Evidence for two evolutionary lineages of highly pathogenic Yersinia species

Multiplex PCR method for differentiating highly pathogenic Yersinia enterocolitica and low pathogenic Yersinia enterocolitica, and Yersinia pseudotuberculosis

A multiplex PCR method for rapid and sensitive diagnosis, differentiating three pathogenic Yersinia groups such as the highly pathogenic Y. enterocolitica, including serotype O8, low pathogenic Y. enterocolitica, and Y. pseudotuberculosis, was developed. Four primer pairs were chosen to detect the genes fyuA, ail, inv, and virF, responsible for the virulence in pathogenic Yersinia species. Under the multiplex PCR conditions, the unique band patterns for the highly pathogenic Y. enterocolitica, low pathogenic Y. enterocolitica, and Y. pseudotuberculosis were generated from Yersinia strains. The detection limit of this method was 10¹-10³ CFU per reaction tube. This multiplex PCR method could detect highly pathogenic Y. enterocolitica O8 from the wild rodent fecal samples that were culture-positive. Therefore, the new multiplex PCR method developed in this study is a useful tool for rapid and sensitive diagnosis, distinguishing three pathogenic Yersinia groups.

Using a bacteriocin structure to engineer a phage lysin that targets Yersinia pestis

Purified phage lysins present an alternative to traditional antibiotics and work by hydrolysing peptidoglycan. Phage lysins have been developed against Gram-positive pathogens such as Bacillus anthracis and Streptococcus pneumoniae, where the peptidoglycan layer is exposed on the cell surface. Addition of the lysin to a bacterial culture results in rapid death of the organism. Gram-negative bacteria are resistant to phage lysins because they contain an outer membrane that protects the peptidoglycan from degradation. We solved crystal structures of a Yersinia pestis outer-membrane protein and the bacteriocin that targets it, which informed engineering of a bacterial-phage hybrid lysin that can be transported across the outer membrane to kill specific Gram-negative bacteria. This work provides a template for engineering phage lysins against a wide variety of bacterial pathogens.

Structure and uptake mechanism of bacteriocins targeting peptidoglycan renewal

Bacteriocins are narrow-spectrum protein antibiotics released to kill related bacteria of the same niche. Uptake of bacteriocins depends critically on the presence of an uptake receptor in the outer membrane, a translocation pore and an energy-dependent activating system of the inner membrane. Most bacteriocins act on the inner membrane as pore-forming toxins or they target cytoplasmic DNA/RNA and ribosomal synthesis respectively. Only two bacteriocins are known to become activated in the periplasmic space and to inhibit the renewal process of the peptidoglycan structure. In Escherichia coli, the Cma (colicin M) phosphatase is activated in the periplasmic space by the FkpA chaperone and subsequently degrades the C55-PP precursor unit of the peptidoglycan. Pst (pesticin) from Yersinia pestis carries a lysozyme homology domain to degrade peptidoglycan. Import of Pst is only achieved if the N-terminal translocation domain can span the outer membrane and if extensive unfolding of the protein during membrane passage is permitted. There is considerable plasticity in the import pathway since a chimaera comprising the activity domain replaced by T4 lysozyme is also translocated and active in killing those bacteria carrying the FyuA receptor.

Pathogenesis of Y. enterocolitica and Y. pseudotuberculosis in Human Yersiniosis

Yersiniosis is a food-borne illness that has become more prevalent in recent years due to human transmission via the fecal-oral route and prevalence in farm animals. Yersiniosis is primarily caused by Yersinia enterocolitica and less frequently by Yersinia pseudotuberculosis. Infection is usually characterized by a self-limiting acute infection beginning in the intestine and spreading to the mesenteric lymph nodes. However, more serious infections and chronic conditions can also occur, particularly in immunocompromised individuals. Y. enterocolitica and Y. pseudotuberculosis are both heterogeneous organisms that vary considerably in their degrees of pathogenicity, although some generalizations can be ascribed to pathogenic variants. Adhesion molecules and a type III secretion system are critical for the establishment and progression of infection. Additionally, host innate and adaptive immune responses are both required for yersiniae clearance. Despite the ubiquity of enteric Yersinia species and their association as important causes of food poisoning world-wide, few national enteric pathogen surveillance programs include the yersiniae as notifiable pathogens. Moreover, no standard exists whereby identification and reporting systems can be effectively compared and global trends developed. This review discusses yersinial virulence factors, mechanisms of infection, and host responses in addition to the current state of surveillance, detection, and prevention of yersiniosis.

Minimization of the Legionella pneumophila genome reveals chromosomal regions involved in host range expansion

Legionella pneumophila is a bacterial pathogen of amoebae and humans. Intracellular growth requires a type IVB secretion system that translocates at least 200 different proteins into host cells. To distinguish between proteins necessary for growth in culture and those specifically required for intracellular replication, a screen was performed to identify genes necessary for optimal growth in nutrient-rich medium. Mapping of these genes revealed that the L. pneumophila chromosome has a modular architecture consisting of several large genomic islands that are dispensable for growth in bacteriological culture. Strains lacking six of these regions, and thus 18.5% of the genome, were viable but required secondary point mutations for optimal growth. The simultaneous deletion of five of these genomic loci had no adverse effect on growth of the bacterium in nutrient-rich media. Remarkably, this minimal genome strain, which lacked 31% of the known substrates of the type IVB system, caused only marginal defects in intracellular growth within mouse macrophages. In contrast, deletion of single regions reduced growth within amoebae. The importance of individual islands, however, differed among amoebal species. The host-specific requirements of these genomic islands support a model in which the acquisition of foreign DNA has broadened the L. pneumophila host range.

Evaluation of Psn, HmuR and a modified LcrV protein delivered to mice by live attenuated Salmonella as a vaccine against bubonic and pneumonic Yersinia pestis challenge

We evaluated the ability of Yersinia pestis antigens HmuR, Psn and modified forms of LcrV delivered by live attenuated Salmonella strains to stimulate a protective immune response against subcutaneous or intranasal challenge with Y. pestis CO92. LcrV196 is a previously described truncated protein that includes aa 131-326 of LcrV and LcrV5214 has been modified to replace five key amino acids required for interaction with the TLR2 receptor. Psn is the outer membrane receptor for the siderophore, yersiniabactin, and the bacteriocin, pesticin. Mice immunized with Salmonella synthesizing Psn, LcrV196 or LcrV5214 developed serum IgG responses to the respective Yersinia antigen and were protected against pneumonic challenge with Y. pestis. Immunization with Salmonella synthesizing Psn or LcrV196 was sufficient to afford nearly full protection against bubonic challenge, while immunization with the strain synthesizing LcrV5214 was not protective. Immunization with Salmonella synthesizing HmuR, an outer membrane protein involved in heme acquisition in Y. pestis, was poorly immunogenic and did not elicit a protective response against either challenge route. These findings indicate that both Psn and LcrV196 delivered by Salmonella provide protection against both bubonic and pneumonic plague.

