Select Phytochemicals Reduce Campylobacter jejuni in Postharvest Poultry and Modulate the Virulence Attributes of C. jejuni

Consumption or handling of poultry and poultry products contaminated with Campylobacter species are a leading cause of foodborne illness in humans. Current strategies employed to reduce Campylobacter in live chickens provide inconsistent results indicating the need for an alternative approach. This study investigated the efficacy of phytochemicals, namely, turmeric, curcumin, allyl sulfide, garlic oil, and ginger oil, to reduce Campylobacter jejuni in postharvest poultry and sought to delineate the underlying mechanisms of action. Two experiments were conducted on the thigh skin of the chicken, and each experiment was repeated twice. Samples were inoculated with 50 μl (∼10⁷ CFU/sample) of C. jejuni strain S-8 and allowed to adhere for 30 min. Skin samples were dipped into their respective prechilled treatment solutions (0.25 and 0.5% in experiments 1 and 2, respectively) at 4°C for an hour to simulate chilling tank treatment, followed by plating to enumerate C. jejuni (n = 3 samples/treatment/trial). The mechanisms of action(s) were investigated using subinhibitory concentration (SIC) in adhesion, quorum sensing, and gene expression analyses. Adhesion assay was conducted on the monolayers of ATCC CRL-1590 chicken embryo cells challenged with C. jejuni and incubated in the presence or absence of phytochemicals for 1.5 h, followed by plating to enumerate adhered C. jejuni. The effects of phytochemicals on quorum sensing and cell viability were investigated using Vibrio harveyi bioluminescence and LIVE/Dead BacLight^TM bacterial viability assays, respectively. In addition, droplet digital PCR determined the gene expression analyses of C. jejuni exposed to phytochemicals. Data were analyzed by GraphPad Prism version 9. C. jejuni counts were reduced by 1.0–1.5 Log CFU/sample with garlic oil or ginger oil at 0.25 and 0.5% (p < 0.05). The selected phytochemicals (except curcumin) reduced the adhesion of C. jejuni to chicken embryo cells (p < 0.05). In addition, all the phytochemicals at SIC reduced quorum sensing of C. jejuni (p < 0.05). The cell viability test revealed that cells treated with 0.25% of phytochemicals had compromised cell membranes indicating this as a mechanism that phytochemicals use to damage/kill C. jejuni. This study supports that the application of phytochemicals in postharvest poultry would significantly reduce C. jejuni in poultry meat.

Assessment of microbiological correlates and immunostimulatory potential of electron beam inactivated metabolically active yet non culturable (MAyNC) Salmonella Typhimurium

This study investigates the microbiological and immunological basis underlying the efficacy of electron beam-inactivated immune modulators. The underlying hypothesis is that exposure to eBeam-based ionization reactions inactivate microorganisms without modifying their antigenic properties and thereby creating immune modulators. The immunological correlates of protection induced by such eBeam based Salmonella Typhimurium (EBST) immune modulators in dendritic cell (DC) (in vitro) and mice (in vivo) models were assessed. The EBST stimulated innate pro inflammatory response (TNFα) and maturation (MHC-II, CD40, CD80 and CD86) of DC. Immuno-stimulatory potential of EBST was on par with both a commercial Salmonella vaccine, and live Salmonella cells. The EBST cells did not multiply under permissive in vitro and in vivo conditions. However, EBST cells remained metabolically active. EBST immunized mice developed Salmonella-specific CD4+ T-cells that produced the Th1 cytokine IFNγ at a level similar to that induced by the live attenuated vaccine (AroA^- ST) formulation. The EBST retained stable immunogenic properties for several months at room temperature, 4°C, and -20°C as well as after lyophilization. Therefore, such eBeam-based immune modulators have potential as vaccine candidates since they offer the safety of a “killed” vaccine, while retaining the immunogenicity of an “attenuated” vaccine. The ability to store eBeam based immune modulators at room temperature without loss of potency is also noteworthy.

