Antimicrobial susceptibility, plasmid profiles and haemocin activities of Avibacterium paragallinarum strains

Prevalence and genomic-based antimicrobial resistance analysis of Avibacterium paragallinarum isolates in Guangdong Province, China

Infectious coryza (IC) is an acute infectious respiratory disease in chickens that is caused by Avibacterium paragallinarum (A. paragallinarum). A. paragallinarum poses a significant threat to poultry health due to its virulence and multidrug resistance. This study isolated and identified 21 A. paragallinarum isolates from Guangdong between 2022 and 2023. Biochemical tests showed that 100% of A. paragallinarum isolates fermented glucose but did not ferment alginate and galactose, and only YZ18 was nicotinamide adenine dinucleotide independent. To determine the genetic relatedness between these isolates and NCBI reference strains, whole-genome-based phylogenetic analysis was employed. In addition, analysis of the 2,000 bp-length hmtp210 gene showed that the hmtp210 gene was strongly associated with A. paragallinarum serotypes. Meanwhile, a PCR assay for serotyping A. paragallinarum was developed based on the hmtp210 gene, this assay has high sensitivity and specificity. The antimicrobial susceptibility of isolates was assessed using the disk diffusion method. The antibiotic resistance genes of isolates were analyzed using the genomic method. Phenotypic resistance to ampicillin (95.2%), streptomycin (95.2%), methotrexate-sulfamethoxazole (90.5%), and tetracycline (85.7%) was most frequent among the isolates. All of the isolates exhibited resistance to multiple drugs, and furthermore, the isolates possessed a collective total of 14 genes associated with antibiotic resistance. This study will contribute to advancing our knowledge of A. paragallinarum antibiotic resistance and provide a scientific basis for the prophylaxis and treatment of IC, and the subsequent rational design of potential clinical therapeutics.

Recommendation of a standardized broth microdilution method for antimicrobial susceptibility testing of Avibacterium paragallinarum and resistance monitoring

This study aimed to develop a method for standardized broth microdilution antimicrobial susceptibility testing (AST) of Avibacterium (Av.) paragallinarum, the causative agent of infectious coryza in chickens. For this, a total of 83 Av. paragallinarum isolates and strains were collected from 15 countries. To select unrelated isolates for method validation steps, macrorestriction analyses were performed with 15 Av. paragallinarum. The visible growth of Av. paragallinarum was examined in six broth media and growth curves were compiled. In Veterinary Fastidious Medium and cation-adjusted Mueller-Hinton broth (CAMHB) + 1% chicken serum + 0.0025% NADH (CAMHB + CS + NADH), visible growth of all isolates was detected and both media allowed adequate bacterial growth. Due to the better readability of Av. paragallinarum growth in microtiter plates, CAMHB + CS + NADH was chosen for AST. Repetitions of MIC testing with five epidemiologically unrelated isolates using a panel of 24 antimicrobial agents resulted in high essential MIC agreements of 96%-100% after 48-h incubation at 35 ± 2°C. Hence, the remaining 78 Av. paragallinarum were tested and demonstrated easily readable MICs with the proposed method. Differences in MICs were detected between isolates from different continents, with isolates from Africa showing lower MICs compared to isolates from America and Europe, which more often showed elevated MICs of aminoglycosides, quinolones, tetracyclines, and/or trimethoprim/sulfamethoxazole. PCR analyses of isolates used for method development revealed that isolates with elevated MICs of tetracyclines harbored the tetracycline resistance gene tet(B) but none of the other tested resistance genes were detected. Therefore, whole-genome sequencing data from 62 Av. paragallinarum were analyzed and revealed the presence of sequences showing nucleotide sequence identity to the genes aph(6)-Id, aph(3″)-Ib, blaTEM-1B, catA2, sul2, tet(B), tet(H), and mcr-like. Overall, the proposed method using CAMHB + CS + NADH for susceptibility testing with 48-h incubation time at 35 ± 2°C in ambient air was shown to be suitable for Av. paragallinarum. Due to a variety of resistance genes detected, the development of clinical breakpoints is highly recommended.

