Acute mesenteric lymphadenitis due to Yersinia pseudotuberculosis lacking a virulence plasmid

Yersinia pseudotuberculosis in an alpaca

A 6-year-old female huacaya alpaca was referred to the clinic for evaluation with a 1-month history of rapid weight loss, inappetence, lethargy, and severe leukocytosis refractory to medical management. Physical examination revealed a body condition score of 1 out of 5 and a large, firm structure palpable in the right caudoventral abdomen. Abdominal ultrasonographic examination revealed 3 masses with hyperechoic, swirling centers. The largest mass measured 15 cm in diameter with a 2-centimeter capsule, and extended from right of midline into the left inguinal region. Transrectal ultrasonography identified a small uterus and clear delineation between the abdominal masses. Complete blood (cell) count findings were consistent with marked systemic inflammation. Based on initial examination and laboratory findings, exploratory laparotomy was elected. Multiple mesenteric masses strongly adhered to the jejunum were observed within the abdomen. Due to the inoperable conditions and the poor long-term prognosis, the alpaca was euthanized under general anesthesia. Bacterial culture of fluid aspirated from the largest mass revealed Yersinia pseudotuberculosis. Key clinical message: Clinical progression and attempted treatment of Yersinia pseudotuberculosis in camelids have not been previously described and the bacterium should be considered as a differential diagnosis for abscessation and persistent leukocytosis. Yersinia pseudotuberculosis is also considered a zoonotic agent and proper precautions should be taken when handling cases of abdominal abscessation.

Case report: a genomics-guided reclassification of a blood culture isolate misassigned by MALDI-TOF as Yersinia pestis

In this report, we describe a case where Gram-negative rods were isolated from a blood culture which subsequently presented a discordant Yersinia species result by MALDI-TOF. Rapid sequencing provided high-resolution identification of the isolate as Yersinia pseudotuberculosis , which was subsequently confirmed by biochemical tests.

Isolation of Yersinia pseudotuberculosis in bovine mastitis: A potential milk-borne hazard

This paper describes the first confirmed case of a subclinical mastitis caused by Yersinia pseudotuberculosis in a dairy cow from Italy. Milk samples from an adult cow of the Bruna breed were analyzed accordingly to standard milk cultivation protocols. Bacteriological examinations allowed to isolate atypical Gram-negative rods identified as Y. pseudotuberculosis using biochemical tests. The isolate was subjected to Whole Genome Sequencing (WGS) and the species identification was confirmed using rMLST. Moreover, the virulence and antibacterial susceptibility of the isolate have been also determined. The most common virulence genes were screened through WGS, showing the presence of inv, ail, pil and HPI genes. No antibiotic resistance was found. Even though scarcely described as causal agent of subclinical mastitis, the detection of Y. pseudotubercolusosis suggests that this pathogen could be spread to humans through raw milk, representing a potential food safety hazard

LAMP-based assay can rectify the diagnosis of Yersinia pseudotuberculosis infections otherwise missed by serology

BACKGROUND

Despite being a well-known but seldom encountered zoonotic pathogen, diagnosis of Yersinia pseudotuberculosis is not necessarily easy. Infected patients occasionally present with various symptoms resembling Kawasaki disease; thus discriminating the two in the acute phase is challenging. In addition to bacterial culture and serology, novel detection methods based on loop-mediated isothermal amplification (LAMP) are reported in the literature. However, the clinical utility of LAMP-based methods in comparison with the other methods is scarcely documented in the literature.

AIM

To clarify the clinical utility of a LAMP-based method in the diagnosis of Yersinia pseudotuberculosis infection.

METHODOLOGY

Inpatients admitted due to suspected Yersinia pseudotuberculosis infection during April 2008 through March 2015 were enrolled. Results of the LAMP-based method as well as culture and serology were collected and compared.

RESULTS

Among 16 eligible cases, serology proved positive in 13 (81.3 %) cases, LAMP in eight (50 %) cases, and bacterial culture in four (25 %) cases. No significant difference among the three methods could be proved statistically. Although serology was the most sensitive method, it is known to miss cases such as young patients, whereas LAMP could complement all three cases missed by serology. Furthermore, LAMP can return the test result within a few hours from specimen receipt, whereas serology and bacterial culture requires days to weeks of time.

