The fimbrial protein FlfA from Gallibacterium anatis is a virulence factor and vaccine candidate

Antibiotic resistance of Gallibacterium anatis biovar haemolytica isolates from chickens

Introduction

Gallibacterium anatis is an opportunistic bacteria inducing a range of clinical signs in poultry. Gallibacterium anatis strains show multidrug resistance to antibacterial substances. The purpose of this study was to examine the susceptibility of G. anatis biovar haemolytica isolates collected from the respiratory, reproduction and gastrointestinal tracts of chickens to different antibiotics from various classes.

Material and Methods

Gallibacterium anatis biovar haemolytica was identified in tracheal swab and gastrointestinal and reproductive tract tissue samples from Polish layer and broiler chicken flocks. Twenty six isolates with β-haemolysis capability, each from a different flock, obtained from the respiratory (n = 8), reproductive (n = 10) and gastrointestinal (n = 8) tracts were selected and identified by matrix-assisted laser desorption/ionisation-time-of-flight mass spectrometry after culturing. A PCR method targeting the 16S genes was used for verification of isolates. The isolates' susceptibility to 20 antimicrobials was evaluated using the disc diffusion method for 8 drugs and the dilution method for the other 12. In addition, they were tested for the presence of the GtxA, gyrB and flfA virulence genes and blaROB, aphA, tetB and tetH antibiotic resistance genes by PCR.

Results

The most prevalent antibiotic resistance was to tilmicosin, tylosin and quinupristin/dalfopristin (all 100%), erythromycin (96.2%), tetracycline (96.2%), linezolid (92.3%) and teicoplanin (92.3%). Universal susceptibility was to only one antibiotic, chloramphenicol. Statistically significant differences were found between the resistance of gastrointestinal tract strains and that of strains from other tracts to daptomycin, gentamicin, ciprofloxacin and colistin. The GtxA and gyrB genes were detected in 100% of isolates and flfA in 19.2%. The isolates most frequently contained tetB and less frequently tetH and aphA, and did not contain blaROB.

Conclusion

Most G. anatis biovar haemolytica isolates were resistant to many classes of antibiotics. Therefore, it is necessary and important to be vigilant for the occurrence of these bacteria and thorough in their diagnosis.

Isolation and characterization of multidrug resistant Gallibacterium anatis biovar haemolytica strains from Polish geese and hens

Gallibacterium anatis biovar haemolytica is a bacterium that is frequently associated with infections of the reproductive tract and respiratory system in poultry. To assess the current prevalence and resistance profile of these bacteria in Poland, we collected and investigated 63 strains of Gallibacterium from diseased domestic poultry flocks including geese, laying hens, breeding hens and an ornamental hen. Detailed characterization of the isolates included the analysis of phenotypic antimicrobial resistance profiles and biofilm formation ability. Furthermore, the genetic background of 40 selected isolates regarding the presence of virulence and antimicrobial resistance genes and mobile genetic elements was determined. All investigated isolates were multidrug resistant, most prominently to β-lactams, fluoroquinolones, sulfonamides and macrolides. A total of 48 different resistance profiles were detected. Of all isolates, 50.8% formed a strong biofilm, where strains isolated from geese appeared to be better at biofilm formation than strains isolated from laying and breeding hens. Single-nucleotide polymorphism genotyping revealed that G. anatis bv. haemolytica strains are restricted in host and geographical distribution, and the geese isolates showed greater phylogenetic similarity. Whole genome sequencing enabled identification of 25 different antimicrobial resistance determinants. The most common resistance genes were tetB, blaROB-1, and blaTEM-1 which may be located on mobile genetic elements. All isolates possessed the toxin gene gtxA, and the fimbrial gene flfA was identified in 95% of strains. Our results indicated that all G. anatis bv. haemolytica isolates showed multidrug resistant phenotypes. Strains isolated from geese were characterized by the highest percentage of isolates resistant to selected antimicrobials, probably reflecting host-related adaptations.

A Maverick-like cluster in the genome of a pathogenic, moderately virulent strain of Gallibacterium anatis, ESV200, a transient biofilm producer

Introduction

Gallibacterium anatis causes gallibacteriosis in birds. These bacteria produce biofilms and secrete several fimbrial appendages as tools to cause disease in animals. G. anatis strains contain up to three types of fimbriae. Complete genome sequencing is the strategy currently used to determine variations in the gene content of G. anatis, although today only the completely circularized genome of G. anatis UMN179 is available.

