Efficacy of gamithromycin againstOrnithobacterium rhinotrachealein turkey poults pre-infected with avian metapneumovirus

Abstract

Ornithobacterium rhinotracheale is an avian respiratory pathogen that affects turkeys. The objective of this study was to evaluate the clinical efficacy of gamithromycin (GAM) against O. rhinotracheale in turkeys. The birds were inoculated oculonasally with 10 8 colony-forming units (cfu) of O. rhinotracheale, preceded by infection with avian metapneumovirus. In addition to a negative (CONTR−) and a positive control group (CONTR+) there were two treated groups administered GAM (6 mg/kg) either subcutaneously (GAM SC) or orally (GAM PO) by administration as a single bolus at one-day post-bacterial infection (p.b.i.). From the start of the avian metapneumovirus infection until the end of the experiment, the turkeys were examined clinically and scored daily. In addition, tracheal swabs were collected at several days p.b.i. Necropsy was performed at 4, 8 and 12 days p.b.i. to evaluate the presence of gross lesions, and to collect trachea and lung tissue samples and air sac swabs for O. rhinotracheale quantification. The clinical score of the GAM SC group showed slightly lower values and birds recovered earlier than those in the GAM PO and CONTR+ groups. O. rhinotracheale cfus were significantly reduced in tracheal swabs of the SC group between 2 and 4 days p.b.i. At necropsy, CONTR+ showed higher O. rhinotracheale cfu in lung tissues compared to the treated groups. Moreover, at 8 days p.b.i. only the lung samples of CONTR+ were positive. In conclusion, the efficacy of GAM against O. rhinotracheale was demonstrated, especially in the lung tissue. However, the PO bolus administration of the commercially available product was not as efficacious as the SC bolus.ARTICLE HISTORY

Ornithobacterium rhinotracheale: An Update Review about An Emerging Poultry Pathogen

“…It is known that ORT easily acquires antimicrobial resistance and there is great inconsistency about sensitivity/resistance distinction, which may depend on the phenotypic profile of the strain and the geographical origin. [69,73,76]. There is no specific standard for the ORT antimicrobial susceptibility profile and the CLSI recommendations for fastidious gram-negative microorganisms are usually applied [76,77].…”

“…[69,73,76]. There is no specific standard for the ORT antimicrobial susceptibility profile and the CLSI recommendations for fastidious gram-negative microorganisms are usually applied [76,77].…”

“…Several antimicrobial agents, including those most recently developed, are becoming inefficient against ORT, reinforcing the hypothesis of continuous resistance transference among them [69,73,76], with an increased resistance for different classes of drugs [74].…”

“…Regarding the susceptibility profile of ORT, studies in Belgium have shown sensitivity to tiamulin [73], florfenicol [78], and gamithromycin [76], and resistance to ampicillin, ceftiofur, tetracycline, cotrimoxazole (sulfamethoxazole + trimethoprim), and enrofloxacin [73]. A study from Mexico has shown sensitivity to amoxicillin, enrofloxacin, and oxytetracycline, and resistance to gentamicin and fosfomycin [77].…”

“…Resistance to ampicillin, ceftiofur, tetracycline, cotrimoxazole, and enrofloxacin has also been observed in the Netherlands [79], the United States [80], and Hungary [81]. Although resistance to enrofloxacin and tetracycline was observed in several countries, isolates from Iran were intermediately susceptible to this agent [54] and sensitive in most countries [76]. In addition, isolates from Pakistan were susceptible to tetracycline [57].…”