Controlling the Colonization of Clostridium perfringens in Broiler Chickens by an Electron-Beam-Killed Vaccine

Clostridium perfringens (Cp) is a Gram-positive anaerobe that is one of the causative agents of necrotic enteritis (NE) in chickens, which leads to high mortality. Owing to the ban of administering antibiotics in feed to chickens, there has been an increase in the number of NE outbreaks all over the world, and the estimated loss is approximately 6 billion U.S. dollars. The best alternative method to control NE without antibiotics could be vaccination. In this study, we exposed three different strains of Cp to electron beam (eBeam) irradiation to inactivate them and then used them as a killed vaccine to control the colonization of Cp in broiler chickens. The vaccine was delivered to 18-day old embryos in ovo and the chickens were challenged with the respective vaccine strain at two different time points (early and late) to test the protective efficacy of the vaccine. The results indicate that an effective eBeam dose of 10 kGy inactivated all three strains of Cp, did not affect the cell membrane or epitopes, induced significant levels of IgY in the vaccinated birds, and further reduced the colonization of Cp strains significantly (p < 0.0001) in late challenge (JGS4064: 4 out of 10; JGS1473: 0 out of 10; JGS4104: 3 out of 10). Further studies are necessary to enhance the efficacy of the vaccine and to understand the mechanism of vaccine protection.

Identification and Characterization of a Poliovirus Capsid Mutant with Enhanced Thermal Stability

Enteric viruses, including poliovirus, are spread by the fecal-oral route. In order to persist and transmit to a new host, enteric virus particles must remain stable once they are in the environment. Environmental stressors such as heat and disinfectants can inactivate virus particles and prevent viral transmission. It has been previously demonstrated that bacteria or bacterial surface glycans can enhance poliovirus virion stability and limit inactivation from heat or bleach. While investigating the mechanisms underlying bacterially enhanced virion thermal stability, we identified and characterized a poliovirus (PV) mutant with increased resistance to heat inactivation. The M132V mutant harbors a single amino acid change in the VP1 capsid coding that is sufficient to confer heat resistance but not bleach resistance. Although the M132V virus was stable in the absence of bacteria or feces at most temperatures, M132V virus was stabilized by feces at very high temperatures. M132V PV had reduced specific infectivity and RNA uncoating compared with those of wild-type (WT) PV, but viral yields in HeLa cells were similar. In orally inoculated mice, M132V had a slight fitness cost since fecal titers were lower and 12.5% of fecal viruses reverted to the WT. Overall, this work sheds light on factors that influence virion stability and fitness.IMPORTANCE Viruses spread by the fecal-oral route need to maintain viability in the environment to ensure transmission. Previous work indicated that bacteria and bacterial surface polysaccharides can stabilize viral particles and enhance transmission. To explore factors that influence viral particle stability, we isolated a mutant poliovirus that is heat resistant. This mutant virus does not require feces for stability at most temperatures but can be stabilized by feces at very high temperatures. Even though the mutant virus is heat resistant, it is susceptible to inactivation by treatment with bleach. This work provides insight into how viral particles maintain infectivity in the environment.

Bacteria Facilitate Enteric Virus Co-infection of Mammalian Cells and Promote Genetic Recombination

RNA viruses exist in genetically diverse populations due to high levels of mutations, many of which reduce viral fitness. Interestingly, intestinal bacteria can promote infection of several mammalian enteric RNA viruses, but the mechanisms and consequences are unclear. We screened a panel of 41 bacterial strains as a platform to determine how different bacteria impact infection of poliovirus, a model enteric virus. Most bacterial strains, including those extracted from cecal contents of mice, bound poliovirus, with each bacterium binding multiple virions. Certain bacterial strains increased viral co-infection of mammalian cells even at a low virus-to-host cell ratio. Bacteria-mediated viral co-infection correlated with bacterial adherence to cells. Importantly, bacterial strains that induced viral co-infection facilitated genetic recombination between two different viruses, thereby removing deleterious mutations and restoring viral fitness. Thus, bacteria-virus interactions may increase viral fitness through viral recombination at initial sites of infection, potentially limiting abortive infections.

Plaques Formed by Mutagenized Viral Populations Have Elevated Coinfection Frequencies