Methods

The appearance of growth of various strains of G. anatis in liquid culture medium was studied. Biofilm production and how the amount of biofilm was affected by DNase, Proteinase K, and Pronase E enzymes were analyzed. Fimbrial gene expression was performed by protein analysis and qRT-PCR. In an avian model, the pathogenesis generated by the strains G. anatis ESV200 and 12656-12 was investigated. Using bioinformatic tools, the complete genome of G. anatis ESV200 was comparatively studied to search for virulence factors that would help explain the pathogenic behavior of this strain.

Results and Discussion

G. anatis ESV200 strain differs from the 12656-12 strain because it produces a biofilm at 20%. G. anatis ESV200 strain express fimbrial genes and produces biofilm but with a different structure than that observed for strain 12656-12. ESV200 and 12656-12 strains are pathogenic for chickens, although the latter is the most virulent. Here, we show that the complete genome of the ESV200 strain is similar to that of the UNM179 strain. However, these strains have evolved with many structural rearrangements; the most striking chromosomal arrangement is a Maverick-like element present in the ESV200 strain.

Sequence Analysis, Antibiogram Profile, Virulence and Antibiotic Resistance Genes of XDR and MDR Gallibacterium anatis Isolated from Layer Chickens in Egypt

Background

Gallibacterium anatis is incriminated frequently in severe economic losses and mortalities in the poultry industry. This study aimed to detect the prevalence of G. anatis in layer chickens, sequence analysis, the antibiogram profiles, and PCR screening of virulence determinants and antibiotic resistance genes.

Methods

Accordingly, 300 samples (tracheal swabs, ovary and oviduct, and lung) were randomly collected from 100 diseased layer chickens from private commercial layer farms at Elsharkia Governorate, Egypt. The bacteriological examination was carried out. The retrieved isolates were tested for 16S rRNA-23S rRNA gene sequencing, antibiogram profiling, PCR screening of virulence (gtxA, fifA, and gyrB), and antibiotic resistance genes (bla_ROB, aphA1, tetB, and tetH).

Results

The prevalence of G. anatis was 25% in the examined diseased layer chickens. The sequence analyses emphasized that the tested strains derived from a common ancestor and exhibited a notable genetic similarity with other G. anatis strains from USA, China, and Denmark. The isolated G. anatis strains were highly resistant to sulfamethoxazole-trimethoprim, oxytetracycline, penicillin, ampicillin, kanamycin, neomycin, and erythromycin. The PCR revealed that the retrieved G. anatis strains carried gtxA, gyrB, and fifA virulence genes with a prevalence of 100%, 100%, and 38.3%, respectively. Approximately 30.1% of the retrieved G. anatis isolates were XDR to six antimicrobial classes and harbored bla_ROB, aphA1, and tetB resistance genes. Moreover, 20.5% of the isolated G. anatis strains were MDR to three different classes and carried bla_ROB and tetH resistance genes.

Conclusion

Briefly, this study emphasized the existence of XDR and MDR G. anatis strains in poultry. Florfenicol and norfloxacin displayed a promising antimicrobial effect against the emerging XDR and MDR G. anatis in poultry. The emergence of XDR and MDR G. anatis is considered a public health alarm.

A putative siderophore receptor of Gallibacterium anatis 12656-12 under Fur control also binds hemoglobin

Pasteurellaceae family members obtain iron directly from host proteins or through siderophore-dependent mechanisms. Although Gallibacterum anatis expresses different virulence factors, its response to growth under iron restriction is unknown. G. anatis cultured in the presence of 2,2′-dipyridyl, up-expressed an approximately 65 kDa protein and repressed the expression of a 70 kDa protein. MALDI-TOF analysis of those proteins indicated homology with CirA (65 kDa), a protein involved in iron-siderophore acquisition in Mannheimia succinoproducens and a TonB-dependent receptor (70 kDa protein), a protein that binds chicken hemoglobin; however, G. anatis siderophore production was not detected by chromo azurol S (CAS)-BHI agar determination. This putative G. anatis siderophore receptor is under Fur control, but not the hemoglobin binding protein, as observed in G. anatis 12656-12 fur mutant (Ω fur 126.13) grown in the presence or not of 2,2′-dipyridyl. The addition of FeCl₃ to the culture medium diminished the growth and biofilm production in approximately 30% and 35%, respectively, in the wild-type strain, but the growth of Ω fur 126.13 strain was not affected and biofilm production increased in 35%. G. anatis Ω fur 126.13 presented lower virulence when it was inoculated to 35-day-old chickens in comparison to the wild-type strain. The induction of more than one iron uptake mechanism could benefit pathogenic microorganisms such as Gallibacterium.