High prevalence iron receptor genes of avian pathogenicEscherichia coli

Avian pathogenic Escherichia coli are known to cause significant losses in the poultry industry worldwide. Although prophylactic measures based on vaccination are advisable, until now no full heterologous protection against colibacillosis has been achieved. Since iron is an essential nutrient to these bacteria, the aim of this study was to investigate the prevalence of 12 outer-membrane iron receptor genes in 239 pathogenic strains isolated from clinical cases of colibacillosis in chickens. Five multiplex polymerase chain reactions were developed as a tool for efficient screening. Among the 239 avian E. coli isolates, 100% were positive for fhuE and fepA, 96.2% for fiu, 92.9% for cir, 92.5% for iroN, 87.4% for iutA, 63.2% for fecA, 53.1% for fyuA, 46.9% for fhuA, 45.6% for ireA, 41.8% for chuA and 4.6% for iha.

The Yersinia high pathogenicity island is present in Salmonella enterica Subspecies I isolated from turkeys

The Yersinia high pathogenicity island (HPI) encodes a yersiniabactin-mediated iron acquisition system present in highly pathogenic strains of Yersinia and several members of the Enterobacteriaceae. In this study, 420 salmonellae representing multiple serovars recovered from diverse hosts were investigated for the presence of the HPI. The isolates were initially screened via PCR with primers specific for irp2, a conserved gene involved in yersiniabactin biosynthesis. Seventeen isolates produced an amplicon of the expected size. These isolates were further investigated using PCR primers spanning the HPI core region and all isolates produced identical results. HPI-positive isolates were recovered only from turkeys (feces) or production samples (feed and water) from a single flock and identified as Salmonella enterica serovar Senftenberg, a Subspecies I. Southern hybridization and genome sequencing of isolate 3-70-31 revealed that the island is plasmid-borne and is 92-97% identical to the core region in Yersinia species. To our knowledge, this is the first report of the HPI in Salmonella Subspecies I. This study illustrates the presence of the HPI in a new species, and the continued importance of poultry as a reservoir and vehicle for the dissemination of zoonotic pathogens.

Amplification of sense-stranded prokaryotic RNA

Microarray expression analysis has proven to be a valuable methodology. In eukaryotic systems where RNA is limiting, established protocols for amplification of mRNA, which rely on the poly(A) tails, are well established. In contrast, the difficulty in amplifying prokaryotic mRNA has limited the application of microarrays to microbiology. Here we present a method for the Linear Amplification of Prokaryotic Transcripts (LAPT) that is efficient and unbiased. The overhang tailing activity of Moloney murine leukemia virus reverse transcriptase is used to add the T7 promoter to cDNAs during reverse transcription. The promoter addition is uncoupled from the initial priming event allowing the promoter to be attached to the 5' end of the RNA transcript. This enables the amplification of sense-stranded RNA that is representative of the complexity and distribution of the original transcript pool. In microarray assays amplified prokaryotic RNA (10 ng total RNA starting material) showed good Spearman correlations to an unamplified control sample. Using genome-directed primers to bias addition of a T7-promoter to bacterial transcripts allowed amplification of prokaryotic transcripts in the presence of mammalian RNA (at a eukaryotic/prokaryotic RNA ratio of 500 to 1). This technology should facilitate the study of prokaryotic transcriptomes in situations, such as in vivo studies or mixed microbial populations, where the prokaryotic RNA amount is limited and/or the nontarget/target RNA ratios is high.

Yersiniabactin production by Pseudomonas syringae and Escherichia coli, and description of a second yersiniabactin locus evolutionary group

The siderophore and virulence factor yersiniabactin is produced by Pseudomonas syringae. Yersiniabactin was originally detected by high-pressure liquid chromatography (HPLC); commonly used PCR tests proved ineffective. Yersiniabactin production in P. syringae correlated with the possession of irp1 located in a predicted yersiniabactin locus. Three similarly divergent yersiniabactin locus groups were determined: the Yersinia pestis group, the P. syringae group, and the Photorhabdus luminescens group; yersiniabactin locus organization is similar in P. syringae and P. luminescens. In P. syringae pv. tomato DC3000, the locus has a high GC content (63.4% compared with 58.4% for the chromosome and 60.1% and 60.7% for adjacent regions) but it lacks high-pathogenicity-island features, such as the insertion in a tRNA locus, the integrase, and insertion sequence elements. In P. syringae pv. tomato DC3000 and pv. phaseolicola 1448A, the locus lies between homologues of Psyr_2284 and Psyr_2285 of P. syringae pv. syringae B728a, which lacks the locus. Among tested pseudomonads, a PCR test specific to two yersiniabactin locus groups detected a locus in genospecies 3, 7, and 8 of P. syringae, and DNA hybridization within P. syringae also detected a locus in the pathovars phaseolicola and glycinea. The PCR and HPLC methods enabled analysis of nonpathogenic Escherichia coli. HPLC-proven yersiniabactin-producing E. coli lacked modifications found in irp1 and irp2 in the human pathogen CFT073, and it is not clear whether CFT073 produces yersiniabactin. The study provides clues about the evolution and dispersion of yersiniabactin genes. It describes methods to detect and study yersiniabactin producers, even where genes have evolved.

Independent acquisition of site-specific recombination factors by asn tRNA gene-targeting genomic islands

Two genomic islands, namely the high-pathogenicity island (HPI) and Ecoc54N target the same asn tRNA genes to integrate into the bacterial chromosome. The HPI encodes the siderophore yersiniabactin in the highly pathogenic Yersinia group (Yersinia pestis, Yersinia pseudotuberculosis and Yersinia enterocolitica 1B) whilst the Ecoc54N island possibly encodes a polyketide synthase with an unknown function in the uropathogenic Escherichia coli CFT073 strain. HPI encodes the recombinase that promotes site-specific recombination (both integrative and excisive) with its corresponding attachment targets. A recombinase orthologue is also present in Ecoc54N. In addition, the HPI(Yps) of the Y. pestis/Y. pseudotuberculosis evolutionary lineage encodes the excisionase (recombination directionality factor, Xis(HPI)) that facilitates excision of the island. However, no sequence resembling the excisionase gene could be found in Ecoc54N. The rate of the HPI(Yps) excision estimated by real-time PCR was 10(-6) in Y. pseudotuberculosis. The presence of the excisionase increased the efficiency of the excisive recombination only eight fold. However, the introduction of the xis(HPI) in E. coli CFT073 did not influence the excision of Ecoc54N. The Xis(HPI) is encoded by the variable AT-rich part of the HPI(Yps) and substantially differs from its cognate recombinase in A+T content and codon usage. Also the Xis(HPI)-protected region, defined in the HPI attachment site, has suffered several nucleotide substitutions in Ecoc54N that could influence interaction with the excisionase. We propose that the pathogenicity islands (PAIs) targeting asn tRNA genes (PAIs(asn tRNA)) might have acquired recombinase and excisionase (HPI) genes independently and sequentially.

