Epidemiology and Antibiogram of Riemerella Anatipestifer Isolated from Waterfowl Slaughterhouses in Taiwan

Epidemiological investigation and β-lactam antibiotic resistance of Riemerella anatipestifer isolates with waterfowl origination in Anhui Province, China

Riemerella anatipestifer (R. anatipestifer) is a highly pathogenic and complex serotypes waterfowl pathogen with inherent resistance to multiple antibiotics. This study was aimed to investigate the antibiotic resistance characteristics and genomic features of R. anatipestifer isolates in Anhui Province, China in 2023. A total of 287 cases were analysed from duck farms and goose farms, and the R. anatipestifer isolates were subjected to drug resistance tests for 30 antimicrobials. Whole genome sequencing (WGS) and bioinformatics analysis were performed on the bacterial genomes, targeting the β-lactam resistance genes. The results showed that a total of 74 isolates of R. anatipestifer were isolated from 287 cases, with a prevalence of 25.8%. The antimicrobial susceptibility testing (AST) revealed that all the 74 isolates were resistant to multiple drugs, ranging from 13 to 26 kinds of drugs. Notably, these isolates showed significant resistance to aminoglycosides and macrolides, which are also commonly used in clinical practices. Data revealed the presence of several β-lactamase-related genes among the isolates, including a novel blaRASA-1 variant (16.2%), the class A extended-spectrum β-lactamase blaRAA-1 (12.2%), and a blaOXA-209 variant (98.6%). Functional analysis of the variants blaRASA-1 and blaOXA-209 showed that the blaRASA-1 variant exhibited activity against various β-lactam antibiotics while their occurrence in R. anatipestifer were not common. The blaOXA-209 variant, on the other hand, did not perform any β-lactam antibiotic resistance. Furthermore, we observed that blaRAA-1 could undergo horizontal transmission among different bacteria via the insertion sequence IS982. In conclusion, this study delves into the high prevalence of R. anatipestifer infection in waterfowl in Anhui, China. The isolated strains exhibit severe drug resistance issues, closely associated with the prevalence of antibiotic resistance genes (ARG). Additionally, our research investigates the β-lactam antibiotic resistance mechanism in R. anatipestifer.

A novel bivalent inactivated vaccine for ducks against Riemerella anatipestifer based on serotype distribution in southern China

Riemerella anatipestifer (RA) causes epizootic infectious polyserositis in ducks with high mortality and leads to huge economic losses worldwide. Bacterial resistance poses a challenge for the control of the disease, vaccines failed to provide ideal cross-protection. Thus, the preparation of vaccines based on popular serotypes is important. In this study, we collected 700 brain and liver tissues of dead ducks from 8 provinces in southern China from 2016 to 2022 and obtained 195 RA isolates with serotypes 1, 2, 7, and 10. Serotypes 1 and 2 were the most prevalent (82%). A novel bivalent inactivated vaccine WZX-XT5 containing propolis adjuvant was prepared, we chose XT5 (serotype 1) and WZX (serotype 2) as vaccine strains and evaluated WZX-XT5-induced immune response and protective efficacy in ducks. Results showed that the XT5 (LD50, 3.5 × 103 CFU) exhibited high virulence and provided better protection against RA compared with ZXP, DCR and LCF1 (LD50, 108 CFU). Notably, the dose of 109 CFU provided ideal protection compared with 108 CFU, propolis and oil emulsion adjuvants induced stronger protective efficacy compared with aluminum hydroxide adjuvant. Importantly, WZX-XT5 immunization induced high levels of RA-specific IgY, IFN-γ, IL-2, and IL-4 in serum and offered over 90% protection against RA with ultra-high lethal dose in ducks. Additionally, no clinical signs of RA infection or obvious pathological damage in tissues were observed in protected ducks. Overall, this study first reports the identification, serotyping and virulence of RA in ducks of southern China and the preparation of a novel bivalent inactivated vaccine, providing useful scientific information to prevent and control RA infection.