The plaque assay is a common technique used to measure virus concentrations and is based upon the principle that each plaque represents a single infectious unit. As such, the number of plaques is expected to correlate linearly with the virus dilution plated, and each plaque should be formed by a single founder virus. Here, we examined whether more than one virus can contribute to plaque formation. By using genetic and phenotypic assays with genetically marked polioviruses, we found that multiple parental viruses are present in 5 to 7% of plaques, even at an extremely low multiplicity of infection. We demonstrated through visual and biophysical assays that, like many viral stocks, our viral stocks contain both single particles and aggregates. These data suggest that aggregated virions are capable of inducing coinfection and chimeric plaque formation. In fact, inducing virion aggregation via exposure to low pH increased coinfection in a flow cytometry-based assay. We hypothesized that plaques generated by viruses with high mutation loads may have higher coinfection frequencies due to processes restoring fitness, such as complementation and recombination. Indeed, we found that coinfection frequency correlated with mutation load, with 17% chimeric plaque formation for heavily mutagenized viruses. Importantly, the frequency of chimeric plaques may be underestimated by up to threefold, since coinfection with the same parental virus cannot be scored in our assay. This work indicates that more than one virus can contribute to plaque formation and that coinfection may assist plaque formation in situations where the amount of genome damage is high.IMPORTANCE One of the most common methods to quantify viruses is the plaque assay, where it is generally presumed that each plaque represents a single infectious virus. Using genetically marked polioviruses, we demonstrate that a plaque can contain more than one parental virus, likely due to aggregates within virus stocks that induce coinfection of a cell. A relatively small number of plaques are the products of coinfection for our standard virus stocks. However, mutagenized virus stocks with increased genome damage give rise to a higher amount of plaques that are chimeric. These results suggest that coinfection may aid plaque formation of viruses with genome damage, possibly due to processes such as complementation and recombination. Overall, our results suggest that the relationship between viral dilution and plaque number may not be linear, particularly for mutagenized viral populations.

Comparison of three neurotropic viruses reveals differences in viral dissemination to the central nervous system

Neurotropic viruses initiate infection in peripheral tissues prior to entry into the central nervous system (CNS). However, mechanisms of dissemination are not completely understood. We used genetically marked viruses to compare dissemination of poliovirus, yellow fever virus 17D (YFV-17D), and reovirus type 3 Dearing in mice from a hind limb intramuscular inoculation site to the sciatic nerve, spinal cord, and brain. While YFV-17D likely entered the CNS via blood, poliovirus and reovirus likely entered the CNS by transport through the sciatic nerve to the spinal cord. We found that dissemination was inefficient in adult immune-competent mice for all three viruses, particularly reovirus. Dissemination of all viruses was more efficient in immune-deficient mice. Although poliovirus and reovirus both accessed the CNS by transit through the sciatic nerve, stimulation of neuronal transport by muscle damage enhanced dissemination only of poliovirus. Our results suggest that these viruses access the CNS using different pathways.

Electron-Beam-Inactivated Vaccine Against Salmonella Enteritidis Colonization in Molting Hens

Electron-beam (eBeam) irradiation technology has a variety of applications in modern society. The underlying hypothesis was that eBeam-inactivated Salmonella enterica serovar Enteritidis (SE) cells can serve as a vaccine to control SE colonization and shedding in poultry birds. An eBeam dose of 2.5 kGy (kilograys) was used to inactivate a high-titer (10(8) colony-forming units [CFU]) preparation of SE cells. Microscopic studies revealed that the irradiation did not damage the bacterial cell membranes. The vaccine efficacy was evaluated by administering the eBeam-killed SE cells intramuscularly (1 x 10(6) CFU/bird) into 50-wk-old single comb white leghorn hens. On day 14 postvaccination, the hens were challenged orally with live SE cells (1 x 10(9) CFU) and SE colonization of liver, spleen, ceca, and ovaries determined on day 23. Blood samples were collected on days 0, 14, and 23 postvaccination and the sera were analyzed to quantify SE-specific IgG titers. The vaccinated chickens exhibited significantly (P < 0.0001) higher SE-specific IgG antibody responses and reduced SE ceca colonization (1.46 ± 0.39 logi10 CFU/g) compared to nonvaccinated birds (5.32 ± 0.32 log10 CFU/g). They also exhibited significantly lower SE colonization of the ovaries (1/30), spleen (3/30), liver (4/30), and ceca (7/30) compared to nonvaccinated birds. These results provide empirical evidence that eBeam-based SE vaccines are immunogenic and are capable of protecting chickens against SE colonization. The advantages of eBeam-based vaccine technology are that it is nonthermal, avoids the use of formalin, and can be used to generate inactivated vaccines rapidly to address strain-specific infections in farms or flocks.