CONCLUSION

Although second to serology in sensitivity, the LAMP-based method proved its utility in making rapid diagnosis, and serving a complementary role to serology.

Yersinia pseudotuberculosis Prevalence and Diversity in Wild Boars in Northeast Germany

In this study, the prevalence of Yersinia pseudotuberculosis in wild boars in northeast Germany was determined. For that purpose, the tonsils of 503 wild boars were sampled. The presence of Y. pseudotuberculosis was studied by diagnostic PCR. Positive samples were analyzed by cultural detection using a modified cold enrichment protocol. Ten Y. pseudotuberculosis isolates were obtained, which were characterized by biotyping, molecular serotyping, and multilocus sequence typing (MLST). In addition, whole-genome sequences and the antimicrobial susceptibility of the isolates were analyzed. Yersinia pseudotuberculosis was isolated from male and female animals, most of which were younger than 1 year. A prevalence of 2% (10/503) was determined by cultural detection, while 6.4% (32/503) of the animals were positive by PCR. The isolates belonged to the biotypes 1 and 2 and serotypes O:1a (n = 7), O:1b (n = 2), and O:4a (n = 1). MLST analysis revealed three sequence types, ST9, ST23, and ST42. Except one isolate, all isolates revealed a strong resistance to colistin. The relationship of the isolates was studied by whole-genome sequencing demonstrating that they belonged to four clades, exhibiting five different pulsed-field gel electrophoresis (PFGE) restriction patterns and a diverse composition of virulence genes. Six isolates harbored the virulence plasmid pYV. Besides two isolates, all isolates contained ail and inv genes and a complete or incomplete high-pathogenicity island (HPI). None of them possessed a gene for the superantigen YPM. The study shows that various Y. pseudotuberculosis strains exist in wild boars in northeast Germany, which may pose a risk to humans.IMPORTANCEYersinia pseudotuberculosis is a foodborne pathogen whose occurrence is poorly understood. One reason for this situation is the difficulty in isolating the species. The methods developed for the isolation of Yersinia enterocolitica are not well suited for Y. pseudotuberculosis We therefore designed a protocol which enabled the isolation of Y. pseudotuberculosis from a relatively high proportion of PCR-positive wild boar tonsils. The study indicates that wild boars in northeast Germany may carry a variety of Y. pseudotuberculosis strains, which differ in terms of their pathogenic potential and other properties. Since wild boars are widely distributed in German forests and even populate cities such as Berlin, they may transmit yersiniae to other animals and crop plants and may thus cause human infections through the consumption of contaminated food. Therefore, the prevalence of Y. pseudotuberculosis should be determined also in other animals and regions to learn more about the natural reservoir of this species.

Effects of urbanization on host-pathogen interactions, using Yersinia in house sparrows as a model

Urbanization strongly affects biodiversity, altering natural communities and often leading to a reduced species richness. Yet, despite its increasingly recognized importance, how urbanization impacts on the health of individual animals, wildlife populations and on disease ecology remains poorly understood. To test whether, and how, urbanization-driven ecosystem alterations influence pathogen dynamics and avian health, we use house sparrows (Passer domesticus) and Yersinia spp. (pathogenic for passerines) as a case study. Sparrows are granivorous urban exploiters, whose western European populations have declined over the past decades, especially in highly urbanized areas. We sampled 329 house sparrows originating from 36 populations along an urbanization gradient across Flanders (Belgium), and used isolation combined with 'matrix-assisted laser desorption ionization- time of flight mass spectrometry' (MALDI-TOF MS) and PCR methods for detecting the presence of different Yersinia species. Yersinia spp. were recovered from 57.43% of the sampled house sparrows, of which 4.06%, 53.30% and 69.54% were identified as Y. pseudotuberculosis, Y. enterocolitica and other Yersinia species, respectively. Presence of Yersinia was related to the degree of urbanization, average daily temperatures and the community of granivorous birds present at sparrow capture locations. Body condition of suburban house sparrows was found to be higher compared to urban and rural house sparrows, but no relationships between sparrows' body condition and presence of Yersinia spp. were found. We conclude that two determinants of pathogen infection dynamics, body condition and pathogen occurrence, vary along an urbanization gradient, potentially mediating the impact of urbanization on avian health.

