Effects of in ovo injection of bacterial peptides and CpG-ODN on Salmonella enterica serovar Heidelberg infection in specific pathogen-free (SPF) chicks

RESEARCH HIGHLIGHTS

Peptides + CpG-ODN reduced SH in caeca at the first week post-infection.Administered formulations did not reduce SH-faecal excretion.Levels of intestinal IgA were similar between all groups.CpG-ODN improved some parameters associated with chick intestinal health.

Molecular Characterisation of Antimicrobial Resistance in E. coli Isolates from Piglets in the West Region of Romania

Antibiotics are widely used for prophylaxis and therapy, reducing morbidity and mortality produced by bacterial pathogensin pigs, including infections caused by Escherichia coli. The aim of this study was to characterise antibiotic resistance phenotypes and genotypes in E. coli isolates in pigs in West Romanian grower farms. Differential phenotypic susceptibility profiles and the contribution of resistance genes to phenotypic expression of susceptibility or resistance were evaluated. A total of 76 E. coli isolates were identified and confirmed by the MicroScan Walk Away System. The occurrence of four resistance genes, ampC, blaZ, blaTEM and tetK in strains resistant to 13 antibiotics was assessed. Of the E. coli isolates, 0% showed resistance to meropenem, 3.9% to tigecycline and 10.5% to piperacillin/tazobactam, whereas, in contrast, 100% were resistant to ampicillin and mezlocillin, 76.31% to piperacillin and 59.3% to tetracycline. The prevalence of resistance genes in resistant isolates detected by q-PCR analysis was 97.0% for ampC, 96% for blaZ, 32.9% for blaTEM and 58.8% for tetK. Penetrance (the proportion of individuals carrying a particular variant of a gene that also expresses an associated trait) was 50% for ampC (32% for amoxicillin/clavulanate, 62% for cefazolin, 32% for cefepime, 100% for cefotaxime, 56% for cefuroxime and 99% for ampicillin), 65% for blaZ (32% for amoxicillin/clavulanate and 99% for ampicillin), 51% for blaTEM (81% for piperacillin) and 44% for the tetK gene (83% for tetracycline). The result of phenotypic antibiotic resistance testing may indicate the presence of plasmid-borne resistance, with a diagnostic odds ratio of a positive phenotypic resistance for tetK being 4.52. As a management decision, the maximum penetrance admitted for using a specific antibiotic for E. coli infections in pigs is recommended to be less than 20%.

Spotlight on avian pathology: Salmonella - new wine and old bottles

Salmonella enterica remains an important avian and human pathogen. Control has been effective in some countries but the hygiene and biosecurity required may not be possible everywhere. Antibiotic resistance is an increasing problem for both veterinary and human medicine. This short review commentary highlights existing and potential new control measures including legislation, hygiene and biosecurity, use of live and inactivated vaccines, and bacteriophages to tackle intestinal colonization, reduce the prevalence of antibiotic resistance and improve carcass decontamination.

Deciphering the role of ttrA and pduA genes for Salmonella enterica serovars in a chicken infection model

Salmonella enterica serovars use self-induced intestinal inflammation to increase electron acceptor availability and to obtain a growth advantage in the host gut. There is evidence suggesting that the ability of Salmonella to use tetrathionate and 1,2-propanediol provides an advantage in murine infection. Thus, we present here the first study to evaluate both systemic infection and faecal excretion in commercial poultry challenged by Salmonella Enteritidis (SE) and S. Typhimurium (STM) harbouring deletions in ttrA and pduA genes, which are crucial to the metabolism of tetrathionate and 1,2-propanediol, respectively. Mutant strains were excreted at higher rates when compared to the wild-type strains. The highest rates were observed with white egg-layer and brown egg-layer chicks (67.5%), and broiler chicks (56.7%) challenged by SEΔttrAΔpduA, and brown egg-layer chicks (64.8%) challenged by STMΔttrAΔpduA. SEΔttrAΔpduA presented higher bacterial counts in the liver and spleen of the three chicken lineages and caecal contents from the broiler chickens, whereas STMΔttrAΔpduA presented higher counts in the liver and spleen of the broiler and brown-egg chickens for 28 days post-infection (P < 0.05). The ttrA and pduA genes do not appear to be major virulence determinants in faecal excretion or invasiveness for SE and STM in chickens. RESEARCH HIGHLIGHTSttrA and pudA do not impair gut colonization or systemic infection in chicks.Mutant strains were present in higher numbers in broilers than in laying chicks.Mutants of SE and STM showed greater pathogenicity in broiler chicks than layers.

Heat stress impairs egg production in commercial laying hens infected by fowl typhoid

Salmonella Gallinarum (SG) is an avian-restricted pathogen that causes fowl typhoid in poultry. Although it has been reported frequently over many decades in poultry flocks worldwide, the microorganism is more commonly associated with poultry in developing countries, particularly those with high ambient temperatures, where the acute form of the disease results in considerable economic losses. A more detailed investigation of environmental factors that affect the course of disease may assist in identifying effective prevention and control measures. Heat stress is known to impair the immunological response to a variety of pathogens and clearly may be an important contributory factor in the prevalence of disease in countries with warm or hot climates. Thus, the objective of the present study was to evaluate the effects of heat stress on chickens infected with SG. For this, light and semi-heavy commercial laying hens were distributed randomly within four groups as follows: infected and non-infected groups in rooms held at ambient temperature, and infected and non-infected groups under heat stress. Clinical signs, egg production, and mortality were recorded daily. Bacteriological counts in liver and spleen samples were estimated at 2, 5, 7, and 14 days post-infection. The results showed that both SG infection and heat stress had similar effects on egg production and a synergistic effect of the two stressors was observed. The data show an interaction between disease and heat stress which could point towards environmental and biosecurity approaches to resolving the possible 30% fall in production observed in such countries.

Reduction of Salmonella contamination on the surface of chicken skin using bacteriophage

Background

Enteric infections caused by Salmonella spp. remain a major public health burden worldwide. Chickens are known to be a major reservoir for this zoonotic pathogen. The presence of Salmonella in poultry farms and abattoirs is associated with financial costs of treatment and a serious risk to human health. The use of bacteriophages as a biocontrol is one possible intervention by which Salmonella colonization of chickens could be reduced. In a prior study, phages Eϕ151 and Tϕ7 significantly reduced broiler chicken caecal colonization by S. Enteritidis and S. Typhimurium respectively.

Methods

Salmonella-free Ross broiler chickens were orally infected with S. Enteritidis P125109 or S. Typhimurium 4/74. After 7 days of infection, the animals were euthanased, and 25cm² sections of skin were collected. The skin samples were sprayed with a phage suspension of either Eϕ151 (S. Enteritidis), Tϕ7 phage suspension (S. Typhimurium) or SM buffer (Control). After incubation, the number of surviving Salmonellas was determined by direct plating and Most Probable Number (MPN). To determine the rate of reduction of Salmonella numbers on the skin surface, a bioluminescent S. Typhimurium DT104 strain was cultured, spread on sections of chicken breast skin, and after spraying with a Tϕ11 phage suspension, skin samples were monitored using photon counting for up to 24 h.