Genome-based assessment of antimicrobial resistance reveals the lineage specificity of resistance and resistance gene profiles in Riemerella anatipestifer from China

Riemerella anatipestifer (R. anatipestifer) is an important pathogen that causes severe systemic infections in domestic ducks, resulting in substantial economic losses for China's waterfowl industry. Controlling R. anatipestifer with antibiotics is extremely challenging due to its multidrug resistance. Notably, large-scale studies on antimicrobial resistance (AMR) and the corresponding genetic determinants in R. anatipestifer remain scarce. To solve this dilemma, more than 400 nonredundant R. anatipestifer isolates collected from 22 provinces in China between 1994 and 2021 were subjected to broth dilution antibiotic susceptibility assays, and their resistance-associated genetic determinants were characterized by whole-genome sequencing. While over 90% of the isolates was resistant to sulfamethoxazole, kanamycin, gentamicin, ofloxacin, norfloxacin, and trimethoprim, 88.48% of the isolates was resistant to the last-resort drug (tigecycline). Notably, R. anatipestifer resistance to oxacillin, norfloxacin, ofloxacin, and tetracycline was found to increase relatively over time. Genome-wide analysis revealed the alarmingly high prevalence of blaOXA-like (93.05%) and tet(X) (90.64%) genes and the uneven distribution of resistance genes among lineages. Overall, this study reveals a serious AMR situation regarding R. anatipestifer in China, with a high prevalence and high diversity of antimicrobial resistance genes, providing important data for the rational use of antibiotics in veterinary practice.IMPORTANCERiemerella anatipestifer (R. anatipestifer), an important waterfowl pathogen, has caused substantial economic losses worldwide, especially in China. Antimicrobial resistance (AMR) is a major challenge in controlling this pathogen. Although a few studies have reported antimicrobial resistance in R. anatipestifer, comprehensive data remain a gap. This study aims to address the lack of information on R. anatipestifer AMR and its genetic basis. By analyzing more than 400 isolates collected over two decades, this study reveals alarming levels of resistance to several antibiotics, including drugs of last resort. The study also revealed the lineage-specificity of resistance profiles and resistance gene profiles. Overall, this study provides new insights and updated data support for understanding AMR and its genetic determinants in R. anatipestifer.

Characterization of Riemerella anatipestifer Strains Isolated from Various Poultry Species in Poland

Riemerella anatipestifer (R. anatipestifer) is one of the common pathogens found in poultry flocks, resulting in serious economic losses for the poultry industry due to high mortality, reduced growth rate, poor feed conversion, increased condemnations, and high treatment costs. The aim of this study was to phenotypically characterize phylogenetic relationships and assess the presence of resistance gene strains of R. anatipestifer obtained from various poultry species in Poland. A total of 57 isolates of Riemerella were included in this study. A polymerase chain reaction (PCR) and matrix assisted laser desorption ionization mass spectrometry (MALDI-TOF MS) were used for identification of the strains. The phylogenetic relationship of the R. anatipestifer isolates was determined by analysing the rpoB gene sequence. The susceptibility to antibiotics was evaluated by minimum inhibitory concentration (MIC) in liquid media. All of the field strains of R. anatipestifer were grouped into one of two clades resulting from rpoB gene sequencing. High MIC50 and MIC90 values were obtained for gentamycin, amikacin, and colistin. Low MIC50 and MIC90 values were obtained for amoxicillin cefuroxime, cefoperazone, piperacillin, and trimethoprim/sulfamethoxazole. Among the resistance genes, tet(X) and ermF were identified most frequently. This is the first phenotypic characterization of R. anatipestifer strains obtained from poultry flocks in Poland.

Epidemiological investigation and drug resistance characteristics of Riemerella anatipestifer strains from large-scale duck farms in Shandong Province, China from March 2020 to March 2022

