Prior exposure to pathogens augments host heterogeneity in susceptibility and has key epidemiological consequences.

Pathogen epidemics are key threats to human and wildlife health. Across systems, host protection from pathogens following initial exposure is often incomplete, resulting in recurrent epidemics through partially-immune hosts. Variation in population-level protection has important consequences for epidemic dynamics, but whether acquired protection influences host heterogeneity in susceptibility and its epidemiological consequences remains unexplored. We experimentally investigated whether prior exposure (none, low-dose, or high-dose) to a bacterial pathogen alters host heterogeneity in susceptibility among songbirds. Hosts with no prior pathogen exposure had little variation in protection, but heterogeneity in susceptibility was significantly augmented by prior pathogen exposure, with the highest variability detected in hosts given high-dose prior exposure. An epidemiological model parameterized with experimental data found that heterogeneity in susceptibility from prior exposure more than halved epidemic sizes compared with a homogeneous population with identical mean protection. However, because infection-induced mortality was also greatly reduced in hosts with prior pathogen exposure, reductions in epidemic size were smaller than expected in hosts with prior exposure. These results highlight the importance of variable protection from prior exposure and/or vaccination in driving host heterogeneity and epidemiological dynamics.

Are Purple Finches (Haemorhous purpureus) the Next Host for a Mycoplasmal Conjunctivitis Epidemic?

Ever since 1994, when the bacterial pathogen Mycoplasma gallisepticum jumped from poultry to wild birds, it has been assumed that the primary host species of this pathogen in wild North American birds was the house finch (Haemorhous mexicanus), in which disease prevalence was higher than in any other bird species. Here we tested two hypotheses to explain a recent increase in disease prevalence in purple finches (Haemorhous purpureus) around Ithaca, New York. Hypothesis 1 is that, as M. gallisepticum evolved and became more virulent, it has also become better adapted to other finches. If this is correct, early isolates of M. gallisepticum should cause less-severe eye lesions in purple finches than in house finches, while more-recent isolates should cause eye lesions of similar severity in the two species. Hypothesis 2 is that, as house finch abundance declined following the M. gallisepticum epidemic, purple finches around Ithaca increased in abundance relative to house finches and purple finches are thus more frequently exposed to M. gallisepticum-infected house finches. This would then lead to an increase in M. gallisepticum prevalence in purple finches. Following an experimental infection with an early and a more-recent M. gallisepticum isolate, eye lesions in purple finches were more severe than in house finches. This did not a support Hypothesis 1; similarly, an analysis of Project Feeder Watch data collected around Ithaca did not show differences in changes in purple and house finches' abundance since 2006, a result which does not support Hypothesis 2. We conclude that purple finch populations will, unlike those of house finches, not suffer a severe decline because of a M. gallisepticum epidemic.

¿Son los pinzones purpúreos (Haemorhous purpureus) los próximos huéspedes de una epidemia de conjuntivitis por micoplasma? Desde el año 1994, cuando el patógeno bacteriano Mycoplasma gallisepticum saltó de las aves comerciales a las aves silvestres, se ha supuesto que la principal especie huésped de este patógeno en las aves silvestres de América del Norte era el pinzón mexicano (Haemorhous mexicanus), en el que la prevalencia de la enfermedad era mayor que en cualquier otra especie aviar. En este estudio se analizaron dos hipótesis para explicar un aumento reciente en la prevalencia de la enfermedad en los pinzones purpúreos (Haemorhous purpureus) alrededor de Ithaca, en Nueva York. La hipótesis 1 es que, a medida que M. gallisepticum evolucionó y se volvió más virulento, también se adaptó mejor a otros pinzones. Si esto es correcto, los aislamientos tempranos de M. gallisepticum deberían causar lesiones oculares menos graves en los pinzones purpúreos que en los pinzones mexicanos, mientras que los aislamientos más recientes deberían causar lesiones oculares de gravedad similar en las dos especies. La hipótesis 2 es que, a medida que la abundancia de pinzones mexicanos disminuyó después de la epidemia de M. gallisepticum, los pinzones purpúreos alrededor de Ithaca aumentaron en abundancia en relación con los pinzones mexicanos y, por lo tanto, los pinzones morados están expuestos con mayor frecuencia a los pinzones caseros infectados con M. gallisepticum. Esto conduciría a un aumento de la prevalencia de M. gallisepticum en los pinzones purpúreos. Después de una infección experimental con un aislamiento temprano y uno más reciente de M. gallisepticum, las lesiones oculares en los pinzones purpúreos fueron más graves que en los pinzones mexicanos. Esto no apoyó la Hipótesis 1; de manera similar, un análisis de los datos del Proyecto Feeder Watch recopilados alrededor de Ithaca no mostró diferencias en los cambios de la abundancia de pinzones purpúreos y mexicanos desde 2006, un resultado que no respalda la Hipótesis 2. Se concluye que las poblaciones de pinzones purpúreos, a diferencia de las de los pinzones mexicanos, no sufrieron un declive severo a causa de una epidemia de M. gallisepticum.

