NAD (V‐factor)‐independent and typicalHaemophilus paragallinaruminfection in commercial chickens: A five year field study

Genotypic divergence of Avibacterium paragallinarum isolates with different growth requirements for nicotinamide adenine dinucleotide

In 2017, for the first time in Asia, we reported the isolation of variants of Avibacterium paragallinarum with atypical NAD dependency. The present study was conducted to characterize the genotypes of 24 isolates of Av. paragallinarum in Korea, including the four variants reported previously. Most of the typical isolates (19/20) showed a unique ERIC-PCR pattern with no ERIC-PCR patterns in common between the typical isolates and the variants. Furthermore, the variants shared no ERIC-PCR patterns among themselves. All the typical NAD-dependent isolates belonged to the same phylogenetic group based on both 16S rRNA and hagA gene sequences. The four variants were placed in several groups distinct from the typical isolates. In the 16S rRNA phylogenetic analysis, two of the variants were not closely aligned to any other Av. paragallinarum, isolate although they were clearly members of the genus Avibacterium. The other variants were clustered together with NAD atypical isolates from geographically diverse global locations. Compared with the Modesto reference strain AY498870, all the variants lacked a TTTTT stretch at positions 182-186 in the 16S rRNA gene and the same deletion was shown in most of the reported variants. The typical isolates and variants shared 97.3-98.2% and 95.2-97.2% nucleotide sequence similarity, for 16S rRNA and hagA, respectively. In addition, the similarities among variants were within 98.3-100% and 96.5-98.4% for the two genes, respectively. Our results indicate that the Av. paragallinarum variants with altered NAD growth requirements were genetically different and highly divergent from the typical NAD-dependent isolates.RESEARCH HIGHLIGHTS NAD variant Korean Av. paragallinarum isolates show genetic diversity, whereas typical Korean Av. paragallinarum isolates do not.The Korean variants were not closely aligned to all other Av. paragallinarum in the 16S rRNA phylogeny.NAD atypical isolates from geographically diverse global locations clustered together.Almost all variants, including all Korean variants of Av. paragallinarum, lack a specific fragment of the 16S rRNA gene.

Identification and characterization of Dutch Avibacterium paragallinarum isolates and the implications for diagnostics

This study reports the results of diagnostic and molecular typing methods for 18 Avibacterium paragallinarum isolates obtained from outbreaks of infectious coryza in commercial layer flocks in the Netherlands. Isolation, biochemical identification, species-specific PCR tests and classical serotyping were performed. In addition, molecular typing by Enterobacterial Repetitive Intergenic Consensus-Based Polymerase Chain Reaction (ERIC-PCR) and sequence analysis of the partial HPG2 region of A. paragallinarum were applied and results of both techniques were compared. Moreover, the pathogenicity of an isolate of the most common genotype detected in the Netherlands was determined in an animal experiment. All 18 Avibacterium isolates were nicotinamide adenine dinucleotide-dependent. All isolates were detected by the species-specific conventional PCR while 33% of the isolates were missed by the species-specific real-time PCR. Sequence analysis showed a probe mismatch as a result of a single nucleotide polymorphism (G1516A). Modification of the probe of the real-time PCR was necessary to overcome false negative results. Molecular typing showed that sequence analysis of the partial HPG2 region was in concordance with ERIC-PCR results and indicated the presence of two major genotypes. Serotyping showed the presence of serovars A-1, A-2 and B-1. There was no correlation between genotyping results and serotyping results. Inoculation of an isolate of the most prevalent genotype, and belonging to serovar A-1, into brown layer hens demonstrated the pathogenicity of this isolate.