IMPORTANCE

Avibacterium paragallinarum is an important pathogen in veterinary medicine that causes infectious coryza in chickens. Since antibiotics are often used for treatment and resistance of the pathogen is known, targeted therapy should be given after resistance testing of the pathogen. Unfortunately, there is currently no accepted method in standards that allows susceptibility testing of this fastidious pathogen. Therefore, we have worked out a method that allows harmonized susceptibility testing of the pathogen. The method meets the requirements of the CLSI and could be used by diagnostic laboratories.

Basic Characterization of Natural Transformation in Avibacterium paragallinarum

Avibacterium paragallinarum is the pathogen involved in infectious coryza (IC), an acute infectious upper respiratory disease in chickens. The prevalence of IC has increased in China in recent years. There is a lack of reliable and effective procedures for gene manipulation, which has limited the research on the bacterial genetics and pathogenesis of A. paragallinarum. Natural transformation has been developed as a method of gene manipulation in Pasteurellaceae by the introduction of foreign genes or DNA fragments into bacterial cells, but there has been no report on natural transformation in A. paragallinarum. In this study, we analyzed the existence of homologous genetic factors and competence proteins underlying natural transformation in A. paragallinarum and established a method for transformation in it. Through bioinformatics analysis, we identified 16 homologs of Haemophilus influenzae competence proteins in A. paragallinarum. We found that the uptake signal sequence (USS) was overrepresented in the genome of A. paragallinarum (1,537 to 1,641 copies of the core sequence ACCGCACTT). We then constructed a plasmid, pEA-KU, that carries the USS and a plasmid, pEA-K, without the USS. These plasmids can be transferred via natural transformation into naturally competent strains of A. paragallinarum. Significantly, the plasmid that carries USS showed a higher transformation efficiency. In summary, our results demonstrate that A. paragallinarum has the ability to undergo natural transformation. These findings should prove to be a valuable tool for gene manipulation in A. paragallinarum. IMPORTANCE Natural transformation is an important mechanism for bacteria to acquire exogenous DNA molecules during the process of evolution. Additionally, it can also be used as a method to introduce foreign genes into bacteria under laboratory conditions. Natural transformation does not require equipment such as an electroporation apparatus. It is easy to perform and is similar to gene transfer under natural conditions. However, there have been no reports on natural transformation in Avibacterium paragallinarum. In this study, we analyzed the presence of homologous genetic factors and competence proteins underlying natural transformation in A. paragallinarum. Our results indicate that natural competence could be induced in A. paragallinarum serovars A, B, and C. Furthermore, the method that we established to transform plasmids into naturally competent A. paragallinarum strains was stable and efficient.

Regions Important for Hemagglutination Activity and Serotypes of Avibacterium paragallinarum HMTp210 Protein

Avibacterium paragallinarum is an important respiratory pathogen of domestic chickens. Avibacterium paragallinarum has been subtyped into three serogroups and nine serovars according to the Page and revised Kume schemes. The major hemagglutinin antigen of A. paragallinarum is HMTp210, which is a large protein of about 2000 amino acids (aa), including a 70-aa signal peptide at its N-terminal end. However, the regions important for the hemagglutination (HA) activity and serotypes of HMTp210 remain unclear. In this study we constructed a series of A. paragallinarum strains expressing HMTp210 in-frame deletion mutants and determined their HA titers to identify the regions important for the HA activity and serotypes of HMTp210. Two distinct types of HA activities were found in HMTp210. The type 1 HA activity resided in the region spanning the full-length HA (aa 71-2084), whereas the type 2 resided in the region spanning aa 1003-2084. The putative ligand binding of the type 1 HA activity was located at aa 176-360, which had a structure similar to YadA of Yersinia enterocolitica. The putative ligand binding site of the type 2 HA activity was located at aa 1003-1125, which had a structure similar to UspA1 from Moraxella catarrhalis. The type 1 HA activity appeared to be Page serogroup specific, whereas type 2 appeared to be Kume serovar specific. Finally, sequence analyses of the regions spanning aa 1-400 and aa 1100-1600 of HMTp210 could be useful for the molecular serotyping (the Page and revised Kume schemes) of A. paragallinarum isolates.

