Biomedical subjects

J P Christensen

Publications and source records attributed to J P Christensen.

At least 19 recordsLinked to original sources

PubMed2006

Geno- and phenotypic diversity of avian isolates of Streptococcus gallolyticus subsp. gallolyticus (Streptococcus bovis) and associated diagnostic problems.

Recently, strains of Streptococcus bovis were reclassified as Streptococcus gallolyticus. In the present study we describe for the first time an outbreak of S. gallolyticus in a broiler flock. Mortality during the first week was normal (<1%), with a final total mortality at the end of production reaching 4.3%. Specific symptoms were not observed. Postmortem pathology demonstrated enlarged and light spleens and livers accompanied by multifocal irregular necroses surrounded by a hemorrhagic zone. In addition, these birds suffered from arthritis and osteomyelitis. Strains isolated from liver and spleen lesions showed clonality as demonstrated by pulsed-field gel electrophoresis. Compared to strains representing previously derived phylogeny, including the S. bovis-S. equinus complex, the 16S rRNA-derived phylogeny of the strains investigated in this study demonstrated a paraphyletic group (S. gallolyticus) well separated from two monophyletic groups: (i) S. equinus-S. bovis plus S. infantarius and (ii) S. alactolyticus plus S. intestinalis. According to information in GenBank, none of the strains included from the two monophyletic groups have been isolated from birds. Further biochemical analyses, including tannase activity, identified for the first time avian isolates belonging to S. gallolyticus subsp. gallolyticus. However, these investigations also demonstrated a clear heterogeneity with pigeon isolates.

Animals↗

PubMed2006

Clonal stability of Pasteurella multocida in free-range layers affected by fowl cholera.

Detailed longitudinal studies of the genetic stability of Pasteurella multocida ssp. multocida, the cause of fowl cholera, have not previously been carried out. Consequently, the aim of the present study was to provide detailed information on the genetic stability and diversity of P. multocida ssp. multocida in poultry flocks over time, enabling new insights into the molecular epidemiology of this important poultry pathogen. Longitudinal investigations of the rate and causes of mortality were carried out on two free-range layer farms (A and B) over a period of 11 months. The total mortality of two flocks, A1 and A2, on farm A were 62 and 91%, respectively, while the total mortality of a single flock B1 on farm B was 6%. Postmortem examinations were performed on 708 layers from flocks A1 and A2 and in 159 from flock B1. Fowl cholera was the main cause of mortality on both farms. Pasteurella multocida isolates recovered from layers on both farms were characterized phenotypically and genotypically, and 322 isolates were identified as P. multocida ssp. multocida. The genetic diversity of 99 isolates from farm A and 31 from farm B was characterized by restriction endonuclease analysis and amplified fragment length polymorphism analysis. The isolates on each farm had a unique restriction endonuclease analysis and amplified fragment length polymorphism analysis type, suggesting a single introduction of a successful clone. Furthermore the clone on farm A was identical to clones previously isolated from outbreaks in the avifauna of Denmark in 1996 and 2001 and in Sweden in 1998. This study provides convincing evidence for the clonal stability of outbreak clones of P. multocida.

Aging↗

PubMed2006

Infection and excretion of Salmonella Enteritidis in two different chicken lines with concurrent Ascaridia galli infection.