B cells oppose Mycoplasma pneumoniae vaccine enhanced disease and limit bacterial colonization of the lungs.

Development of an effective vaccine for Mycoplasma pneumoniae has been hindered by reports of Vaccine Enhanced Disease (VED) in test subjects vaccinated and challenged in studies conducted in the 1960s. The exact mechanism of disease exacerbation has yet to be fully described, but host immune responses to Lipid-Associated Membrane Proteins (LAMPs) lipoprotein lipid moieties have been implicated. LAMPs-induced exacerbation appears to involve helper T cell recall responses, due in part to their influence on neutrophil recruitment and subsequent inflammatory responses in the lung. Herein, we characterized the functions of host B cell responses to M. pneumoniae LAMPs and delipidated-LAMPs (dLAMPs) by conducting passive transfer and B cell depletion studies to assess their contribution to disease exacerbation or protection using a BALB/c mouse model. We found that antibody responses to M. pneumoniae LAMPs and dLAMPs differ in magnitude, but not in isotype or subclass. Passive transfer, dLAMP denaturation, and monoclonal antibody studies indicate that antibodies do not cause VED, but do appear to contribute to control of bacterial loads in the lungs. Depletion of B cells prior to LAMPs-vaccination results in significantly enhanced pathology in comparison to B cell competent controls, suggesting a possible regulatory role of B cells distinct from antibody secretion. Taken together, our findings suggest that B cell antibody responses to M. pneumoniae contribute to, but are insufficient for protection against challenge on their own, and that other functional properties of B cells are necessary to limit exacerbation of disease in LAMPs-vaccinated mice after infection.

CHANGES IN TISSUE TROPISM OF MYCOPLASMA GALLISEPTICUM FOLLOWING HOST JUMP.

Mycoplasma gallisepticum, a pathogen of worldwide economic importance in poultry, is recovered in chickens, especially from the respiratory tract. Some strains, however, are specialized to other tissues and because it jumps from poultry to wild birds, the new strains also cause severe conjunctivitis in new hosts. Nevertheless, most studies of M. gallisepticum in wild birds use choanal swabs or combine choanal and conjunctival swabs to quantify bacterial load. Because the clinical signs associated with M. gallisepticum infection differ markedly between poultry and House Finches (Haemorhous mexicanus), we compared the bacterial load in choanal and conjunctival samples following experimental inoculation of House Finches with M. gallisepticum isolates originating from poultry or from House Finches. This allowed us to test two hypotheses: M. gallisepticum changed tissue tropism, or M. gallisepticum simply expanded its within-host niche. By comparing bacterial loads from choanal and conjunctival swabs in birds inoculated with one of a suite of M. gallisepticum isolates, we found support for hypothesis 2. The choanal loads in House Finches did not differ between isolates, while the conjunctival loads of birds inoculated with poultry isolates were lower than in birds inoculated with House Finch isolates. When measuring the bacterial load of M. gallisepticum in birds, it is important to sample and analyze separately choanal and conjunctival swabs, as quantifying bacterial loads in pooled samples may not provide reliable information on differences in virulence.