Infectious serositis is a common disease caused by Riemerella anatipestifer (R. anatipestifer) in ducks, characterized by respiratory distress, septicemia, and neurological symptoms. In this study, 1,020 samples (brain and liver) were collected from ducks with suspected R. anatipestifer infection from March 2020 to March 2022 in Shandong Province, of which 171 R. anatipestifer strains were identified by PCR and isolation culture. The serotype of all strains was analyzed, and 74 strains were subjected to drug sensitivity tests and drug resistance genes detection. The results showed that the overall prevalence rate of R. anatipestifer in Shandong Province was 16.7% (171/1,020), with most strains coming from brain samples of ducklings under 3-mo old collected from September to December each year. Histopathological examination showed that heart vessels of the diseased duck were highly dilated and filled with red blood cells, with obvious fibrin exudates outside the pericardium, and fatty degeneration of liver cells. There were 45 strains of serotype 1, 45 strains of serotype 2, 2 strains of serotype 4, 33 strains of serotype 6, 44 strains of serotype 7, and 2 strains of serotype 10. The minimum inhibitory concentration (MIC) of 10 common antibiotics against 74 representative strains was determined by the agar dilution method. It was found that 74 strains had the most severe resistance to gentamicin (77%) and fully susceptible to ceftriaxone, but the 81.1% isolated strains were multidrug resistant. Resistance genes testing of 74 R. anatipestifers showed that tetracycline resistance gene tet X had the highest detection rate of 95.9%, followed by macrolide resistance gene ermF with 77%, and the rate of β-lactam resistance gene blaTEM is the lowest (10.8%). The animal experiment of 4 R. anatipestifer strains with different serotypes showed that they had strong pathogenicity to 7-day-old ducklings, which could cause nervous symptoms, and the mortality rate was 58% to 70%. The autopsy showed obvious pathological changes. These findings of this study on R. anatipestifer will help us to understand the latest prevalence, drug resistance characteristics, and pathogenicity of R. anatipestifer in Shandong, China, and provide a scientific guide for the treatment and control of the disease.

Sifting through the core-genome to identify putative cross-protective antigens against Riemerella anatipestifer

Infectious serositis of ducks, caused by Riemerella anatipestifer, is one of the main infectious diseases that harm commercial ducks. Whole-strain-based vaccines with no or few cross-protection were observed between different serotypes of R. anatipestifer, and so far, control of infection is hampered by a lack of effective vaccines, especially subunit vaccines with cross-protection. Since the concept of reverse vaccinology was introduced, it has been widely used to screen for protective antigens in important pathogens. In this study, pan-genome binding reverse vaccinology, an emerging approach to vaccine candidate screening, was used to screen for cross-protective antigens against R. anatipestifer. Thirty proteins were identified from the core-genome as potential cross-protective antigens. Three of these proteins were recombinantly expressed, and their immunoreactivity with five antisera (anti-serotypes 1, 2, 6, 10, and 11) was demonstrated by Western blotting. Our study established a method for high-throughput screening of cross-protective antigens against R. anatipestifer in silico, which will lay the foundation for the development of a cross-protective subunit vaccine controlling R. anatipestifer infection. KEY POINTS: • Pan-genome binding reverse vaccine approach was first established in R. anatipestifer to screen for subunit vaccine candidates. • Thirty potential cross-protective antigens against R. anatipestifer were identified by this method. • The reliability of the method was verified preliminarily by the results of Western blotting of three of these potential antigens.

Molecular Detection and Phylogenetic Analysis of Riemerella anatipestifer in Poultry and Wild Geese in Poland

Riemerella anatipestifer (RA) is one of the most relevant bacterial pathogens of commercial waterfowl from clinical and economic points of view. Our study aimed to evaluate the prevalence of RA infection in different types of commercial poultry in Poland and verify the potential role of wild geese as vectors of this pathogen. We tested a total of 126 poultry flocks, including geese (N = 20), ducks (N = 42), turkeys (N = 64) and 19 wild geese, including greater white-fronted geese (N = 9), greylag geese (N = 5) and Taiga bean geese (N = 5). Tracheal swabs were examined for RA using a PCR targeting a conserved region of the 16S rRNA gene. Selected PCR products were sequenced to perform the phylogenetic analysis. Among the commercial poultry, the highest RA prevalence was found in flocks of ducks (35.7%) and geese (30.0%), whereas the lowest one was found in turkeys (3.2%). Most tested wild geese (94.7%) were RA positive. The phylogenetic analysis showed relatively low genetic diversity of the sequences analyzed, which gathered in two clusters of the phylogenetic tree, and the minimum nucleotide identity was 98.6%. Our results would support the contention that RA isolates from commercial poultry circulate in wild bird populations but are not transmitted back to poultry.

groEL gene-based molecular detection and antibiogram profile of Riemerella anatipestifer from duck in Bangladesh

Objectives

This study was designed to detect Riemerella anatipestifer through polymerase chain reaction (PCR) from duck farming areas of the Mymensingh and Sylhet divisions and to determine the antibiogram profile of the PCR-positive isolates using the disc diffusion method.