Studies on the impact of interaction of Salmonella enterica serovar Enteritidis and the parasitic nematode Ascaridia galli with the avian host were undertaken with particular emphasis on infection and excretion of these pathogens in two different layer lines. A total of 148 salmonella-free 1-day-old chickens (73 Hellevad and 75 Lohmann Brown) were randomly divided into five groups for each line. Group 1 served as an uninoculated control group. Groups 2 and 3 were infected with A. galli and S. Enteritidis, respectively. Group 4 was first infected with S. Enteritidis and subsequently with A. galli, and vice versa for group 5. The number of chickens excreting S. Enteritidis was significantly higher (P < 0.001) in the groups infected with both S. Enteritidis and A. galli compared with those only infected with S. Enteritidis over time. Furthermore, excretion of S. Enteritidis over time was significantly higher (P < 0.001) in the group first infected with S. Enteritidis and subsequently with A. galli compared with the group infected in the reverse order. No significant differences were observed between the two lines concerning excretion of S. Enteritidis over time in any group (P = 0.61 (group 3), P = 0.73 (group 4), P = 0.31 (group 5)). A. galli established itself significantly better (P = 0.02) in the group first infected with A. galli and subsequently with S. Enteritidis compared with the group infected in the reverse order. Furthermore, the A. galli infection rate was significantly higher (P = 0.02) in Hellevad chickens compared with Lohmann Brown chickens at the end of the experiment.

Animals↗

PubMed2006

Role of very late antigen-1 in T-cell-mediated immunity to systemic viral infection.

The T-cell response to lymphocytic choriomeningitis virus was studied in mice lacking very late antigen-1 (VLA-1). The generation of virus-specific effector T cells was unimpaired in VLA-1(-/-) mice. In the memory phase, VLA-1 deficiency did not influence the number of memory CD8(+) T cells or their distribution between lymphoid and nonlymphoid organs. Regarding a functional role of VLA-1, we found that intracerebral infection of both VLA-1(-/-) and wild-type (wt) mice resulted in lethal T-cell-mediated meningitis, and quantitative and qualitative analyses of the cellular exudate did not reveal any significant differences between the two strains. Expression of VLA-1 was also found to be redundant regarding the ability of effector T cells to eliminate virus from internal organs of i.v. infected mice. Using delayed-type hypersensitivity (DTH) assays to evaluate subdermal CD8(+) T-cell-mediated inflammation, no significant influence of VLA-1 was found either in the primary response or in the memory phase. However, alpha-VLA-4 antibody reduced the DTH-like reaction in VLA-1(-/-) mice to a higher degree than in wt mice, suggesting a synergistic effect of blocking both integrins. Taken together, the current findings indicate that the expression of VLA-1 is not pivotal for T-cell-mediated antiviral immunity to a systemic infection.

Animals↗

PubMed2006

Consequences of concurrent Ascaridia galli and Escherichia coli infections in chickens.

Three experiments were carried out to examine the consequences of concurrent infections with Ascaridia galli and Escherichia coli in chickens raised for table egg production. Characteristic pathological lesions including airsacculitis, peritonitis and/or polyserositis were seen in all groups infected with E. coli. Furthermore, a trend for increased mortality rates was observed in groups infected with both organisms which, however, could not be confirmed statistically. The mean worm burden was significantly lower in combined infection groups compared to groups infected only with A. galli. It was also shown that combined infections of E. coli and A. galli had an added significant negative impact on weight gain.

Animals↗

PubMed2005

Reproduction of sepsis and endocarditis by experimental infection of chickens with Streptococcus gallinaceus and Enterococcus hirae.

This study describes experimental infections in 4-week-old chickens inoculated intravenously with approximately 10(8) colony-forming units Streptococcus gallinaceus strain CCUG 42692T (C13156) or Enterococcus hirae strain DSM 20160 (C17410). Birds were necropsied following death and obvious clinical signs of disease or were euthanized weekly after infection for up to 4 weeks. At necropsy, lesions included splenomegaly, hepatomegaly, valvular and/or mural endocarditis. Cardiac lesions included focal necrotizing myocarditis and/or yellow-white vegetative valvular endocarditis or greyish proliferations associated with the mitral valves in 35% (6/20) and 79% (19/24) of birds infected with S. gallinaceus and in 20% (4/20) and 55% (12/22) of birds infected with E. hirae via the brachial and jugular veins, respectively. S. gallinaceus was reisolated from heart valves in 45% (9/20) and 75% (18/24) and E. hirae in 35% (7/20) and 73% (16/22) after inoculation via brachial and jugular veins, respectively. Both challenge strains were also isolated from liver, spleen, bone marrow and hock joints. A significant difference between the infections with the two strains was seen only with reisolation of E. hirae from hock joints (P < 0.007). Significant differences were apparent between the two inoculation routes only with E. hirae, where infection via the jugular vein was associated with higher culture positive isolations from the heart (P = 0.029), bone marrow (P = 0.002) and hock joints (P < 0.001) compared with the brachial vein. Birds injected with sterile phosphate-buffered saline were negative for culture of the challenge strains and no lesions were observed in these controls. The results confirm that both S. gallinaceus and E. hirae can cause endocarditis in experimentally infected chickens.

