Development and Preliminary Application of a Quantitative PCR Assay for Detecting gtxA-Containing Gallibacterium Species in Chickens

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.

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.

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.

First Report of Isolation of Gallibacterium anatis from Layer Chickens in Morocco with Decrease in Laying Performance

Gallibacterium is a genus of the family of Pasteurellaceae. It is well known as a commensal inhabitant of the respiratory and reproductive tract of healthy chickens. But in the last years, Gallibacterium anatis is increasingly reported in field cases with a decrease in laying performance due to infections of the reproductive tract. The aim of the present study was to investigate the implication of G. anatis infection in layer flocks facing a decrease in laying performance in Morocco. Birds were received from five different laying hen farms in two regions in Morocco showing a drop of egg production. Necropsy revealed 46.1 % (24/52) of sampled birds showed variable lesions in ovaries, salpinx, and trachea. In fact, 24 birds were affected by salpingitis, 18 by oophoritis, and 11 birds by atrophy of ovaries. Furthermore, tracheitis was observed in 24 birds. Bacteriological investigation was done from different organs, and G. anatis was found in ovaries (n = 20), trachea (n = 17), and cloaca (n = 3). Identification was based on growth morphology, Gram staining, and biochemical properties. Additionally, polymerase chain reaction test using specific primers for the genus identification was carried out. All isolates showed bands of 925 bp specific for G. anatis expressing the virulent toxin GtxA. Antibiotic resistance testing was performed and revealed that isolates were sensitive to enrofloxacin, florfenicol, and gentamycin but resistant to ampicillin, erythromycin, oxytetracycline, and sulfamethoxazole-trimethoprim. The present study is the first report of G. anatis in Morocco, demonstrating the need for further epidemiologic investigations as well as in regard to antibiotic resistance development.

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.

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.

A loop-mediated isothermal amplification procedure targeting the sodA gene for rapid and specific identification of Gallibacterium anatis

This paper reports on the development and validation of a real-time loop-mediated isothermal amplification assay (LAMP) for rapid and specific identification of Gallibacterium anatis. To design a set of 6 primers using the LAMP technique, the conserved region of the G. anatis sodA gene was selected as a target. To evaluate primer specificity we used 120 field strains, the reference strain G. anatis ATCC 43329, and 9 non-G. anatis bacteria. The results confirmed positive reactions for all G. anatis strains tested by LAMP at 63°C for 60 min, with no cross-reactivity observed for the negative control bacteria, i.e., Haemophilus parainfluenzae (ATCC 51505 and ATCC 33392), Aggregatibacter aphrophilus ATCC 7901, Avibacterium endocarditis, Pasteurella multocida, Actinobacillus pleuropneumoniae, Avibacterium paragallinarum, Ornithobacterium rhinotracheale, and Escherichia coli. The lowest detectable amount of DNA for the LAMP reaction was 0.2561 pg, which was detected in about 34 min, while the highest available concentration of the G. anatis reference strain was detected in about 10 min. The lowest detectable amount of DNA for the real-time PCR reaction was 21.24 pg, which was detected in about 20 min, while the highest available concentration of the G. anatis reference strain was detected in about 7 min. Moreover, using the real-time LAMP assay the reaction could be effectively carried out in a volume of just 13 μL, about half the officially recommended reaction volume (25 μL). The aim of this study was to develop a highly sensitive and specific G. anatis real-time LAMP assay that is less time-consuming and less costly than quantitative PCR.

Post mortem Survival of Gallibacterium anatis in a Laying Hen Experimental Infection Model