Comparative Genomics Analysis and Outer Membrane Vesicle-Mediated Horizontal Antibiotic-Resistance Gene Transfer in Avibacterium paragallinarum

Avibacterium paragallinarum is the etiological agent of infectious coryza, an acute respiratory disease of chickens that is globally distributed and causes serious economic losses for chicken production. A. paragallinarum is a Gram-negative bacterium that releases outer membrane vesicles (OMVs). In this study, a comparative genomic analysis of A. paragallinarum isolate P4chr1 and its OMVs was carried out, and the ability to transfer antibiotic resistance genes (ARGs) via the OMVs was studied. Sequencing and data analyses demonstrated that the genomic size of A. paragallinarum P4chr1 was approximately 2.77 Mb with a 25 kb tolerance island that covered six types of antibiotics and 11 ARGs. The genomic size of its OMVs was approximately 2.69 Mb, covering 97% of the genomic length and almost all the gene sequences of P4chr1. Purified and DNase-treated A. paragallinarum P4chr1 OMVs were cocultured with the antibiotic-sensitive A. paragallinarum Modesto strain on an antibiotic (chloramphenicol, erythromycin, tetracycline, or streptomycin)-containing plate, and the corresponding ARGs were detected in the colonies grown on the plates. However, using an antimicrobial susceptibility test, we found that ARGs delivered by OMVs were not persistent but only appeared transiently on the antibiotic-containing plates. Antibiotic resistance and ARGs were lost by the second bacterial passage. IMPORTANCE The functions and roles of OMVs on ARG and virulent gene transfer and dissemination have been reported in numerous Gram-negative bacteria. However, the role of OMVs in mediating antibiotic resistance in A. paragallinarum has not been reported. This study is the first report to compare the genomic characteristics of OMVs with its parent A. paragallinarum strain and to study A. paragallinarum ARG transfer via OMVs. This work has provided useful data for further studies focusing on nonplasmid ARG transfer mediated by A. paragallinarum OMVs.

Pathogenicity of Avibacterium paragallinarum Strains from Peru and the Selection of Candidate Strains for an Inactivated Vaccine

Worldwide, Avibacterium paragallinarum is the aetiological agent of infectious coryza in poultry. Vaccines are the best means of control, helping reduce clinical signs and colonization of this bacterium. Most vaccines are based on international reference strains, or, lately, regional strains, but, generally, without any information regarding their virulence. The characterization of the pathogenicity of 24 Av. paragallinarum strains of the three Page serogroups, including four variant strains of serogroup B, all isolated from infectious coryza outbreaks in Peru, was performed. After experimental inoculation into the infraorbital sinuses, information regarding their capacity to induce infectious coryza typical clinical signs, spreading, and colonization was recorded. Furthermore, after intraperitoneal inoculation, septicaemia and death were registered. Differences among strains in these parameters were observed, even within strains from the same serogroup. Finally, the four most pathogenic strains, one from each serogroup, were chosen to formulate an experimental vaccine that was tested successfully against homologous challenges in reducing clinical signs and colonization in vaccinated birds compared to unvaccinated ones. This is the first time that Av. paragallinarum strains from Peru were studied thoroughly for their virulence in a search for improving vaccine formulation.

Isolation, Serovar Identification, and Antimicrobial Susceptibility of Avibacteriumparagallinarum from Chickens in China from 2019 to 2020