Co-Infection of Escherichia coli, Enterococcus faecalis and Chlamydia psittaci Contributes to Salpingitis of Laying Layers and Breeder Ducks

Salpingitis is manifested as hemorrhagic follicular inflammation exudations and peritonitis, leading to reduced egg production and high culling of breeder flocks. From 2018 to 2021, increasing salpingitis during egg peak is threatening the poultry industry post-artificial insemination, both in breeder layers and breeder ducks across China. In our study, Escherichia coli (E. coli), Enterococcus faecalis(E. faecalis) and Chlamydia psittaci (C. psittaci) were isolated and identified from the diseased oviducts using biochemical tests and PCR. To identify and isolate pathogenicity, we inoculated the isolates into laying hens via an intravaginal route. Later, laying hens developed typical salpingitis after receiving the combination of the aforementioned three isolates (1 × 10⁵ IFU/mL of C. psittaci and 1 × 10⁶ CFU/mL of E. faecalis and E. coli, respectively), while less oviduct inflammation was observed in the layers inoculated with the above isolate alone. Furthermore, 56 breeder ducks were divided into seven groups, eight ducks per group. The birds received the combination of three isolates, synergic infection of E. coli and E. faecalis, and C. psittaci alone via vaginal tract, while the remaining ducks were inoculated with physiological saline as the control group. Egg production was monitored daily and lesions of oviducts and follicles were determined post-infection on day 6. Interestingly, typical salpingitis, degenerated follicles and yolk peritonitis were obviously found in the synergic infection of three isolates and the birds inoculated with C. psittaci alone developed hemorrhagic follicles and white exudates in oviducts, while birds with E. faecalis or E. coli alone did not develop typical salpingitis. Finally, higher E. coli loads were determined in the oviducts as compared to E. faecalis and C. psittaci infection. Taken together, the combination of E. coli and E. faecalis, and C. psittaci could induce typical salpingitis and yolk peritonitis both in laying hens and breeder ducks. Secondary infection of E. coli and E. faecalis via artificial insemination is urgently needed for investigation against salpingitis.

Antibacterial Activity of Lactic Acid Producing Leuconostoc mesenteroides QZ1178 Against Pathogenic Gallibacterium anatis

Lactic acid bacteria (LAB) convert carbohydrates into organic acids [mainly lactic acid (LA)], which reportedly have bactericidal activities. Gallibacterium anatis is a Gram-negative bacteria which infects birds, and causes significant economic losses. In this study, we investigated the antibacterial activity of the LA producing, Leuconostoc mesenteroides QZ1178 from Qula (fermented food), against G. anatis, using the Oxford cup method. Our data showed that L. mesenteroides QZ1178 inhibited G. anatis isolates from different origins; however, L. mesenteroides QZ1178 antibacterial activity dropped dramatically at pH 5.5–pH 6. The LA concentration and pH of the liquid broth containing L. mesenteroides QZ1178 after 24 h culture was 29 mg/mL and 3.6, respectively. This concentration (29 mg/mL at pH 3.6) and the antibiotic, cefotaxime (minimum inhibitory concentration (MIC) 2.5 μg/mL) effectively inhibited G. anatis (GAC026) growth as observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Gallibacterium anatis treated with LA exhibited extensive cell surface collapse, increased cell damage, cell membrane disruption, and cytoplasmic leakage, indicative of cell lysis. We suggest L. mesenteroides QZ1178 exerts potential antibacterial effects against the poultry pathogen, G. anatis via LA.

