Uncovering genomic differences in human pathogenic Yersinia enterocolitica

A comprehensive review on the prevalence, pathogenesis and detection ofYersinia enterocolitica

Food safety is imperative for a healthy life, but pathogens are still posing a significant life threat. “Yersiniosis” is caused by a pathogen named Yersinia enterocolitica and is characterized by diarrheal, ileitis, and mesenteric lymphadenitis types of sicknesses. This neglected pathogen starts its pathogenic activity by colonizing inside the intestinal tract of the host upon the ingestion of contaminated food. Y. enterocolitica remains a challenge for researchers and food handlers due to its growth habits, low concentrations in samples, morphological similarities with other bacteria and lack of rapid, cost-effective, and accurate detection methods. In this review, we presented recent information about its prevalence, biology, pathogenesis, and existing cultural, immunological, and molecular detection approaches. Our ultimate goal is to provide updated knowledge regarding this pathogen for the development of quick, effective, automated, and sensitive detection methods for the systematic detection of Y. enterocolitica.

Food safety is imperative for a healthy life, but pathogens are still posing a significant life threat.

Detection of Yersinia enterocolitica in food: an overview

Yersinia enterocolitica is a gastrointestinal pathogen which causes yersiniosis, an illness characterized by diarrhea, ileitis, and mesenteric lymphadenitis. Y. enterocolitica is transmitted via the feco-oral route by the consumption of contaminated food or water. Several phenotypic and genotypic methods have been developed to reliably detect Y. enterocolitica in food. However, the source of infection of many recently reported foodborne outbreaks remains obscure. The detection of this pathogen in food is a challenging task, since it shares similarities with other enteric bacteria. The presence of other microorganisms in the food samples makes it even more difficult to identify this slow-growing pathogen. Therefore, the present-day emphasis is on the development of sensitive, easily automated methods suitable for in-situ detection, allowing quick and cost-effective characterization of food samples. This review summarizes and compares the currently available cultural, immunological, and molecular methods, particularly in relation to their specific merits or demerits when implemented for the detection of Y. enterocolitica in food.

Ca2+-binding motif of βγ-crystallins

βγ-Crystallin-type double clamp (N/D)(N/D)XX(S/T)S motif is an established but sparsely investigated motif for Ca(2+) binding. A βγ-crystallin domain is formed of two Greek key motifs, accommodating two Ca(2+)-binding sites. βγ-Crystallins make a separate class of Ca(2+)-binding proteins (CaBP), apparently a major group of CaBP in bacteria. Paralleling the diversity in βγ-crystallin domains, these motifs also show great diversity, both in structure and in function. Although the expression of some of them has been associated with stress, virulence, and adhesion, the functional implications of Ca(2+) binding to βγ-crystallins in mediating biological processes are yet to be elucidated.

Identification and distribution of putative virulence genes in clinical strains of Yersinia enterocolitica biovar 1A by suppression subtractive hybridization

AIMS

To detect putative virulence genes in clinical strains of Yersinia enterocolitica biovar 1A by suppression subtractive hybridization between two closely related strains of clinical and nonclinical origin having the same serotype (O:6,30-6,31).

METHODS AND RESULTS

Suppression Subtractive Hybridization (SSH) was used to identify genomic differences between clinical (serotype O:6,30-6,31, from diarrhoeic human stools) and nonclinical (serotype O:6,30-6,31, from wastewater) strains of Y. enterocolitica biovar 1A. Following genomic subtraction and DNA sequencing, nine DNA sequences that were present only in clinical biovar 1A strains were identified. The sequences identified using SSH showed similarity to conserved hypothetical proteins, proteins related to iron acquisition and haemin storage, type 1 secretion proteins, flagellar hook proteins, exported protein and ABC transport system. All these sequences showed high similarity with Y. enterocolitica 8081 (biovar 1B). The distribution of these genes was further analysed using PCR in 26 clinical strains of Y. enterocolitica biovar 1A. The results revealed that the distribution of these genes was not uniform.

CONCLUSIONS

Genes related to iron acquisition and storage, and flagellar proteins might be responsible for virulence of some of the clinical strains of Y. enterocolitica biovar 1A.

SIGNIFICANCE AND IMPACT OF THE STUDY

Genes identified in this study might be useful in understanding the pathogenic potential of clinical strains of Y. enterocolitica biovar 1A.

Translocated effectors of Yersinia

Currently, all known translocated effectors of Yersinia are delivered into host cells by type III secretion systems (T3SSs). Pathogenic Yersinia maintain the plasmid-encoded Ysc T3SS for the specific delivery of the well-studied Yop effectors. New horizons for effector biology have opened with the discovery of the Ysps of Y. enterocolitica Biovar 1B, which are translocated into host cells by the chromosome-endoded Ysa T3SS. The reported arsenal of effectors is likely to expand since genomic analysis has revealed gene-clusters in some Yersinia that code for other T3SSs. These efforts also revealed possible type VI secretion (T6S) systems, which may indicate that translocation of effectors occurs by multiple mechanisms.