To assess the survival of Gallibacterium anatis in dead laying hens, 21-wk-old laying hens were injected intraperitoneally with 0.5 ml brain hearth infusion broth containing 10⁸ colony-forming units (CFU) of G. anatis 12656-12 liver ( n = 16), Escherichia coli ST141 ( n = 16), or a mix of G. anatis 12656-12 liver and E. coli ST141 ( n = 16), respectively. Birds were euthanatized 24 hr post injection. From each group eight dead birds were kept at 4 C and eight at room temperature. Swab samples were taken at different time points post euthanatization and streaked on blood agar plates. From the birds kept at 4 C, G. anatis was reisolated from the G. anatis and the G. anatis- E. coli co-injected groups at least 12 days post euthanization. From birds kept at room temperature, G. anatis was reisolated up to 2 days post euthanatization. When using the gyrB-based G. anatis-specific quantitative PCR (qPCR), G. anatis was detected within at least 5 days, and up to 5 days post euthanatization, from birds kept at room temperature and 4 C, respectively. Escherichia coli was reisolated from all the time points independent of how the birds were kept. No difference was observed between the reisolation rates for G. anatis or E. coli when comparing similar detection methods. For birds kept at 4 C, bacterial cultivation was a more sensitive method for detecting G. anatis ( P < 0.05), whereas for birds kept at room temperature, the G. anatis-specific qPCR outperformed bacterial culture ( P < 0.05). In conclusion, we demonstrated that G. anatis has a poorer survival rate than does E. coli in dead chickens kept at room temperature. That finding may affect the overall diagnostic sensitivity and lead to underdiagnosis of G. anatis in a normal production setting.

Transmission and pathogenicity of Gallibacterium anatis and Escherichia coli in embryonated eggs

In laying hens, Escherichia coli (E. coli) and Gallibacterium anatis (G. anatis) are considered the two major pathogens causing reproductive tract disorders, either as single infections or as co-infections. Vertical transmission has been confirmed for E. coli but remains to be clearly demonstrated for G. anatis. The aim of the present study was to investigate the ability of both G. anatis and E. coli at eggshell transmission using an embryonated egg dipping model, and to investigate the possible interaction between the two organisms in an embryonated egg injection model. Embryonated eggs were dipped into brain heart infusion broth containing 10⁸ CFU/ml either of G. anatis 12656-12 liver, E. coli ST95 or E. coli ST141, respectively. E. coli ST95 and ST141 were re-isolated from the interior egg contents in 60% (12/20) and 85% (17/20) of the eggs, respectively, while G. anatis 12656-12 was only re-isolated from the interior egg contents in 6.7% (3/45) eggs. Eggs were injected with 10-1000 CFU of either G. anatis 12656-12, E. coli ST95 or ST141 into the allantoic cavity. As few as 10 CFU of G. anatis 12656-12 resulted in 100% mortality within 24 h post injection whereas the E. coli injected embryos all died at 48 h post injection. Significant difference in CFU counts were observed for G. anatis when compared G. anatis injection group with either of the two G. anatis - E. coli co-injection groups. Sixteen hours post injection, a significant difference in embryo mortality could be observed when comparing co-injected embryonated eggs (G. anatis and E. coli) and single-injected (G. anatis or E. coli) embryonated eggs. In conclusion, bacterial transmission via the eggshell was demonstrated for both G. anatis and E. coli although at different magnitudes. The embryonated egg injection model revealed that G. anatis in particular was highly pathogenic when exposed directly to the developing embryo.

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.

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.

Development of real-time polymerase chain reaction assay for detection of Ornithobacterium rhinotracheale in poultry

Ornithobacterium rhinotracheale (ORT) is an emerging bacterium causing severe economic losses in poultry mostly due to respiratory and locomotory disturbances. Due to the fastidious nature of the organism, ORT is often overgrown by faster-growing commensal and pathogenic bacteria. In this study we developed a real-time polymerase chain reaction (qPCR) assay for rapid and sensitive detection of ORT in samples collected from chickens and turkeys. The qPCR assay developed was able to detect 17 reference strains of ORT (serotypes A to Q) tested in this study, and no false-positive results were obtained from other organisms associated with respiratory tract infections. The qPCR assay was 100 times more sensitive than the modified conventional PCR. Using tenfold serial dilutions of the recombinant plasmid DNA containing the target gene fragment, the detection limit of the qPCR was estimated to be > or = 100 plasmid copies per reaction. Out of 42 examined poultry flocks, 26 cases were tested positive by both assays. The qPCR assay reduces turnaround time to about 2 hr, two times faster than the modified conventional PCR.

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.