Isolation, identification, antibiotic resistance profile and molecular analysis of Ornithobacterium rhinotracheal isolates from turkeys.

BACKGROUND: Ornithobacterium rhinotracheal (ORT) infects numerous birds, particularly chickens and turkeys. ORT is an emerging bacterial pathogen of global concern in the poultry industry. As ORT is rapidly spreading throughout commercial poultry, it requires intensive studies of its epidemiology, diagnostic procedures, molecular typing, virulence genes and antimicrobial resistance. OBJECTIVES: The present study was conducted in isolation and identification of ORT from slaughtered turkeys. METHODS: Cleft palate swabs of 200 were collected from slaughtered turkeys and cultured on blood agar. ORT was characterized using biochemical tests and PCR targeting the ORT 16S rRNA gene. Virulence genes of isolates were determined targeting adenylate kinase (adk), copA and virulence-associated protein D (vapD) genes. Additionally, diversity of ORT isolates was performed by enterobacterial repetitive intergenic consensus (ERIC) and RAPD PCR. Disk diffusion was used to determine the antibiotic sensitivity of the isolates. RESULTS: ORT was identified in 23 (11.5%) samples using both the biochemical tests and PCR. The result of detecting virulence genes showed that all the isolates (23: 100%) had the adk gene, whereas two (8.7%) isolates had the copA gene, and seven (30.43%) isolates had the vapD gene. Molecular typing of isolates revealed 21 different patterns by RAPD PCR assay using M13 primer and 20 distinct patterns by ERIC PCR test. Both ERIC and RAPD PCR were distinctive methods for investigating the genetic diversity of ORT isolates. The antibiotic resistance test showed that 18 (78.26%) isolates were resistant to gentamicin, amikacin, cefazolin, streptomycin and penicillin. All isolates (100%) were resistant to cloxacillin and fosfomycin. CONCLUSIONS: This study showed the prevalence of ORT in turkey and high resistance of this bacterium to many common veterinary antibiotics. Moreover, both ERIC and RAPD PCR are distinctive methods for investigating the genetic diversity of ORT isolates. These data may help monitor antibiotic resistance and typing of ORT in epidemiological studies and serve as the foundation for designing region-specific vaccines for future use.

Epitope mapping of bovine viral diarrhea virus nonstructural protein 3.

Six consecutive overlapped coding regions (F1-F6) of whole NS3 molecule of bovine viral diarrhea virus (BVDV) were cloned into pMAL-c2X plasmid vector and expressed in Escherichia coli cells (BL21 strain). The recombinant proteins were then purified by amylose resin to determine the most immunogenic domain(s) of the NS3 molecule. Evaluation of the recombinant proteins was carried out by indirect ELISAs using several bovine sera (previously characterized by virus neutralization test, a commercial ELISA kit, and a newly developed NS3-ELISA) and 6 monoclonal antibodies. The experiments showed that the most immunogenic domain of the NS3 protein was the fourth designed fragment (F4), a 122 amino-acid (AA) region of about 13.5 kDa (nucleotide 1003-1368; residue 335-456). Purified recombinant F4 was also evaluated as single ELISA antigen (F4-ELISA) for the detection of anti-BVDV antibodies in sera of infected cattle. Although this small recombinant fragment of NS3 protein was almost completely soluble and expressed more efficient respect to whole NS3 molecule, it did not show enough sensitivity and specificity to be a proper substitute for NS3 as ELISA antigen to detect specific antibodies against BVDV. However, statistical analyses showed a medium correlation between the results of the developed F4-ELISA and virus neutralization test (kappa coefficient=0.63, P<0.001), with the relative sensitivity and specificity of 78.05% and 84.91%, respectively, suggesting the potential use of this fragment as an ELISA antigen along with other antigens or monoclonal antibody(s) in a competitive ELISA.