Clonal spread of multi-resistant Gallibacterium anatis isolates among Iranian broilers and layers

Gallibacterium anatis is a common cause of reproductive tract infection in chickens, which leads to reduced egg production and increased mortality. This study was undertaken to investigate prevalence of G. anatis in 12 poultry flocks originating from Iranian provinces with leading chicken production and to determine genetic diversity, antimicrobial resistance, and the presence of major antigens of the isolates investigated. Out of the 120 chicken tracheal samples collected and tested, 84 (70%) were positive for G. anatis. Genotyping by Pulse Field Gel Electrophoresis and genome sequencing revealed a total of 24 pulsotypes for 71 strains (at a 87% similarity level) and seven genome clusters comprising 21 strains (97% similarity level), respectively. The combination of the two typing methods confirmed the presence of several genotypes originating from a common ancestor affecting poultry yet also suggested that identical clones were shared among chickens within farms and between different farms. The latter finding is to our knowledge the first example of clonal presence of G. anatis in epidemiologically unrelated farms. The 21 sequenced strains were characterized against a panel of commonly used antibiotics and showed lowered sensitivity to tetracycline (76.2%) and enrofloxacin (90.5%). The widespread presence of multiresistant G. anatis isolates calls for non-antibiotic prophylactics. Three major immunogen genes, gtxA, Gab_1309 and Gab_2312 were detected in the isolates indicating these antigens likely represent effective vaccine targets. A conserved sequence of the gtxA gene across a range of epidemiologically independent strains suggests the use of GtxA for future vaccine development purposes.

Immune Suppression Induced by Gallibacterium anatis GtxA During Interaction with Chicken Macrophage-Like HD11 Cells

The RTX toxin GtxA expressed by Gallibacterium anatis biovar haemolytica has been proposed a major virulence factor during disease manifestations in the natural host, the chicken. To better understand the role of GtxA in the pathogenesis of G. anatis, we compared the GtxA expressing wildtype strain with its isogenic ∆gtxA mutant that was unable to express GtxA during exposure to chicken macrophage-like HD11 cells. From adhesion and invasion assays, we showed that GtxA appears to promote adhesion and invasion of HD11 cells. By using quantitative RT-PCR, we also demonstrated that the G. anatis expressing GtxA induced a mainly anti-inflammatory (IL-10) host cell response as opposed to the pro-inflammatory (IL-1β, IL-6 and TNF-α) response induced by the GtxA deletion mutant. Interestingly, these results, at least partly, resemble recent responses observed from spleen tissue of chickens infected with the same two bacterial strains. The effect of the GtxA toxin on the type of cell death was less clear. While GtxA clearly induced cell death, our efforts to characterize whether this was due to primarily necrosis or apoptosis through expression analysis of a broad range of apoptosis genes did not reveal clear answers.

Etiology, epidemiology, pathology, and advances in diagnosis, vaccine development, and treatment of Gallibacterium anatis infection in poultry: a review

Gallibacterium anatis is a Gram-negative bacterium of the Pasteurellaceae family that resides normally in the respiratory and reproductive tracts in poultry. It is a major cause of oophoritis, salpingitis, and peritonitis, decreases egg production and mortality in hens thereby severely affecting animal welfare and overall productivity by poultry industries across Europe, Asia, America, and Africa. In addition, it has the ability to infect wider host range including domesticated and free-ranging avian hosts as well as mammalian hosts such as cattle, pigs and human. Evaluating the common virulence factors including outer membrane vesicles, fimbriae, capsule, metalloproteases, biofilm formation, hemagglutinin, and determining novel factors such as the RTX–like toxin GtxA, elongation factor-Tu, and clustered regularly interspaced short palindromic repeats (CRISPR) has pathobiological, diagnostic, prophylactic, and therapeutic significance. Treating this bacterial pathogen with traditional antimicrobial drugs is discouraged owing to the emergence of widespread multidrug resistance, whereas the efficacy of preventing this disease by classical vaccines is limited due to its antigenic diversity. It will be necessary to acquire in-depth knowledge on important virulence factors, pathogenesis and, concerns of rising antibiotic resistance, improvised treatment regimes, and novel vaccine candidates to effectively tackle this pathogen. This review substantially describes the etio-epidemiological aspects of G. anatis infection in poultry, and updates the recent development in understanding the pathogenesis, organism evolution and therapeutic and prophylactic approaches to counter G. anatis infection for safeguarding the welfare and health of poultry.