Materials and Methods

Fifty two samples were collected, comprising clinically sick (32 ducks) and dead ducks (20). PCR confirmation was accomplished, and consistent findings were observed, employing R. anatipestifer groEL (271-bp) gene as appropriate molecular markers. For further clarification, see R. anatipestifer specific PCR assay (546-bp) and gyrB-based PCR (162-bp) were also done. The disc diffusion method was followed for the antibiotic susceptibility test of the isolates against commonly used antibiotics.

Results

A total of 21 samples, 8 from clinically sick birds and 13 from dead birds, showed positive results in both conventional and molecular assays out of 52 samples. High occurrences were found in oropharyngeal swabs from sick ducks and the liver and heart from dead ducks. Antibiotic susceptibility testing revealed that the isolates were 100% resistant to penicillin G, cefradine, streptomycin, neomycin, gentamycin, meropenem, and erythromycin, but 100% sensitive to -cotrimoxazole, florfenicol, and levofloxacin.

Conclusion

For diverse duck-populated areas in Bangladesh, this study shows the severity of R. anatipestifer infection among ducks.

PK/PD integration of florfenicol alone and in combination with doxycycline against Riemerella anatipestifer

Riemerella anatipestifer (RA) is an important pathogen found in poultry. RA infection can kill ducks and lead to significant economic losses. Seven RA strains with different susceptibility phenotypes were chosen to study the pharmacokinetic/pharmacodynamic (PK/PD) integration of florfenicol (FF) alone and in combination with doxycycline (DOX). The checkerboard assay indicated that synergy [fractional inhibitory concentration index (FICI) ≤ 0.5] was detected in the CVCC3952 strain of RA and that additivity (FICI >0.5 to ≤ 1) was observed in other strains. Static time–kill curves showed that the bactericidal effect of FF against RA was produced at a FF concentration ≥4 MIC, and the antibacterial activity of FF against RA was enhanced from the aspects of efficacy and efficacy in combination with DOX. Dynamic time–kill curves indicated that FF elicited bactericidal activity against the CVCC3857 strain with a reduction ≥4.88 log₁₀CFU/ml when the dose was ≥8 mg/L. However, a bactericidal effect was not achieved at the maximum administered dose of FF monotherapy (20 mg/L) for isolates with a MIC ≥4 μg/ml. The effect of FF against RA was enhanced upon combination with DOX. The combination of FF with DOX reduced the bacterial burden ≥4.53 log₁₀CFU/ml for all strains with a MIC ≥4 μg/ml. Data were fitted to a sigmoidal E_max model. The PK/PD parameters of AUC_24h/MIC (the area under the concentration–time curve over 24 h divided by the MIC) and %T >MIC (the cumulative percentage of time over a 24-h period at which the concentration exceeded the MIC) of FF for eliciting a reduction of 3 log₁₀CFU/ml was 40.10 h and 58.71, respectively. For strains with a MIC ≤ 16 μg/ml, the magnitude of the AUC_24h/MIC and C_max/MIC required for a 3 log₁₀CFU/ml of bacterial killing was 34.84 h and 4.74 in the presence of DOX at 0.5 MIC, respectively. These data suggest that combination of FF with DOX enhanced the activity against RA strains with various susceptibilities to FF and DOX.

Putative Riemerella anatipestifer Outer Membrane Protein H Affects Virulence

Riemerella anatipestifer causes serious contagious disease in ducks, geese, and other fowl. However, as a harmful pathogen causing significant economic losses in the poultry industry, R. anatipestifer is still poorly understood for its pathogenesis mechanisms. In a previous study, we developed an indirect ELISA method for detecting R. anatipestifer infection using B739_0832 protein, a putative outer membrane protein H (OmpH) that is conserved among different serotypes of R. anatipestifer. Although OmpH in some pathogenic bacteria, such as Pasteurella, has been reported as a virulence factor, it is still not clear whether B739_0832 protein contributes to the virulence of R. anatipestifer. In this study, we confirmed that B739_0832 protein in R. anatipestifer localizes to the outer membrane. We constructed a B739_0832 deletion mutant strain (ΔB739_0832) and assayed various effects from the deletion of B739_0832. ΔB739_0832 strain had a similar growth rate to wild-type R. anatipestifer CH-1. However, the survival rate of ducklings in 10 days after infection from ΔB739_0832 strain was 50%, whereas no ducklings survived from wild-type R. anatipestifer infection. Furthermore, the median lethal dose (LD₅₀) of the ΔB739_0832 strain was approximately 150 times higher than that of the wild-type strain. Pathology examinations on infected ducklings found that, at 36 h after infection, bacterial loads in blood, liver, and brain tissues from ΔB739_0832-infected ducklings were considerably lower than those from wild-type infected ducklings. These results demonstrate that the B739_0832 protein contributes to the virulence of R. anatipestifer CH-1.