Vaccination with Mycoplasma pneumoniae membrane lipoproteins induces IL-17A driven neutrophilia that mediates Vaccine-Enhanced Disease.

Bacterial lipoproteins are an often-underappreciated class of microbe-associated molecular patterns with potent immunomodulatory activity. We previously reported that vaccination of BALB/c mice with Mycoplasma pneumoniae (Mp) lipid-associated membrane proteins (LAMPs) resulted in lipoprotein-dependent vaccine enhanced disease after challenge with virulent Mp, though the immune responses underpinning this phenomenon remain poorly understood. Herein, we report that lipoprotein-induced VED in a mouse model is associated with elevated inflammatory cytokines TNF-α, IL-1ß, IL-6, IL-17A, and KC in lung lavage fluid and with suppurative pneumonia marked by exuberant neutrophilia in the pulmonary parenchyma. Whole-lung-digest flow cytometry and RNAScope analysis identified multiple cellular sources for IL-17A, and the numbers of IL-17A producing cells were increased in LAMPs-vaccinated/Mp-challenged animals compared to controls. Specific IL-17A or neutrophil depletion reduced disease severity in our VED model-indicating that Mp lipoproteins induce VED in an IL-17A-dependent manner and through exuberant neutrophil recruitment. IL-17A neutralization reduced levels of TNF-α, IL-1ß, IL-6, and KC, indicating that IL-17A preceded other inflammatory cytokines. Surprisingly, we found that IL-17A neutralization impaired bacterial clearance, while neutrophil depletion improved it-indicating that, while IL-17A appears to confer both maladaptive and protective responses, neutrophils play an entirely maladaptive role in VED. Given that lipoproteins are found in virtually all bacteria, the potential for lipoprotein-mediated maladaptive inflammatory responses should be taken into consideration when developing vaccines against bacterial pathogens.

Lipid moieties of Mycoplasma pneumoniae lipoproteins are the causative factor of vaccine-enhanced disease.

Vaccine-enhanced disease (VED) occurs as a result of vaccination followed by infection with virulent Mycoplasma pneumoniae. To date VED has prevented development of an efficacious vaccine against this significant human respiratory pathogen. Herein we report that vaccination of BALB/c mice with M. pneumoniae lipid-associated membrane proteins (LAMPs) induces lung lesions consistent with exacerbated disease following challenge, without reducing bacterial loads. Removal of lipid moieties from LAMPs prior to vaccination eliminates VED and reduces bacterial loads after infection. Collectively, these data indicate that lipid moieties of lipoproteins are the causative factors of M. pneumoniae VED.

Immunologic Pathways in Protective versus Maladaptive Host Responses to Attenuated and Pathogenic Strains of Mycoplasma gallisepticum.

Mycoplasmas are small bacterial commensals or pathogens that commonly colonize host mucosal tissues and avoid rapid clearance, in part by stimulating inflammatory, immunopathogenic responses. We previously characterized a wide array of transcriptomic perturbations in avian host tracheal mucosae infected with virulent, immunopathologic Mycoplasma gallisepticum; however, mechanisms delineating these from protective responses, such as those induced upon vaccination, have not been thoroughly explored. In this study, host transcriptomic responses to two experimental M. gallisepticum vaccines were assessed during the first 2 days of infection. Relative to virulent infection, host metabolic and immune gene responses to both vaccines were greatly decreased, including early innate immune responses critical to disease development and subsequent adaptive immunity. These data specify host genes and potential mechanisms contributing to maladaptive versus beneficial host responses-information critical for design of vaccines efficacious in both limiting inflammation and enabling pathogen clearance.

