Correlation between Antibiotics and Herbal Extracts against Multidrug Resistant Gallibacterium anatis Isolated from Layer Chickens

Herbal extracts are potential safe sources of bioactive compounds, antioxidants, antibacterial agents which might be applied in different foods and pharmaceutical products. This study aimed to detect the minimal inhibitory concentrations for antibacterial agents and herbal extracts, Using DAA method (decimal assay for additivity) to determine interaction effect between combination of herbal extracts and antimicrobial agent methods and pathogenicity test of isolated G. anatis. The total incidence of G. anatis was 30% in the examined infected layer chickens. By using antibiotic sensitivity test, the retrieved strains were resistant to doxycycline (98.3%), amoxicillin (95.8%) and gentamycin (95%). But susceptible to erythromycin (95.8%), florfenicol (90%), sulfamethoxazole- trimethoprim (57.5%) and difloxacin (44.17%). The minimum inhibitory concentration of the methanolic herbal extract of rosemary leaves was 64 µg/ml and for Eucalyptus globules was 256 µg/ml, while for cinnamon was 1024 µg/ml. The current study revealed that rosemary gave the best results in combination with amoxicillin at ratios 9:1 and 7:3. Moreover, combination with doxycycline gave acceptable results at ratios 9:1, 8:2 and 7:3 but with florfenicol gave good results at ratios 9:1 and 8:2. Moreover, with erythromycin gave good results at ratios of 9:1 and 8:2. While Eucalyptus  globules mixed with four antibiotics at ratios of 9:1and 8:2 gave the best results with amoxicillin, but for doxycycline was at three ratios (9:1, 8:2 and 7:3). After intra nasal (IN) experimental infection of chicks with Gallibacterium anatis strains, majority of chickens exhibited dullness, depression, decreased feed and water intake, and respiratory signs. Treatment was effective by DAA method by combination between doxycycline and rosemary at ratio 9:1. In addition, combination of amoxicillin and rosemary, between erythromycin with rosemary, and florfenicol with rosemary at 9:1 were very effective.