Bacterial lipopolysaccharide binding enhances virion stability and promotes environmental fitness of an enteric virus

Enteric viruses, including poliovirus and reovirus, encounter a vast microbial community in the mammalian gastrointestinal tract, which has been shown to promote virus replication and pathogenesis. Investigating the underlying mechanisms, we find that poliovirus binds bacterial surface polysaccharides, which enhances virion stability and cell attachment by increasing binding to the viral receptor. Additionally, we identified a poliovirus mutant, VP1-T99K, with reduced lipopolysaccharide (LPS) binding. Although T99K and WT poliovirus cell attachment, replication, and pathogenesis in mice are equivalent, VP1-T99K poliovirus was unstable in feces following peroral inoculation of mice. Consequently, the ratio of mutant virus in feces is reduced following additional cycles of infection in mice. Thus, the mutant virus incurs a fitness cost when environmental stability is a factor. These data suggest that poliovirus binds bacterial surface polysaccharides, enhancing cell attachment and environmental stability, potentially promoting transmission to a new host.

Electron beam inactivation of selected microbial pathogens and indicator organisms in aerobically and anaerobically digested sewage sludge

Microbial pathogens in municipal sewage sludges need to be inactivated prior to environmental disposal. The efficacy of high energy (10 MeV) e-beam irradiation to inactivate a variety of selected microbial pathogens and indicator organisms in aerobically and anaerobically digested sewage sludge was evaluated. Both bacterial and viral pathogens and indicator organisms are susceptible to e-beam irradiation. However, as expected there was a significant difference in their respective e-beam irradiation sensitivity. Somatic coliphages, bacterial endospores and enteric viruses were more resistant compared to bacterial pathogens. The current US EPA mandated 10 kGy minimum dose was capable of achieving significant reduction of both bacterial and viral pathogens. Somatic coliphages can be used as a microbial indicator for monitoring e-beam processes in terms of pathogen inactivation in sewage sludges.

Isolimonic acid interferes with Escherichia coli O157:H7 biofilm and TTSS in QseBC and QseA dependent fashion

BACKGROUND

E. coli O157:H7 (EHEC) is an important human pathogen. The antibiotic treatment of EHEC reportedly results in release of Shiga toxin and is therefore discouraged. Consequently, alternative preventive or therapeutic strategies for EHEC are required. The objective of the current study was to investigate the effect of citrus limonoids on cell-cell signaling, biofilm formation and type III secretion system in EHEC.

RESULTS

Isolimonic acid and ichangin were the most potent inhibitors of EHEC biofilm (IC25=19.7 and 28.3 μM, respectively) and adhesion to Caco-2 cells. The qPCR analysis revealed that isolimonic acid and ichangin repressed LEE encoded genes by ≈3 to 12 fold. In addition, flhDC was repressed by the two limonoids (≈3 to 7 fold). Further studies suggested that isolimonic acid interferes with AI-3/epinephrine activated cell-cell signaling pathway. Loss of biofilm inhibitory activity of isolimonic acid in ΔqseBC mutant, which could be restored upon complementation, suggested a dependence on functional QseBC. Additionally, overexpression of qseBC in wild type EHEC abated the inhibitory effect of isolimonic acid. Furthermore, the isolimonic acid failed to differentially regulate ler in ΔqseA mutant, while plasmid borne expression of qseA in ΔqseA background restored the repressive effect of isolimonic acid.

CONCLUSIONS

Altogether, results of study seem to suggest that isolimonic acid and ichangin are potent inhibitors of EHEC biofilm and TTSS. Furthermore, isolimonic acid appears to interfere with AI-3/epinephrine pathway in QseBC and QseA dependent fashion.

Comparing extraction buffers to identify optimal method to extract somatic coliphages from sewage sludges

Somatic coliphages are present in high numbers in sewage sludge. Since they are conservative indicators of viruses during wastewater treatment processes, they are being used to evaluate the effectiveness of sludge treatment processes. However, efficient methods to extract them from sludge are lacking. The objective was to compare different virus extraction procedures and develop a method to extract coliphages from sewage sludge. Twelve different extraction buffers and procedures varying in composition, pH, and sonication were compared in their ability to recover indigenous phages from sludges. The 3% buffered beef extract (BBE) (pH 9.0), the 10% BBE (pH 9.0), and the 10% BBE (pH 7.0) with sonication were short-listed and their recovery efficiency was determined using coliphage-spiked samples. The highest recovery was 16% for the extraction that involved 10% BBE at pH 9.0. There is a need to develop methods to extract somatic phages from sludges for monitoring sludge treatment processes.