Molecular analysis of a novel Toll/interleukin-1 receptor (TIR)-domain containing virulence protein of Y. pseudotuberculosis among Far East scarlet-like fever serotype I strains

Pathogenicity of Yersinia pseudotuberculosis is determined by an arsenal of virulence factors. Particularly, the Yersinia outer proteins (Yops) and the Type III secretion system (T3SS) encoded on the pYV virulence plasmid are required for Yersinia pathogenicity. A specific group of Y. pseudotuberculosis, responsible for the clinical syndrome described as Far East scarlet-like fever (FESLF), is known to have an altered virulence gene cluster. Far East strains cause unique clinical symptoms for which the pYV virulence plasmid plays apparently a rather secondary role. Here, we characterize a previously unknown protein of Y. pseudotuberculosis serotype I strains (TcpYI) which can be found particularly among the FESLF strain group. The TcpYI protein shares considerable sequence homology to members of the Toll/IL-1 receptor family. Bacterial TIR domain containing proteins (Tcps) interact with the innate immune system by TIR-TIR interactions and subvert host defenses via individual, multifaceted mechanisms. In terms of virulence, it appears that the TcpYI protein of Y. pseudotuberculosis displays its own virulence phenotype compared to the previously characterized bacterial Tcps. Our results clearly demonstrate that TcpYI increases the intracellular survival of the respective strains in vitro. Furthermore, we show here that the intracellular survival benefit of the wild-type strain correlates with an increase in tcpYI gene expression inside murine macrophages. In support of this, we found that TcpYI enhances the survival inside the spleens of mice in a mouse model of peritonitis. Our results may point toward involvement of the TcpYI protein in inhibition of phagocytosis, particularly in distinct Y. pseudotuberculosis strains of the FESLF strain group where the pYV virulence plasmid is absent.

Population structure and evolution of pathogenicity of Yersinia pseudotuberculosis

Yersinia pseudotuberculosis is an enteric human pathogen but is widespread in the environment. Pathogenicity is determined by a number of virulence factors, including the virulence plasmid pYV, the high-pathogenicity island (HPI), and the Y. pseudotuberculosis-derived mitogen (YPM), a superantigen. The presence of the 3 virulence factors varies among Y. pseudotuberculosis isolates. We developed a multilocus sequence typing (MLST) scheme to address the population structure of Y. pseudotuberculosis and the evolution of its pathogenicity. The seven housekeeping genes selected for MLST were mdh, recA, sucA, fumC, aroC, pgi, and gyrB. An MLST analysis of 83 isolates of Y. pseudotuberculosis, representing 19 different serotypes and six different genetic groups, identified 61 sequence types (STs) and 12 clonal complexes. Out of 26 allelic changes that occurred in the 12 clonal complexes, 13 were mutational events while 13 were recombinational events, indicating that recombination and mutation contributed equally to the diversification of the clonal complexes. The isolates were separated into 2 distinctive clusters, A and B. Cluster A is the major cluster, with 53 STs (including Y. pestis strains), and is distributed worldwide, while cluster B is restricted to the Far East. The YPM gene is widely distributed on the phylogenetic tree, with ypmA in cluster A and ypmB in cluster B. pYV is present in cluster A only but is sporadically absent in some cluster A isolates. In contrast, an HPI is present only in a limited number of lineages and must be gained by lateral transfer. Three STs carry all 3 virulence factors and can be regarded as high-pathogenicity clones. Isolates from the same ST may not carry all 3 virulence factors, indicating frequent gain or loss of these factors. The differences in pathogenicity among Y. pseudotuberculosis strains are likely due to the variable presence and instability of the virulence factors.