HOUSE FINCH ( HAEMORHOUS MEXICANUS)-ASSOCIATED MYCOPLASMA GALLISEPTICUM IDENTIFIED IN LESSER GOLDFINCH ( SPINUS PSALTRIA) AND WESTERN SCRUB JAY ( APHELOCOMA CALIFORNICA) USING STRAIN-SPECIFIC QUANTITATIVE PCR.

: In 1994 Mycoplasma gallisepticum was found to be the etiologic agent of House Finch ( Haemorhous mexicanus) conjunctivitis, a rapidly expanding epidemic caused by a genetically discrete, House Finch-associated strain of M. gallisepticum (HFMG). While most prominent in House Finches, HFMG has been reported in other members of the family Fringillidae, including American Goldfinches ( Spinus tristis), Purple Finches ( Haemorhous purpureus), Pine Grosbeaks ( Pinicola enucleator), and Evening Grosbeaks ( Coccothraustes vespertinus). Herein we report two new potential host species of HFMG strain, the Lesser Goldfinch ( Spinus psaltria), belonging to the Fringillidae family, and the Western (California) Scrub Jay ( Aphelocoma californica), belonging to the Corvidae family. The latter is one of only two reports of HFMG being found outside the Fringillidae family, and of these is the only one reported outside of captivity. Furthermore, non-HFMG M. gallisepticum was identified in an American Crow ( Corvus brachyrhynchos), indicating presence of additional strains in wild birds. Strain typing of M. gallisepticum isolates was done via HFMG-specific quantitative PCR analysis and validated using random amplified polymorphic DNA analysis. Our results suggested an expanded host range of HFMG strain, and further suggested that the host range of HFMG was not limited to members of the family Fringillidae.

House Finch (Haemorhous mexicanus) Conjunctivitis, and Mycoplasma spp. Isolated from North American Wild Birds, 1994-2015.

Sampling wild birds for mycoplasma culture has been key to the study of House Finch (Haemorhous mexicanus) conjunctivitis, yielding isolates of Mycoplasma gallisepticum spanning the temporal and geographic ranges of disease from emergence to endemicity. Faced with the challenges and costs of sample collection over time and from remote locations for submission to our laboratory for mycoplasma culture, protocols evolved to achieve a practical optimum. Herein we report making M. gallisepticum isolates from House Finches almost every year since the disease emerged in 1994, and we now have 227 isolates from 17 states. Our wild bird host range for M. gallisepticum isolates includes Blue Jay ( Cyanocitta cristata ), American Goldfinch (Spinus tristis), Lesser Goldfinch (Spinus psaltria), Purple Finch (Haemorhous purpureus), Evening Grosbeak ( Coccothraustes vespertinus ), and herein first reports for Western Scrub-jay ( Aphelocoma californica ), and American Crow ( Corvus brachyrhynchos ). By collecting and identifying isolates from birds with clinical signs similar to those of House Finch conjunctivitis, we also expanded the known host range of Mycoplasma sturni and obtained isolates from additional wild bird species. Accumulating evidence shows that a diverse range of wild bird species may carry or have been exposed to M. gallisepticum in the US, as in Europe and Asia. Therefore, the emergence of a pathogenic M. gallisepticum strain in House Finches may actually be the exception that has allowed us to identify the broader epidemiologic picture.

Mycoplasma gallisepticum in vivo induced antigens expressed during infection in chickens.

