strains should be performed in three steps: O typing of the prevailing enteropathogenic Y. enterocolitica serogroups in the medical routine laboratory; O and H typing of Y. enterocolitica by National Reference Centres applying a typing scheme reduced to this species; and O and H typing of Y. enterocolitica, Y. frederiksenii, Y. kristensenii and Y. intermedia by specialized International Centres using an extended typing scheme. The need for international standards comparable to those established for Salmonella is emphasized.

[Phenomenon of pili formation in Yersinia enterocolitica]

In Y. enterocolitica strain, serovar 0:10, the capacity for the formation of pili inducing the mannose-resistant hemagglutination (MRHA) of formolated sheep red blood cells was due to the presence of plasmid pYE10. MRHA-inducing pili differed serologically from Y. pestis and Y. tuberculosis adhesion pili. Plasmid pYE10 was immobilized for transfer to cells of Escherichia coli strain HB101 (rec A) by means of pRP 4. The expression of MRHA-inducing pili in the new host the rec A-independent character of the synthesis. Y. enterocolitica cells containing pYE10 agglutinated in tissue-culture media with 10% of serum added at 37 degrees C.

Temperature-inducible surface fibrillae associated with the virulence plasmid of Yersinia enterocolitica and Yersinia pseudotuberculosis

When cultivated at 37 degrees C in static broth, human clinical isolates of Yersinia enterocolitica (serogroups O:3, O:8, and O:9) and Yersinia pseudotuberculosis (serogroup O:III) produced numerous nonflagellar surface appendages, which appeared as a lawn of fine fibrillae, each having a diameter of 1.5 to 2.0 nm and a length of 50 to 70 nm. Cultivation at 22 degrees C resulted in complete disappearance of the fibrillae. The phenotypic expression of these appendages was correlated with the presence of the 40- to 48-megadalton virulence plasmid and was strongly affected by the growth medium. Evidence is presented which suggests that these plasmid-mediated, temperature-inducible surface fibrillae are responsible for autoagglutination and are related to production of one prominent, Sarkosyl-insoluble polypeptide of ca. 180 kilodaltons in the bacterial outer membrane.

Association of fibril structure formation with cell surface properties of Yersinia enterocolitica

Electron microscopic examination of virulence plasmid-bearing cells of Yersinia enterocolitica revealed the formation of a fibril structure when grown at 37 degrees C but not at 22 degrees C. Plasmidless cells did not exhibit any surface matrix. The formation of this surface component was associated with increased cell surface charge and hydrophobicity, formation of long chains of cells, and autoagglutination. This structure is distinct from the rigid appendages (fimbriae) which are elaborated by certain Yersinia strains.

Lack of correlation between the presence of plasmids and fimbriae in Yersinia enterocolitica and Yersinia pseudotuberculosis

Thirty-nine strains of Yersinia enterocolitica and 10 strains of Yersinia pseudotuberculosis were studied for the presence of fimbriae, plasmids and two plasmid associated phenotypic expressions, autoagglutination and Ca2+ dependent growth at 37 degrees C. All of the strains studied became fimbriated, which was confirmed by electron microscopy and haemagglutination tests. Fimbriation was not correlated with the presence or absence of plasmids.

Autoaggregating Yersinia enterocolitica express surface fimbriae with high surface hydrophobicity

For 13 strains of Yersinia enterocolitica, there was a good correlation between the production of the broad-spectrum, mannose-resistant Yersinia haemagglutinin (MR/Y HA), the presence of fimbriae and high surface hydrophobicity. Each of these characters was expressed in cultures grown at low (less than 32 degrees C) but not at high (Greater than 35 degrees C) temperatures.

Invasion of Burkitt's lymphoma cell lines by Yersinia enterocolitica

We attempted to determine whether or not Yersinia enterocolitica could invade two cell lines derived from Burkitt's lymphoma (BL), P3HR-1, and Raji cells, and if the expression of Epstein-Barr virus (EBV) genome could be activated by the invasion of the organisms into the cells. The invasiveness of Y. enterocolitica into BL cells was examined morphologically, using transmission and scanning electron microscopy, and the induction of EBV antigens in the BL cells was examined by indirect immunofluorescence. Y. enterocolitica was clearly observed to invade P3HR-1 and Raji cells within 2 hr incubation at 37 degrees, after bacterial challenge. However, the invaded BL cells did not show significant induction of EBV early antigen after cultivation for 72 hr at 37 degrees. Although the present experiment failed to yield positive findings pertaining to the activation of EBV genome, our experimental system per se may still be a useful model when attempting to assess the effects of invading bacteria on the viral genome persistently carried in the host cells.