Infectious coryza is an acute infectious respiratory disease in chickens that is caused by Avibacterium paragallinarum (A. paragallinarum). Infectious coryza has major economic effects due to decreased egg production in growing birds and slowed growth in broilers. In this study, we isolated and identified 40 strains of A. paragallinarum from chickens that showed typical clinical signs of coryza in part of China from 2019 to 2020. Using a hemagglutination-inhibition test, 11 isolates were identified as serovar A, 10 isolates were identified as serovar B, and 19 isolates were identified as serovar C. Antimicrobial sensitivity tests showed that high minimum inhibitory concentration (MIC) values were encountered for compounds sulfamethoxine sodium and oxytetracycline hydrochloride. Especially, of the 40 A. paragallinarum isolates, 30% had an MIC value of compound sulfamethoxine sodium of 64 μg/mL, 10% of 128 μg/mL, and 15% of 256 μg/mL. For oxytetracycline hydrochloride, 85% of isolates showed MIC values of 64 μg/mL or more. Excitingly, the MIC values of β-lactamase (amoxicillin, ampicillin, and ceftiofur) were low, with 77.5%, 70%, and 92.5% of isolates having an MIC value of ≤1 μg/mL, respectively. Our results may provide a reference for the treatment of infectious coryza.

Antimicrobial sensitivity of Avibacterium paragallinarum isolates from layers in the special region of Yogyakarta, Indonesia

Background and Aim:

Infectious coryza (IC) is an upper respiratory disease of chicken caused by Avibacterium paragallinarum. Its clinical symptoms are swollen face and malodorous sinus exudate. This study was conducted to determine the antimicrobial sensitivity of A. paragallinarum isolates from layers in the Special Region of Yogyakarta, Indonesia.

Materials and Methods:

The samples used in this study were 30 layers that showed IC symptoms. The colony and cell morphology were observed with Gram staining; then, biochemical tests (catalase, oxidase, urease, indole, and motility tests, and carbohydrate fermentation tests using lactose, maltose, mannitol, and sorbitol) were performed to the suspected colony to identify A. paragallinarum. An antibiotic sensitivity test was performed using several antibiotic disks against A. paragallinarum isolates that were cultured on Mueller-Hinton Agar.

Results:

Out of 30 samples, 24 samples (80%) were found positive for A. paragallinarum. All isolates were sensitive to ampicillin (AMP) and amoxicillin (AML) (100%), and chloramphenicol (C) (91.6%). The antibiotics with intermediate sensitivity were enrofloxacin (79.2%), fosfomycin (75%), and ciprofloxacin (54.2%). The isolates were most resistant to erythromycin (100%), followed by tetracycline (87.5%), streptomycin (83.3%), doxycycline and kanamycin (70.8%), and trimethoprim (62.5%).

Conclusion:

Out of the total samples, 24 samples (80%) from layers with IC symptoms were identified biochemically as A. paragallinarum. It was sensitive to AMP, AML, and C.

Complete Genome Sequences of Seven Avibacterium paragallinarum Isolates from Poultry Farms in Pennsylvania, USA

Avibacterium paragallinarum, the causative agent of infectious coryza, causes significant economic losses to the poultry industry due to increased culling rates in growing chickens and decreased egg production in layers. We present the complete genome sequences of seven strains of Avibacterium paragallinarum isolated from poultry farms in Pennsylvania during 2019.

Avibacterium paragallinarum, the causative agent of infectious coryza, causes significant economic losses to the poultry industry due to increased culling rates in growing chickens and decreased egg production in layers. We present the complete genome sequences of seven strains of Avibacterium paragallinarum isolated from poultry farms in Pennsylvania during 2019.

Antimicrobial Resistance in Pasteurellaceae of Veterinary Origin

Members of the highly heterogeneous family Pasteurellaceae cause a wide variety of diseases in humans and animals. Antimicrobial agents are the most powerful tools to control such infections. However, the acquisition of resistance genes, as well as the development of resistance-mediating mutations, significantly reduces the efficacy of the antimicrobial agents. This article gives a brief description of the role of selected members of the family Pasteurellaceae in animal infections and of the most recent data on the susceptibility status of such members. Moreover, a review of the current knowledge of the genetic basis of resistance to antimicrobial agents is included, with particular reference to resistance to tetracyclines, β-lactam antibiotics, aminoglycosides/aminocyclitols, folate pathway inhibitors, macrolides, lincosamides, phenicols, and quinolones. This article focusses on the genera of veterinary importance for which sufficient data on antimicrobial susceptibility and the detection of resistance genes are currently available (Pasteurella, Mannheimia, Actinobacillus, Haemophilus, and Histophilus). Additionally, the role of plasmids, transposons, and integrative and conjugative elements in the spread of the resistance genes within and beyond the aforementioned genera is highlighted to provide insight into horizontal dissemination, coselection, and persistence of antimicrobial resistance genes. The article discusses the acquisition of diverse resistance genes by the selected Pasteurellaceae members from other Gram-negative or maybe even Gram-positive bacteria. Although the susceptibility status of these members still looks rather favorable, monitoring of their antimicrobial susceptibility is required for early detection of changes in the susceptibility status and the newly acquired/developed resistance mechanisms.