Results

The median levels of Salmonella reduction following phage treatment were 1.38 log₁₀ MPN (Enteritidis) and 1.83 log₁₀ MPN (Typhimurium) per skin section. Treatment reductions were significant when compared with Salmonella recovery from control skin sections treated with buffer (p < 0.0001). Additionally, significant reduction in light intensity was observed within 1 min of phage Tϕ11 spraying onto the skin contaminated with a bioluminescent Salmonella recombinant strain, compared with buffer-treated controls (p < 0.01), implying that some lysis of Salmonella was occurring on the skin surface.

Conclusions

The results of this study suggest that phages may be used on the surface of chicken skin as biocontrol agents against Salmonella infected broiler chicken carcasses. The rate of bioluminescence reduction shown by the recombinant Salmonella strain used supported the hypothesis that at least some of the reduction observed was due to lysis occurred on the skin surface.

Evaluation of pathogenicity of Salmonella Gallinarum strains harbouring deletions in genes whose orthologues are conserved pseudogenes in S. Pullorum

The diseases caused by Salmonella Gallinarum and S. Pullorum in chickens known as fowl typhoid and pullorum disease, respectively, pose a great threat to the poultry industry mainly in developing countries, since they have already been controlled in the developed ones. These bacteria are very similar at the genomic level but develop distinct host-pathogen relationships with chickens. Therefore, a deep understanding of the molecular mechanisms whereby S. Gallinarum and S. Pullorum interact with the host could lead to the development of new approaches to control and, perhaps, eradicate both diseases from the chicken flocks worldwide. Based on our previous study, it was hypothesised that metabolism-related pseudogenes, fixed in S. Pullorum genomes, could play a role in the distinct host-pathogen interaction with susceptible chickens. To test this idea, three genes (idnT, idnO and ccmH) of S. Gallinarum str. 287/91, which are pseudogenes on the S. Pullorum chromosomes, were inactivated by mutations. These genetically engineered strains grew well on the solid media without any colony morphology difference. In addition, similar growth curves were obtained by cultivation in M9 minimal medium containing D-gluconate as the sole carbon source. Infection of chickens with idnTO mutants led to increased numbers of bacteria in the livers and spleens at 5 days post-infection, but with slightly decreased heterophil infiltration in the spleens when compared to the wild-type strain. On the other hand, no significant phenotypic change was caused by mutation to ccmH genes. Apart from the above-mentioned alterations, all S. Gallinarum strains provoked similar infections, since mortality, clinical signs, macroscopic alterations and immune response were similar to the infected chickens. Therefore, according to the model applied to this study, mutation to the idnTO and ccmH genes showed minor impact on the fowl typhoid pathogenesis and so they may be relics from the ancestor genome. Our data hints at a more complex mechanism driving the distinct host-pathogen interaction of S. Gallinarum/Pullorum with chickens than differential inactivation of a few genes.

Contribution of flagella and motility to gut colonisation and pathogenicity of Salmonella Enteritidis in the chicken

Salmonella Enteritidis causes fowl paratyphoid in poultry and is frequently associated to outbreaks of food-borne diseases in humans. The role of flagella and flagella-mediated motility into host-pathogen interplay is not fully understood and requires further investigation. In this study, one-day-old chickens were challenged orally with a wild-type strain Salmonella Enteritidis, a non-motile but fully flagellated (SE ΔmotB) or non-flagellated (SE ΔfliC) strain to evaluate their ability to colonise the intestine and spread systemically and also of eliciting gross and histopathological changes. SE ΔmotB and SE ΔfliC were recovered in significantly lower numbers from caecal contents in comparison with Salmonella Enteritidis at early stages of infection (3 and 5dpi). The SE ΔmotB strain, which synthesises paralysed flagella, showed poorer intestinal colonisation ability than the non-flagellated SE ΔfliC. Histopathological analyses demonstrated that the flagellated strains induced more intense lymphoid reactivity in liver, ileum and caeca. Thus, in the present study the flagellar structure and motility seemed to play a role in the early stages of the intestinal colonisation by Salmonella Enteritidis in the chicken.

Further investigations on the epidemiology of fowl typhoid in Brazil

Salmonella Gallinarum (SG) causes fowl typhoid (FT), a disease responsible for economic losses to the poultry industry worldwide. FT has been considered to be under control in Brazil; nevertheless, since 2012 it has frequently been identified in poultry farming of several Brazilian states. The present study was aimed at assessing (i) the pathogenicity of a SG strain recently isolated from an FT outbreak affecting chickens of both white and brown layers; (ii) the transmission of SG through eggs and hatching; (iii) the effects of antibiotic therapy on SG persistence in poultry tissues and on its vertical transmission and (iv) the genetic profiles of strains isolated over 27 years by Pulsed Field Gel Electrophoresis. Clinical signs, mortality and gross pathologies were very marked amongst brown-egg layers. In contrast, clinical manifestation of FT and mortality were barely present amongst the white-egg layers, although bacteria could be re-isolated from their tissues up to 35 days after infection. No bacteria were re-isolated from the laid eggs, so vertical transmission was not achieved, although newly hatched uninfected chicks became infected spontaneously after hatching. Antibiotic therapy was shown to be effective at reducing mortality, but was not able to clear infection or to favour SG transmission via eggs. Our pulsed field gel electrophoresis results revealed an endemic SG clone that may have been circulating in the Brazilian poultry flocks in the south and southeast regions for more than 20 years. The results suggest that the industrial incubation of SG-contaminated eggs could be one of the factors responsible for the spread of FT in Brazil.

Molecular identification of Salmonella enterica subsp. enterica serovar Gallinarum biovars Gallinarum and Pullorum by a duplex PCR assay

Salmonella enterica subsp. enterica serovar Gallinarum biovar Gallinarum ( S. Gallinarum) and biovar Pullorum ( S. Pullorum) are 2 poultry pathogens that cause major economic losses to the poultry industry worldwide. Control of both diseases mainly relies on the adoption of biosecurity programs, and success is dependent on accurate and fast detection. Based on this concept, we developed a duplex PCR assay, targeting 2 chromosomal sequences, which allowed us to precisely identify and differentiate S. Gallinarum and S. Pullorum field strains. This assay was validated by testing genomic DNA from 40 S. Gallinarum and 29 S. Pullorum field strains, 87 other Salmonella serovars, and 7 non- Salmonella strains. The serovar identifier region (SIR) primers produced a fragment only in S. Gallinarum and S. Pullorum strains, whereas the fragment from the ratA coding sequence, which was previously demonstrated to differentiate the 2 biovars, was also amplified from other Salmonella serovars. Our results showed that the combination of both SIR and ratA amplifications could be used to identify as well as to differentiate colonies of S. Gallinarum and S. Pullorum reliably. Thus, we believe this methodology can be a useful ancillary tool for routine veterinary diagnostic laboratories by providing rapid, accurate results.

Polymerase chain reaction assay based on ratA gene allows differentiation between Salmonella enterica subsp. enterica serovar Gallinarum biovars Gallinarum and Pullorum

Salmonella Pullorum and Salmonella Gallinarum are classified as biovars of Salmonella enterica subsp. enterica serovar Gallinarum. These salmonellae are the causative agents of Pullorum disease and fowl typhoid, respectively, and are widely distributed throughout the world. Although many developed countries have eradicated these diseases from commercial poultry, they are still the cause of significant economic loss in developing countries. When serovar Gallinarum is isolated, it is difficult to immediately differentiate between biovars because they are antigenically identical by serotyping. However, they cause distinct diseases with different epidemiology, and therefore it is important to differentiate them. This may be done biochemically but takes 2 to 3 days. In the present study, S. Pullorum and S. Gallinarum whole genomes were compared, and 1 genomic region of difference, which is part of the ratA gene, was chosen as a molecular marker for a polymerase chain reaction assay to differentiate rapidly between these organisms. In all, 26 strains of S. Gallinarum and 17 S. Pullorum strains were tested and successfully differentiated by the assay.