Detection of autoinducer (AI-2)-like activity in food samples

The contamination, survival, and possible foodborne disease outbreaks are major issues confronting the food industry. However, from a microbial perspective, any food whether natural or processed is just another environmental niche that is available for colonization. Quorum sensing or cell-cell communication is a process by which microorganisms are thought to communicate with each other using a variety of small molecules termed autoinducers. The autoinducer AI-2 is thought to be a universal signaling molecule due to its ability to modulate the gene expression of a number of different bacterial species and genera. Pathogens such as Pseudomonas aeruginosa, Aeromonas hydrophila, Vibrio anguillarum, Streptococcus sp., and Burkholderia cepacia form biofilms on a variety of man-made and natural surfaces using cell-cell mechanisms. It is important to detect and study autoinducers and their activities in foods, since a better understanding of these molecules in food and food ingredients may help in designing new approaches to thwart microbial persistence and biofilm formation. The autoinducer AI-2 is thought to be involved in microbial attachment and biofilm formation leading to food spoilage. To better understand microbial cell-cell signaling in foods especially as it relates to pathogen persistence, biofilm formation, and food spoilage, methods to process, extract, and purify autoinducer molecules need to be developed. This chapter details methods to process food samples to obtain cell-free supernatants (CFS), which could subsequently be tested for the presence of AI-2 or "AI-2-like activity" in the extracted CFS using autoinducer bioassays. Additionally, the method of synthesizing AI-2 in the laboratory is also provided. The methods that are presented in this chapter are based on previously published research articles from the authors' laboratory.

Citrus flavonoid represses Salmonella pathogenicity island 1 and motility in S. Typhimurium LT2

Salmonellosis is one of the leading health problems worldwide. With the rise of drug resistance strains, it has become imperative to identify alternative strategies to counter bacterial infection. Natural products were used historically to identify novel compounds with various bioactivities. Citrus species is a rich source of flavonoids. Naringenin, a flavonone, is present predominantly in grapefruit. Previously we have demonstrated that naringenin is potent inhibitor of cell-cell signaling. The current study was undertaken to understand the effect of naringenin on Salmonella Typhimurium LT2. The cDNA microarrays were employed to study the response of S. Typhimurium to naringenin treatment. Naringenin specifically repressed 24 genes in the Salmonella pathogenicity island 1 and down-regulated 17 genes involved in flagellar and motility. Furthermore, phenotypic assays support the result of microarray analysis. In addition, naringenin seems to repress SPI-1 in pstS/hilD-dependent manner. Altogether the data suggest that naringenin attenuated S. Typhimurium virulence and cell motility. This is the first molecular evidence to demonstrate effect of naringenin on bacterial virulence and cell motility.

Citrus limonoids interfere with Vibrio harveyi cell-cell signalling and biofilm formation by modulating the response regulator LuxO

Citrus limonoids are unique secondary metabolites, characterized by a triterpenoid skeleton with a furan ring. Studies have demonstrated beneficial health properties of limonoids. In addition, certain citrus limonoids play a role in plant defence against insect pests. In the present study, five limonoids were purified from sour orange and evaluated for their ability to inhibit cell-cell signalling. The purified limonoids were tested for their ability to interfere with cell-cell signalling and biofilm formation in Vibrio harveyi. Isolimonic acid, deacetylnomilinic acid glucoside and ichangin demonstrated significant inhibition of autoinducer-mediated cell-cell signalling and biofilm formation. Furthermore, isolimonic acid and ichangin treatment resulted in induced expression of the response regulator gene luxO. In addition, luxR promoter activity was not affected by isolimonic acid or ichangin. Therefore, the ability of isolimonic acid and ichangin to interfere with cell-cell signalling and biofilm formation seems to stem from the modulation of luxO expression. The results suggest that isolimonic acid and ichangin are potent modulators of bacterial cell-cell signalling.

Transcriptome analysis of genes controlled by luxS/autoinducer-2 in Salmonella enterica serovar Typhimurium