Isolation, identification, and serotyping of Avibacterium paragallinarum from quails in Indonesia with typical infectious coryza disease symptoms

Background and Aim

Infectious coryza (IC) or snot is an infectious upper respiratory disease affecting chickens and birds, including quails, and it is caused by Avibacterium paragallinarum. The symptoms of IC are facial swelling, malodorous nasal discharge, and lacrimation. This study aimed to isolate, identify, and serotype the A. paragallinarum of snot in quails and to determine the sensitivity and resistance to several antibiotics.

Materials and Methods

Nine quails from Yogyakarta, Indonesia with typical snot disease symptoms were used in this study. The nasal swab was obtained and directly streaked onto a chocolate agar plate and blood agar plate (BAP), then incubated in 5% CO₂ at 37°C for 24-48 h. Staphylococcus spp. was cross-streaked onto the BAP to show the satellite growth. The observation of the morphology of the suspected colony, Gram staining, and biochemical tests (catalase test, oxidase test, urease test, peptone test, and carbohydrate fermentation such as maltose, mannitol, lactose, and sorbitol) are done to identify the species of bacteria. This research also detects the serovar of A. paragallinarum using hemagglutination inhibition test.The antibiotic sensitivity tests were also performed using several antibiotics against five A. paragallinarum isolates that were cultured on Mueller–Hinton Agar and added with antibiotic discs, then incubated in 5% CO₂ at 37°C for 24–48 h.

Results

Five isolates out of nine suspected isolates (55.5%) were A. paragallinarum. The growth of isolates from quails did not depend on the nicotinamide adenine dinucleotide (NAD) (NAD-independent). Sensitivity test was done using the five identified A. paragallinarum isolates, results showed that they were 100% sensitive to amoxicillin (AMC) and ampicillin (AMP); 100% resistant toward amikacin (AK), erythromycin (E), gentamycin (CN), and tetracycline (TE); 80% resistant toward kanamycin (K) and trimethoprim (W); 60% resistant toward chloramphenicol (C); and 20% toward enrofloxacin (ENR). The antibiotics that have an intermediate sensitivity (in between sensitive and resistant) were ENR and K, 80% and 20%, respectively. Three out of five A. paragallinarum isolates were identified as serovar B of A. paragallinarum using HI test.

Conclusion

Five out of nine isolates (55.5%) from quails with typical IC disease symptoms identified as A. paragallinarum and sensitive toward AMC and AMP. Three out of five A. paragallinarum isolates were identified as serovar B.

Antimicrobial susceptibility of Avibacterium paragallinarum isolates from outbreaks of infectious coryza in Dutch commercial poultry flocks, 2008-2017

The objective of the present study was to determine the in vitro antimicrobial susceptibility of Avibacterium paragallinarum isolates from infectious coryza outbreaks in Dutch commercial poultry, from 2008 till mid-2017. By using a broth microdilution method, minimal inhibitory concentrations (MICs) of 15 antimicrobial agents were assessed, and MIC₅₀ and MIC₉₀ values were determined. Additionally, isolates were subjected to different PCRs for the presence of genes that may confer antimicrobial resistance. Besides field isolates, a set of reference strains, among which the nine Kume strains and one Page serovar strain, were included in the study. For broth microdilution testing a new growth medium, recently developed for susceptibility testing of Haemophilus parasuis, was used. The medium proved to be suitable for broth microdilution susceptibility testing of NAD dependent Av. paragallinarum as well; visible growth was obtained in growth control wells and accepting a deviation of one dilution step, MIC values were reproducible. Results of 44 field isolates originating from 25 outbreaks showed relatively good susceptibility to antimicrobial agents that are recommended for the treatment of infectious coryza in the Netherlands, except for tetracycline; circa 75% of the isolates were characterized by MIC values of tetracycline of ≥16 μg/ml. In almost a quarter of these isolates with high MICs of tetracycline, tet genes were detected. For the remaining isolates with elevated MIC values, the mechanism conferring resistance remains to be studied. Of most agents, low MIC values were determined for the nine Kume and one Page serovar reference strains, as well as negative PCR results for resistance genes, being concordant with agar diffusion results reported for these strains.