Innate immune response during Yersinia infection: critical modulation of cell death mechanisms through phagocyte activation

Yersinia pestis, the etiological agent of plague, is one of the most deadly pathogens on our planet. This organism shares important attributes with its ancestral progenitor, Yersinia pseudotuberculosis, including a 70-kb virulence plasmid, lymphotropism during growth in the mammalian host, and killing of host macrophages. Infections with both organisms are biphasic, where bacterial replication occurs initially with little inflammation, followed by phagocyte influx, inflammatory cytokine production, and tissue necrosis. During infection, plasmid-encoded attributes facilitate bacterial-induced macrophage death, which results from two distinct processes and corresponds to the inflammatory crescendo observed in vivo: Naïve cells die by apoptosis (noninflammatory), and later in infection, activated macrophages die by pyroptosis (inflammatory). The significance of this redirected cell death for the host is underscored by the importance of phagocyte activation for immunity to Yersinia and the protective role of pyroptosis during host responses to anthrax lethal toxin and infections with Francisella, Legionella, Pseudomonas, and Salmonella. The similarities of Y. pestis and Y. pseudotuberculosis, including conserved, plasmid-encoded functions inducing at least two distinct mechanisms of cell death, indicate that comparative studies are revealing about their critical pathogenic mechanism(s) and host innate immune responses during infection. Validation of this idea and evidence of similar interactions with the host immune system are provided by Y. pseudotuberculosis-priming, cross-protective immunity against Y. pestis. Despite these insights, additional studies indicate much remains to be understood concerning effective host responses against Yersinia, including chromosomally encoded attributes that also contribute to bacterial evasion and modulation of innate and adaptive immune responses.

Macrophage activation redirects yersinia-infected host cell death from apoptosis to caspase-1-dependent pyroptosis

Infection of macrophages by Yersinia species results in YopJ-dependent apoptosis, and naïve macrophages are highly susceptible to this form of cell death. Previous studies have demonstrated that macrophages activated with lipopolysaccharide (LPS) prior to infection are resistant to YopJ-dependent cell death; we found this simultaneously renders macrophages susceptible to killing by YopJ⁻Yersinia pseudotuberculosis (Yptb). YopJ⁻Yptb-induced macrophage death was dependent on caspase-1 activation, resulting in rapid permeability to small molecules, followed by membrane breakdown and DNA damage, and accompanied by cleavage and release of proinflammatory interleukin-18. Induction of caspase-1-dependent death, or pyroptosis, required the bacterial type III translocon but none of its known translocated proteins. Wild-type Yptb infection also triggered pyroptosis: YopJ-dependent activation of proapoptotic caspase-3 was significantly delayed in activated macrophages and resulted in caspase-1-dependent pyroptosis. The transition to susceptibility was not limited to LPS activation; it was also seen in macrophages activated with other Toll-like receptor (TLR) ligands and intact nonviable bacteria. Yptb infection triggered macrophage activation and activation of caspase-1 in vivo. Y. pestis infection of activated macrophages also stimulated caspase-1 activation. These results indicate that host signaling triggered by TLR and other activating ligands during the course of Yersinia infection redirects both the mechanism of host cell death and the downstream consequences of death by shifting from noninflammatory apoptosis to inflammatory pyroptosis.

Pathogenic Yersinia are bacteria capable of interacting with host immune cells and inhibiting their function. Macrophages are potent antimicrobial immune cells that eliminate invading microbes, and represent a major target for Yersinia during infection. Yersinia triggers death of resting macrophages by apoptosis, a process thought to be advantageous for Yersinia growth during early stages of infection because important host cells are eliminated without perturbing the surrounding tissue. However, activated macrophages with enhanced antimicrobial activity play a crucial role in controlling Yersinia infection. To elucidate the mechanisms involved in successful defense against infection, the authors investigated the response of activated macrophages to Yersinia, which revealed induction of a proinflammatory cell death pathway termed pyroptosis. Unlike apoptosis, pyroptosis unleashes inflammatory mediators capable of enhancing immune responses and clearing bacteria. Macrophage activation and pyroptosis was observed in infected host tissue. Thus, regulating the mechanism of cell death is important for effective responses to Yersinia infection: activated macrophages resisting apoptosis are redirected to utilize pyroptosis, an inflammatory process facilitating host resistance.