The enteric pathogen Salmonella enterica serovar Typhimurium uses autoinducer-2 (AI-2) as a signaling molecule. AI-2 requires the luxS gene for its synthesis. The regulation of global gene expression in Salmonella Typhimurium by luxS/AI-2 is currently not known; therefore, the focus of this study was to elucidate the global gene expression patterns in Salmonella Typhimurium as regulated by luxS/AI-2. The genes controlled by luxS/AI-2 were identified using microarrays with RNA samples from wild-type (WT) Salmonella Typhimurium and its isogenic DeltaluxS mutant, in two growth conditions (presence and absence of glucose) at mid-log and early stationary phases. The results indicate that luxS/AI-2 has very different effects in Salmonella Typhimurium depending on the stage of cell growth and the levels of glucose. Genes with p < or = 0.05 were considered to be significantly expressed differentially between WT and DeltaluxS mutant. In the mid-log phase of growth, AI-2 activity was higher (1500-fold) in the presence of glucose than in its absence (450-fold). There was differential gene expression of 13 genes between the WT and its isogenic DeltaluxS mutant in the presence of glucose and 547 genes in its absence. In early stationary phase, AI-2 activity was higher (650-fold) in the presence of glucose than in its absence (1.5-fold). In the presence of glucose, 16 genes were differentially expressed, and in its absence, 60 genes were differentially expressed. Our microarray study indicates that both luxS and AI-2 could play a vital role in several cellular processes including metabolism, biofilm formation, transcription, translation, transport, and binding proteins, signal transduction, and regulatory functions in addition to previously identified functions. Phenotypic analysis of DeltaluxS mutant confirmed the microarray results and revealed that luxS did not influence growth but played a role in the biofilm formation and motility.

Suppression of bacterial cell-cell signalling, biofilm formation and type III secretion system by citrus flavonoids

AIM

This study investigated the quorum sensing, biofilm and type three secretion system (TTSS) inhibitory properties of citrus flavonoids.

METHODS AND RESULTS

Flavonoids were tested for their ability to inhibit quorum sensing using Vibrio harveyi reporter assay. Biofilm assays were carried out in 96-well plates. Inhibition of biofilm formation in Escherichia coli O157:H7 and V. harveyi by citrus flavonoids was measured. Furthermore, effect of naringenin on expression of V. harveyi TTSS was investigated by semi-quantitative PCR. Differential responses for different flavonoids were observed for different cell-cell signalling systems. Among the tested flavonoids, naringenin, kaempferol, quercetin and apigenin were effective antagonists of cell-cell signalling. Furthermore, these flavonoids suppressed the biofilm formation in V. harveyi and E. coli O157:H7. In addition, naringenin altered the expression of genes encoding TTSS in V. harveyi.

CONCLUSION

The results of the study indicate a potential modulation of bacterial cell-cell communication, E. coli O157:H7 biofilm and V. harveyi virulence, by flavonoids especially naringenin, quercetin, sinensetin and apigenin. Among the tested flavonoids, naringenin emerged as potent and possibly a nonspecific inhibitor of autoinducer-mediated cell-cell signalling. Naringenin and other flavonoids are prominent secondary metabolites present in citrus species. Therefore, citrus, being a major source of some of these flavonoids and by virtue of widely consumed fruit, may modulate the intestinal microflora.

SIGNIFICANCE AND IMPACT OF THE STUDY

Currently, a limited number of naturally occurring compounds have demonstrated their potential in inhibition of cell-cell communications; therefore, citrus flavonoids may be useful as lead compounds for the development of antipathogenic agents.

Autoinducer AI-2 is involved in regulating a variety of cellular processes in Salmonella Typhimurium

Salmonella Typhimurium is known to exhibit LuxS/AI-2-mediated cell signaling. We investigated the role of LuxS/AI-2 system on Salmonella Typhimurium protein expression using a proteomics approach based on two-dimensional gel electrophoresis (2DGE)-MALDI-MS. The global protein expression profiles of the wild-type, a luxS mutant, and a luxS mutant strain supplemented with AI-2 were compared. Seven proteins were differentially expressed when comparing the wild-type and luxS mutant strains, whereas 13 proteins were differentially expressed when comparisons were made between luxS mutant strains with and without AI-2 supplementation. The seven proteins that were differentially expressed between the wild-type and the luxS mutant strain were also differentially expressed in the luxS mutant strain supplemented with AI-2. The level of PhoP, a virulence determinant, was higher in the presence of AI-2. Proteins associated with the carbohydrate metabolism (pfkA, gpmI, and talB) and ATP synthesis (Pta gene product) were up-regulated by the presence of AI-2 molecules. These results provide experimental evidence that AI-2 molecules regulate a variety of cellular processes in Salmonella Typhimurium.