Animals↗

PubMed2005

Characterization of Enterococcus hirae outbreaks in broiler flocks demonstrating increased mortality because of septicemia and endocarditis and/or altered production parameters.

In Denmark, increased problems associated with streptococci and enterococci have been observed in broilers and broiler parent flocks, resulting in increased mortalities, uneven flocks, and subsequent downgrading and increased condemnations. Postmortem lesions associated with recent outbreaks due to Enterococcus hirae have been accompanied or dominated by septicemia and endocarditis. As a result of infection at an early age and relatively low mortality rates, outbreaks are not always clearly defined and may go unnoticed or may be attributed to poor chick quality. For the same reasons, the pathogenesis and epidemiology of observed outbreaks has only remained speculative. Four separate outbreaks associated with E. hirae infections in broiler flocks occurring between 1998 and 2002 have been investigated. Two of the outbreaks indicated evidence of two separate clones, with 89% and 79% of isolates involved in the individual outbreaks belonging to a single pulsed-field gel electrophoresis (PFGE) profile, respectively. Another outbreak (outbreak 4) demonstrated clear clonality, with all isolates demonstrating affinity to one of two PFGE profiles that differed by only two bands. However, all three outbreaks demonstrated a different clone. The remaining outbreak was nondonal, with isolates distributed between six separate PFGE profiles. One of the outbreaks (outbreak 4) was descended from a parent broiler flock previously associated with an outbreak of Streptococcus gallinaceus; the flock also exhibited septicemia and endocarditis. Initial indications suggested the possibility of vertical transmission of S. gallinaceus to the current broiler flock, causing infection. By extended phenotypic characterization and subsequent genetic characterization, including 16S rRNA sequencing, all strains from the four outbreaks were confirmed as E. hirae. This investigation highlights the problems associated with characterizing enterococci infections in broiler flocks.

Animal Husbandry↗

PubMed2004

Characterization of streptococci and enterococci associated with septicaemia in broiler parents with a high prevalence of endocarditis.

Increased mortality due to septicaemia, where 29% of the affected birds had developed valvular endocarditis, was observed in a flock of broiler parents affected by myelocytomatosis. Bacterial investigations resulted in isolation of streptococci, the classification of which was unknown according to present taxonomy. Strains were isolated from the liver, spleen, heart and salpinx in clinical cases of septicaemia from the affected flock of Ross broiler parents aged between 26 and 56 weeks. Phenotypic characterization followed by genotypic investigation by ribotyping with HindIII and pulsed-field gel electrophoresis (PFGE) with SmaI demonstrated three ribotypes and six different PFGE profile types, respectively. Ribotype A with variant A1, together with the PFGE profile type represented by the three subtypes Ia, Ib and Ic, dominated the outbreak constituting 85% of the strains investigated, indicating clonality. 16S rRNA sequencing of strains representing this genotype demonstrated the occurrence of a recently described new Streptococcus sp., Streptococcus gallinaceus. Sequence analysis of the other genotypes demonstrated in the outbreak, resulted in identical 16S rRNA sequences to the type strain of Enterococcus faecalis. S. gallinaceus appears to represent a new opportunistic pathogen within the poultry industry.