The complete genome sequence of Yersinia pseudotuberculosis IP31758, the causative agent of Far East scarlet-like fever

The first reported Far East scarlet-like fever (FESLF) epidemic swept the Pacific coastal region of Russia in the late 1950s. Symptoms of the severe infection included erythematous skin rash and desquamation, exanthema, hyperhemic tongue, and a toxic shock syndrome. The term FESLF was coined for the infection because it shares clinical presentations with scarlet fever caused by group A streptococci. The causative agent was later identified as Yersinia pseudotuberculosis, although the range of morbidities was vastly different from classical pseudotuberculosis symptoms. To understand the origin and emergence of the peculiar clinical features of FESLF, we have sequenced the genome of the FESLF-causing strain Y. pseudotuberculosis IP31758 and compared it with that of another Y. pseudotuberculosis strain, IP32953, which causes classical gastrointestinal symptoms. The unique gene pool of Y pseudotuberculosis IP31758 accounts for more than 260 strain-specific genes and introduces individual physiological capabilities and virulence determinants, with a significant proportion horizontally acquired that likely originated from Enterobacteriaceae and other soil-dwelling bacteria that persist in the same ecological niche. The mobile genome pool includes two novel plasmids phylogenetically unrelated to all currently reported Yersinia plasmids. An icm/dot type IVB secretion system, shared only with the intracellular persisting pathogens of the order Legionellales, was found on the larger plasmid and could contribute to scarlatinoid fever symptoms in patients due to the introduction of immunomodulatory and immunosuppressive capabilities. We determined the common and unique traits resulting from genome evolution and speciation within the genus Yersinia and drew a more accurate species border between Y. pseudotuberculosis and Y. pestis. In contrast to the lack of genetic diversity observed in the evolutionary young descending Y. pestis lineage, the population genetics of Y. pseudotuberculosis is more heterogenous. Both Y. pseudotuberculosis strains IP31758 and the previously sequenced Y. pseudotuberculosis strain IP32953 have evolved by the acquisition of specific plasmids and by the horizontal acquisition and incorporation of different genetic information into the chromosome, which all together or independently seems to potentially impact the phenotypic adaptation of these two strains.

Oral inoculation with Type III secretion mutants of Yersinia pseudotuberculosis provides protection from oral, intraperitoneal, or intranasal challenge with virulent Yersinia

The enteric pathogen Yersinia pseudotuberculosis (Yptb) causes gastroenteritis, mesenteric lymphadenitis, and systemic infections in humans, livestock, and wild animals. Yptb Type III secretion system (pTTSS) mutants efficiently colonize lymphoid tissues, but not the gastrointestinal tract, spleen, or liver. Here, we show that a single oral inoculation of pTTSS mutants prevents morbidity in almost 100% of mice challenged intragastrically with virulent Yptb. In addition, a single oral inoculation of a pTTSS mutant protected 50% of mice challenged intraperitoneally or intranasally with virulent Yptb. In addition, the intranasally challenged mice that succumbed to infection lived significantly longer than non-immunized mice. Thus, pTTSS mutants can function as live attenuated vaccine when delivered orally. Potential uses for these attenuated strains include use as a livestock vaccine, a rodent plague control reagent in endemic areas around the world, and a vector for delivery of other antigens to the mesenteric lymph nodes.

Yersinia has a tropism for B and T cell zones of lymph nodes that is independent of the type III secretion system

Pathogenic Yersinia have a pronounced tropism for lymphatic tissues and harbor a virulence plasmid that encodes a type III secretion system, pTTSS, that transports Yops into host cells. Yops are critical virulence factors that prevent phagocytosis by macrophages and neutrophils and Yersinia mutants lacking one or more Yops are defective for survival in lymphatic tissues, liver, and gastrointestinal tract. However, here we demonstrate that Y. pseudotuberculosis (Yptb) mutants lacking the pTTSS survived as well as or better than wild-type (WT) Yptb in the mesenteric lymph nodes (MLN). Infection with pTTSS mutants caused lymphadenitis with little necrosis, whereas infection with WT Yptb provoked lymphadenitis with multiple necrotic suppurative foci. Gentamicin protection assays and microscopic examination of the MLN revealed that pTTSS mutants resided extracellularly adjacent to B and T lymphocytes in the cortex and paracortex. WT Yptb was found extracellularly adjacent to neutrophils and macrophages in necrotic areas and adjacent to B and T lymphocytes in less-inflamed areas. To determine whether lymphocytes protected pTTSS mutants from phagocytic cells, Rag1(-/-) mice were infected with pTTSS mutants or WT Yptb. pTTSS mutants but not WT, were impaired for survival in MLN of Rag1(-/-) mice, suggesting that lymphocyte-rich regions constitute a protective niche for pTTSS mutants. Finally, we show that invasin and the chromosomally encoded TTSS were not required for Yptb survival in MLN. In summary, chromosomally encoded factors are sufficient for Yptb replication in the cortex and paracortex of MLN; the pTTSS enables Yersinia to survive within phagocyte-rich areas of lymph nodes, and spread to other tissues.