Protection against experimental fowl typhoid by parenteral administration of live SL5828, an aroA-serC (aromatic dependent) mutant of a wild-type Salmonella Gallinarum strain made lysogenic for P22 sie

A wild-type strain of Salmonella enterica serotype Gallinarum, lysogenized with P22 sie (superinfection-exclusion defective) was greatly attenuated for newly hatched or 21-day-old chickens. An aroA transductant of the lysogenic strain and an aroA-serC tetracycline-sensitive deletion or deletioninversion mutant of the latter were equally attenuated. Intramuscular administration of the aroA-serC strain to 21-day-old chickens protected them against oral challenge with 10(6) colony forming units of a highly virulent Gallinarum strain (no deaths in the 30 vaccinated chickens versus 14 of 30 in the control group). There was evidence of protection in the contents, mucosa and lymphoid tissue of the alimentary tract, in addition to that which occurred in the liver and spleen.A weak serological response was detected by enzyme-linked immunosorbent assay, indicating that use of such a strain is compatible with serological monitoring and would be a useful adjunct to control schemes for fowl typhoid.

Effect of enrofloxacin administration on excretion of Salmonella ententidis by experimentally infected chickens and on quinolone resistance of their Escherichia coli flora

Chickens which had been experimentally-infected with a strain of Salmonella ententidis and treated by administration of enrofloxacin at commercially recommended concentrations in the drinking water, virtually eliminated this organism from the alimentary tract. However, an initially quinolone-sensitive Escherichia coli flora present in the birds' faeces was rapidly replaced by a quinolone-resistant flora which persisted after withdrawal of the medication. Resistance to quinolone in the form of nalidixic acid was transducible from a strain of S. typhimurium to S. enterinais with bacteriophage P22.

Early immune dynamics following infection with Salmonella enterica serovars Enteritidis, Infantis, Pullorum and Gallinarum: cytokine and chemokine gene expression profile and cellular changes of chicken cecal tonsils

Salmonella enterica subspecies enterica infection remains a serious problem in a wide range of animals and in man. Poultry-derived food is the main source of human infection with the non-host-adapted serovars while fowl typhoid and pullorum disease are important diseases of poultry. We have assessed cecal colonization and immune responses of newly hatched and older chickens to Salmonella serotypes Enteritidis, Infantis, Gallinarum and Pullorum. S. Enteritidis and S. Infantis colonized the ceca more efficiently than S. Gallinarum and S. Pullorum. Salmonella infection was also associated with increased staining for B-lymphocytes and macrophages in the cecal tonsils of infected birds. S. Enteritidis infection in newly hatched birds stimulated the expression of CXCLi1 and CXCLi2 chemokines in the cecal tonsils, while S. Gallinarum up-regulated the expression of LITAF. In older chickens, S. Enteritidis infection resulted in a significantly higher expression of CXCLi2, iNOS, LITAF and IL-10 while S. Pullorum appeared to down-regulate CXCLi1 expression in the cecal tonsils. Data from spleens showed either no expression or down-regulation of the tested genes.

Endotoxin transiently inhibits protein synthesis through Akt and MAPK mediating pathways in C2C12 myotubes

In this study, the effect of lipopolysaccharide (LPS) on protein synthesis (PS) and intracellular signaling factors that regulate it have been investigated in C2C12 murine-derived myotubes. In particular, the role of Akt/mammalian target of rapamycin (mTOR) and the mitogen-activated protein kinases (MAPKs) [p38 and extracelluar regulated protein kinase (ERK1/2)] have been examined. The direct effect of LPS on PS was measured at 3 and 18 h. LPS significantly decreased PS at 3 h but not at the 18-h time point. This effect was preceded by decreased Akt phosphorylation at 5 and 30 min after LPS administration. The mTOR phosphorylation exhibited a long time dose-dependent increase at all the time points. Similarly, the activity-related phosphorylation of p38 and ERK1/2 significantly increased in a time- and dose-dependent manner at all the time points. Polymyxin B abolished the LPS-induced decrease in PS rate. The phosphatidylinositol 3-kinase inhibitor LY-0294002 in combination with LPS significantly decreased the rate of PS by 81% and alone by 66%, respectively, for the 3- and 18-h time points, whereas p38 and ERK inhibitors in combination with LPS significantly decreased the rate PS rate at the 18-h time point by 41% and 59%, respectively, compared with control cells. In conclusion, LPS alone transiently decreased the rate of PS by 50% at 3 h; this effect is most likely mediated via the Toll-like receptor 4 (TLR4)-Akt/mTOR pathway, and both p38 and ERK when inhibited in the presence of LPS at 3 h have a similar effect in preventing the LPS-induced reduction in PS.

Exploitation of intestinal colonization-inhibition between salmonella organisms for live vaccines in poultry: potential and limitations

Immunization represents one of the most important methods to increase the resistance of chickens against Salmonella infection. In addition to the development of an adaptive immune response, oral administration of live Salmonella strains to day-old chicks provides protection against infection within hours by intestinal colonization-inhibition. For the exploitation of this phenomenon, practical information on colonization-inhibition between Salmonella organisms is needed. Colonization-inhibition capacity between Salmonella strains from serogroups B, C1, C2, D and G was assessed in chickens. The most profound level of intestinal colonization-inhibition occurred between isogenic strains. Inhibition between strains of the same serovar was greater than that between strains of different serovars. The degree of inhibition between different serovars was not sufficiently high to identify a single strain which might inhibit a wide range of other Salmonella organisms. However, as Salmonella Enteritidis is the dominant serovar in poultry in many countries and because of the profound colonization-inhibition within this serovar there is a considerable potential to exploit this phenomenon in the development of novel live S. Enteritidis vaccines. Treatment of young chicks with mixtures of different Salmonella serovars resulted not only in a very strong growth inhibition of the isogenic strains but also in a substantial inhibition of heterologous serovars. The potential of mixtures of heterologous Salmonella strains as a 'Salmonella Inhibition Culture' and as a 'live Salmonella vaccine' should be further explored.

The contribution of genes required for anaerobic respiration to the virulence of Salmonella enterica serovar Gallinarum for chickens

Salmonella enterica serovar Gallinarum (SG) is an intracellular pathogen of chickens. To survive, to invade and to multiply in the intestinal tract and intracellularly it depends on its ability to produce energy in anaerobic conditions. The fumarate reductase (frdABCD), dimethyl sulfoxide (DMSO)-trimethylamine N-oxide (TMAO) reductase (dmsABC), and nitrate reductase (narGHIJ) operons in Salmonella Typhimurium (STM) encode enzymes involved in anaerobic respiration to the electron acceptors fumarate, DMSO, TMAO, and nitrate, respectively. They are regulated in response to nitrate and oxygen availability and changes in cell growth rate. In this study mortality rates of chickens challenged with mutants of Salmonella Gallinarum, which were defective in utilising anaerobic electron acceptors, were assessed in comparison to group of bird challenged with wild strain. The greatest degree of attenuation was observed with mutations affecting nitrate reductase (napA, narG) with additional attenuations induced by a mutation affecting fumarate reductase (frdA) and a double mutant (dmsA torC) affecting DMSO and TMAO reductase.