A hypervariable N-terminal region of Yersinia LcrV determines Toll-like receptor 2-mediated IL-10 induction and mouse virulence

The virulence antigen LcrV of Yersinia enterocolitica O:8 induces IL-10 in macrophages via Toll-like receptor 2 (TLR2). The TLR2-active region of LcrV is localized within its N-terminal amino acids (aa) 31-57. Sequencing of codons 25-92 of the lcrV gene from 59 strains of the three pathogenic Yersinia species revealed a hypervariable hotspot within aa 40-61. According to these sequence differences, seven LcrV groups were identified, with Y. pestis and Y. pseudotuberculosis represented in group I and the other six distributed within Y. enterocolitica. By testing LcrV sequence-derived synthetic oligopeptides of all seven LcrV groups in CD14/TLR2-transfected human embryonic kidney 293 cells, we found the highest TLR2 activity with a peptide derived from group IV comprising exclusively Y. enterocolitica O:8 strains. These findings were verified in murine peritoneal macrophages by using recombinant LcrV truncates representing aa 1-130 from different Yersinia spp. By systematically replacing charged aa residues by glutamine in synthetic oligopeptides, we show that the K42Q substitution leads to abrogation of TLR2 activity in both in vitro cell systems. This K42Q substitution was introduced in the lcrV gene from Y. enterocolitica O:8 WA-C(pYV), resulting in WA-C(pYVLcrV(K42Q)), which turned out to be less virulent for C57BL/6 mice than the parental strain. This difference in virulence was not observed in TLR2(-/-) or IL-10(-/-) mice, proving that LcrV contributes to virulence by TLR2-mediated IL-10 induction. LcrV is a defined bacterial virulence factor shown to target the TLR system for evasion of the host's immune response.

Horizontal transfer of Yersinia high-pathogenicity island by the conjugative RP4 attB target-presenting shuttle plasmid

The high-pathogenicity island (HPI) encodes a highly efficient yersiniabactin system of iron acquisition responsible for mouse lethality in Yersinia. Although the HPI is widely disseminated among Enterobacteriaceae it lacks functions necessary for its replication and transmission. Therefore, the mechanism of its horizontal transfer and circulation is completely obscure. On the other hand, the HPI is a genetically active island in the bacterial cell. It encodes a functional recombinase and is able to transpose to new targets on the chromosome. Here we report on a possible mechanism of the HPI dissemination based on site-specific recombination of the excised HPI with the attB-presenting (asn tRNA gene) RP4 promiscuous conjugative shuttle plasmid. The resulting cointegrate can be transferred by conjugation to a new host, where it dissociates, and the released HPI integrates into any unoccupied asn tRNA gene target in the genome. This mechanism has been proven both with the 'mini' island carrying only the attP recognition site and genes coding for recombination enzymes and with the complete HPI labelled with an antibiotic resistance marker. After acquisition of the mobilized complete form of the HPI, the ability of the HPI-cured Yersinia enterocolitica WA-TH(-) strain to produce yersiniabactin has been restored. Such 'trapping' of pathogenicity islands and subsequent shuffling to new hosts by a conjugative replicon carrying a suitable attB site could be applied to other functional integrative elements and explain wide dissemination of PAIs.

Horizontal transfer of the high-pathogenicity island of Yersinia pseudotuberculosis

The horizontal transfer of genetic elements plays a major role in bacterial evolution. The high-pathogenicity island (HPI), which codes for an iron uptake system, is present and highly conserved in various Enterobacteriaceae, suggesting its recent acquisition by lateral gene transfer. The aim of this work was to determine whether the HPI has kept its ability to be transmitted horizontally. We demonstrate here that the HPI is indeed transferable from a donor to a recipient Yersinia pseudotuberculosis strain. This transfer was observable only when the donor and recipient bacteria were cocultured at low temperatures in a liquid medium. When optimized conditions were used (bacteria actively growing in an iron-deprived medium at 4 degrees C), the frequency of HPI transfer reached approximately 10(-8). The island was transferable to various serotype I strains of Y. pseudotuberculosis and to Yersinia pestis, but not to Y. pseudotuberculosis strains of serotypes II and IV or to Yersinia enterocolitica. Upon transfer, the HPI was inserted almost systematically into the asn3 tRNA locus. Acquisition of the HPI resulted in the loss of the resident island, suggesting an incompatibility between two copies of the HPI within the same strain. Transfer of the island did not require a functional HPI-borne insertion-excision machinery and was RecA dependent in the recipient but not the donor strain, suggesting that integration of the island into the recipient chromosome occurs via a mechanism of homologous recombination. This lateral transfer also involved the HPI-adjacent sequences, leading to the mobilization of a chromosomal region at least 46 kb in size.

Virulence-associated traits in avian Escherichia coli: Comparison between isolates from colibacillosis-affected and clinically healthy layer flocks

Colibacillosis appears to be of increasing importance in layer flocks. The aim of this study was to determine characteristics of avian pathogenic Escherichia coli associated with the occurrence of colibacillosis outbreaks at flock level. Forty E. coli strains originating from layers from healthy flocks ('control isolates'), consisting of 25 caecal and 15 extra-intestinal isolates, were compared with 40 strains isolated from layers originating from colibacillosis-affected flocks ('outbreak isolates'), consisting of 20 caecal and 20 extra-intestinal isolates. The examined characteristics were adhesins, invasivity in T84 cell culture, serum resistance, iron uptake, colicin production, and toxinogenicity. The following traits were significantly more often detected in the outbreak isolates than in the control isolates: tsh, iss, iucA, iutA, irp2, fyuA, iroC, cvaC, colicin and colicin V production. A comparison of the extra-intestinal outbreak isolates and the caecal control isolates yielded the same results as when the caecal isolates, extra-intestinal isolates and total number of isolates of the outbreak and the control group were compared. When comparing the caecal and extra-intestinal isolates within the control and within the outbreak group, no significant differences were detected. The O78 and O2 groups showed significant differences with other O-types and NT strains for prevalence of most of the same characteristics. The combination of type 1 fimbriae, tsh, serum resistance, iss, traT, iucA, fyuA, iroC and colicin or colicin V production was significantly more often present in extra-intestinal outbreak isolates than in extra-intestinal control isolates. Only the combination of serum resistance, fyuA and colicin production was present in all outbreak isolates, with a significantly lower prevalence in the control isolates. None of the characteristics or combinations examined were exclusive to the outbreak isolates.

The Yersinia high-pathogenicity island (HPI): evolutionary and functional aspects

The high-pathogenicity island (HPI) is a genomic island essential for the mouse-virulence phenotype in Yersinia and indispensable for pathogenicity of Yersinia and certain pathotypes of Escherichia coli. In contrast to most genomic islands, the HPI is a functional island widely disseminated among members of the family of Enterobacteriaceae. The HPI-encoded phage P4-like integrase together with excisionase and recombination sites make up the genetic mobility module of the island, while the siderophore yersiniabactin biosynthesis and uptake system comprises its functional part with respect to fitness and pathogenicity. The HPI-integrase promotes integration of the island into attB sites represented by three to four asn tDNAs in Yersinia pestis and E. coli. An additional enzyme, excisionase, is essential for efficient excision of the HPI from the initial site of integration. Furthermore a unique type of HPI has been characterized in the E. coli strain ECOR31 carrying a functional conjugative mating pair formation (Mpf) and a DNA-processing system, both of which are characteristic of integrative and conjugative elements (ICE). A model of conjugative transfer for the dissemination of HPIs is proposed in which the excised HPI is mobilized to a new recipient either trapped by a transmissive asn tDNA-carrying plasmid or autonomously as an ICE named ICEEcl.