Antimicrobial Sensitivity of Avibacterium paragallinarum Isolates from Four Latin American Countries

The antimicrobial sensitivity of 11 reference strains and 66 Avibacterium paragallinarum isolates from four Latin American countries was investigated. All 11 reference strains were sensitive to amoxicillin-clavulanic acid, ampicillin, fosfomycin, gentamicin, kanamycin, neomycin, penicillin, tetracycline, and trimethoprim-sulfamethoxazole. The 11 reference strains were all resistant to lincomycin. All isolates (100%) from Mexico, Panama, and Peru were sensitive to amoxicillin-clavulanic acid, ampicillin, and fosfomycin. The Ecuadorian isolates showed some level of resistance to all 16 agents tested. The Ecuadorian isolates were significantly more sensitive to erythromycin, lincomycin, and streptomycin, and significantly more resistant to gentamicin, kanamycin, penicillin, and tetracycline, than the Mexican isolates. A total of 57.5% (38/66) of tested isolates were multi-drug resistant (MDR), with 16 MDR patterns detected in 88.4% (23/26) of the antimicrobial-resistant isolates from Ecuador, and 8 MDR patterns detected in 42.8% (15/35) of the antimicrobial-resistant isolates from Mexico. In conclusion, the variation in antimicrobial sensitivity patterns between isolates from Ecuador and Mexico emphasizes the importance of active, ongoing monitoring of A. paragallinarum isolates.

Antimicrobial Resistance in Bacterial Poultry Pathogens: A Review

Antimicrobial resistance (AMR) is a global health threat, and antimicrobial usage and AMR in animal production is one of its contributing sources. Poultry is one of the most widespread types of meat consumed worldwide. Poultry flocks are often raised under intensive conditions using large amounts of antimicrobials to prevent and to treat disease, as well as for growth promotion. Antimicrobial resistant poultry pathogens may result in treatment failure, leading to economic losses, but also be a source of resistant bacteria/genes (including zoonotic bacteria) that may represent a risk to human health. Here we reviewed data on AMR in 12 poultry pathogens, including avian pathogenic Escherichia coli (APEC), Salmonella Pullorum/Gallinarum, Pasteurella multocida, Avibacterium paragallinarum, Gallibacterium anatis, Ornitobacterium rhinotracheale (ORT), Bordetella avium, Clostridium perfringens, Mycoplasma spp., Erysipelothrix rhusiopathiae, and Riemerella anatipestifer. A number of studies have demonstrated increases in resistance over time for S. Pullorum/Gallinarum, M. gallisepticum, and G. anatis. Among Enterobacteriaceae, APEC isolates displayed considerably higher levels of AMR compared with S. Pullorum/Gallinarum, with prevalence of resistance over >80% for ampicillin, amoxicillin, tetracycline across studies. Among the Gram-negative, non-Enterobacteriaceae pathogens, ORT had the highest levels of phenotypic resistance with median levels of AMR against co-trimoxazole, enrofloxacin, gentamicin, amoxicillin, and ceftiofur all exceeding 50%. In contrast, levels of resistance among P. multocida isolates were less than 20% for all antimicrobials. The study highlights considerable disparities in methodologies, as well as in criteria for phenotypic antimicrobial susceptibility testing and result interpretation. It is necessary to increase efforts to harmonize testing practices, and to promote free access to data on AMR in order to improve treatment guidelines as well as to monitor the evolution of AMR in poultry bacterial pathogens.

