Histopathologic Findings in Chickens Experimentally Infected with Gallibacterium anatis by Nasal Instillation

Gallibacterium anatis infection in poultry: a comprehensive review

Gallibacterium anatis (G. anatis), a member of the Pasteurellaceae family, normally inhabits the upper respiratory and lower genital tracts of poultry. However, under certain circumstances of immunosuppression, co-infection (especially with Escherichia coli or Mycoplasma), or various stressors, G. anatis caused respiratory, reproductive, and systemic diseases. Infection with G. anatis has emerged in different countries worldwide. The bacterium affects mainly chickens; however, other species of domestic and wild birds may get infected. Horizontal, vertical, and venereal routes of G. anatis infection have been reported. The pathogenicity of G. anatis is principally related to the presence of some essential virulence factors such as Gallibacterium toxin A, fimbriae, haemagglutinin, outer membrane vesicles, capsule, biofilms, and protease. The clinical picture of G. anatis infection is mainly represented as tracheitis, oophoritis, salpingitis, and peritonitis, while other lesions may be noted in cases of concomitant infection. Control of such infection depends mainly on applying biosecurity measures and vaccination. The antimicrobial sensitivity test is necessary for the correct treatment of G. anatis. However, the development of multiple drug resistance is common. This review article sheds light on G. anatis regarding history, susceptibility, dissemination, virulence factors, pathogenesis, clinical picture, diagnosis, and control measures.

Molecular epidemiological studies on avian pathogenic Escherichia coli associated with septicemia in chickens in India

Bacterial septicemia causes huge economic losses in the poultry industry and there is no systematic research available in India on the connection of various pathogens associated with septicemia. The present molecular epidemiological study was conducted to investigate the association of different bacterial and immunosuppressive viral pathogens in septicemia suspected chickens. A total of 443 chicken carcasses with septicemic conditions from 71 different flocks were included in this study. Heart blood swabs were subjected to bacterial culture for Salmonella spp., Pasteurella multocida, Escherichia coli, and Gallibacterium anatis. Of these 51 flocks tested for E. coli, 49 (96.1%) flocks were found positive. Among flocks tested for Salmonella spp., 2 flocks were found positive. All tested flocks were found negative for G. anatis and P. multocida as well as air sac swabs tested negative for Mycoplasma spp. Bacterial cultural examination revealed that majority of septicemic chickens were found to be infected with E. coli and these E. coli isolates showed the highest resistance to vancomycin (60%), followed by erythromycin (50%) and cefotaxime (38%) and maximum sensitivity to cefotaxime and clavulanic acid combinations (81.5%), followed by chloramphenicol (69.6%) and ertapenem (67.2%). Among the 5 avian pathogenic E. coli (APEC) virulence genes were detected in 36 flocks and highest frequency of iss (100%), followed by ompT or iutA (97.2%), hly (61.1%) and iroN (47.2%) genes. On polymerase chain reaction (PCR) screening, 10.5, 4.5, 52.2, 19.4, 9.0, 4.5, 20.1 and 19.4% of the flocks were positive for G. anatis, Ornithobacterium rhinotracheale, APEC, Salmonella spp., Mycoplasma gallisepticum, Mycoplasma synoviae, chicken infectious anemia virus and Marek's disease virus, respectively. To our knowledge, the present study is first on the etiology of septicemia in chicken flocks in India. The present study infers that the majority of septicemic deaths in broiler chickens less than 8 weeks have been connected with APEC and majority of E. coli isolates are multidrug resistance, suggesting the need for surveillance and intervention to curb the inadvertent use of antibiotics. Although, incidence of G. anatis association with septicemia was reported, still requires a rigorous epidemiological study to determine the actual prevalence. However, more detailed studies encompassing vast geographical area with large sample size and long duration of the studies are necessary to provide a clear picture of the interaction of different pathogens causing septicemia in chicken.