Animals↗

PubMed2003

Phylogenetic analysis by 16S rDNA gene sequence comparison of avian taxa of Bisgaard and characterization and description of two new taxa of Pasteurellaceae.

AIMS: Characterization and classification of members of Pasteurellaceae isolated from birds by extended phenotypic characterization and 16S rDNA gene sequence comparison. METHODS AND RESULTS: A total of 95 avian isolates were subjected to extended phenotypic characterization. Thirteen bacterial strains selected from main phenotypic clusters and isolated from parrot, parakeet, budgerigar, partridge, pheasant, chicken, duck, hawk and gull were subsequently characterized by 16S rDNA gene sequencing. Eight of the sequenced strains were classified with six taxa of Bisgaard of which two (34 and 40) have not been published before, and the properties of four others (14, 22, 26 and 32) changed upon the characterization of these new isolates. Of the remaining strains, one was identified as a phenotypic variant in maltose and dextrin of Pasteurella gallinarum another as a trehalose positive variant of taxon 3 of Bisgaard. The remaining three strains sequenced were not closely related to existing taxa of Pasteurellaceae. However, they were found to belong to the Avian cluster with 92-97% 16S rDNA gene sequence similarity. CONCLUSION: The study allowed the classification of bacteria isolated from birds by the integrated use of extended phenotypic characterization and 16S rDNA gene sequence analysis. Only the application of 16S rDNA gene sequencing allows a correct identification of variant strains. SIGNIFICANCE AND IMPACT OF THE STUDY: The description of new taxa within the bacterial family Pasteurellaceae will subsequently allow additional isolates of these taxa to be identified and improve the diagnosis and epidemiological understanding of bacteria causing disease in birds.

Animals↗

PubMed2002

The effect of concurrent infections with Pasteurella multocida and Ascaridia galli on free range chickens.

Pasteurella multocida and Ascaridia galli are observed with high prevalences in free range chickens in Denmark, but the impact is unknown. A study was carried out to examine the interaction between A. galli and P. multocida in chickens and the impact on production. Five groups, each with 20 18-week-old Lohmann Brown chickens were infected. Group 1 was orally infected with 1000+/-50 embryonated A. galli eggs. Group 2 received 10(4) cfu P. multocida intratracheally. Group 3 was infected with A. galli and subsequently with P. multocida. Group 4 was infected with P. multocida followed by A. galli. Group 5 was the control. The study ran for 11 weeks where clinical manifestations, weight gain and egg production were recorded. Excretion of P. multocida was determined on individual basis and blood smears were made for differential counts. At the end of the study pathological lesions and the number of adult worms, larvae and eggs in the faeces were recorded. The birds were more severely affected when infected with both pathogens compared to single infections with A. galli or P. multocida, respectively. A lower weight gain and egg production was observed with dual infections. A. galli infection followed by a secondary P. multocida infection resulted in more birds with pathological lesions and continued P. multocida excretion. In conclusion a negative interaction between A. galli and P. multocida was observed and it is postulated that free range chickens are at higher risk of being subjected to outbreaks of fowl cholera when they are infected with A. galli.

Animals↗

PubMed2002

Quantitative comparison of intestinal invasion of zoonotic serotypes of Salmonella enterica in poultry.

The aim of the present study was to compare the invasion of selected zoonotic Salmonella serotypes of poultry in an in vivo chicken intestinal loop model and also in vitro in epithelial cell cultures. Invasion was measured relative to a reference strain, Salmonella Typhimurium 4/74 invH201::TnphoA. Two serotypes demonstrated intracellular log(10) counts that differed significantly from all other serotypes tested: Salmonella Enteritidis PT4 being 1.5 log(10) colony forming units (CFU) (31-fold) higher, and Salmonella Tennessee being 0.7 log(10) CFU (fivefold) lower than the reference strain (P < or = 0.0001). A group of serotypes, which can be vertically transmitted, showed significantly higher intracellular counts (fourfold to eightfold) than the reference strain. The group included S. Typhimurium 4/74, S. Typhimurium DT104 (poultry and porcine isolates), S. Enteritidis PT1, S. Enteritidis PT6, S. Enteritidis PT8, and Salmonella Berta. The serotypes Salmonella Hadar, Salmonella Virchow, S. 4,12:b:-, S. Typhimurium DT41, and Salmonella Infantis, most of which are considered horizontally transmitted, did not show significantly different intracellular counts from the reference strain. Results from the cell culture invasion studies agreed with the in vivo data, with the exception of S. Berta and the poultry isolate of S. Typhimurium DT104.