Identification of genetic differences between two clinical isolates of Streptococcus mutans by suppression subtractive hybridization

Streptococcus mutans is generally considered to be the principal aetiological agent for dental caries. Phenotypic variation in strains is often associated with differences in gene content, so the isolation of DNA fragments from these genes or associated regions is illuminating. The S. mutans strains 9-1 and 9-2, which both colonized the same oral cavity, were selected after screening for the possession of suspected virulence traits. Genomic DNA of strain 9-1 was used as the tester, and that of 9-2 was used as the driver. Suppression subtractive hybridization (SSH) was applied between the tester and the driver DNAs. The subtractive products were cloned into a pCR2.1 vector. Clone libraries representing sequence differences were obtained. The subtractive fragments that were found specifically in strain 9-1 but not in strain 9-2 were identified by dot blotting and then sequenced. BLASTn and BLASTx sequence homology analyses were subsequently performed. Twenty-seven sequences were found in the genome of strain 9-1 that were not in 9-2. Among them, three revealed no homology to published nucleotide sequences while the remaining sequences showed 81-100% homology to known genes of S. mutans strain UA159. These sequences are involved in competence development, signal transduction and transcriptional regulation, repairing stress damage, transport, carbohydrate catabolism, biochemical synthesis, or unknown functions. Differences exist in the genomes of different S. mutans isolates. SSH is effective in screening for S. mutans strain specific DNA sequences.

Mutagenesis of all eight avr genes in Xanthomonas campestris pv. campestris had no detected effect on pathogenicity, but one avr gene affected race specificity

Suppression subtractive hybridization (SSH) was used to identify genes present in the systemic crucifer black rot pathogen Xanthomonas campestris pv. campestris 528T but missing from the nonsystemic crucifer leaf spot pathogen, X. campestris pv. armoraciae 417. Among the DNA fragments unique to 528T was Xcc2109, one of eight putative avr genes identified in the published 528T genome (NC_003902). Individual and sequential deletion, insertion mutations, or both of all eight 528T avr gene loci were made, but no change in pathogenicity was observed with any combination of avr mutations, including a strain with all eight avr genes deleted. However, insertion or deletion mutants affecting the Xcc2109 locus lost avirulence (i.e., became virulent) on Florida Mustard, an X. campestris pv. campestris race-determining, differential host. The Xcc2109 open reading frame as annotated was cloned and found to be nonfunctional. A longer gene, encompassing Xcc2109 and here designated avrXccFM, was cloned and found to complement the Xcc2109 mutants and to confer avirulence to two additional wild-type X. campestris pv. campestris strains, thereby changing their races. Resistance in Florida Mustard to 528T strains carrying avrXccFM occurred without a typical hypersensitive response (HR) on leaves, although a vascular HR was observed in seedlings.

Type III secretion: more systems than you think

The type III secretion (T3S) pathway allows bacteria to inject effector proteins into the cytosol of target animal or plant cells. T3S systems evolved into seven families that were distributed among Gram-negative bacteria by horizontal gene transfer. There are probably a few hundred effectors interfering with control and signaling in eukaryotic cells and offering a wealth of new tools to cell biologists.

Calcium-binding Crystallins from Yersinia pestis

Betagamma-crystallin is a superfamily with diverse members from vertebrate lens to microbes. However, not many members have been identified and studied. Here, we report the identification of a putative exported protein from Yersinia pestis as a member of the betagamma-crystallin superfamily. Even though calcium has been known to play an important role in the physiology and virulence of the Yersinia genus, calcium-binding proteins have not yet been identified. We have studied the calcium-binding properties of two of the three crystallin domains present in this putative exported protein designated "Yersinia crystallin." These two domains (D1 and D2) have unique AA and BB types of arrangement of their Greek key motifs unlike the domains of other members of the betagamma-crystallin superfamily, which are either AB or BA types. These domains bind two calcium ions with low and high affinity-binding sites. We showed their calcium-binding properties using various probes for calcium and the effect of calcium on their secondary and tertiary structures. Although both domains bind calcium, D1 underwent drastic changes in secondary and tertiary structure and hydrodynamic volume upon calcium binding. Domain D1, which is intrinsically unstructured in the apo form, requires calcium for the typical betagamma-crystallin fold. Calcium exerted an extrinsic stabilization effect on domain D1 but not on D2, which is also largely unstructured. We suggest that this protein might be involved in calcium-dependent processes, such as stress response or physiology in the Yersinia genus, similar to its microbial relatives and mammalian lens crystallins.