Respiratory and Reproductive Impairment of Commercial Layer Chickens After Experimental Infection with Gallibacterium anatis Biovar haemolytica

The prevalence of Gallibacterium anatis in poultry production has increased over the last two decades. However, only a few studies have explored the pathogenicity of this bacterium in commercial layer chickens. This trial studied the aspects of the pathogenicity of a Gallibacterium anatis biovar haemolytica local Egyptian isolate (previously registered as strain B14 with GenBank accession no. KJ026147). We used 500 base pairs of a 16S ribosomal RNA gene and the 16S-23S ribosomal RNA intergenic spacer, partial sequence in an experimental infection trial in commercial White Shaver layer chickens aged 19 wk. The hens were divided into three groups of 40 birds each. The hens in Groups 1 and 2 were experimentally infected through the intranasal (IN) and intravenous (IV) routes, respectively, with a dose of 0.2 ml/bird containing 1.2 × 109 colony-forming units/ml. In contrast, Group 3 was kept as a noninfected control group. Both IN and IV infections resulted in a delayed egg laying for 1 wk and a significant (P ≤ 0.05) drop in egg production by 7.81% and 10.28% compared with the control group over 7 wk. Severe lesions in the form of hemorrhagic pneumonia, catarrhal tracheitis, ovarian follicle and oviductal regression, and septicemia were evident on necropsy, demonstrating the pathogenicity of G. anatis as a primary pathogen.

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.

Presence of Avibacterium paragallinarum and Histopathologic Lesions Corresponds with Clinical Signs in a Co-infection Model with Gallibacterium anatis

Recently we demonstrated that co-infection with Avibacterium paragallinarum and Gallibacterium anatis leads to increased severity of clinical signs of infectious coryza in birds. The present study examined the interaction of these two pathogens in chickens by evaluation of histologic lesions in sinus infraorbitalis and nasal turbinates, applying a defined scoring scheme ranging from 0 to 3. Furthermore, for the first time, an in situ hybridization (ISH) technique was applied to detect A. paragallinarum in tissues. The samples were received from vaccinated and nonvaccinated birds that were infected with A. paragallinarum and/or G. anatis. Vaccinated birds were mostly devoid of any histopathologic lesions except a few birds with lesion score 1 at 7 and 14 days postinfection (dpi). Likewise, nonvaccinated birds infected with G. anatis only did not present microscopic changes in the sinus infraorbitalis, except in a single bird at 7 dpi. Interestingly, median lesion scores caused by G. anatis infection were significantly higher in the nasal turbinates of infected birds than in negative control at 7 and 14 dpi. The most prominent histologic changes were recorded from sinus infraorbitalis and nasal turbinates of nonvaccinated birds that were infected either with A. paragallinarum only or together with G. anatis. ISH demonstrated positive signals for A. paragallinarum in exudates present in the lumen or attached to the epithelial layer of investigated tissues. Such signals were mainly detected in tissues from birds with the highest histopathologic lesion scores.

Detection of Gallibacterium anatis by TaqMan fluorescent quantitative PCR

To better understand the prevalence of Gallibacterium anatis in different poultry species, a rapid and accurate method was developed to detect G. anatis using a TaqMan fluorescent quantitative polymerase chain reaction (qPCR). Specific primers and a TaqMan probe were designed based on the reference gtxA gene sequence. The qPCR standard curve showed a good linear relationship, and the method showed good reproducibility, sensitivity, and specificity, indicating its suitability for G. anatis identification and quantitative analysis. A comparison of the detection results in 160 clinical swab samples showed that the detection rate (54.4%) of the qPCR for G. anatis was better than that of two conventional methods: gyrB gene-based qPCR for G. anatis (51.9%) and culture-based identification (34.4%). G. anatis was detected in layer chicken (77.3%), Silkie chicken (72.7%), and duck (27.1%) with relatively high detection rates, whereas dove (8.8%) and quail (3.0%) showed lower detection rates, indicating the different prevalence of G. anatis in different fowl species.