Until now only a few genes encoding virulence factors have been characterized in the avian pathogen Mycoplasma gallisepticum. In order to identify candidate targets associated with infection we applied an immunoscreening technique-in vivo induced antigen technology (IVIAT)-to detect immunogens of M. gallisepticum strain Rlow expressed preferentially during in vivo infection. We identified 13 in vivo-induced (IVI) proteins that correspond to different functional categories including: previously reported putative virulence factors (GapA, PlpA, Hlp3, VlhA 1.07 and VlhA 4.01), transport (PotE, MGA_0241 and 0654), translation (L2, L23, ValS), chaperone (GroEL) and a protein with unknown function (MGA_0042). To validate the in vivo antigenic reactivity, 10 IVI proteins were tested by Western blot analysis using serum samples collected from chickens experimentally (with strain Rlow) and naturally (outbreaks, N=3) infected with M. gallisepticum. All IVI proteins tested were immunogenic. To corroborate these results, we tested expression of IVI genes in chickens experimentally infected with M. gallisepticum Rlow, and in MRC-5 human lung fibroblasts cell culture by using relative real time reverse-transcription PCR (RT-PCR). With the exception of MGA_0338, all six genes tested (MGA_1199, 0042, 0654, 0712, 0928 and 0241) were upregulated at least at one time point during experimental infection (2-4 week post-infection). In contrast, the expression of seven out of eight IVI genes (MGA_1199, 0152, 0338, 0042, 0654, 0712, 0928) were downregulated in MRC-5 cell culture at both 2 and 4h PI; MGA_0241 was upregulated 2h PI. Our data suggest that the identified IVI antigens may have important roles in the pathogenesis of M. gallisepticum infection in vivo.

Semi-automated curation of metabolic models via flux balance analysis: a case study with Mycoplasma gallisepticum.

Primarily used for metabolic engineering and synthetic biology, genome-scale metabolic modeling shows tremendous potential as a tool for fundamental research and curation of metabolism. Through a novel integration of flux balance analysis and genetic algorithms, a strategy to curate metabolic networks and facilitate identification of metabolic pathways that may not be directly inferable solely from genome annotation was developed. Specifically, metabolites involved in unknown reactions can be determined, and potentially erroneous pathways can be identified. The procedure developed allows for new fundamental insight into metabolism, as well as acting as a semi-automated curation methodology for genome-scale metabolic modeling. To validate the methodology, a genome-scale metabolic model for the bacterium Mycoplasma gallisepticum was created. Several reactions not predicted by the genome annotation were postulated and validated via the literature. The model predicted an average growth rate of 0.358±0.12[Formula: see text], closely matching the experimentally determined growth rate of M. gallisepticum of 0.244±0.03[Formula: see text]. This work presents a powerful algorithm for facilitating the identification and curation of previously known and new metabolic pathways, as well as presenting the first genome-scale reconstruction of M. gallisepticum.

MalF is essential for persistence of Mycoplasma gallisepticum in vivo.

There is limited understanding of the molecular basis of virulence in the important avian pathogen Mycoplasma gallisepticum. To define genes that may be involved in colonization of chickens, a collection of mutants of the virulent Ap3AS strain of M. gallisepticum were generated by signature-tagged transposon mutagenesis. The collection included mutants with single insertions in the genes encoding the adhesin GapA and the cytadherence-related protein CrmA, and Western blotting confirmed that these mutants did not express these proteins. In two separate in vivo screenings, two GapA-deficient mutants (ST mutants 02-1 and 06-1) were occasionally recovered from birds, suggesting that GapA expression may not always be essential for persistence of strain Ap3AS. CrmA-deficient ST mutant 33-1 colonized birds poorly and had reduced virulence, indicating that CrmA was a significant virulence factor, but was not absolutely essential for colonization. ST mutant 04-1 contained a single transposon insertion in malF, a predicted ABC sugar transport permease, and could not be reisolated even when inoculated by itself into a group of birds, suggesting that expression of MalF was essential for persistence of M. galliseptium strain Ap3AS in infected birds.

A microarray biosensor for multiplexed detection of microbes using grating-coupled surface plasmon resonance imaging.