Molecular Characterization, Virulence and Antimicrobial Susceptibility Testing of Riemerella anatipestifer Isolated from Ducklings

This pilot study aimed to characterize Riemerella anatipestifer from ducklings, testing their susceptibility to antimicrobial agents and to detect their virulence markers. Seven R. anatipestifer isolates with 11.67% infection rate were identified out of sixty freshly dead ducklings and confirmed by PCR assay targeting gyrB gene. The gyrB gene sequences of R. anatipestifer isolates were 100% identical to each other and also showed 100% sequence similarity to the published gyrB genes. Four virulence genes namely ompA, prtC, hagA, and sspA were identified in all isolates except sspA was detected in 5 isolates. The antibiogram revealed higher sensitive to imipenem, amikacin, and rifampin, while, a remarkably high resistance was displayed against ampicillin, penicillin, cefipime, trimethoprim/sulfamethoxazole, gentamicin, ceftazidime, streptomycin and cefoperazone. Proper and rapid identification of R. anatipestifer with detection of their antimicrobial susceptibility and its virulence potential is essential for understanding the epidemiology of R. anatipestifer and to apply the effective control strategies.

Identification by MALDI-TOF MS and Antibiotic Resistance of Riemerella anatipestifer, Isolated from a Clinical Case in Commercial Broiler Chickens

The Gram-negative bacterium Riemerella anatipestifer (RA) is known to cause clinical disease with severe economic impacts primarily in ducks and less frequently in geese and turkeys. RA was isolated and identified in broiler chickens, from a clinical case in a commercial broiler farm located in the southwest mainland of Greece. The morbidity and the mortality in the broiler house were estimated at 10% and 5% respectively. The observed clinical signs appeared at the age of 30 to 42 days with respiratory distress (dyspnea), white fluid feces and stunting. Post-mortem examinations displayed serositis, pericarditis, perihepatitis and airsacculitis. Edematous swelling around the tibio-tarsal joints was observed in some birds. Tissue samples from lesions were streaked on selective media. Three bacterial isolates were identified by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS). Moreover, an antibiogram analysis was performed for the three RA strains, using a pattern of 16 common antibiotics to advocate the most effective drugs for a proper treatment. All the RA isolates were sensitive to ceftiofur, sulphamethoxazole-trimethoprim and amoxicillin, whereas all were resistant to gentamicin, tylosin, tetracyclin, colistin sulphate, spectinomycin, lincomycin and oxytetracycline.

The protective efficacy of specific egg yolk immunoglobulin Y(IgY) against Riemerella Anatipestifer infections

Riemerella anatipestifer (RA) is the significant pathogen of septicemia and duck infectious serositis, diseases which can result in high mortality for ducklings. However, these diseases are difficult to treat because of the bacteria's broad resistance to multiple drugs. The purpose of this study was to produce a specific egg yolk immunoglobulin Y (IgY) targeted to RA, and to evaluate the protective efficacy of this IgY against RA infection. An RA-inactivated vaccine was produced via centrifugation and formalin treatment, using the most predominant serotype 2 wild-type strains in terms of worldwide prevalence. Anti-RA IgY was produced by immunizing Beijing Red No.1 hens with the inactivated vaccine. Enzyme-linked immunosorbent assays showed that the titer levels of anti-RA IgY antibodies increased significantly after exposure. Specific IgY isolated and purified from yolks effectively inhibited the growth of RA in the antibacterial activity assay, which revealed an 80 % reduction of bacteria populations. Animal experiments showed that duckling survival rates were able to reach up to 100 % after the ducklings were treated with 10 mg intramuscular injections of anti-RA IgY from 1 to 12 h after infection. However, the survival rates of ducklings treated with 30 mg of nonspecific IgY at 1 h after infection were 0%. Additionally, ducklings injected once with anti-RA IgY received complete protection in the first week, but the efficacy of this protection almost entirely disappeared after two weeks. The results suggested that specific anti-RA IgY has the potential to improve the degree of protection and responsiveness of ducklings to RA infections and provide them with passive immunity to RA. With further study, this is expected to become a new method for controlling RA infections.