Immunomodulation of innate immune responses by vasoactive intestinal peptide (VIP): its therapeutic potential in inflammatory disease

Since the late 1970s a number of laboratories have studied the role of vasoactive intestinal peptide (VIP) in inflammation and immunity. These studies have highlighted the dramatic effect of VIP on immune cell activation and function, and studies using animal models of disease have indicated that VIP has significant therapeutic and prophylactic potential. This review will focus on the effects of VIP on innate immune cell function and discuss the therapeutic potential for VIP in inflammatory diseases of humans.

Experimental infection of egg-laying hens with Salmonella enteritidis phage type 4

Chickens were inoculated intravenously with 10(5) or 10(6) organisms. Heavy infection of the ovaries occurred and some infection persisted in this organ for several weeks. Most of the ovarian infections were confined to the interstitial tissues and not to the yolk contained in the large follicles. Infections of the ovary did not result from contamination from infected air sacs. None of 810 eggs laid contained S. enteritidis. Chickens infected orally gave similar results to those following intravenous inoculation although the number of isolations obtained from the caeca and cloaca were higher. S. enteritidis was isolated from two of 633 eggs in which the contents only were cultured and from 36 of 614 eggs in which both shell and contents were cultured. The serum IgG response to oral inoculation was monitored by an ELISA using a whole cell sonicate or lipopolysaccharide antigen. High titres of IgG were detected for 27 weeks after infection when the experiment was terminated. The experiments suggest that most infected eggs laid by 5. enteritidis-infected hens are surface-contaminated and do not result from infected ovaries.

Bacteriophage therapy to reduce salmonella colonization of broiler chickens

Acute enteric infections caused by salmonellas remain a major public health burden worldwide. Poultry, particularly chickens, are known to be the main reservoir for this zoonotic pathogen. Although some progress has been made in reducing Salmonella colonization of broiler chickens by using biosecurity and antimicrobials, it still remains a considerable problem. The use of host-specific bacteriophages as a biocontrol is one possible intervention by which Salmonella colonization could be reduced. A total of 232 Salmonella bacteriophages were isolated from poultry farms, abattoirs, and wastewater in 2004 and 2005. Three phages exhibiting the broadest host ranges against Salmonella enterica serotypes Enteritidis, Hadar, and Typhimurium were characterized further by determining their morphology and lytic activity in vitro. These phages were then administered in antacid suspension to birds experimentally colonized with specific Salmonella host strains. The first phage reduced S. enterica serotype Enteritidis cecal colonization by > or = 4.2 log10 CFU within 24 h compared with controls. Administration of the second phage reduced S. enterica serotype Typhimurium by > or = 2.19 log10 CFU within 24 h. The third bacteriophage was ineffective at reducing S. enterica serotype Hadar colonization. Bacteriophage resistance occurred at a frequency commensurate with the titer of phage being administered, with larger phage titers resulting in a greater proportion of resistant salmonellas. The selection of appropriate bacteriophages and optimization of both the timing and method of phage delivery are key factors in the successful phage-mediated control of salmonellas in broiler chickens.

Salmonella infections: immune and non-immune protection with vaccines

Salmonella enterica in poultry remains a major political issue. S. enterica serovar Enteritidis, particularly, remains a world-wide problem. Control in poultry by immunity, whether acquired or innate, is a possible means of containing the problem. Widespread usage of antibiotics has led to the emergence of multiple antibiotic-resistant bacteria. This problem has indicated an increasing requirement for effective vaccines to control this important zoonotic infection. An attempt is made in the present review to explain the relatively poor success in immunizing food animals against these non-host-specific Salmonella serotypes that usually produce food-poisoning, compared with the success obtained with the small number of serotypes that more typically produce systemic "typhoid-like" diseases. New examinations of old problems such as the carrier state and vertical transmission, observed with S. Pullorum, is generating new information of relevance to immunity. Newer methods of attenuation are being developed. Live vaccines, if administered orally, demonstrate non-specific and rapid protection against infection that is of biological and practical interest. However, from the point of view of consumer safety, there is a school of thought that considers inactivated or sub-unit vaccines to be the safest. The benefits of developing effective killed or sub-unit vaccines over the use of live vaccines are enormous. Recently, there have been significant advances in the development of adjuvants (e.g. microspheres) that are capable of potent immuno-stimulation, targeting different arms of the immune system. The exploitation of such technology in conjunction with the ongoing developments in identifying key Salmonella virulence determinants should form the next generation of Salmonella sub-unit vaccines for the control of this important group of pathogens. There are additional areas of concern associated with the use of live vaccines, particularly if these are generated by genetic manipulation.

Identification of putative ancestors of the multidrug-resistant Salmonella enterica serovar typhimurium DT104 clone harboring the Salmonella genomic island 1

The origin of multidrug-resistant Salmonella enterica serovar typhimurium (S. typhimurium) harboring the Salmonella Genomic Island 1 (SGI1), which was detected for the first time in the mid-1980s is unknown. In this study, we performed microarray genomotyping of four multidrug-resistant SGI1 positive strains and found that unlike the S. typhimurium LT2 strain, the multidrug-resistant strains lacked genes STM0517-0529 allowing the utilization of allantoin as a sole nitrogen source. We extended this observation by PCR screening of additional 120 S. typhimurium field strains and found that this locus was absent in all SGI1 positive and also in 24% of SGI1 negative strains, which were proposed to be the original recipients of SGI1. To prove this hypothesis, we compared the STM0517-0529 negative strains (with or without the SGI1) by PFGE and PCR prophage typing and found that 8 out of 11 of the SGI1 negative strains and 17 out of 22 SGI1 positive strains were of identical PFGE pattern and PCR prophage pattern, while this specific pattern was never observed among STM0517-0529 positive strains. We therefore propose that a lineage of the S. typhimurium DT104 sensitive strain first lost the ability to metabolize allantoin and then acquired SGI1.

Vasoactive intestinal peptide (VIP) prevents killing of virulent and phoP mutant Salmonella typhimurium by inhibiting IFN-γ stimulated NADPH oxidative pathways in murine macrophages

Vasoactive intestinal peptide is an immunomodulator with great potential in the treatment of inflammatory pathology. In this study, we have examined the effect of VIP on the growth dynamics of virulent Salmonella enterica. Serovar typhimurium (S. typhimurium) 14028 and 4/74 and an avirulent mutant (14028 phoP) in a murine, macrophage cell line (J774.2). In contrast to standard growth dynamics, in which phoP mutants do not survive in macrophages, we show that VIP (10(-10) M) significantly enhances phoP growth over a 24 h post-infection period even when the cells are co-cultured with IFN-gamma. We examined the effect of VIP on the generation of NADPH-induced reactive oxygen species (ROS) in Salmonella-infected/IFN-gamma cultured J774 cells. VIP inhibited gp91 mRNA levels, gp91 protein and subsequent ROS. The importance of ROS in killing of Salmonella by J774 cells was highlighted by experiments in which ROS production by J774 cells was inhibited using a conventional inhibitor, N-acetyl-L-cysteine captopril (ACC) and in which Salmonella growth significantly increased. Our findings suggest that although VIP inhibits inflammatory pathways in myeloid cells it also promotes the growth of avirulent (phoP) mutants.