Hydrostatic Filtration Enables Large-Scale Production of Outer Membrane Vesicles That Effectively Protect Chickens against Gallibacterium anatis

Gallibacterium anatis is a Gram-negative opportunistic avian pathogen representing an emerging threat to poultry meat and egg production worldwide. To date, no vaccine able to effectively prevent the morbidity associated with G. anatis infections has been developed yet. Our group previously reported that inoculation of different combinations of G. anatis outer membrane vesicles (OMVs), FlfA and GtxA-N proteins is effective in preventing lesions caused by G. anatis infections in layer chickens. Here we report the testing of the efficacy as vaccine prototypes of G. anatis OMVs isolated by hydrostatic filtration, a simple technique that allows the cost-effective isolation of high yields of OMVs. Layer chickens were immunized with OMVs alone or in combination with FlfA and/or GtxA-N proteins. Subsequent challenge with a heterologous G. anatis strain showed that immunization with OMVs alone could significantly reduce the lesions following a G. anatis infection. A second study was carried out to characterize the dose-response (0.25, 2.5 and 25 µg) relationship of G. anatis OMVs as immunogens, showing that 2.5 μg of OMVs represent the optimal dose to elicit protection in the immunized animals after a similar challenge. Additionally, administration of ≥2.5 μg of G. anatis OMVs induced specific IgY titers and possibly vertical transfer of immunity.

GtxA is a virulence factor that promotes a Th2-like response during Gallibacterium anatis infection in laying hens

GtxA, a leukotoxic RTX-toxin, has been proposed a main virulence factor of Gallibacterium anatis. To evaluate the impact of GtxA during infection, we experimentally infected laying hens with a G. anatis wild-type (WT) strain and its isogenic gtxA deletion mutant (ΔgtxA), respectively, and monitored the birds during a 6 day period. Birds inoculated with ΔgtxA had significantly reduced gross lesions and microscopic changes compared to the birds inoculated with the WT strain. To assess the host response further, we quantified the expression of pro-inflammatory cytokines and apoptosis genes by RT-qPCR. In the ovarian tissue, the expression levels of IL-4 and TNF-α were significantly lower in the ΔgtxA group compared to the WT group, while IL-6 and IL-10 levels appeared similar in the two groups. In the spleen tissue of ΔgtxA infected chickens, IL-4 expression was also lower compared to the WT infected chickens. The results indicated that GtxA plays a key role in an acute cytokine-mediated Th2-like response against G. anatis infection in the ovary tissue. The pro-inflammatory response in the ovary tissue of birds inoculated with ΔgtxA mutant was thus significantly lower than the wild-type response. This was, at least partly, supported by the apoptosis gene expression levels, which were significantly higher in the ΔgtxA mutant compared to the wild-type infected chickens. In conclusion, GtxA clearly plays an important role in the pathogenesis of G. anatis infections in laying hens. Further investigations into the specific factors regulating the host response is however needed to provide a more complete understanding of the bacteria-host interaction.

Isolation, characterization, and antibiotic sensitivity assessment of Gallibacterium anatis biovar haemolytica, from diseased Egyptian chicken flocks during the years 2013 and 2015

Gallibacterium anatis biovar haemolytica constitutes a part of the normal microflora in the upper respiratory and genital tracts of healthy chickens, but it is also associated with different pathological conditions. In the current study, 102 commercial chicken flocks suffering from respiratory disease and/or drop in egg production were investigated for the presence of G. anatis during 2013 and 2015. These flocks comprised 8 breeder, 32 layer, and 62 broiler flocks. By culture method, 20 flocks were found positive: one isolate derived from broiler breeders, 6 isolates from layers, and 13 isolates from broilers. G. anatis biovar haemolytica was identified by phenotyping and PCR. Additionally, partial genome sequencing of 11 isolates (5 layer isolates of 2013 and 6 broiler isolates of 2015) based on 16S rRNA and 23S rRNA gene sequences was performed and revealed 96.5% to 100% genetic relatedness. Antibiotic sensitivity of these isolates revealed that the 2013 isolates were highly susceptible to florfenicol while the isolates of 2015 were highly susceptible to cefotaxime. Gallibacterium anatis biovar haemolytica is a newly introduced bacteria in Egypt causing salpingitis, peritonitis, drop in egg production, and/or respiratory signs.