Animals↗

PubMed2002

Application of molecular methods for identification of strains classified as Salmonella enterica serovar 6, 7:-:- by conventional serotyping.

An increased prevalence of Salmonella enterica serovar Tennessee (6, 7: z(29):-) was observed in broiler flocks in Denmark in 1994 and a parallel increase in the prevalence of Salmonella enterica serovar 6, 7:-:- was demonstrated, albeit at a lower level. Plasmid profiling and ribotyping revealed similar genotypes and it was speculated that serovar 6, 7:-:- could represent a non-motile variant of Salmonella Tennessee. Re-testing of the Salmonella 6, 7:-:- isolates demonstrated the presence of flagella through positive motility. All isolates but one demonstrated motility using both tube tests and light microscopy of overnight broth cultures. Molecular characterization indicated that all but two isolates previously classified as Salmonella 6, 7:-:, were isolates of Salmonella Tennessee and Salmonella Infantis, exhibiting reduced motility. Re-serotyping and multiplex polymerase chain reaction analysis for the phase 2 gene fljB demonstrated variants of Salmonella Infantis (6, 7: r: z(49)) expressing the R-phase antigen (Rz(49)) and possessing the gene for normal phase 2 antigen H: 1, 5. One of the two undefined strains demonstrated genotypic identity with a Salmonella Livingstone reference strain. The remaining putative 6, 7:-:- strain could not be identified and was genuinely non-motile. Diagnostic procedures performed initially were thus insufficient to differentiate between the different levels of motility and also resulted in mis-serotyping. As similar observations were made with two of 14 isolates received from a foreign laboratory, this may represent a general diagnostic problem.

Animals↗

PubMed2001

Dissecting the host response to a gamma-herpesvirus.

The murine gamma-herpesvirus 68 (MHV-68) provides a unique experimental model for dissecting immunity to large DNA viruses that persist in B lymphocytes. The analysis is greatly facilitated by the availability of genetically disrupted (-/-) mice that lack key host-response elements, and by the fact that MHV-68 is a lytic virus that can readily be manipulated for mutational analysis. The mutant virus strategy is being used, for example, to characterize the part played in vivo by an MHV-68-encoded chemokine-binding protein that may ultimately find an application in human therapeutics. Experiments with various -/- mice and monoclonal antibody depletion protocols have shown very clearly that type I interferons (IFNs) are essential for the early control of MHV-68 replication, while CD4+ T cells producing IFN-gamma function to limit the consequences of viral persistence. Virus-specific CD8+ effectors acting in the absence of the CD4+ subset seem initially to control the lytic phase in the lung following respiratory challenge, but are then unable to prevent the reactivation of replicative infection in epithelia and the eventual death of CD4+ T-cell-deficient mice. This could reflect the fact that the interaction between the CD8+ T cells and the virus-infected targets is partially compromised by the MHV-68 K3 protein, which inhibits antigen presentation by MHC class I glycoproteins. Immunization strategies focusing on the CD8+ T-cell response to epitopes expressed during the lytic phase of MHV-68 infection can limit virus replication, but are unable to prevent the establishment of latency. Other experiments with mutant viruses also suggest that there is a disconnection between lytic MHV-68 infection and latency. The massive nonspecific immunoglobulin response and the dramatic expansion of Vbeta4+ CD8+ T cells, which is apparently MHC independent, could represent some sort of 'smoke screen' used by MHV-68 to subvert immunity. Although MHV-68 is neither Epstein-Barr virus nor human herpesvirus-8, the results generated from this system suggest possibilities that may usefully be addressed with these human pathogens. Perhaps the main lesson learned to date is that all the components of immunity are likely to be important for the control of these complex viruses.