Cross-reactive cellular and humoral immune responses to Salmonella enterica serovars Typhimurium and Enteritidis are associated with protection to heterologous re-challenge

Chickens infected with Salmonella enterica serovars Typhimurium (ST) and Enteritidis (SE) still represent a major source of human food poisoning via consumption of contaminated meat and eggs. Vaccination represents a sustainable approach to control Salmonella in the chicken and the serovar specificity of immunity has the potential to impact on the need for multivalent vaccines. The issue of cross-reactive immune responses and cross-serovar protection was examined in these experiments. Cellular and humoral immune responses were measured by antigen-specific ELISA and splenocyte proliferation assays during primary infections (with ST and SE) and during a second challenge with homologous or heterologous serovars. Primary infection with ST or SE induced strong lymphocyte proliferation and high levels of specific antibody (IgM, IgG and IgA) responses with substantial serovar cross-reactivity. The occurrence of high levels of splenocyte proliferation and strong antibody responses corresponded to the initiation of clearance with both ST and SE. Re-challenge of ST and SE infection-primed chickens with either serovar resulted in significant levels of protection (assessed by bacterial numbers and rate of clearance) with little difference between homologous or heterologous challenge schedules. Relatively low levels of antigen-specific splenocyte proliferation were detected during secondary infection, which may be caused by splenic T cells exiting to the gut. In contrast, the more rapid specific antibody responses (compared with primary infection controls) indicate the development of a secondary antigen-specific adaptive response. The substantial level of cross-protection between serovars and the level of antigenic cross-reactivity indicates the potential for single serovar live vaccines to protect against both group B and D salmonellae.

Vaccination and early protection against non-host-specific Salmonella serotypes in poultry: exploitation of innate immunity and microbial activity

A recent European Union Directive required member states to put monitoring and control programmes in place, of which vaccination is a central component. Live Salmonella vaccines generally confer better protection than killed vaccines, because the former stimulate both cell-mediated and humoral immunity. Administering Salmonella bacteria orally to newly hatched chickens results in extensive gut colonization and a strong adaptive immune stimulus but broiler chickens are immunologically immature. However, colonization exerts a variety of rapid (within 24 h) protective effects. These include specific colonization-inhibition (competitive exclusion) in which the protective bacteria exert a profound resistance to establishment and colonization by other related bacteria. This is thought to be primarily a metabolic attribute of the vaccinating bacteria but may also involve competition for attachment sites. The presence of large numbers of bacteria originating from a live Salmonella vaccine in the intestine can also induce infiltration of polymorphonuclear cells into the intestinal wall, which confers resistance to invasion and systemic spread by virulent Salmonella strains. This opens new perspectives for vaccine usage in broilers, layers and breeding poultry but also in other animals which show increased susceptibility to infection because of their young age or for other reasons, such as oral chemoprophylaxis or chemotherapy, where the lack of established normal gut flora is an issue. We recommend that all live vaccines considered for oral administration should be tested for their ability to induce the two protective effects described above. Further developments in live Salmonella vaccines are, however, currently hindered by fears associated with the use and release of live vaccines which may be genetically modified.

Campylobacter jejuni gene expression in the chick cecum: evidence for adaptation to a low-oxygen environment

Transcriptional profiling of Campylobacter jejuni during colonization of the chick cecum identified 59 genes that were differentially expressed in vivo compared with the genes in vitro. The data suggest that C. jejuni regulates electron transport and central metabolic pathways to alter its physiological state during establishment in the chick cecum.

Age at primary infection with Salmonella enterica serovar Typhimurium in the chicken influences persistence of infection and subsequent immunity to re-challenge

Salmonella enterica remains one of the most important food-borne pathogens of humans and is often acquired through consumption of infected poultry meat or eggs. Control of Salmonella infections in chicken is therefore an important public health issue. Infection with S. enterica serovar Typhimurium results in a persistent enteric infection without clinical disease in chickens of more than 3 days of age, and represents a source for contamination of carcass at slaughter and entry into the human food chain. Data presented indicate a profound effect of age at initial exposure on the persistence of infection and a lesser effect on the development of effective immunity to re-challenge. The percentage of birds positive for Salmonella was high until 8-9 weeks of age, regardless of the age at which the birds were infected (1, 3 or 6 weeks). The birds infected at 3 and 6 weeks of age produced a more rapid and higher antibody response (IgY and IgA) than those infected at 1 week of age, but in all cases infection persisted for a considerable period despite the presence of high antibody levels. Following a re-challenge infection with S. Typhimurium, all three previously-infected groups had fewer bacteria in the gut, spleen and liver compared with age-matched birds receiving a parallel primary infection. However, the birds primary infected at 3 and 6 weeks of age cleared infection more rapidly than those infected at a younger age. Interestingly older-primed birds had higher specific T lymphocyte proliferative responses and specific circulating levels of IgY antibody at time of re-challenge. Although birds initially infected at 1 week of age and those that were previously uninfected produced a stronger antibody response following re-challenge, they were slower to clear Salmonella from the gut than the older-primed groups which expressed a stronger T lymphocyte response. The data presented indicate that clearance of Salmonella from the gut is age-dependent and we propose that this relates to the increased competence of the enteric T cell response. The findings that Salmonella persists beyond 8-9 weeks, irrespective of age at exposure, has implications for the broiler sector and indicates the need to remain Salmonella free throughout the rearing period. Moreover, the re-challenge data demonstrates that infection at a young age is less effective in producing protective immunity than in older chickens. This feature of the development of protective immunity needs to be considered when developing vaccines for the broiler sector of the poultry industry.

Faecal shedding and intestinal colonization of Salmonella enterica in in-bred chickens: the effect of host-genetic background

Considerable and reproducible differences were observed in the amount and duration of faecal excretion when in-bred lines of chickens were infected orally with S. enterica serovar Typhimurium at 6 weeks of age after being given a gut flora preparation when newly hatched. Similar but less pronounced results were observed with S. Enteritidis or S. Infantis. Differences in the viable numbers of the inoculated bacteria in caecal contents were detectable within 24 h of inoculation. No major differences were seen in Salmonella-specific serum IgA or IgG titres. Small differences were seen in the numbers of circulating heterophilic cells. Caecal contents taken from the more resistant lines immediately prior to challenge appeared to be no more inhibitory for Salmonella in vivo than contents taken from susceptible lines. The more resistant lines showed a slightly higher rate of intestinal flow, as indicated by the rate of production of faecal droppings, although there was no difference in the rate of emptying of the caeca. In an F1 generation resistance was dominant and not sex-linked. There was no MHC linkage or any association with SAL1, the gene implicated in resistance to systemic salmonellosis in chickens, or NRAMP1.

Temporal dynamics of the cellular, humoral and cytokine responses in chickens during primary and secondary infection withSalmonella entericaserovar Typhimurium

Salmonella enterica serovar Typhimurium (S. Typhimurium) infections cause systemic disease in the young chick, whereas in the older chicken the infection is mainly restricted to the intestine. Chickens infected orally with S. Typhimurium (F98) at 6 weeks of age and re-infected 10 weeks later were monitored for antibody production, T-cell proliferation and production of selected cytokines (interferon-gamma, interleukin-1beta and transforming growth factor-beta(4)). A strong coordinated antigen-specific humoral and cellular immune response was temporally linked to resolution of the primary infection. Enhanced levels of mRNA encoding the cytokines, interleukin-1beta, transforming growth factor-beta(4) and interferon-gamma were also evident during early phases of primary infection. Secondary infection was restricted to the intestine and of shorter duration than primary infection. Splenic immune responses were not further enhanced by secondary infection; indeed, antigen-specific proliferation was significantly reduced at 1 day after secondary infection, which may be interpreted as the trafficking of reactive T cells from the spleen to the gut.