Vaccination with outer membrane vesicles and the fimbrial protein FlfA offers improved protection against lesions following challenge with Gallibacterium anatis

Gallibacterium anatis is an opportunistic poultry pathogen belonging to the Pasteurellaceae family. It has been shown to cause oophoritis, salpingitis and peritonitis in hens, as well as being associated with reduced semen quality in cockerels. Widespread multidrug resistance and substantial antigenic variation among strains of Gallibacterium anatis is a major constraint to treatment with antimicrobials and prevention of infection by vaccination. Novel vaccine strategies targeting G. anatis are therefore necessary. Outer membrane vesicles (OMVs) are nanosized vesicles formed from the outer membrane of Gram-negative bacteria. These vesicles have shown promising potential as both adjuvants and as vaccine candidates against numerous bacterial species. A high vesiculating mutant of G. anatis (G. anatis ΔtolR) has previously been made, enabling production of OMVs in large scale. In this study, we elucidated the potential of G. anatis ΔtolR OMVs as adjuvant for the conserved antigens GtxA-N (the N-terminal part of the RTX like toxin Gallibacterium toxin A) and FlfA (F17-like fimbria), as well as evaluated if combinations of OMVs together with antigens could facilitate cross-protective immunity against three different strains of G. anatis. We showed that ΔtolR OMVs function as an adjuvant for GtxA-N by inducing antigen specific antibody production. However, OMVs in combination with GtxA-N failed to induce protection against lesions after challenge infection. In contrast, vaccination with OMVs in combination with FlfA protected against lesions, especially in the salpinx, caused by two diverse strains of G. anatis, thereby indicating a cross-protective potential. No protection against the third G. anatis strain 7990 could be obtained in any of the experimental settings. In conclusion, ΔtolR OMVs and FlfA could serve as potential future vaccine components againt G. anatis.

Commensal or pathogen - a challenge to fulfil Koch's Postulates

1. Infectious diseases have a large impact on poultry health and economics. Elucidating the pathogenesis of a certain disease is crucial to implement control strategies.

2. Multiplication of a pathogen and its characterisation in vitro are basic requirements to perform experimental studies. However, passaging of the pathogen in vitro can influence the pathogenicity, a process targeted for live vaccine development, but limits the reproduction of clinical signs.

3. Numerous factors can influence the outcome of experimental infections with some importance on the pathogen, application route and host as exemplarily outlined for Histomonas meleagridis, Gallibacterium anatis and fowl aviadenoviruses (FAdVs).

4. In future, more comprehensive and detailed settings are needed to obtain as much information as possible from animal experiments. Processing of samples with modern diagnostic tools provides the option to closely monitor the host–pathogen interaction.

Recombinant proteins from Gallibacterium anatis induces partial protection against heterologous challenge in egg-laying hens

Gallibacterium anatis is a Gram-negative bacterium and major cause of salpingitis and peritonitis in egg-laying hens, thereby contributing to decreased egg production and increased mortality among the hens. Due to widespread drug resistance and antigenic diversity, novel prophylactic measures are urgently required. The aim of the present study was to evaluate the cross-protective capacity of three recombinant proteins recently identified as potential vaccine candidates; GtxA-N, GtxA-C, and FlfA, in an in vivo challenge model. Nine groups of birds were immunized twice with each protein, respectively, with 14 days separation. Additionally, three groups served as non-immunized controls. After 3 weeks, the birds were challenged with either of three G. anatis strains: 12656-12, 7990 or IPDH 697-78, respectively. Blood samples were taken at three different time points prior to challenge, as well as 48 h after challenge. All birds were euthanized and subjected to a post mortem procedure including scoring of lesions and sampling for bacterial growth. Moreover, ELISA assays were used to quantify antigen-specific IgG titers in serum. The results showed that all three proteins induced protection against the homologous strain 12656-12. No protein induced complete protection against strain 7990, although FlfA reduced the bacterial re-isolation rate. Moreover, immunization with GtxA-N and FlfA induced protection, while GtxA-C reduced the bacterial re-isolation, against strain IPDH 697-78. Thus although complete cross-protection against all three strains was not achieved, the results hold great promise for a new generation of immunogens in the search for novel prophylactic measures against G. anatis.