Experimental kinetics of infection induced by Yersinia pseudotuberculosis isolated from stock animals

The course of in vivo infection of five isolates of Yersinia pseudotuberculosis was followed for three weeks in Swiss mice. The strains were isolated from diarrheic and normal feces and mesenteric lymph nodes of healthy and sick stock animals. Four strains of serogroup O:3 and one of serogroup O:1a, with and without the virulence plasmid, were inoculated intragastrically and intravenously in the mice. Groups of five animals were sacrificed at 6 h and 3, 6, 10, 15, and 21 days after inoculation, and organs and tissues were checked for possible macroscopic alterations. Development of infection was monitored at these times by performing viable bacterial counts in homogenates of selected tissues. The animals were checked daily for clinical alterations. The results of the study showed that strains with the virulence plasmid infected organs and tissues at various times and at varying intensity by both routes of infection, the strain of type O:1a being the most invasive. Moreover, clinical and pathological alterations occurred only in animals inoculated with bacteria carrying the virulence plasmid, regardless of the route of infection.

Excision of the high-pathogenicity island of Yersinia pseudotuberculosis requires the combined actions of its cognate integrase and Hef, a new recombination directionality factor

The Yersinia high-pathogenicity island (HPI) encodes the siderophore yersiniabactin-mediated iron uptake system. The HPI of Yersinia pseudotuberculosis I has previously been shown to be able to excise precisely from the bacterial chromosome by recombination between the attB-R and attB-L sites flanking the island. However, the nature of the Y. pseudotuberculosis HPI excision machinery remained unknown. We show here that, upon excision, the HPI forms an episomal circular molecule. The island thus has the ability to excise from the chromosome, circularize and reintegrate itself, either in the same location or in another asn tRNA copy. We also demonstrate that the HPI-encoded bacteriophage P4-like integrase (Int) plays a critical role in HPI excision and that, like phage integrases, it acts as a site-specific recombinase that catalyses both excision and integration reactions. However, Int alone cannot efficiently promote recombination between the attB-R and attB-L sites, and we demonstrate that a newly identified HPI-borne factor, designated Hef (for HPI excision factor) is also required for this activity. Hef belongs to a family of recombination directionality factors. Like the other members of this family, Hef probably plays an architectural rather than a catalytic role and promotes HPI excision from the chromosome by driving the function of Int towards an excisionase activity. The fact that the HPI, and probably several other pathogenicity islands, carry a machinery of integration/excision highly similar to those of bacteriophages argues for a phage-mediated acquisition and transfer of these elements.

The osmotic regulator OmpR is involved in the response of Yersinia enterocolitica O:9 to environmental stresses and survival within macrophages

Various environmental signals control the expression of the virulence factors in pathogenic Yersinia enterocolitica strains. The role of the osmotic regulator OmpR protein in controlling the production of Yop proteins, virulence determinants in Y. enterocolitica O:9 (European type) has been studied. An ompR deletion mutant was constructed via allelic exchange with an ompR gene of Y. enterocolitica mutagenized in vitro by a reverse genetic polymerase chain reaction (PCR)-based strategy. The ompR mutant showed a reduced ability to survive under conditions of various environmental stresses in vitro. In particular, low pH stress resulted in increased cell mortality levels. Under conditions of high osmolarity, the wild strain's Yop protein production was reduced, whereas protein levels from the mutant strain remained constant regardless of osmolarity variance. In J774A.1 macrophage cell culture survival of the ompR mutant was decidedly lower than that of the wild-type strain, suggesting that the OmpR protein may play a significant role in protecting cells against intracellular conditions associated with macrophage phagocytosis.

The Yersinia HPI is present in Serratia liquefaciens isolated from meat

AIMS

The aim of the study was to screen the Enterobacteriaceae flora of meat for the presence of bacteria harbouring the Yersinia high-pathogenicity island (HPI).

METHODS AND RESULTS

Bacteria from 29 meat and 29 liver samples were isolated on violet-red bile glucose agar. A total of 197 isolates were screened for the presence of the irp2 gene, encoded within the HPI, by PCR. One isolate that was positive for irp2 gene was also positive for the fyuA, irp1, ybtP/ybtQ, ybtX/ybtS and int/asn tRNA genes by PCR. The presence of fyuA, irp1 and irp2 genes was confirmed by Southern hybridization.

CONCLUSIONS

The isolate was identified as Serratia liquefaciens by sequencing of the 16S rRNA gene and by ribotyping.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first report of a Serratia harbouring the Yersinia HPI. Serratia is a frequently occurring Enterobacteriaceae genus in chill-stored meat.

Transfer of the core region genes of the Yersinia enterocolitica WA-C serotype O:8 high-pathogenicity island to Y. enterocolitica MRS40, a strain with low levels of pathogenicity, confers a yersiniabactin biosynthesis phenotype and enhanced mouse virulence

The high-pathogenicity island (HPI) of yersiniae encodes an iron uptake system represented by its siderophore yersiniabactin (Ybt). The HPI is present in yersiniae with high levels of pathogenicity--i.e., Yersinia pestis, Y. pseudotuberculosis, and Y. enterocolitica biogroup (BG) 1B--but absent in Y. enterocolitica strains with low (BG 2 to 5) and no (BG 1A) levels of pathogenicity and has been shown to be an important virulence factor. Comparison of the HPI in Y. enterocolitica (Yen-HPI) and that in Y. pestis and Y. pseudotuberculosis revealed that, in contrast to genes of the variable region, genes of the core region (genes irp9 to fyuA) are highly homologous. In the present work the Yen-HPI core genes were rescued from the chromosome of Y. enterocolitica WA-C (BG 1B, serotype O:8) using the FRT-FLP recombinase system. Transfer of the resulting plasmid pCP1 into the siderophore-deficient strain Y. enterocolitica NF-O (BG 1A) led to no halo on siderophore indicator chrome azurol S (CAS) agar. Transfer of pCP1 into the Y. enterocolitica strain MRS40 (serotype O:9, BG 2; phenotype, CAS negative) led to a CAS halo larger than that of parental strain WA-C, indicating high Ybt production. pCP1 was highly unstable in iron-deficient medium, and no enhanced mouse virulence conferred by MRS40 carrying pCP1 could be detected. To overcome the problem of instability, pCP1 was integrated into the chromosome of MRS40, leading to the formation of a CAS halo comparable to that seen with WA-C and correspondingly to increased mouse virulence. Thus, the core genes of Yen-HPI are sufficient to confer a positive CAS phenotype and mouse virulence to Y. enterocolitica MRS40, BG 2, but are insufficient to confer this phenotype to Y. enterocolitica NF-O, BG 1A.

Geographical heterogeneity between Far Eastern and Western countries in prevalence of the virulence plasmid, the superantigen Yersinia pseudotuberculosis-derived mitogen, and the high-pathogenicity island among Yersinia pseudotuberculosis strains

Yersinia pseudotuberculosis produces novel superantigenic toxins designated YPMa (Y. pseudotuberculosis-derived mitogen), YPMb, and YPMc and has a pathogenicity island termed HPI (high-pathogenicity island) and R-HPI (the right-hand part of the HPI with truncation in its left-hand part) on the chromosome. Analysis of the distribution of these virulence factors allowed for differentiation of species Y. pseudotuberculosis into six subgroups, thus reflecting the geographical spread of two main clones: the YPMa(+) HPI(-) Far Eastern systemic pathogenic type belonging to serotypes O1b, -2a, -2b, -2c, -3, -4a, -4b, -5a, -5b, -6, -10, and UT (untypeable) and the YPMs(-) HPI(+) European gastroenteric pathogenic type belonging to serotypes O1a and -1b. The YPMa(+) HPI(+) pathogenic type belonging to serotypes O1b, -3, -5a, -5b, and UT and the YPMb(+) HPI(-) nonpathogenic type belonging to non-melibiose-fermenting serotypes O1b, -5a, -5b, -6, -7, -9, -10, -11, and -12 were prevalent in the Far East. The YPMc(+) R-HPI(+) European low-pathogenicity type belonging to non-melibiose-fermenting serotype O3 and the YPMs(-) HPI(-) pathogenic type belonging to 15 serotypes were found to be prevalent all over the world. This new information is useful for a better understanding of the evolution and spread of Y. pseudotuberculosis.