Animals↗

PubMed2001

Depletion of CD4+ T cells precipitates immunopathology in immunodeficient mice infected with a noncytocidal virus.

IFN-gamma-deficient (IFN-gamma(-/-)) mice inoculated with intermediate doses of a slowly replicating strain of lymphocytic choriomeningitis virus become chronically infected. In such mice a hypercompensated CTL response is observed that partially controls virus replication. Here we have investigated whether CD4(+) Th cells are required to establish and maintain this new equilibrium. The absence of IFN-gamma does not impair the generation of IL-2-producing CD4(+) cells, and depletion of these cells precipitates severe CD8(+) T cell-mediated immunopathology in IFN-gamma(-/-) mice, indicating an important role of CD4(+) T cells in preventing this syndrome. Analysis of organ virus levels revealed a further impairment of virus control in IFN-gamma(-/-) mice following CD4(+) cell depletion. Initially the antiviral CTL response did not require CD4(+) cells, but with time an impaired reactivity toward especially the glycoprotein 33--41 epitope was noted. Enumeration of epitope-specific (glycoprotein 33--41 and nucleoprotein 396--404) CD8(+) T cells by use of tetramers gave similar results. Finally, limiting dilution analysis of CTL precursors reveal an impaired capacity to sustain this population in CD4(+)-depleted mice, especially in mice also deficient in IFN-gamma. Thus, our findings disclose that T cell help is required to sustain the expanded CTL precursor pool required in IFN-gamma(-/-) mice. This interpretation is supported by mathematical modeling that predicts an increased requirement for help in IFN-gamma(-/-) hosts similar to what is found with fast replicating virus strains in normal hosts. Thus, the functional integrity of CD8(+) effector T cells is one important factor influencing the requirement for T cell help during viral infection.

Acute Disease↗

PubMed2001

Relationships among Pasteurellaceae isolated from free ranging chickens and their animal contacts as determined by quantitative phenotyping, ribotyping and REA-typing.

One hundred and forty-three Pasteurella spp. strains and 10 unclassified strains obtained from free ranging poultry, dogs and cats were investigated by extended phenotypic characterization. One hundred and forty-nine of these strains were selected for further studies using ribotyping and REA-typing to evaluate the role of dogs and cats in Pasteurella multocida transmission. Seven and six type strains were included for comparison in phenotyping and genotyping, respectively. Eleven clusters and six unclustered strains were revealed by phenotyping. Ribotyping outlined 12 clusters and six unclustered strains. A correlation between clusters obtained by phenotyping and ribotyping was demonstrated which indicated that a genetic basis exists for clusters outlined by quantitative evaluation of phenotypic data. Similarities and differences in hosts, phenotype, ribotype, and zone of isolation were demonstrated among Pasteurella strains investigated. Isolates of P. multocida from ducks were shown to be clonal by both phenotyping and ribotyping. These strains were identical to one of the chickens strains. REA-typing, however, showed that the chicken strain was different underlining that exchange of clones of P. multocida between avian species rarely happens under village conditions. Management practise in the villages suggest the potential for exchange of P. multocida between poultry and animals kept in contact. The present findings, however, did not indicate that clones of P. multocida are widely exchanged between poultry and other animal species, even though close contact exists. In the present investigation exchange of clones of P. multocida was only demonstrated among animals belonging to the same species. Caution is drawn to the use of ribotyping as the sole method for epidemiological typing and tracing of P. multocida. The present results also underline the importance of proper phenotyping in the identification of P. multocida and related species.

Animals↗

PubMed2001

Occurrence of Pasteurella multocida and related species in village free ranging chickens and their animal contacts in Tanzania.