The current epidemiological status of infectious coryza and efficacy of PoulShot Coryza in specific pathogen-free chickens

Infectious coryza (IC) is an infectious disease caused by Avibacterium (Av.) paragallinarum. IC is known to cause economic losses in the poultry industry via decreased egg production in layers. Between 2012 and 2013, Av. paragallinarum was isolated from seven chicken farms by Chungbuk National University. We identified Av. paragallinarum, the causative pathogen of IC by polymerase chain reaction (PCR) and serovar serotype A, by multiplex PCR. Antibiotic sensitivity tests indicated that a few field-isolated strains showed susceptibility to erythromycin, gentamicin, lincomycin, neomycin, oxytetracycline, spectinomycin, and tylosin. A serological survey was conducted to evaluate the number of flocks that were positive for Av. paragallinarum by utilizing a HI test to determine the existence of serovar A. Serological surveys revealed high positivity rates of 86.4% in 2009, 78.9% in 2010, 70.0% in 2011, and 69.6% in 2012. We also challenged specific pathogen-free chickens with isolated domestic strains, ADL121286 and ADL121500, according to the measured efficacy of the commercial IC vaccine, PoulShot Coryza. We confirmed the effectiveness of the vaccine based on relief of clinical signs and a decreased re-isolation rate of ADL121500 strain. Our results indicate IC is currently prevalent in Korea, and that the commercial vaccine is effective at protecting against field strains.

p518, a small floR plasmid from a South American isolate of Actinobacillus pleuropneumoniae

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Smallest floR plasmid in the Pasteurellaceae.

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Unique arrangement with complete strA, but partial strB and sul2 sequences.

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Loss of mobilisation genes indicated by partial mobC; no other mob genes.

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Not transferrable by conjugation or natural transformation.

A small (3.9 kb) plasmid (p518), conferring resistance to florfenicol (MIC >8 μg/mL) and chloramphenicol (MIC >8 μg/mL) was isolated from an Actinobacillus pleuropneumoniae clinical isolate from Southeastern Brazil. To date, this is the smallest florfenicol resistance plasmid isolated from a member of the Pasteurellaceae. The complete nucleotide of this plasmid revealed a unique gene arrangement compared to previously reported florfenicol resistance plasmids found in other members of the Pasteurellaceae. In addition to the floR gene and a lysR gene, common to various florfenicol resistance plasmids, p518 also encodes strA and a partial strB sequence. An origin of replication (oriV) similar to that in the broad host range plasmid, pLS88, was identified in p518, and transformation into Escherichia coli MFDpir confirmed the ability to replicate in other species. Mobilisation genes appear to have been lost, with only a partial mobC sequence remaining, and attempts to transfer p518 from a conjugal donor strain (E. coli MFDpir) were not successful, suggesting this plasmid is not mobilisable. Similarly, attempts to transfer p518 into a competent A. pleuropneumoniae strain, MIDG2331, by natural transformation were also not successful. These results suggest that p518 may be only transferred by vertical descent.

Loss of the Capsule Increases the Adherence Activity but Decreases the Virulence of Avibacterium paragallinarum

Avibacterium paragallinarum is the causative agent of infectious coryza, an important respiratory disease of chickens. The capsule is an important virulence determinant of many pathogenic bacteria, but the function of the capsule in Av. paragallinarum is not well defined. In this study, acapsular mutants of Av. paragallinarum were constructed by inactivation of the hctA gene using the TargeTron gene knockout system. The acapsular mutants were found to have greater hemagglutination activity than did the wild-type strain. Further, acapsular mutants exhibited an increased ability to adhere to DF-1 cells and to form biofilms on abiotic surfaces. Virulence assays showed that acapsular mutants were less virulent than the wild-type strain. Taken together, these results indicated that loss of capsule increases hemagglutination and adhesion activities but decreases the virulence of Av. paragallinarum. These results could be valuable to further elucidate the function of the capsule and the mechanism of pathogenicity of Av. paragallinarum.