Identification of a Hemagglutinin from Gallibacterium anatis

Gallibacterium anatis has the ability to hemagglutinate rabbit erythrocytes; however, no bacterial component has yet been associated with this function. In the present work, a protein of approximately 65 kDa with hemagglutinating activity for glutaraldehyde-fixed chicken erythrocytes was purified by ion interchange chromatography from G. anatis F149(T) secreted proteins. The protein was recognized by a rabbit polyclonal serum against a hemagglutinin from Avibacterium paragallinarum. The 65 kDa purified protein presented identity with a G. anatis filamentous hemagglutinin by mass spectrometric analysis. As well, the bacterial surface of G. anatis was labeled by immune gold assays using a polyclonal serum against the 65-kDa protein. A similar protein was recognized in four other G. anatis strains by immunoblots using the same antiserum. The protein binds sheep or pig biotinylated fibrinogen, suggesting an interaction with basement membrane eukaryotic cells components, and the protein is present in G. anatis biofilms. Overall, the results suggest that the 65 kDa hemagglutinin is a common antigen and a potential virulence factor in G. anatis.

Bacterial determinants of importance in the virulence of Gallibacterium anatis in poultry

Gallibacterium anatis, a member of the Pasteurellaceae family, constitute a part of the normal micro-flora of the upper respiratory tract and the lower genital tract in chickens. However, increasing evidence indicate that G. anatis is also associated with a wide range of pathological changes, particularly in the reproductive organs, which leads to decreased egg production, lowered animal welfare and increased mortality. As a recently defined opportunistic pathogen limited focus has been placed on the pathogenesis and putative virulence factors permitting G. anatis to cause disease. One of the most studied virulence determinants is a large RTX-like toxin (GtxA), which has been demonstrated to induce a strong leukotoxic effect on avian macrophages. A number of fimbria of different sizes and shapes has been described. Particularly fimbriae belonging to the F17-like family appears to be common in a diverse selection of G. anatis strains. Mutants lacking the FlfA fimbria were severely attenuated in experimentally infected chickens. Additional characteristics including the ability to express capsular material possibly involved in serum resistance; secretion of metalloproteases capable of degrading immunoglobulins, and hemagglutinins, which may promote biofilm formation are all factors likely linked to the virulence of G. anatis. A major advantage for the study of how G. anatis interact with its host is the ability to perform biologically relevant experimental infections where natural routes of exposure allows reproduction of lesions observed during spontaneous infections. This review summarizes the current understanding of the G. anatis pathogenesis and discusses the contribution of the established and putative virulence factors described for this bacterium to date.

Chaperone-usher fimbriae in a diverse selection of Gallibacterium genomes

Background

Fimbriae are bacterial cell surface organelles involved in the pathogenesis of many bacterial species, including Gallibacterium anatis, in which a F17-like fimbriae of the chaperone-usher (CU) family was recently shown to be an important virulence factor and vaccine candidate. To reveal the distribution and variability of CU fimbriae 22 genomes of the avian host-restricted bacteria Gallibacterium spp. were investigated. Fimbrial clusters were classified using phylogeny-based and conserved domain (CD) distribution-based approaches. To characterize the fimbriae in depth evolutionary analysis and in vitro expression of the most prevalent fimbrial clusters was performed.

Results

Overall 48 CU fimbriae were identified in the genomes of the examined Gallibacterium isolates. All fimbriae were assigned to γ4 clade of the CU fimbriae of Gram-negative bacteria and were organized in four-gene clusters encoding a putative major fimbrial subunit, a chaperone, an usher and a fimbrial adhesin. Five fimbrial clusters (Flf-Flf4) and eight conserved domain groups were defined to accommodate the identified fimbriae. Although, the number of different fimbrial clusters in individual Gallibacterium genomes was low, there was substantial amino acid sequence variability in the major fimbrial subunit and the adhesin proteins. The distribution of CDs among fimbrial clusters, analysis of their flanking regions, and evolutionary comparison of the strains revealed that Gallibacterium fimbrial clusters likely underwent evolutionary divergence resulting in highly host adapted and antigenically variable fimbriae. In vitro, only the fimbrial subunit FlfA was expressed in most Gallibacterium strains encoding this protein. The absence or scarce expression of the two other common fimbrial subunits (Flf1A and Flf3A) indicates that their expression may require other in vitro or in vivo conditions.