Intestinal colonisation-inhibition and virulence of Salmonella phoP, rpoS and ompC deletion mutants in chickens

Administration of live Salmonella strains to day-old chicks provides profound protection against superinfection with a related strain within a matter of hours by a colonisation-inhibition mechanism, which is primarily a bacterial physiological process. Although currently available, commercial, live attenuated Salmonella vaccines induce protection by adaptive immunity, none of them is able to induce protection against Salmonella organisms by colonisation-inhibition and, therefore, they are unable to protect newly-hatched birds immediately after oral vaccination. In this study, mutants of Salmonella Typhimurium and Enteritidis with deletions in phoP and rpoS, either alone or in combination with ompC, were characterised and tested for their level of attenuation and their ability to inhibit the intestinal colonisation of the isogenic parent strains in chickens. Mutants with deletions only in rpoS demonstrated an unaffected potential to inhibit the intestinal colonisation of the challenge strain but were still fully virulent for the chickens. Mutants with deletions in phoP, either alone or in combination with rpoS, resulted in a high level of attenuation, unimpaired ability to colonise the gut and a nearly unaffected potential to inhibit the challenge strain from caecal colonisation. Mutants with an additional deletion in ompC revealed a reduced capacity of intestinal colonisation-inhibition when compared to the control strains and both the single rpoS and the phoP deletion mutants. Mutations in phoP- or phoP-regulated genes may therefore be used for the development of live attenuated Salmonella vaccines possessing these novel characteristics.

Induction of antimicrobial pathways during early-phase immune response to Salmonella spp. in murine macrophages: gamma interferon (IFN-gamma) and upregulation of IFN-gamma receptor alpha expression are required for NADPH phagocytic oxidase gp91-stimulated oxidative burst and control of virulent Salmonella spp

The effect of gamma interferon (IFN-gamma) on elevation of reactive oxygen species and the viability of virulent wild-type and avirulent mutants of Salmonella enterica serovar Typhimurium and S. enterica serovar Infantis was studied in a murine macrophage cell line (J774.2 cells). S. enterica serovar Typhimurium 14028 phoP and a rough lipopolysaccharide mutant of S. enterica serovar Infantis 1326/28 (phi(r)) (avirulent mutants) induced NADPH phagocytic oxidase gp91 (gp91(phox)) activity and a significant (P < 0.05) elevation of reactive oxygen species within 12 h without coculture with IFN-gamma. This coincided with reduced survival of S. enterica serovar Typhimurium14028 phoP or stasis of S. enterica serovar Infantis phi(r). Fluorometric studies indicated that expression of IFN-gamma on infected J774.2 cells was not significantly (P > 0.05) elevated. However, studies with the virulent S. enterica serovar Typhimurium strains showed that a comparable level of control of bacterial numbers could only be achieved by coculture with IFN-gamma. This coincided with significant upregulation of IFN-gamma receptor alpha expression on the surface of J774.2 cells and was completely abolished by N-acetyl-L-cysteine captopril (an inhibitor of reactive oxygen species). Delay in reactive oxygen species induction due to a requirement for IFN-gamma and upregulation of IFN-gamma receptor alpha in macrophages infected with virulent salmonellae may result in greater dissemination of virulent salmonellae in host tissue.

Reduction of experimental Salmonella and Campylobacter contamination of chicken skin by application of lytic bacteriophages

Lytic bacteriophages, applied to chicken skin that had been experimentally contaminated with Salmonella enterica serovar Enteritidis or Campylobacter jejuni at a multiplicity of infection (MOI) of 1, increased in titer and reduced the pathogen numbers by less than 1 log(10) unit. Phages applied at a MOI of 100 to 1,000 rapidly reduced the recoverable bacterial numbers by up to 2 log(10) units over 48 h. When the level of Salmonella contamination was low (< log(10) 2 per unit area of skin) and the MOI was 10(5), no organisms were recovered. By increasing the number of phage particles applied (i.e., MOI of 10(7)), it was also possible to eliminate other Salmonella strains that showed high levels of resistance because of restriction but to which the phages were able to attach.

Contribution of proton-translocating proteins to the virulence of Salmonella enterica serovars Typhimurium, Gallinarum, and Dublin in chickens and mice

We investigated the attenuating effects of a range of respiratory chain mutations in three Salmonella serovars which might be used in the development of live vaccines. We tested mutations in nuoG, cydA, cyoA, atpB, and atpH in three serovars of Salmonella enterica: Typhimurium, Dublin, and Gallinarum. All three serovars were assessed for attenuation in their relevant virulence assays of typhoid-like infections. Serovar Typhimurium was assessed in 1-day-old chickens and the mouse. Serovar Gallinarum 9 was assessed in 3-week-old chickens, and serovar Dublin was assessed in 6-week-old mice. Our data show variation in attenuation for the nuoG, cydA, and cyoA mutations within the different serovar-host combinations. However, mutations in atpB and atpH were highly attenuating for all three serovars in the various virulence assays. Further investigation of the mutations in the atp operon showed that the bacteria were less invasive in vivo, showing reduced in vitro survival within phagocytic cells and reduced acid tolerance. We present data showing that this reduced acid tolerance is due to an inability to adapt to conditions rather than a general sensitivity to reduced pH. The data support the targeting of respiratory components for the production of live vaccines and suggest that mutations in the atp operon provide suitable candidates for broad-spectrum attenuation of a range of Salmonella serovars.

Rapid protection of gnotobiotic pigs against experimental salmonellosis following induction of polymorphonuclear leukocytes by avirulent Salmonella enterica

Oral inoculation of 5-day-old gnotobiotic pigs with Salmonella enterica serovar Typhimurium strain F98 resulted in severe enteritis and invasive disease. Preinoculation 24 h earlier with an avirulent mutant of Salmonella enterica serovar Infantis (1326/28) completely prevented disease for up to 14 days (when the experiment was terminated). S. enterica serovar Infantis colonized the alimentary tract well, with high bacterial counts in the intestinal lumen but with almost no invasion into the tissues. Unprotected pigs had high S. enterica serovar Typhimurium counts in the intestines, blood, and major nonintestinal organs. Recovery of this strain from the blood and major organs in S. enterica serovar Infantis-protected pigs was substantially reduced despite the fact that intestinal counts were also very high. Protection against disease thus did not involve a colonization exclusion phenomenon. Significant (P < 0.05) infiltration of monocytes/macrophages was observed in the submucosal regions of the intestines of both S. enterica serovar Infantis-protected S. enterica serovar Typhimurium-challenged pigs and unprotected S. enterica serovar Typhimurium-challenged pigs. However, only polymorphonuclear neutrophils (PMNs) were observed throughout the villus, where significant (P < 0.05) numbers infiltrated the lamina propria and the subnuclear and supranuclear regions of the epithelia, indicating that PMN induction and positioning following S. enterica serovar Infantis inoculation was consistent with rapid protection against the challenge strain. Similarly, in vitro experiments using a human fetal intestinal epithelial cell line (INT 407) demonstrated that, although significantly (P < 0.05) fewer S. enterica serovar Infantis than S. enterica serovar Typhimurium organisms invaded the monolayers, S. enterica serovar Infantis induced an NF-kappaB response and significantly (P < 0.05) raised interleukin 8 levels and transmigration of porcine PMN. The results of this study suggest that attenuated Salmonella strains can protect the immature intestine against clinical salmonellosis by PMN induction. They also demonstrate that PMN induction is not necessarily associated with clinical symptoms and/or intestinal pathology.