Grating-coupled surface plasmon resonance imaging (GCSPRI) utilizes an optical diffraction grating embossed on a gold-coated sensor chip to couple collimated incident light into surface plasmons. The angle at which this coupling occurs is sensitive to the capture of analyte at the chip surface. This approach permits the use of disposable biosensor chips that can be mass-produced at low cost and spotted in microarray format to greatly increase multiplexing capabilities. The current GCSPRI instrument has the capacity to simultaneously measure binding at over 1000 unique, discrete regions of interest (ROIs) by utilizing a compact microarray of antibodies or other specific capture molecules immobilized on the sensor chip. In this report, we describe the use of GCSPRI to directly detect multiple analytes over a large dynamic range, including soluble protein toxins, bacterial cells, and viruses, in near real-time. GCSPRI was used to detect a variety of agents that would be useful for diagnostic and environmental sensing purposes, including macromolecular antigens, a nontoxic form of Pseudomonas aeruginosa exotoxin A (ntPE), Bacillus globigii, Mycoplasma hyopneumoniae, Listeria monocytogenes, Escherichia coli, and M13 bacteriophage. These studies indicate that GCSPRI can be used to simultaneously assess the presence of toxins and pathogens, as well as quantify specific antibodies to environmental agents, in a rapid, label-free, and highly multiplexed assay requiring nanoliter amounts of capture reagents.

Effects of sialidase knockout and complementation on virulence of Mycoplasma gallisepticum.

Reannotation of the pathogenic Mycoplasma gallisepticum strain R(low) genome identified the hypothetical gene MGA_0329 as a homolog of the sialidase gene MS53_0199 of Mycoplasma synoviae strain MS53. Potent sialidase activity was subsequently quantitated in several M. gallisepticum strains. Because sialidase activity levels correlate significantly with differing M. synoviae strain virulence, we hypothesized this enzyme may also influence the virulence of M. gallisepticum. MGA_0329 was disrupted in strain R(low) to create mutants 6, 358 and P1C5, which resulted in the loss of sialidase activity in all three mutants. Chickens infected with the knockout mutants had significantly less severe (P<0.05) tracheal lesions and tracheal mucosal thickening than chickens infected with equal doses of strain R(low). Significantly fewer (P<0.05) CCU especially of strains 6 and P1C5 were recovered at necropsy. Mini-Tn4001tet plasmid pTF20 carrying a wild-type copy of MGA_0329 with its native promoter was used to complement the genetic lesion in strain P1C5. Three clones derived from P1C5, each having one copy of MGA_0329 stably transposed into a different site in its genome, expressed sialidase restored to wild-type activity levels (1.58×10(-8)U/CFU). Complementation of P1C5 with MGA_0329 did not restore it to wild-type levels of virulence, indicating that the contribution of sialidase to M. gallisepticum virulence is not straightforward.

Meningitis caused by Mycoplasma mycoides subspecies capri in a goat.

A 2-year-old, female goat from Connecticut was submitted for necropsy with a 5-day history of pyrexia and intermittent neurologic signs, including nystagmus, seizures, and circling. Postmortem examination revealed suppurative meningitis. Histologic examination of the brain revealed that the meninges were diffusely infiltrated by moderate numbers of lymphocytes, macrophages, and fibrin, with scattered foci of dense neutrophilic infiltrate. Culture of pus and brainstem yielded typical mycoplasma colonies. DNA sequencing of the 16S ribosomal RNA gene revealed 99% sequence homology with Mycoplasma mycoides subspecies capri and Mycoplasma mycoides subspecies mycoides Large Colony biotype, which are genetically indistinguishable and likely to be combined as a single subspecies labeled M. mycoides subsp. capri. The present case is unusual in that not only are mycoplasma an uncommon cause of meningitis in animals, but additionally, in that all other reported cases of mycoplasma meningitis in goats, systemic lesions were also present. In the present case, meningitis was the only lesion, thus illustrating the need to consider mycoplasma as a differential diagnosis for meningitis in goats.

Identification of 'Candidatus Piscichlamydia salmonis' in Arctic charr Salvelinus alpinus during a survey of charr production facilities in North America.

