The genetic basis of tetrathionate respiration in Salmonella typhimurium.
ABSTRACT A range of bacteria are able to use tetrathionate as a terminal respiratory electron acceptor. Here we report the identification and characterization of the ttrRSBCA locus required for tetrathionate respiration in Salmonella typhimurium LT2a. The ttr genes are located within Salmonella pathogenicity island 2 at centisome 30.5. ttrA, ttrB and ttrC are the tetrathionate reductase structural genes. Sequence analysis suggests that TtrA contains a molybdopterin guanine dinucleotide cofactor and a [4Fe-4S] cluster, that TtrB binds four [4Fe-4S] clusters, and that TtrC is an integral membrane protein containing a quinol oxidation site. TtrA and TtrB are predicted to be anchored by TtrC to the periplasmic face of the cytoplasmic membrane implying a periplasmic site for tetrathionate reduction. It is inferred that the tetrathionate reductase, together with thiosulphate and polysulphide reductases, make up a previously unrecognized class of molybdopterin-dependent enzymes that carry out the reductive cleavage of sulphur-sulphur bonds. Cys-256 in TtrA is proposed to be the amino acid ligand to the molybdopterin cofactor. TtrS and TtrR are the sensor and response regulator components of a two-component regulatory system that is absolutely required for transcription of the ttrBCA operon. Expression of an active tetrathionate reduction system also requires the anoxia-responsive global transcriptional regulator Fnr. The ttrRSBCA gene cluster confers on Escherichia coli the ability to respire with tetrathionate as electron acceptor.
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ABSTRACT: The human intestinal epithelium consists of a single layer of epithelial cells that forms a barrier against food antigens and the resident microbiota within the lumen. This delicately balanced organ functions in a highly sophisticated manner to uphold the fidelity of the intestinal epithelium and to eliminate pathogenic microorganisms. On the luminal side, this barrier is fortified by a thick mucus layer, and on the serosal side exists the lamina propria containing a resident population of immune cells. Pathogens that are able to breach this barrier disrupt the healthy epithelial lining by interfering with the regulatory mechanisms that govern the normal balance of intestinal architecture and function. This disruption results in a coordinated innate immune response deployed to eliminate the intruder that includes the release of antimicrobial peptides, activation of pattern-recognition receptors, and recruitment of a variety of immune cells. In the case of Salmonella enterica serovar typhimurium (S. typhimurium) infection, induction of an inflammatory response has been linked to its virulence mechanism, the type III secretion system (T3SS). The T3SS secretes protein effectors that exploit the host's cell biology to facilitate bacterial entry and intracellular survival, and to modulate the host immune response. As the role of the intestinal epithelium in initiating an immune response has been increasingly realized, this review will highlight recent research that details progress made in understanding mechanisms underlying the mucosal inflammatory response to Salmonella infection, and how such inflammatory responses impact pathogenic fitness of this organism.Frontiers in Immunology 01/2014; 5:311.
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ABSTRACT: A total of 200 samples of milk and dairy products as well as 120 samples of dairy handlers were randomly collected from different dairy farms and supermarkets in Dakahlia Governorate, Egypt. The conventional cultural and serotyping methods for detection of Salmonella in dairy products were applied and the results were compared with those obtained by molecular screening assay using (ttr sequence). The obtained results revealed that 21% of milk and dairy products (42/200) were positive for Salmonella species using enrichment culture-based PCR method, while 12% of different dairy samples (24/200) were found to be positive for Salmonella species by using the conventional culture methods. Two stool specimens out of 40 apparently healthy dairy handlers were positive by the PCR method. Serotyping of Salmonella isolates revealed that 58.3% (14/24) from different dairy products were contaminated with Salmonella Typhimurium. We conclude that the enrichment culture-based PCR assay has high sensitivity and specificity for detection of Salmonella species in dairy products and handlers. High incidence of Salmonella Typhimurium in the examined dairy samples highlights the important role played by milk and dairy products as a vehicle in disease prevalence. Great effort should be applied for reducing foodborne risk for consumers.Veterinary medicine international. 01/2014; 2014:502370.
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ABSTRACT: During the last decade Campylobacter jejuni has been recognized as the leading cause of bacterial gastroenteritis worldwide. This facultative intracellular pathogen is a member of the Epsilonproteobacteria and requires microaerobic atmosphere and nutrient rich media for efficient proliferation in vitro. Its catabolic capacity is highly restricted in contrast to Salmonella Typhimurium and other enteropathogenic bacteria because several common pathways for carbohydrate utilization are either missing or incomplete. Despite these metabolic limitations, C. jejuni efficiently colonizes various animal hosts as a commensal intestinal inhabitant. Moreover, C. jejuni is tremendously successful in competing with the human intestinal microbiota; an infectious dose of few hundreds bacteria is sufficient to overcome the colonization resistance of humans and can lead to campylobacteriosis. Besides the importance and clear clinical manifestation of this disease, the pathogenesis mechanisms of C. jejuni infections are still poorly understood. In recent years comparative genome sequence, transcriptome and metabolome analyses as well as mutagenesis studies combined with animal infection models have provided a new understanding of how the specific metabolic capacity of C. jejuni drives its persistence in the intestinal habitat of various hosts. Furthermore, new insights into the metabolic requirements that support the intracellular survival of C. jejuni were obtained. Because C. jejuni harbors distinct properties in establishing an infection in comparison to pathogenic Enterobacteriaceae, it represents an excellent organism for elucidating new aspects of the dynamic interaction and metabolic cross talk between a bacterial pathogen, the microbiota and the host.Frontiers in Cellular and Infection Microbiology 09/2014; · 2.62 Impact Factor