The Effect of Serial Culture and Storage on the Protective Potential of a Competitive Exclusion Preparation

The competitive exclusion method (EC) was used to protect day-old birds against colonisation of the intestinal tract by Salmonella enterica serovar Enteritidis (SE). The culture prepared in nutrient broth incubated at 37ºC/24 h inhibited SE growth in the caecal contents. The beneficial effect was also observed after serial passage of the feces culture for up to 14 times. The material obtained after 12 serial sub-cultures after storage for 28 days at 4-6ºC also kept its action on SE.

[Specificity of inhibition between Salmonella strains]

A phenomenon of inhibition among Salmonella organisms colonizing the gut of young animals can be demonstrated which is important in connection with immunization using live Salmonella vaccines. For practical utilization of this inhibition phenomenon, research into its specificity is very important. In vitro broth culture and animal experiments have shown inhibition to be genus-specific, i.e. there is no inhibition between strains of different genera of Enterobacteriaceae in most cases. The strongest inhibition occurs between isogenic (identical genotype) strains (strain-specific inhibition). This applies to Salmonella and other genera of Enterobacteriaceae. There was a close correlation between the degree of the inhibitory effect and the genetic relatedness of the strains, as has been demonstrated in Salmonella strains of different epidemiological classification. The inhibitory capacity was most pronounced among closely related strains. Clonal strains of Salmonella Enteritidis phage type 4 fully inhibited caecal colonization by Salmonella Enteritidis phage type 4 strains in 65% of the combinations tested in chicks. In broth culture experiments, the share of combinations with complete inhibition was above 90%. A significant inhibitory competence of a selected strongly inhibitory Salmonella Enteritidis phage type 4 strain against the majority of Salmonella Enteritidis field isolates can be expected. However, Salmonella Enteritidis strains of all phase types showed almost no inhibitory competence against other Salmonella serotypes.

Salmonella enterica serovar Pullorum persists in splenic macrophages and in the reproductive tract during persistent, disease-free carriage in chickens

Salmonella enterica serovar Pullorum is worldwide a poultry pathogen of considerable economic importance, particularly in those countries with a developing poultry industry. In addition to the characteristic high mortality rates among young chicks, one of the features of Salmonella serovar Pullorum infection is that it persists for long periods in convalescent chicks in the absence of clinical disease. This can lead to colonization of the reproductive tract of chickens and at sexual maturity can result in infected progeny through transovarian transmission to eggs. The sites of Salmonella serovar Pullorum persistence in convalescent birds are not known, and the mechanisms of persistence are not understood. Here we show that Salmonella serovar Pullorum can persist in both the spleen and the reproductive tract for over 40 weeks following experimental infection in chickens. During the period of sexual maturity, Salmonella serovar Pullorum colonized both the ovary and the oviduct of hens and led to 6% of laid eggs being infected by Salmonella serovar Pullorum. The colonization of several different sites of the reproductive tract suggests that Salmonella serovar Pullorum may employ more than one mechanism of egg infection. Persistence occurred despite a strong humoral response, suggesting an intracellular site of infection. By use of a Salmonella serovar Pullorum strain containing a plasmid stably expressing green fluorescent protein, we demonstrated that the main site of carriage in the spleen is within macrophages. This raises interesting questions about the biology of Salmonella serovar Pullorum, including why there is an increase in bacterial numbers when birds become sexually mature and in particular how Salmonella serovar Pullorum avoids clearance by macrophages and whether it modulates the immune system in other ways.

Localization to chicken chromosome 5 of a novel locus determining salmonellosis resistance

Clear genetic differences in the susceptibility of chickens to visceral infection by Salmonella have been observed and it has been possible to identify resistant and susceptible lines of inbred chickens. We report here the results of experiments to map directly the gene(s) controlling this trait in chickens by examining crosses between highly susceptible and highly resistant lines. In the mapping panel, a region on chicken Chromosome (Chr) 5 was found to have a large effect on resistance, and this effect was observed in three separate resource populations. Mapping of additional marker loci in the region of the resistance gene further localized it to a region of approximately 2 cM, close to the genes for creatine kinase (CKB) and dynein (DNCH1). This region shows conserved synteny with telomeric regions of human Chr 14 and mouse Chr 12. On the basis of this conserved synteny, this resistance gene seems unlikely to correspond to the previously identified salmonellosis resistance genes Lps (located on mouse Chr 4) or Nos(2) (located on mouse Chr 11). There was no association between Nramp1 and resistance in these crosses, although this gene was shown to contribute to resistance in other crosses. The homologous human and mouse regions at present contain no likely candidate genes for this trait. Thus this appears to be a novel resistance gene, which we designate SAL1.

Salmonella enterica serovar Gallinarum requires the Salmonella pathogenicity island 2 type III secretion system but not the Salmonella pathogenicity island 1 type III secretion system for virulence in chickens

Salmonella enterica serovar Gallinarum is a host-specific serotype that causes the severe systemic disease fowl typhoid in domestic poultry and a narrow range of other avian species but rarely causes disease in mammalian hosts. Specificity of the disease is primarily at the level of the reticuloendothelial system, but few virulence factors have been described other than the requirement for an 85-kb virulence plasmid. In this work, by making functional mutations in the type III secretion systems (TTSS) encoded by Salmonella pathogenicity island 1 (SPI-1) and SPI-2, we investigated the role of these pathogenicity islands in interactions between Salmonella serovar Gallinarum and avian cells in vitro and the role of these pathogenicity islands in virulence in chickens. The SPI-1 mutant showed decreased invasiveness into avian cells in vitro but was unaffected in its ability to persist within chicken macrophages. In contrast the SPI-2 mutant was fully invasive in nonphagocytic cells but failed to persist in macrophages. In chicken infections the SPI-2 mutant was attenuated while the SPI-1 mutant showed full virulence. In oral infections the SPI-2 mutant was not observed in the spleen or liver, and following intravenous inoculation it was cleared rapidly from these sites. SPI-2 function is required by Salmonella serovar Gallinarum for virulence, primarily through promoting survival within macrophages allowing multiplication within the reticuloendothelial system, but this does not preclude the involvement of SPI-2 in uptake from the gut to the spleen and liver. SPI-1 appears to have little effect on virulence and survival of Salmonella serovar Gallinarum in the host.

The virulence for gnotobiotic pigs of live attenuated vaccine strains of Salmonella enterica serovars Typhimurium and Enteritidis

Gnotobiotic pigs were inoculated orally with wild-type or defined aroA or cya crp vaccine strains of Salmonella enterica serovars Typhimurium and S. Enteritidis. The parental strains were virulent, inducing severe diarrhoea, dehydration and systemic disease. The cya crp mutant was also highly virulent whereas the aroA strains were attenuated.

