Adherence of Gallibacterium anatis to Inert Surfaces

Epinephrine and norepinephrine regulate the expression of virulence factors in Gallibacterium anatis

Gallibacterium anatis is a member of the Pasteurellaceae family and is an opportunistic pathogen that causes gallibacteriosis in chickens. Stress plays a relevant role in promoting the development of pathogenicity in G. anatis. Epinephrine (E) and norepinephrine (NE) are relevant to stress; however, their effects on G. anatis have not been elucidated. In this work, we evaluated the effects of E and NE on the growth, biofilm formation, expression of adhesins, and proteases of two G. anatis strains, namely, the hemolytic 12656-12 and the nonhemolytic F149T biovars. E (10 μM/mL) and NE (30 and 50 μM/mL) increased the growth of G. anatis 12656-12 by 20 % and 25 %, respectively. E did not affect the growth of F149T, whereas 40 μM/mL NE decreased bacterial growth by 25 %. E and NE at a dose of 30-50 μM/mL upregulated five fibrinogen adhesins in the 12565-12 strain, whereas no effect was observed in the F149T strain. NE increased proteolytic activity in both strains, whereas E diminished proteolytic activity in the 12656-12 strain. E and NE reduced biofilm formation (30 %) and increased Congo red binding (15 %) in both strains. QseBC is the E and NE two-component detection system most common in bacteria. The qseC gene, which is the E and NE receptor in bacteria, was identified in the genomic DNA of the 12565-12 and F149TG. anatis strains via PCR amplification. Our results suggest that QseC can detect host changes in E and NE concentrations and that catecholamines can modulate the expression of several virulence factors in G. anatis.

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.

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.

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.

Characterization of Actinobacillus seminis biofilm formation

Actinobacillus seminis is an autochthonous gram-negative bacterium that affects reproductive organs, causing epididymitis, low fertility, and occasional abortions in ovine and goats. The virulence factors and the pathogenicity mechanisms of A. seminis have not been clearly elucidated yet. In this work, biofilm production by A. seminis in in vitro assays is described and characterized. After 48-h incubation at 37 °C in trypticase soy broth, A. seminis formed biofilms containing an extracellular matrix comprised mainly of fibrillar material. Microaerophilia or the presence of calcium diminished biofilm formation in approximately 50% and 70%, respectively, but low iron concentrations increased it 40%. Through enzymatic digestion, it was found that proteins were the main component of these biofilms. Structural observations through scanning electron microscopy indicated the presence of a high amount of fibrillar material in which bacteria were immersed. Antibodies against different bacterial surface proteins, such as anti-biofilm matrix and anti-adhesin, diminished biofilm formation in 70% and 25%, respectively; whereas furanone C-30 and LED-209, compounds described as quorum-sensing inhibitors, completely inhibited biofilm formation. In conclusion, environmental conditions can influence strongly biofilm formation in A. seminis, and this could be an advantageous strategy that allows bacteria to persist inside a host.

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.

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.

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.

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

The Gram-negative bacterium Gallibacterium anatis is a major cause of salpingitis and peritonitis in egg-laying chickens, leading to decreased egg production worldwide. Widespread multidrug resistance largely prevents treatment of this organism using traditional antimicrobial agents, while antigenic diversity hampers disease prevention by classical vaccines. Thus, insight into its pathogenesis and knowledge about important virulence factors is urgently required. A key event during the colonization and invasion of mucosal surfaces is adherence, and recently, at least three F17-like fimbrial gene clusters were identified in the genomes of several G. anatis strains. The objective of this study was to characterize the putative F17-like fimbrial subunit protein FlfA from G. anatis 12656-12 and determine its importance for virulence. In vitro expression and surface exposure of FlfA was demonstrated by flow cytometry and immunofluorescence microscopy. The predicted function of FlfA as a fimbrial subunit protein was confirmed by immunogold electron microscopy. An flfA deletion mutant (ΔflfA) was generated in G. anatis 12656-12, and importantly, this mutant was significantly attenuated in the natural chicken host. Furthermore, protection against G. anatis 12656-12 could be induced by immunizing chickens with recombinant FlfA. Finally, in vitro expression of FlfA homologs was observed in a genetically diverse set of G. anatis strains, suggesting the potential of FlfA as a serotype-independent vaccine candidate This is the first study describing a fimbrial subunit protein of G. anatis with a clear potential as a vaccine antigen.

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.