The haemagglutinin of Avibacterium paragallinarum is a trimeric autotransporter adhesin that confers haemagglutination, cell adherence and biofilm formation activities

The haemagglutinin (HA) protein plays a key role in the immunogenicity and pathogenicity of Avibacterium paragallinarum. A 210-kDa protein (HMTp210) was previously reported to be the HA of Av. paragallinarum, but the biological function of HMTp210 is not well defined. In this study, mutant strains that lacked HMTp210 were constructed using the TargeTron(®) gene knockout system. Haemagglutination and haemagglutination-inhibition (HI) assays showed that the HMTp210-deficient mutants exhibited no HA activity and failed to elicit HI antibodies in immunized chickens. Additionally, HMTp210-deficient mutants exhibited reduced ability to adhere to HeLa cells and to form biofilms on abiotic surfaces. Virulence assays showed that HMTp210-deficient mutants are less virulent than their isogenic wild-type strains. HMTp210 bears significant similarity to proteins of the trimeric autotransporter adhesin (TAA) family, and recombinant HMTp210 expressed in E. coli formed a trimeric structure. Taken together, these results indicated that HMTp210 is a trimeric autotransporter adhesin that confers haemagglutination, cell adherence and biofilm formation activities. These results should prove valuable to further elucidate the biological function of HA and the mechanism of pathogenicity of Av. paragallinarum.

ICEPmu1, an integrative conjugative element (ICE) of Pasteurella multocida: analysis of the regions that comprise 12 antimicrobial resistance genes

BACKGROUND

In recent years, multiresistant Pasteurella multocida isolates from bovine respiratory tract infections have been identified. These isolates have exhibited resistance to most classes of antimicrobial agents commonly used in veterinary medicine, the genetic basis of which, however, is largely unknown.

METHODS

Genomic DNA of a representative P. multocida isolate was subjected to whole genome sequencing. Genes have been predicted by the YACOP program, compared with the SWISSProt/EMBL databases and manually curated using the annotation software ERGO. Susceptibility testing was performed by broth microdilution according to CLSI recommendations.

RESULTS

The analysis of one representative P. multocida isolate identified an 82 kb integrative and conjugative element (ICE) integrated into the chromosomal DNA. This ICE, designated ICEPmu1, harboured 11 resistance genes, which confer resistance to streptomycin/spectinomycin (aadA25), streptomycin (strA and strB), gentamicin (aadB), kanamycin/neomycin (aphA1), tetracycline [tetR-tet(H)], chloramphenicol/florfenicol (floR), sulphonamides (sul2), tilmicosin/clindamycin [erm(42)] or tilmicosin/tulathromycin [msr(E)-mph(E)]. In addition, a complete bla(OXA-2) gene was detected, which, however, appeared to be functionally inactive in P. multocida. These resistance genes were organized in two regions of approximately 15.7 and 9.8 kb. Based on the sequences obtained, it is likely that plasmids, gene cassettes and insertion sequences have played a role in the development of the two resistance gene regions within this ICE.

CONCLUSIONS

The observation that 12 resistance genes, organized in two resistance gene regions, represent part of an ICE in P. multocida underlines the risk of simultaneous acquisition of multiple resistance genes via a single horizontal gene transfer event.

Analysis of an Actinobacillus pleuropneumoniae multi-resistance plasmid, pHB0503

A plasmid containing multidrug resistance genes has been discovered from a clinical Actinobacillus pleuropneumoniae strain isolated in China. The complete 15079kb sequence of this plasmid, designated pHB0503, was analyzed with regard to the organization and evolution of multidrug resistance genes. The deduced amino acid sequences from seven open reading frames (sul2 catA3, aacC2, strA, truncated strB (strB'), bla(ROB-1) and aph(3')-I) identified in pHB0503 were entirely or nearly identical to resistance genes of plasmids both within and outside of the family Pasteurellaceaea, indicating that pHB0503 arose through inter-plasmid recombination processes among them. In addition, co-transcription of the cluster of resistance genes from the promoter upstream of sul2 and bla(ROB-1) was confirmed by RT-PCR. This is the first report of a complete sequence of the plasmid containing seven resistance genes from A. pleuropneumoniae.