Isolation and characterization of Avibacterium paragallinarum with different nicotinamide adenine dinucleotide requirements

Twenty field isolates of Avibacterium paragallinarum were obtained from chickens in South Korea during 2011-2015. The isolates were identified by a HPG-2 PCR assay specific for A. paragallinarum and by biochemical tests. Growth requirements, Page serovars, carbohydrate fermentation patterns, and antimicrobial susceptibility were also examined. Most isolates (16/20) showed the typical requirement for nicotinamide adenine dinucleotide (NAD) and an enriched CO₂ atmosphere for growth. One isolate needed increased levels of NAD and serum for good growth. Three isolates showed NAD-independent growth on blood agar under aerobic conditions. In terms of carbohydrate fermentation patterns, three biochemical biovars were recognized; these varied with respect to acid production from maltose and D-xylose. The 16 typical NAD-dependent isolates were serovar A while the variants, both NAD-independent isolates and the isolate with increased NAD dependency were non-typeable. All isolates were sensitive to amoxicillin-clavulanic acid, ceftiofur, gentamicin, and spectinomycin. High rates of resistance, including intermediate resistance, to lincomycin (100%), cloxacillin (75%), and erythromycin (70%) were observed. The four variant strains (the three NAD-independent isolates and the isolate showing unusual growth requirements) were more resistant to antibiotics than the typical NAD-dependent strains. The finding of NAD-independent forms of A. paragallinarum extends the known distribution of this form, previously only reported in South Africa, Mexico and Peru. There is clearly a need for increased caution in the diagnosis and, possibly, the control of infectious coryza.

Further studies on the use of a polymerase chain reaction test for the diagnosis of infectious coryza

Further information is reported on the use of a polymerase chain reaction (PCR) test for the diagnosis of infectious coryza in China. The majority of sinus swabs taken from artificially infected chickens and stored in glycerol-enriched phosphate-buffered saline were still positive by PCR after storage for 180 days at either 4 degrees C or - 20 degrees C. Storage of swabs in either saline or nutrient broth was not as effective. Traditional culture failed to detect H. paragallinarum after storage for 3 days, regardless of storage medium or storage temperature. With dry swabs, the PCR could detect H. paragallinarum after storage for 7 days or longer at either 4 degrees C or - 20 degrees C, while traditional culture could not. In PCR tests on 64 artificially-challenged chickens, all were positive by PCR at the six sampling dates up to 18 days post-challenge. Traditional culture gave a similar result. Both PCR and culture detected 50% or less of chickens as positive at 21 and 24 days post challenge. Antibiotic treatment reduced the ability of both culture and the PCR test to detect H. paragallinarum. The value of the PCR test and its superiority over traditional culture for the diagnosis of infectious coryza has been confirmed in these experiments.

The presence of nicotinamide adenine dinucleotide-independent Haemophilus paragallinarum in México

Two isolates of Haemophilus paragallinarum were obtained from a layer chicken in Mexico. The isolates were confirmed as H. paragallinarum by polymerase chain reaction and conventional biochemical identification. The isolates were nicotinamide adenine dinucleotide (NAD) independent-growing on blood agar without the need of a nurse colony as well as on a complex medium that lacked both NAD and chicken serum. Both isolates were pathogenic, causing the typical clinical signs of infectious coryza in susceptible chickens. One isolate was Page serovar B/Kume serovar B-1 and the other isolate was Page serovar C/Kume serovar C-2. The isolates were associated with a field outbreak that involved an egg drop of 20% over a 3-wk period and a doubling of weekly mortality (from 0.1% to 0.2%). This is the first report of NAD-independent H. paragallinarum outside South Africa and is the first time that NAD-independent H. paragallinarum of serovar B has been reported.

Infectious coryza: overview of the disease and new diagnostic options

Infectious coryza is a well-recognized and commonly encountered upper respiratory tract disease of chickens that is caused by the bacterium Haemophilus paragallinarum. The occurrence of recent outbreaks in North America has emphasized that the disease can be significant in meat chickens as well as layer chickens. In developing countries, coryza is commonly complicated by the presence of a range of other infections, resulting in severe disease and significant economic losses. Unusual forms of the disease, involving arthritis and septicemia, again associated with the presence of other pathogens, have been found in South America. Newly recognized bacteria such as Ornithobacterium rhinotracheale and phenotypic variant forms of both H. paragallinarum and close relatives (variant in that they no longer require V-factor for growth in vitro) have increased the difficulty associated with diagnosing the disease. There have been suggestions in both South America and South Africa that new serovars or serovar variants, associated with unusual clinical manifestations and causing vaccine failures, are emerging. Definitive evidence to confirm or deny the role of these "variants" in vaccine failures is currently not available. A new DNA-based diagnostic technique, involving PCR, has been recently described and will greatly assist in the diagnosis of infectious coryza.