The role of wild birds and the environment in the epidemiology of Yersiniae in New Zealand

A survey was carried out to determine the prevalence of Yersiniae in wild passerines in the lower half of the North island of New Zealand over a period of 12 months. Samples of soil, water and foliage were also collected. Out of a total of 1370 avian samples, only two strains of Y. pseudotuberculosis were isolated and a total of 98 strains of environmental yersiniae were identified, including Y. enterocolitica biotype 1a, Y. frederiksenii, Y. kristensenii and Y. intermedia. No strains of Y. pseudotuberculosis were isolated from 1032 non-avian samples collected, which included 100 samples taken from wild mammals. From the non-avian samples, 51 strains of environmental Yersiniae were identified, of which the relative prevalence of Yersinia enterocolitica, biotype 1a, Y. frederiksenii, Y. kristensenii and Y. intermedia was similar to that in the rural passerines. The prevalence of Yersiniae in soil samples was greater in rural areas than in urban areas of the survey region. In both rural and urban passerine populations, the prevalence of Yersiniae was greater in the winter and early summer than at other times of the year.

Application of high-density array-based signature-tagged mutagenesis to discover novel Yersinia virulence-associated genes

Yersinia pestis, the causative agent of plague, and the enteropathogen Yersinia pseudotuberculosis have nearly identical nucleotide similarity yet cause markedly different diseases. To investigate this conundrum and to study Yersinia pathogenicity, we developed a high-density oligonucleotide array-based modification of signature-tagged mutagenesis (STM). Y. pseudotuberculosis YPIII mutants constructed with the tagged transposons were evaluated in the murine yersiniosis infection model. The DNA tags were amplified using biotinylated primers and hybridized to high-density oligonucleotide arrays containing DNA complementary to the tags. Comparison of the hybridization signals from input pools and output pools identified a mutant whose relative abundance was significantly reduced in the output pool. Sequence data from 31 transposon insertion regions was compared to the complete Y. pestis CO92 genome sequence. The 26 genes present in both species were found to be almost identical, but five Y. pseudotuberculosis genes identified through STM did not have counterparts in the Y. pestis genome and may contribute to the different tropisms in these closely related pathogens. Potential virulence genes identified include those involved in lipopolysaccharide biosynthesis, adhesion, phospholipase activity, iron assimilation, and gene regulation. The phospholipase A (PldA) mutant exhibited reduced phospholipase activity compared to the wild-type strain and in vivo attenuation of the mutant was confirmed. The combination of optimized double tag sequences and high-density array hybridization technology offers improved performance, efficiency, and reliability over classical STM and permits quantitative analysis of data.

Identification of pathogenic strains within serogroups of Yersinia pseudotuberculosis and the presence of non-pathogenic strains isolated from animals and the environment

The existence of apathogenic strains of Yersinia pseudotuberculosis (Yp) has not so far been reported. Recently, the authors characterized new serogroups and a new subgroup in Yp, that is, O9, O10, O12, O13 and O14 and O1c, and the pathogenicity of these new strains was of interest. A total of 137 strains of serogroups O1c, O6, O7, O9, O10, O11, O12, O13 and O14 of Yp were investigated for their pathogenicity in vivo and in vitro. Although catalase activity and the inv gene were detected in all strains except those of groups O13 and O14, only a few strains, from serogroups O6 and O10 caused severe infection in mice. The remaining strains caused no mortality or severe infection even when they grew in limited tissues of infected mice. All the strains of Yp not possessing the virulence plasmid p YV caused no severe infection in mice. It is evident that less pathogenic Yp exists and that not only pathogenic but also less pathogenic Yp organisms exist in the same serogroup.