Investigation was done to determine the presence of Pasteurella multocida and related species in free ranging chickens and ducks, dogs, cats and pigs in three climatic zones (cool, warm and hot) of rural Morogoro, Tanzania. A total of 153 isolates of P. multocida ssp. multocida and related species were obtained by direct culture on blood agar, selective medium and mouse inoculation. P. multocida ssp. multocida was isolated from 0.7% of chickens and 7% of ducks. In dogs and cats, P. multocida ssp. multocida was isolated from 1 and 68%, respectively. One isolate of Pasteurella gallinarum was isolated from a duck. Other species obtained were; P. multocida ssp. septica, Pasteurella stomatis and taxon 16 from dogs and cats, while Pasteurella dagmatis and Pasteurella canis were found in dogs only. Prevalence of P. multocida ssp. multocida was significantly higher (P<0.01) in ducks of the warm zone (22%) than in ducks of other zones (0%). No significant difference was observed between the prevalence of P. multocida ssp. multocida in chickens of the warm zone (2%) and chickens of the cool and hot zones (0%). Extended phenotypic characterization revealed phenotypic similarities between two isolates from chickens and the duck strains. Mouse inoculation appeared to be more sensitive in detecting P. multocida ssp. multocida than blood agar and selective medium. Direct culture on blood agar recovered most of the isolates from dogs. This study has demonstrated for the first time the presence of P. multocida and related species in the village free ranging chickens, ducks, dogs and cats in Tanzania. Other non-classified Pasteurella spp. were also observed in the study, but further characterization is required before the final classification can be made. This paper reports for the first time the isolation of unclassified Pasteurella from dogs and cats in Africa. The results implies that fowl cholera might be occurring in free ranging poultry, and dogs and cats kept in contact might serve as sources of P. multocida to chickens and ducks. Subsequent applications of molecular techniques to analyse the epidemiological relatedness of clones isolated from different host species is indicated.

Animals↗

PubMed2001

Studies on the prevalence of Riemerella anatipestifer in the upper respiratory tract of clinically healthy ducklings and characterization of untypable strains.

A total of 44 bacterial strains obtained from 49 clinically healthy ducklings of different ages originating from four different farms were identified as members of the species Riemerella anatipestifer (RA) using conventional biochemical test methods. Numerical analysis of the whole-cell fatty acid patterns of these isolates resulted in two different clusters, one of which showed a similar pattern to that of the type strain of RA. Strains having a different fatty acid methyl esters (FAME)-profile (cluster II) were designated R. anatipestifer-like (RA-like). Sequencing of 16S rRNA genes of RA-like field isolates revealed 99% identity to RA. The significance of these observations are discussed. The present findings document for the first time that RA seems to represent a normal part of the pharyngeal flora of healthy Pekin ducks.

Animals↗

PubMed2001

CD11b expression as a marker to distinguish between recently activated effector CD8(+) T cells and memory cells.

CD8(+) T cells in different activation states have been difficult to identify phenotypically. In this study we have investigated whether Mac-1 (CD11b) expression can be used as a criterion to distinguish between recently activated effector cells and memory cells belonging to the CD8(+) T cell subset. Polyclonal virus-specific effector and memory CD8(+) T cells from lymphocytic choriomeningitis- and vesicular stomatitis virus-infected mice were visualized through staining for intracellular IFN-gamma or binding of MHC-peptide tetramers, and Mac-1 expression was evaluated. Naive T cells and most virus-specific memory CD8(+) T cells express little or no Mac-1 independent of the virus model employed. In contrast, the majority of CD8(+) T cells present during acute infection express a significant level of Mac-1 and, similarly, Mac-1 expression is found on secondary effectors generated in response to viral re-exposure. We therefore suggest that high Mac-1 expression defines a subset of circulating effector cells and that the presence of this marker on antigen-specific CD8(+) T cells signifies recent activation.

Acute Disease↗