Arctic charr Salvelinus alpinus production facilities, nonproduction water sources and effluents in the United States and Canada were sampled to determine if chlamydiae associated with epitheliocystis were present in water and were associated with inclusions of epitheliocystis in gill tissue. Gills from 607 fish from 13 sites were processed for histopathologic examination and DNA extraction. Water was collected from 21 locations for DNA testing. Eighteen fish from one location had inclusions of epitheliocystis with proliferative and inflammatory gill lesions. Inclusions were stained using the Gimenez technique and, at the ultrastructural level, consisted of intracytoplasmic membrane-bound vacuoles containing reticulate and intermediate bodies in a fibrillar matrix. PCR using Order Chlamydiales-specific primers performed on DNA extracts from 12 of 13 infected fish yielded amplicons that were identical to (GQ302988) or differed at one base from (GQ302987) the 16S ribosomal RNA gene signature sequence of 'Candidatus Piscichlamydia salmonis', which is the chlamydia that was previously identified in epitheliocystis inclusions of farmed Atlantic salmon. In situ hybridization using a approximately 1.5 kb riboprobe corresponding to the 'Candidatus Piscichlamydia salmonis' 16S rRNA genetic sequence (AY462244) confirmed its presence within Arctic charr gill inclusions. DNA isolated from water samples was tested by Chlamydiales-specific PCR and yielded 54 partial 16S rRNA genetic sequences spanning the signature region; however, no 16S rRNA genetic sequences associated with epitheliocystis were identified. This is the first report of 'Candidatus Piscichlamydia salmonis' associated with epitheliocystis in Arctic charr, the first identification of 'Candidatus Piscichlamydia salmonis' from a freshwater production location, and the first reported occurrence in North America.

Structural and functional characterization of an organic hydroperoxide resistance protein from Mycoplasma gallisepticum.

As obligate parasites, Mycoplasma species are continuously exposed to oxidative damage due to host-generated peroxides and reactive oxygen species (ROS). In addition, the production of endogenous oxidants is believed to be a primary virulence mechanism of several Mollicute species, indicating that oxidative stress resistance is crucial to survival of these bacteria in the host milieu. Despite the abundance of oxidants at the site of infection, enzymes responsible for the detoxification of ROS have never been characterized in mycoplasmas. Here we characterize a homolog of the ohr (organic hydroperoxide resistance) family from Mycoplasma gallisepticum (encoding MGA1142). Unlike previously characterized ohr genes, the mga1142 gene is not upregulated in response to oxidative stress but displays a novel pattern of expression. Both organic and inorganic peroxides can act as substrates for MGA1142, but they are degraded with various efficiencies. Furthermore, cumene hydroperoxide, an aromatic peroxide metabolized with high efficiency by other Ohr proteins, was shown to rapidly inactivate MGA1142, accounting for the sensitivity of M. gallisepticum cells to this compound. Comparative modeling of the MGA1142 quaternary structure revealed that the active site of this molecule has a relatively wide conformation. These data indicate that the natural substrate for MGA1142 differs from that for previously characterized Ohr proteins. Triton X-114 partitioning demonstrated that MGA1142 is located in both cytosol and membrane fractions, suggesting that in vivo this molecule plays a role in the detoxification of both endogenous and exogenous peroxides. A model describing how MGA1142 is likely to be oriented in the cell membrane is presented.

Chemokine and cytokine gene expression profiles in chickens inoculated with Mycoplasma gallisepticum strains Rlow or GT5.