The Yersinia high-pathogenicity island: an iron-uptake island

Highly pathogenic Yersinia carry a pathogenicity island termed high-pathogenicity island (HPI). The Yersinia HPI comprises genes involved in the synthesis of the siderophore yersiniabactin and can thus be regarded as an iron-uptake island. A unique characteristic of the HPI is its wide distribution among different enterobacteria such as Escherichia coli, Klebsiella, Citrobacter and Salmonella. Other types of iron-uptake systems are also carried by different pathogenicity islands in enterobacteria.

Functional analysis of yersiniabactin transport genes of Yersinia enterocolitica

Yersinia enterocolitica O:8, biogroup (BG) IB, strain WA-C carries a high-pathogenicity island (HPI) including iron-repressible genes (irp1-9, fyuA) for biosynthesis and uptake of the siderophore yersiniabactin (Ybt). The authors report the functional analysis of irp6,7,8, which show 98-99% similarity to the corresponding genes ybtP,Q,X on the HPI of Yersinia pestis. It was demonstrated that irp6,7 are involved in ferric (Fe)-Ybt utilization and mouse virulence of Y. enterocolitica, thus confirming corresponding results for Y. pestis. Additionally it was shown that inactivation of the ampG-like gene irp8 did not affect either Fe-Ybt utilization or mouse virulence. To determine whether irp6, irp7 and fyuA (encoding the outer-membrane Fe-Ybt/pesticin receptor FyuA) are sufficient to mediate Fe-Ybt transport/utilization, these genes were transferred into Escherichia coli entD,F and into non-pathogenic Y. enterocolitica, BG IA, strain NF-O. Surprisingly, E. coli entD,F but not Y. enterocolitica NF-O gained the capability to utilize exogenous Fe-Ybt as a result of this gene transfer, although both strains expressed functional FyuA (pesticin sensitivity). These results suggest that besides irp6, irp7 and fyuA, additional genes are required for sufficient Fe-Ybt transport/utilization. Finally, it was shown that irp6, irp7 and fyuA but not irp8 are involved in controlling Ybt biosynthesis and fyuA gene expression: irp6 and/or irp7 mutation leads to upregulation whereas fyuA mutation leads to downregulation. However, fyuA-dependent control of Ybt biosynthesis could be bypassed in a fyuA mutant by ingredients of chrome azurol S (CAS) siderophore indicator agar.

Integrative module of the high-pathogenicity island of Yersinia

The high-pathogenicity island of Yersinia pestis (Yps HPI) encodes virulence-associated genes involved in siderophore yersiniabactin-mediated iron uptake. The Yps HPI contains a P4-type integrase (Int-HPI), associated with the asn-tRNA locus, and is flanked by 17 bp direct repeats. We constructed a minimal integrative module of the pathogenicity island carrying the reconstituted 266 bp attP (POP') attachment site derived from putative attR and attL junctions of the Yps HPI and the functional int-HPI gene from Y. pestis KUMA. The attP-int-HPI module recombined efficiently, site specifically and RecA independently with the bacterial attB site present either in the chromosome (asn-tDNA) or on a plasmid, with no preference for a certain asn-tRNA gene. The excision of the integrated suicide plasmid carrying the integrative module, on the other hand, was a rare event and could be demonstrated only by polymerase chain reaction. Analysis of the 5' terminus of the transcript for int-HPI revealed that the integration of attP-int-HPI was coupled with the replacement of the endogenous int-HPI promoter, localized in the P' part of the attP site, by the adjacent asn-tRNA promoter. These results suggest that two alternative promoters control integration and excision of the HPI by its integrase.

High-pathogenicity island of Yersinia spp. in Escherichia coli strains isolated from diarrhea patients in China

The high-pathogenicity island (HPI) of Yersinia has been observed in 93% of 60 enteroadhesive Escherichia coli strains and 80% of E. coli strains isolated from blood samples. In the present study we investigated 671 fecal samples from patients with diarrhea in Shandong Province, China, and isolated HPI-harboring E. coli from 6. 26% of the samples. The isolation rates for patients with diarrhea in three age groups, 10 to 20, 30 to 40, and 50 to 60 years, were 6. 70, 12.35, and 10.81%, respectively. Therefore, HPI-harboring E. coli is the third most frequently isolated enteric pathogen from patients with diarrhea. Vomiting and abdominal pain were recorded for 33.33 and 66.67% of the patients, respectively. Stools with blood were observed for 9.52% of the patients. Twenty-four of 42 (57%) patients experienced a temperature over 37.4 degrees C. These observations indicate that HPI-harboring E. coli is one of the major causes of diarrheal disease in China and that the clinical symptoms caused by HPI-harboring E. coli differ from those caused by enteroadhesive E. coli.

Characterization of the O-antigen gene clusters of Yersinia pseudotuberculosis and the cryptic O-antigen gene cluster of Yersinia pestis shows that the plague bacillus is most closely related to and has evolved from Y. pseudotuberculosis serotype O:1b

One of the most virulent and feared bacterial pathogens is Yersinia pestis, the aetiologic agent of bubonic plague. Characterization of the O-antigen gene clusters of 21 serotypes of Yersinia pseudotuberculosis and the cryptic O-antigen gene cluster of Y. pestis showed that the plague bacillus is most closely related to and has evolved from Y. pseudotuberculosis serotype O:1b. The nucleotide sequences of both gene clusters (about 20.5 kb each) were determined and compared to identify the differences that caused the silencing of the Y. pestis gene cluster. At the nucleotide sequence level, the loci were 98.9% identical and, of the 17 biosynthetic genes identified from the O:1b gene cluster, five were inactivated in the Y. pestis cluster, four by insertions or deletions of one nucleotide and one by a deletion of 62 nucleotides. Apparently, the expression of the O-antigen is not beneficial for the virulence or to the lifestyle of Y. pestis and, therefore, as one step in the evolution of Y. pestis, the O-antigen gene cluster was inactivated.

Conjugation of hydroxyethyl starch to desferrioxamine (DFO) modulates the dual role of DFO in Yersinia enterocolitica infection

The iron chelator desferrioxamine (DFO) B is widely used in the therapy of patients with iron overload. As a side effect, DFO may favor the occurrence of fulminant Yersinia infections. Previous work from our laboratory showed that this might be due to a dual role of DFO: growth promotion of the pathogen and immunosuppression of the host. In this study, we sought to determine whether conjugation of DFO to hydroxyethyl starch (HES-DFO) may prevent exacerbation of Yersinia infection in mice. We found HES-DFO to promote neither growth of Yersinia enterocolitica nor mitogen-induced T-cell proliferation and gamma interferon production by T cells in vitro. Nevertheless, in vivo HES-DFO promoted growth of Y. enterocolitica possibly due to cleavage of HES and release of DFO. The pretreatment of mice with DFO resulted in death of all mice 2 to 5 days after application of a normally sublethal inoculum of Y. enterocolitica, while none of the mice pretreated with HES-DFO died within the first 7 days postinfection. However, some of the HES-DFO-treated mice died 8 to 14 days postinfection. Thus, due to the delayed in vivo effect HES-DFO failed to trigger Yersinia-induced septic shock, which accounts for early mortality in DFO-associated septicemia. Moreover, our data suggest that DFO needs to be taken up by host cells in order to exert its immunosuppressive action. These results strongly suggest that HES-DFO might be a favorable drug with fewer side effects than DFO in terms of DFO-promoted fulminant infections.