Conclusions

This is the first approach establishing a systematic fimbria classification system within Gallibacterium spp., which indicates a species-wide distribution of γ₄ CU fimbriae among a diverse collection of Gallibacterium isolates. The expression of only one out of up to three fimbriae present in the individual genomes in vitro suggests that fimbriae expression in Gallibacterium is highly regulated. This information is important for future attempts to understand the role of Gallibacterium fimbriae in pathogenesis, and may prove useful for improved control of Gallibacterium infections in chickens.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-1093) contains supplementary material, which is available to authorized users.

In silico prediction of Gallibacterium anatis pan-immunogens

The Gram-negative bacterium Gallibacterium anatis is a major cause of salpingitis and peritonitis in commercial egg-layers, leading to reduced egg production and increased mortality. Unfortunately, widespread multidrug resistance and antigenic diversity makes it difficult to control infections and novel prevention strategies are urgently needed. In this study, a pan-genomic reverse vaccinology (RV) approach was used to identify potential vaccine candidates. Firstly, the genomes of 10 selected Gallibacterium strains were analyzed and proteins selected on the following criteria; predicted surface-exposure or secretion, none or one transmembrane helix (TMH), and presence in six or more of the 10 genomes. In total, 42 proteins were selected. The genes encoding 27 of these proteins were successfully cloned in Escherichia coli and the proteins expressed and purified. To reduce the number of vaccine candidates for in vivo testing, each of the purified recombinant proteins was screened by ELISA for their ability to elicit a significant serological response with serum from chickens that had been infected with G. anatis. Additionally, an in silico prediction of the protective potential was carried out based on a protein property prediction method. Of the 27 proteins, two novel putative immunogens were identified; Gab_1309 and Gab_2312. Moreover, three previously characterized virulence factors; GtxA, FlfA and Gab_2156, were identified. Thus, by combining the pan-genomic RV approach with subsequent in vitro and in silico screening, we have narrowed down the pan-proteome of G. anatis to five vaccine candidates. Importantly, preliminary immunization trials indicated an in vivo protective potential of GtxA-N, FlfA and Gab_1309.

Draft Genome Sequence of Gallibacterium anatis bv. haemolytica 12656-12 Liver, an Isolate Obtained from the Liver of a Septicemic Chicken

We report the draft genome sequence of Gallibacterium anatis bv. haemolytica strain 12656-12 Liver. This strain was isolated from the liver of a septicemic layer chicken in Denmark in 1981. The strain has been used extensively for experimental purposes.

Assessing pathogenicity of Gallibacterium anatis in a natural infection model: the respiratory and reproductive tracts of chickens are targets for bacterial colonization

Two separate bird trials were performed to establish a reliable route of infection for Gallibacterium anatis in chickens, comparing intranasal (i.n.) and intravenous (i.v.) applications. Additionally, three mutually divergent isolates from three geographical locations, as shown by MALDI-TOF-MS and partial rpoB gene sequence analysis, were compared. In the first trial, birds were infected with one of the selected isolates by the i.v. or i.n. route. Subsequently, birds were killed 3, 12 and 24 h post infection following i.v. infection while at 3, 7 and 10 days post infection (dpi) in the case of i.n. infection along with birds of the control group. As a result, i.n. infection showed prominent and consistent bacterial tissue distribution in different organs persisting until 10 dpi, which was a striking contrast to the i.v. infection route. Likewise, histopathology revealed mild to severe tracheal lesions following i.n. infection. The second trial was set up to confirm both the achieved results and the robustness of i.n. infection but with an extended observation period, until 28 dpi In agreement with the preceding trial, identical results for bacteriological and histopathological examinations were obtained with persistency of bacteria until 28 dpi Comparing the three different isolates from Mexico, China and Austria, the Mexican isolate showed a somewhat higher pathogenicity than the other strains. Consequently, pathogenesis of G. anatis strains was studied in chickens elucidating i.n. infection as the most reliable route characterized by a long-lasting bacteraemia, targeting the respiratory and reproductive tract.

Gallibacterium anatis bacteremia in a human

We describe the first case of bacteremia due to Gallibacterium anatis. The patient, a 26-year-old woman, developed bacteremia and diarrhea. The origin of infection was possibly due to a diet contaminated by G. anatis in this highly immunocompromised patient.