Mycoplasma gallisepticum infection in chickens leads to tracheitis, airsacculitis, poor feed conversion and reduced egg production, resulting in considerable economic hardship on the poultry industry. The chemokines and cytokines responsible for recruitment, activation and proliferation of leukocytes in affected tissues have not been described. In the current study, chemokine and cytokine gene expression profiles were investigated in tracheas of chickens inoculated with M. gallisepticum strains R(low) (pathogenic) and GT5 (attenuated) at days 1, 4 and 8 post-inoculation. Expression of lymphotactin mRNA was higher in R(low)-inoculated chickens than GT5- or PBS-inoculated chickens, while CXCL13/BCA1 mRNA expression level was higher in both GT5- or R(low)-inoculated chickens than in PBS-inoculated controls on day 1 post-inoculation. However, both R(low) and GT5 strains induced a down-regulation in mRNA expression of CCL20, IL-1beta, IL-8 and IL-12p40 genes, with CCL20 and IL-12 mRNA levels remaining lower on days 4 and 8 post-inoculation. On day 4, R(low)-inoculated chickens exhibited significantly higher tracheal lesion scores and higher levels of lymphotactin, CXCL13, CXCL14, RANTES, MIP-1beta, IL-1beta and IFN-gamma mRNA compared to PBS-inoculated controls. The mRNA levels of these genes were also higher in R(low)-inoculated chickens that had moderate to severe tracheal lesion scores on day 8 post-inoculation. These results reflect the importance of lymphocyte and monocyte chemotactic factors in the development of tracheal lesions in chickens inoculated with M. gallisepticum strain R(low). Our data also suggest that M. gallisepticum may modulate the host response causing dramatic decreases in CCL20, IL-8 and IL-12 mRNA levels in GT5- or R(low)-inoculated chickens as early as one day post-inoculation.

Characterization of a Neochlamydia-like bacterium associated with epitheliocystis in cultured Arctic charr Salvelinus alpinus.

Infections of branchial epithelium by intracellular gram-negative bacteria, termed epitheliocystis, have limited culture of Arctic charr Salvelinus alpinus. To characterize a bacterium associated with epitheliocystis in cultured charr, gills were sampled for histopathologic examination, conventional and immunoelectron microscopy, in situ hybridization, 16S ribosomal DNA (rDNA) amplification, sequence analysis and phylogenetic inference. Sampling was conducted at the Freshwater Institute (Shepherdstown, West Virginia, USA) during outbreaks of epitheliocystis in April and May 2002. Granular, basophilic, cytoplasmic inclusions in charr gill were shown to stain with Macchiavello, Lendrum's phloxine-tartrazine and Gimenez histochemical techniques. Ultrastructurally, inclusions were membrane-bound and contained round to elongate reticulate bodies that were immunoreactive to an antibody against chlamydial lipopolysaccharide, suggesting the presence of similar epitopes. DNA extracted from gills supported amplification of the most polymorphic and phylogenetically relevant region of the 16S rRNA gene, which had 97 to 100% identity with several uncultured clinical Neochlamydia spp. (order Chlamydiales) Clones WB13 (AY225593.1) and WB258 (AY225594.1). Sequence-specific riboprobes localized to inclusions during in situ hybridization experiments. Taxonomic affiliation was inferred by distance- and parsimony-based phylogenetic analyses of the 16S sequence, which branched with Neochlamydia hartmannellae in the order Chlamydiales with high confidence. This is the first molecular characterization of a chlamydia associated with epitheliocystis in Arctic charr and the fourth Neochlamydia spp. sequence to be associated with epitheliocystis. Presence of a clinical neochlamydial sequence, first identified from a cat, in Arctic charr suggests a possible mammalian and piscine host range for some environmental chlamydiae.

Transcriptional responses of Mycoplasma gallisepticum strain R in association with eukaryotic cells.

Mycoplasma gallisepticum is an etiologic agent of chronic respiratory disease in chickens and infectious sinusitis in turkeys. Other than proteins important for cytadherence, few M. gallisepticum factors or pathways contributing to host cell interactions have been identified. In this study, an oligonucleotide-based microarray was utilized to investigate transcriptional changes in M. gallisepticum strain R(low) upon exposure to eukaryotic cells. Fifty-eight genes were either up- or downregulated upon exposure to MRC-5 lung fibroblasts grown in vitro, including genes encoding transport-, metabolism-, and translation-associated proteins. Twenty of the 58 regulated genes have no assigned function. These results indicate that M. gallisepticum regulates gene expression upon exposure to eukaryotic cells, revealing genes and pathways likely to be important for host-bacterium interaction.