The Yersinia high-pathogenicity island is present in different members of the family Enterobacteriaceae

A pathogenicity island termed high-pathogenicity island (HPI) is present in pathogenic Yersinia. This 35 to 45 kb island carries genes involved in synthesis, regulation and transport of the siderophore yersiniabactin. Recently, the HPI was also detected in various strains of Escherichia coli. In this study, the distribution of the HPI in the family Enterobacteriaceae was investigated. Among the 67 isolates pertaining to 18 genera and 52 species tested, nine (13.4%) harbored the island. These isolates were three E. coli, one Citrobacter diversus and five Klebsiella of various species (Klebsiella pneumoniae, Klebsiella rhinoscleromatis, Klebsiella ozaenae, Klebsiella planticola, and Klebsiella oxytoca). As in Yersinia sp., all nine isolates synthesized the HPI-encoded iron-repressible proteins HMWP1 and HMWP2. In the K. oxytoca strain, the right-end portion of the HPI was deleted, whereas the entire core region of the island was present in the eight other enterobacteria strains analyzed. In most of these isolates, the HPI was bordered by an asn tRNA locus, as in Yersinia sp. This report thus demonstrates the spread of the HPI among various members of the family Enterobacteriaceae.

Local hopping of IS3 elements into the A+T-rich part of the high-pathogenicity island in Yersinia enterocolitica 1B, O:8

The high-pathogenicity island (Yen HPI) of Yersinia enterocolitica biogroup (BG) 1B strains is associated with mouse virulence. Three repeated sequences are clustered on the A+T-rich part of the Yen HPI downstream of the fyuA yersiniabactin receptor gene in Y. enterocolitica O:8 strains WA-314 and 8081. In addition to IS1328 and IS1400, the RS3 repeated sequence consists of a novel insertion sequence, IS1329, inserted into the remnants of IS1222. This partial IS retains both 44-bp inverted terminal repeats (ITRs) of IS1222 but has suffered deletions of different sizes in strains WA-314 and 8081. IS1329 is 1243-bp long, carries 25-bp imperfect ITRs and two consecutive orfs capable to encode 110-amino acid (aa) and 249-aa proteins, respectively. IS1329 is present only in BG 1B Y. enterocolitica strains. Similarly to IS1400, IS1329 and IS1222 belong to the IS3 group of mobile elements and seem to have preference for the 'local hopping' into the A+T-rich part of the Yen HPI. These insertion sequences may be responsible for the imprecise deletions of the Yen HPI in strain WA-314.

A genomic island, termed high-pathogenicity island, is present in certain non-O157 Shiga toxin-producing Escherichia coli clonal lineages

Shiga toxin-producing Escherichia coli (STEC) strains cause a wide spectrum of diseases in humans. In this study, we tested 206 STEC strains isolated from patients for potential virulence genes including stx, eae, and enterohemorrhagic E. coli hly. In addition, all strains were examined for the presence of another genetic element, the high-pathogenicity island (HPI). The HPI was first described in pathogenic Yersinia species and encodes the pesticin receptor FyuA and the siderophore yersiniabactin. The HPI was found in the genome of distinct clonal lineages of STEC, including all 31 eae-positive O26:H11/H(-) strains and 7 of 12 eae-negative O128:H2/H(-) strains. In total, the HPI was found in 56 (27.2%) of 206 STEC strains. However, it was absent from the genome of all 37 O157:H7/H(-), 14 O111:H(-), 13 O103:H2, and 13 O145:H(-) STEC isolates, all of which were positive for eae. Polypeptides encoded by the fyuA gene located on the HPI could be detected by using immunoblot analysis in most of the HPI-positive STEC strains, suggesting the presence of a functional yersiniabactin system. The HPI in STEC was located next to the tRNA gene asnT. In contrast to the HPI of other pathogenic enterobacteria, the HPI of O26 STEC strains shows a deletion at its left junction, leading to a truncated integrase gene int. We conclude from this study that the Yersinia HPI is disseminated among certain clonal subgroups of STEC strains. The hypothesis that the HPI in STEC contributes to the fitness of the strains in certain ecological niches rather than to their pathogenic potential is discussed.

Common and specific characteristics of the high-pathogenicity island of Yersinia enterocolitica

Yersinia pestis, Y. pseudotuberculosis O:1, and Y. enterocolitica biogroup 1B strains carry a high-pathogenicity island (HPI), which mediates biosynthesis and uptake of the siderophore yersiniabactin and a mouse-lethal phenotype. The HPI of Y. pestis and Y. pseudotuberculosis (Yps HPI) are highly conserved in sequence and organization, while the HPI of Y. enterocolitica (Yen HPI) differs significantly. The 43,393-bp Yen HPI sequence of Y. enterocolitica WA-C, serotype O:8, was completed and compared to that of the Yps HPI of Y. pseudotuberculosis PB1, serotype O:1A. A common GC-rich region (G+C content, 57.5 mol%) of 30.5 kb is conserved between yersinia strains. This region carries genes for yersiniabactin biosynthesis, regulation, and uptake and thus can be considered the functional "core" of the HPI. In contrast, the second part of the HPI is AT rich and completely different in two evolutionary lineages of the HPI, being 12.8 kb in the Yen HPI and 5.6 kb in the Yps HPI. The variable part acquired one IS100 element in the Yps HPI and accumulated four insertion elements, IS1328, IS1329, IS1400, and IS1222, in the Yen HPI. The insertion of a 125-bp ERIC sequence modifies the structure of the promoter of the ybtA yersiniabactin regulator in the Yen HPI. In contrast to the precise excision of the Yps HPI in Y. pseudotuberculosis, the Yen HPI suffers imprecise deletions. The Yen HPI is stably integrated in one of the three asn tRNA copies in Y. enterocolitica biogroup 1B (serotypes O:8, O:13, O:20, and O:21), probably due to inactivation of the putative integrase. The 17-bp duplications of the 3' end of the asnT RNA are present in both Yersinia spp. The HPI attachment site is unoccupied in nonpathogenic Y. enterocolitica NF-O, biogroup 1A, serotype O:5. The HPI of Yersinia is a composite and widely spread genomic element with a highly conserved yersiniabactin functional "core" and a divergently evolved variable part.