A prevalence survey for zoonotic enteric bacteria in a research monkey colony with specific emphasis on the occurrence of enteric Yersinia

Transmissible pathogenic and opportunistic zoonotic enteric bacteria comprise a recognized occupational health threat to exposed humans from non-human primates (NHPs). In an effort to evaluate the occurrence of selected enteric organisms with zoonotic and biohazard potential in a research colony setting, we performed a prevalence study examining 61 juvenile and young adult rhesus macaques participating in a transplant immunology project. Primary emphasis was directed specifically to detection of pathogenic enteric Yersinia, less well-documented and reported NHP pathogens possessing recognized significant human disease potential. NHPs were surveyed by rectal culture during routine health monitoring on three separate occasions, and samples incubated using appropriate media and specific selective culture methods. Enteric organisms potentially transmissible to humans were subcultured and identified to genus and species. Significant human pathogens of the Salmonella/Shigella, Campylobacter, and enteric Yersinia groups were not isolated throughout the survey, suggesting prevalence of these organisms may generally be quite low.

Flow cytometry characterisation of Salmonella typhimurium mutants defective in proton translocating proteins and stationary-phase growth phenotype

We have shown that the growth, starvation and population heterogeneity of Salmonella typhimurium and its isogenic nuoG and cydA mutants can be monitored by flow cytometry. Bacterial cells were analysed unstained, and after staining with rhodamine 123, propidium iodide and acridine orange. In unstained cultures it was possible to distinguish flagellated and non-flagellated cells. nuoG and cydA mutants were less stained with rhodamine confirming their defects in generating membrane potential. Increase in propidium iodide staining associated with reduced membrane integrity was seen between day 4 and 14 in all the strains. Acridine orange staining showed that there was retarded development in stationary phase in nuoG and cydA mutants. Furthermore, up to day 28, a small portion of cells showed high RNA and DNA levels. To determine whether these cells represent a sub-population better adapted for long term survival, we measured the growth of the population by both OD values and viable counts. Because the OD values increased throughout the whole study in both wild-type and mutant strains, while the viable counts gradually decreased, we propose that even in very old cultures there must be a population of cells undergoing replication.

The paratyphoid salmonellae

The paratyphoid Salmonella bacteria, comprising more than 2,000 serovars or serotypes, are a major problem to the poultry industry. This is largely the result of entry of the bacteria into the human food chain. Human infection takes the form of a gastroenteritis, which in highly susceptible individuals can result in death. Some strains of certain serotypes have the capacity to produce morbidity and mortality in very young chickens. In adult birds, some serovars become localised in the reproductive tract with concomitant vertical transmission. The association between S. Enteritidis and table eggs has produced a great deal of publicity and concern with resulting national and international attempts at controlling the major serotypes, S. Typhimurium and S. Enteritidis, at the breeder and layer level. Control is possible through rigorous hygiene and management procedures, but is not always economically viable. As a result, control by serological and bacteriological testing and slaughter may also not be feasible. Antibiotics have been used to reduce carriage but can cause problems of resistance and increased susceptibility. The use of growth promoting antibiotics can also increase susceptibility to infection. Other means of increasing the resistance of poultry to infection are therefore being sought. These include the use of intestinal flora preparations for competitive exclusion of Salmonella from newly hatched chicks. Killed and live vaccines are used, both with some success. However, the safety of some live vaccines is still uncertain.

Functional phenotype in transgenic mice expressing mutant human presenilin-1

Mutations in the presenilin-1 (PS1) gene cause approximately 50% of cases of early onset familial Alzheimer's disease. The function of this protein remains unknown. We have made an electrophysiological study of hippocampal slices from transgenic mice expressing either a normal human PS1 transgene (WT) or one of two human PS1 transgenes bearing pathogenic mutations at codon M146 (M146L and M146V). Medium and late afterhyperpolarizations in CA3 pyramidal cells were larger in mice expressing either mutant form compared with WT and nontransgenic controls. Calcium responses to depolarization were larger in M146L mice compared with nontransgenic littermates; synaptic potentiation of the CA3 to CA1 projection was also stronger. These results demonstrate disruption of the control of intracellular calcium and electrophysiological dysfunction in PS1 mutant mice.

Inhibition of colonisation of the alimentary tract in young chickens with Campylobacter jejuni by pre-colonisation with strains of C. jejuni

Strains of Campylobacter jejuni, isolated from human gastro-intestinal infection and inoculated orally into 1-day-old chicks, colonised the alimentary tract (caecum) well. There was evidence of invasion from the intestine to the spleen. Oral inoculation with some but not all strains of C. jejuni 24 h earlier (within 12 h of hatching) prevented establishment by challenge strains administered orally 1 day later. One strain which was less able to colonise the gut was less inhibitory than other strains. Precolonisation of newly hatched chicks with a strain of Salmonella typhimurium had no inhibitory effect on establishment by the challenge strain of C. jejuni and may even have exacerbated it. Inhibition of multiplication of a nalidixic acid-resistant mutant of a C. jejuni strain was prevented when it was added to a stationary-phase broth culture of the antibiotic-sensitive parent strain and the mixed culture re-incubated.

Intrinsic physiological and morphological properties of principal cells of the hippocampus and neocortex in hamsters infected with scrapie

Scrapie is a transmissible spongiform encephalopathy, or "prion disease." We investigated the effects of intracerebral Sc237 scrapie inoculation in hamsters on the physiology and morphology of principal cells from neocortical and hippocampal slices. Scrapie inoculation resulted in increased branching of basal dendrites of hippocampal CA1 pyramidal cells (Sholl analysis), reduced amplitudes of medium and late afterhyperpolarizations (AHPs) in CA1 pyramidal cells and layer V neocortical cells, loss of frequency potentiation of depolarizing afterpotentials (DAPs), and double action potentials in synaptically evoked CA1 pyramidal cell responses. Postsynaptic double action potentials could also be evoked in normal hamster CA1 pyramidal cells by acute pharmacological block of AHPs, suggesting that the depressed AHPs in scrapie-infected hamsters caused the action potential doublets. Both the AHP and the DAP potentiations depend on increased intracellular calcium, which suggests that the underlying deficit, in hamsters infected with Sc237 scrapie, may lie in calcium entry and/or homeostasis. Fast IPSPs, passive membrane properties, and density of dendritic spines remained unchanged. These last two results differ markedly from recent studies on mice infected with ME7 scrapie, indicating diversity of pathophysiology in this group of diseases, perhaps associated with the progressive and substantial neuronal loss found in the ME7, and not the Sc237, model.

Intestinal colonisation of gnotobiotic pigs by Salmonella organisms: interaction between isogenic and unrelated strains

The effect of intestinal colonisation by a Salmonella strain on the establishment in the gut of an isogenic mutant administered orally 24 h after the first strain was studied in gnotobiotic pigs. Irrespective of the clinical outcome of the infection, the extensive colonisation of one Salmonella strain prevented a similar degree of colonisation by an otherwise isogenic antibiotic resistant strain; in some cases the second strain was hardly detectable. The poor colonisation of the challenge Salmonella strains was generally reflected in very low counts of organisms in the tissues. Colonisation by a strain of Escherichia coli reduced the rate of establishment of an isogenic E. coli, strain but did not prevent colonisation by an S. Typhimurium strain. S. Typhimurium with mutations in the tsr (serine chemotaxis receptor protein) or oxrA (transcriptional regulator of anaerobic metabolism) genes did not inhibit colonisation. Mutations in cya (adenylate cyclase), tar and trg (chemotaxis receptor proteins for aspartate and ribose respectively) genes were less inhibitory, while motB (non-motile) and cheR (impaired motility) mutants were fully inhibitory.