Virulence of Serovar C-1 Strains of Avibacterium paragallinarum

The bacterium Avibacterium paragallinarum is the etiologic agent of infectious coryza of chickens. There are nine serovars of A. paragallinarum , and serovar C-1 has emerged in outbreaks of infectious coryza in layer hens in the Americas, with all isolates having been obtained from infectious coryza-vaccinated chickens. In the current study, the clinical and histopathologic outcomes of experimental infections in chickens with A. paragallinarum of serovar C-1 were investigated. The Japanese serovar reference strain, H-18, and a Mexican isolate, ESV-135, were included in the study. No differences in clinical sign scores or morbidity were observed between the two strains. The two bacterial strains caused microscopic lesions of lymphoplasmacytic inflammation in the mucosa of the nasal cavity, infraorbital sinus, and trachea. Similar severe lesions were observed in birds inoculated with both H-18 and ESV-135 strains. The lesions were present 48 hr after inoculation and persisted until day 10 after inoculation. Slight to severe, extensive hemorrhages were observed in the lumen, mucous membranes, and lamina propria of the nasal cavity and infraorbital sinus in most of the chickens inoculated with either the reference strain H-18 or the ESV-135 isolate. Hemorrhages in the upper respiratory tract of chickens experimentally infected with A. paragallinarum are reported here for the first time. The results have confirmed the high virulence of the reference strain H-18 as previously reported and have shown that the Mexican isolate was as virulent as the reference strain. The virulence of A. paragallinarum isolates may play a role in explaining why severe infectious coryza outbreaks are being seen in both vaccinated and nonvaccinated chicken flocks.

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.

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.

A 5-year retrospective report of Gallibacterium anatis and Pasteurella multocida isolates from chickens in Mississippi

A 5-yr retrospective study (November 2006-December 2011) was conducted to determine the isolation frequency of Pasteurella multocida and Gallibacterium anatis and their antibiograms from chickens submitted to the Mississippi Poultry Research and Diagnostic Laboratory. The number of isolations of G. anatis increased over the last 5 yr in broiler and broiler breeder type chickens. For P. multocida, the number of isolations increased from 2006 to 2010, but decreased through 2011 with all isolations being from boiler breeder type chickens. Gallibacterium anatis demonstrated almost complete resistance to novobiocin, tylosin, lincosamide, and tetracycline antimicrobials with moderate to high sensitivity to sulfonamides, fluoroquinolones, and florfenicol. There was intermediate sensitivity for spectinomycin and erythromycin and variable resistance to β-lactam and aminoglycoside antimicrobials. In sharp contrast, P. multocida showed moderate to high sensitivity to β-lactam, novobiocin, and tetracycline antimicrobials, but had antibiograms similar to G. anatis for the other antimicrobials. Sensitivities were determined using minimum inhibitory concentration. This study examines the trends over a 5-yr period of the number of isolates of P. multocida and G. anatis and their sensitivities. These 2 pathogens produce very similar clinical signs and lesions (fowl cholera-like) in breeders despite having extremely antagonistic sensitivity patterns. This study shows the necessity for producers to attempt culture and sensitivity in suspect fowl cholera-like flocks before initiating antimicrobial treatment commonly used with P. multocida for fear that the culprit may actually be the more antimicrobial-resistant G. anatis.

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.

Genome analysis and phylogenetic relatedness of Gallibacterium anatis strains from poultry

Peritonitis is the major disease problem of laying hens in commercial table egg and parent stock operations. Despite its importance, the etiology and pathogenesis of this disease have not been completely clarified. Although avian pathogenic Escherichia coli (APEC) isolates have been incriminated as the causative agent of laying hen peritonitis, Gallibacterium anatis are frequently isolated from peritonitis lesions. Despite recent studies suggesting a role for G. anatis in the pathogenesis of peritonitis, little is known about the organism’s virulence mechanisms, genomic composition and population dynamics. Here, we compared the genome sequences of three G. anatis isolates in an effort to understand its virulence mechanisms and identify novel antigenic traits. A multilocus sequence typing method was also established for G. anatis and used to characterize the genotypic relatedness of 71 isolates from commercial laying hens in Iowa and 18 international reference isolates. Genomic comparisons suggest that G. anatis is a highly diverse bacterial species, with some strains possessing previously described and potential virulence factors, but with a core genome containing several antigenic candidates. Multilocus sequence typing effectively distinguished 82 sequence types and several clonal complexes of G. anatis, and some clones seemed to predominate among G. anatis populations from commercial layers in Iowa. Biofilm formation and resistance to antimicrobial agents was also observed in several clades. Overall, the genomic diversity of G. anatis suggests that multiple lineages exist with differing pathogenic potential towards birds.