The 102-kilobase pgm locus of Yersinia pestis: sequence analysis and comparison of selected regions among different Yersinia pestis and Yersinia pseudotuberculosis strains

We report the complete 119,443-bp sequence of the pgm locus from Yersinia pestis and its flanking regions. Sequence analysis confirms that the 102-kb unstable pgm locus is composed of two distinct parts: the pigmentation segment and a high-pathogenicity island (HPI) which carries virulence genes involved in iron acquisition (yersiniabactin biosynthetic gene cluster). Within the HPI, three genes coding for proteins related to phage proteins were uncovered. They are located at both extremities indicating that the entire HPI was acquired en bloc by phage-mediated horizontal transfer. We identified, within the pigmentation segment, two novel loci that may be involved in virulence: a fimbriae gene cluster and a locus probably encoding a two component regulatory system similar to the BvgAS regulatory system of Bordetella pertussis. Three genes containing frameshift mutations and two genes interrupted by insertion element insertion were found within this region. To investigate diversity among different Y. pestis and Yersinia pseudotuberculosis strains, the sequence of selected regions of the pgm locus and flanking regions were compared from 20 different Y. pestis and 10 Y. pseudotuberculosis strains. The results showed that the genes interrupted in Y. pestis are intact in Y. pseudotuberculosis. However, one of these mutations, in the bvgS homologue, is only present in Y. pestis strains of biovar Orientalis and not in those of the biovars Antiqua and Medievalis. The results obtained by analysis of variable positions in the sequence are in accordance with historical records, confirming that biovar Orientalis is the most recent lineage. Furthermore, sequence comparisons among 29 Yersinia strains suggest that Y. pestis is a recently emerged pathogen that is probably entering the initial phase of reductive evolution.

A 55-kilodalton immunodominant antigen of Porphyromonas gingivalis W50 has arisen via horizontal gene transfer

A 55-kDa outer membrane protein of Porphyromonas gingivalis W50 is a significant target of the serum immunoglobulin G antibody response of periodontal disease patients and hence may play an important role in host-bacterium interactions in periodontal disease. The gene encoding the 55-kDa antigen (ragB, for receptor antigen B) was isolated on a 9.5-kb partial Sau3AI fragment of P. gingivalis W50 chromosomal DNA in pUC18 by immunoscreening with a monoclonal antibody to this antigen. The 1.6-kb open reading frame (ORF) encoding RagB was located via subcloning and nested-deletion analysis. Sequence analysis demonstrated the presence of an upstream 3.1-kb ORF (ragA) which is cotranscribed with ragB. A number of genetic characteristics suggest that the ragAB locus was acquired by a horizontal gene transfer event. These include a significantly reduced G+C content relative to that of the P. gingivalis chromosome (42 versus 48%) and the presence of mobility elements flanking this locus in P. gingivalis W50. Furthermore, Southern blotting and PCR analyses showed a restricted distribution of this locus in laboratory and clinical isolates of this bacterium. The association of ragAB+ P. gingivalis with clinical status was examined by PCR analysis of subgingival samples. ragAB+ was not detected in P. gingivalis-positive shallow pockets from periodontal disease patients but was present in 36% of the P. gingivalis-positive samples from deep pockets. These data suggest that the ragAB locus was acquired by certain P. gingivalis strains via horizontal gene transfer and that the acquisition of this locus may facilitate the survival of these strains at sites of periodontal destruction.

Independent acquisition and insertion into different chromosomal locations of the same pathogenicity island in Yersinia pestis and Yersinia pseudotuberculosis

We show that Yersinia pestis and pesticin-sensitive isolates of Y. pseudotuberculosis possess a common 34 kbp DNA region that has all the hallmarks of a pathogenicity island and is inserted into different asparaginyl tRNA genes at different chromosomal locations in each species. This pathogenicity island (YP-HPI) is marked by IS100, has a G + C content different from its host, is flanked by 24 bp direct repeats, encodes a putative, P4-like integrase and contains the iron uptake virulence genes from the pgm locus of Y. pestis. These findings indicate independent horizontal acquisition of this island by Y. pestis and Y. pseudotuberculosis. The two YP-HPI locations and their possession of an integrase gene support a model of site-specific integration of the YP-HPI into these bacteria.

The high-pathogenicity island of Yersinia pseudotuberculosis can be inserted into any of the three chromosomal asn tRNA genes

Pathogenicity islands (PAIs) have been identified in several bacterial species. A PAI called high-pathogenicity island (HPI) and carrying genes involved in iron acquisition (yersiniabactin system) has been previously identified in Yersinia enterocolitica and Yersinia pestis. In this study, the HPI of the third species of Yersinia pathogenic for humans, Y. pseudotuberculosis, has been characterized. We demonstrate that the HPI of strain IP32637 has a physical and genetic map identical to that of Y. pestis. A gene homologous to the bacteriophage P4 integrase gene is located downstream of the asn tRNA locus that borders the HPI of strain IP32637. This int gene is at the same position on the HPI of all three pathogenic Yersinia species. However, in contrast to Y. pestis 6/69, the HPI of Y. pseudotuberculosis IP32637 is not invariably adjacent to the pigmentation segment and can be inserted at a distance > or = 190 kb from this segment. Also, in contrast to Y. pestis and Y. enterocolitica, the HPI of Y. pseudotuberculosis IP32637 can precisely excise from the chromosome, and, strikingly, it can be found inserted in any of the three asn tRNA loci present on the chromosome of this species, one of which is adjacent to the pigmentation segment. The pigmentation segment, which is present in Y. pestis but not in Y. enterocolitica, is also present and well conserved in all strains of Y. pseudotuberculosis studied. In contrast, the presence and size of the HPIs vary depending on the serotype of the strain: an entire HPI is found in strains of serotypes I only, a HPI with a 9 kb truncation in its left-hand part that carries the IS100 sequence and the psn and ybtE genes characterizes the strains of serotype III, and no HPI is found in strains of serotypes II, IV and V.

Development of rRNA-targeted PCR and in situ hybridization with fluorescently labelled oligonucleotides for detection of Yersinia species

In this report, we present details of two rapid molecular detection techniques based on 16S and 23S rRNA sequence data to identify and differentiate Yersinia species from clinical and environmental sources. Near-full-length 16S rRNA gene (rDNA) sequences for three different Yersinia species and partial 23S rDNA sequences for three Y. pestis and three Y. pseudotuberculosis strains were determined. While 16S rDNA sequences of Y. pestis and Y. pseudotuberculosis were found to be identical, one base difference was identified within a highly variable region of 23S rDNA. The rDNA sequences were used to develop primers and fluorescently tagged oligonucleotide probes suitable for differential detection of Yersinia species by PCR and in situ hybridization, respectively. As few as 10(2) Yersinia cells per ml could be detected by PCR with a seminested approach. Amplification with a subgenus-specific primer pair followed by a second PCR allowed differentiation of Y. enterocolitica biogroup 1B from biogroups 2 to 5 or from other pathogenic Yersinia species. Moreover, a set of oligonucleotide probes suitable for rapid (3-h) in situ detection and differentiation of the three pathogenic Yersinia species (in particular Y. pestis and Y. pseudotuberculosis) was developed. The applicability of this technique was demonstrated by detection of Y. pestis and Y. pseudotuberculosis in spiked throat and stool samples, respectively. These probes were also capable of identifying Y. enterocolitica within cryosections of experimentally infected mouse tissue by the use of confocal laser scanning microscopy.