Chicken CD69 and CD94/NKG2-like genes in a chromosomal region syntenic to mammalian natural killer gene complex

In mammals, natural killer (NK) cell C-type lectin receptors were encoded in a gene cluster called natural killer gene complex (NKC). The NKC is not reported in chicken yet. Instead, NK receptor genes were found in the major histocompatibility complex. In this study, two novel chicken C-type lectin-like receptor genes were identified in a region on chromosome 1 that is syntenic to mammalian NKC region. The chromosomal locations were validated with fluorescent in situ hybridization. Based on 3D structure modeling, sequence homology, chromosomal location, and phylogenetic analysis, one receptor is the orthologue of mammalian cluster of differentiation 69 (CD69), and the other is highly homologous to CD94 and NKG2. Like CD94/NKG2 gene found in teleostean fishes, chicken CD94/NKG2 has the features of both human CD94 and NKG2A. Unlike mammalian NKC, these two chicken C-type lectin receptors are not closely linked but separated by 42 million base pairs according to the chicken draft genome sequence. The arrangement of several other genes that are located outside the mammalian NKC is conserved among chicken, human, and mouse. The chicken NK C-type lectin-like receptors in the NKC syntenic region indicate that this chromosomal region existed before the divergence between mammals and aves.

A S-adenosylmethionine synthetase gene from the pathogenic piscine hemoflagellate, Cryptobia salmositica

We report on the identification of a Cryptobia genomic DNA gene, predict it to encode a S-adenosylmethionine synthetase signature 1 motif and propose to name it S-adenosylmethionine synthetase (MAT). The open reading frame of MAT is 1,046 bp with 341 deduced amino acids. The MAT gene was identified using universal genome walking and Southern blot analysis revealed it to be a multi-copy gene. The S-adenosylmethionine synthetase of Cryptobia salmositica amino acid sequence is similar to those of other pathogenic kinetoplastids (Leishmania donovani 71%, Leishmania major 70%, Leishmania infantum 71%, Trypanosoma brucei 72%, Trypanosoma cruzi 70% and T. cruzi strain CL Brener 70%). The C. salmositica MAT has a conserved hexapeptide GAGDQG, which is widely found in bacteria, parasitic protozoans and also in humans. These suggest that MAT may have highly conserved functions such as regulation of gene expression and biosynthesis of a multitude of essential metabolites.

Differential Expression of Virulence-Related Genes in A Salmonella enterica Serotype Typhimurium luxS Mutant in Response to Autoinducer AI-2 And Poultry Meat–Derived AI-2 Inhibitor

Bacterial cells communicate with each other and respond to external stimuli using signal molecules called autoinducers (AIs). Poultry meat contains inhibitors that apparently interfere with AI-2 signaling. Our objective was to understand the expression of Salmonella Typhimurium genes (using spotted microarrays) in response to AI-2 in the presence, and absence, of poultry meat (PM) derived AI-2 inhibitors. Expression of 1136 virulence-related genes in Salmonella Typhimurium wildtype and its isogenic luxS mutant strain (unable to produce AI-2) was monitored when the cells were exposed for 3 hours to different treatments containing in vitro synthesized AI-2 and a PM inhibitor (AI-2, AI-2 + PM, or PM alone). The responses of the genes were unique in the presence of in vitro synthesized AI-2. Of 1136 genes on the array, 23 genes were differentially expressed (either upregulated or downregulated) at least 1.5-fold (P < 0.05) in the presence of AI-2. Exposure to the PM inhibitor resulted in 36 genes being differentially expressed, while the combined AI-2 + PM treatment resulted in 22 genes being differentially expressed, of which only 7 genes showed overlap with the PM treatment, suggesting a unique response when AI-2 interacts with the inhibitor molecules. The results suggest that Salmonella gene expression can vary depending on the presence or absence of the poultry meat matrix and/or AI-2 molecules. Understanding the interaction of AI-2 and inhibitors of AI-2 activity found in poultry meat can help explain Salmonella survival and virulence on poultry products.

A metalloproteinase gene from the pathogenic piscine hemoflagellate, Cryptobia salmositica

We report the identification of a Cryptobia genomic DNA gene predicted to encode a hydrophobic protein containing a zinc metalloproteinase motif, HEXXH, and hence named it a major surface proteinase 1-like (MSP-1). The MSP-1 gene was identified using universal genome walking. Southern blot analysis revealed it to be a multicopy gene. Fragments of DNA encoding a segment homologous to the HEXXH motif of MSP-1 are widely found in bacteria, yeast, parasitic protozoans, plants, and animals including humans. These results suggest that the MSP-1 may have highly conserved functions, such as in intracellular proteolysis.