The nonribosomal peptide synthetase HMWP2 forms a thiazoline ring during biogenesis of yersiniabactin, an iron-chelating virulence factor of Yersinia pestis

Pathogenic Yersinia species have been shown to synthesize a siderophore molecule, yersiniabactin, as a virulence factor during iron starvation. Here we provide the first biochemical evidence for the role of the Yersinia pestis high molecular weight protein 2 (HMWP2), a nonribosomal peptide synthetase homologue, and YbtE in the initiation of yersiniabactin biosynthesis. YbtE catalyzes the adenylation of salicylate and the transfer of this activated salicyl group to the N-terminal aryl carrier protein domain (ArCP; residues 1-100) of HMWP2. A fragment of HMWP2, residues 1-1491, can adenylate cysteine and with the resulting cysteinyl-AMP autoaminoacylate the peptidyl carrier protein domain (PCP1; residues 1383-1491) either in cis or in trans. Catalytic release of hydroxyphenylthiazoline carboxylic acid (HPT-COOH) and/or N-(hydroxyphenylthiazolinylcarbonyl)cysteine (HPT-cys) is observed upon incubation of YbtE, HMWP2 1-1491, L-cysteine, salicylate, and ATP. These products presumably arise from nucleophilic attack by water or cysteine of a stoichiometric hydroxyphenylthiazolinylcarbonyl-S-PCP1-HMWP2 intermediate. Detection of the heterocyclization capacity of HMWP2 1-1491 implies salicyl-transferring and thiazoline-forming activity for the HMWP2 condensation domain (residues 101-544) and is the first demonstration of such heterocyclization ability in a nonribosomal peptide synthetase enzyme.

Prevalence of the "high-pathogenicity island" of Yersinia species among Escherichia coli strains that are pathogenic to humans

The fyuA-irp gene cluster contributes to the virulence of highly pathogenic Yersinia (Yersinia pestis, Yersinia pseudotuberculosis, and Yersinia enterocolitica 1B). The cluster encodes an iron uptake system mediated by the siderophore yersiniabactin and reveals features of a pathogenicity island. Two evolutionary lineages of this "high pathogenicity island" (HPI) can be distinguished on the basis of DNA sequence comparison: a Y. pestis group and a Y. enterocolitica group. In this study we demonstrate that the HPI of the Y. pestis evolutionary group is disseminated among species of the family Enterobacteriaceae which are pathogenic to humans. It prevails in enteroaggregative Escherichia coli and in E. coli blood culture isolates (93 and 80%, respectively), but is rarely found in enteropathogenic E. coli, enteroinvasive E. coli, and enterotoxigenic E. coli isolates. In contrast, the HPI was absent from enterohemorrhagic E. coli, Shigella, and Salmonella enterica strains investigated. Polypeptides encoded by the fyuA, irp1, and irp2 genes located on the HPI could be detected in E. coli strains pathogenic to humans. However, these E. coli strains showed a reduced sensitivity to the bacteriocin pesticin, whose uptake is mediated by the FyuA receptor. Escherichia strains do not possess the hms gene locus thought to be a part of the HPI of Y. pestis. Deletions of the juA-irp gene cluster affecting solely the fyuA part of the HPI were identified in 3% of the E. coli strains tested. These results suggest horizontal transfer of the HPI between Y. pestis and some pathogenic E. coli strains.

The yersiniabactin biosynthetic gene cluster of Yersinia enterocolitica: organization and siderophore-dependent regulation

The ability to synthesize and uptake the Yersinia siderophore yersiniabactin is a hallmark of the highly pathogenic, mouse-lethal species Yersinia pestis, Y. pseudotuberculosis, and Y. enterocolitica 1B. We have identified four genes, irp1, irp3, irp4, and irp5, on a 13-kb chromosomal DNA fragment of Y. enterocolitica 08, WA-314. These genes constitute the yersiniabactin biosynthetic gene cluster together with the previously defined irp2. The irp1 gene consists of 9,486 bp capable of encoding a 3,161-amino-acid high-molecular-weight protein 1 (HMWP1) polypeptide with a predicted mass of 384.6 kDa. The first 3,000 bp of irp1 show similarity to the corresponding regions of the polyketide synthase genes of Bacillus subtilis and Streptomyces antibioticus. The remaining part of irp1 is most similar to irp2, encoding HMWP2, which might be the reason for immunological cross-reactivity of the two polypeptides. Irp4 was found to have 41.7% similarity to thioesterase-like protein of the anguibactin biosynthetic genes of Vibrio anguillarum. Irp5 shows 41% similarity to EntE, the 2,3-dihydroxybenzoic acid-activating enzyme utilized in enterobactin synthesis of Escherichia coli. Irp4 and Irp5 are nearly identical to YbtT and YbtE, recently identified in Y. pestis. irp3 has no similarity to any known gene. Inactivation of either irp1 or irp2 abrogates yersiniabactin synthesis. Mutations in irp1 or fyuA (encoding yersiniabactin/pesticin receptor) result in downregulation of irp2 that can be upregulated by the addition of yersiniabactin. A FyuA-green fluorescent protein translational fusion was downregulated in an irp1 mutant. Upregulation was achieved by addition of yersiniabactin but not desferal, pesticin, or pyochelin, which indicates high specificity of the FyuA receptor and autoregulation of genes involved in synthesis and uptake of yersiniabactin.

Homology with a repeated Yersinia pestis DNA sequence IS100 correlates with pesticin sensitivity in Yersinia pseudotuberculosis

We have identified IS100 sequences in a specific subset of Yersinia pseudotuberculosis isolates that were also sensitive to the Y. pestis-produced bacteriocin, pesticin. In contrast, Y. pseudotuberculosis strains which did not contain IS100 sequences were not sensitive to pesticin. We propose that IS100 serves as a molecular marker that identifies a subset of Y. pseudotuberculosis isolates that have a particularly close evolutionary and/or ecological relationship with Y. pestis.

Periplasmic location of the pesticin immunity protein suggests inactivation of pesticin in the periplasm

The pesticin activity and immunity genes on plasmid pPCP1 of Yersinia pestis were sequenced. They encoded proteins of 40 kDa (pesticin) and 16 kDa (immunity protein); the latter was found in the periplasm. The location of the immunity protein suggests that imported pesticin is inactivated in the periplasm before it hydrolyzes murein. Pesticin contains a TonB box close to the N-terminal end that is identical to the TonB box of colicin B. The DNA sequences flanking the pesticin determinant were highly homologous to those flanking the colicin 10 determinant. It is proposed that through these highly homologous DNA sequences, genes encoding bacteriocins may be exchanged between plasmids by recombination. In the case of pesticin, recombination may have destroyed the lysis gene, of which only a rudimentary fragment exists on pPCP1.

Molecular mechanisms of bacterial virulence: type III secretion and pathogenicity islands

Recently, two novel but widespread themes have emerged in the field of bacterial virulence: type III secretion systems and pathogenicity islands. Type III secretion systems, which are found in various gram-negative organisms, are specialized for the export of virulence factors delivered directly to host cells. These factors subvert normal host cell functions in ways that seem beneficial to invading bacteria. The genes encoding several type III secretion systems reside on pathogenicity islands, which are inserted DNA segments within the chromosome that confer upon the host bacterium a variety of virulence traits, such as the ability to acquire iron and to adhere to or enter host cells. Many of these segments of DNA appear to have been acquired in a single step from a foreign source. The ability to obtain complex virulence traits in one genetic event, rather than by undergoing natural selection for many generations, provides a mechanism for sudden radical changes in bacterial-host interactions. Type III secretion systems and pathogenicity islands must have played critical roles in the evolution of known pathogens and are likely to lead to the emergence of novel infectious diseases in the future.