A Retrospective Study about Antibiotic Susceptibility of the Bacteria Isolated from Broiler Chicken Mortality Referred to Veterinary Laboratory of Kazerun City

Bacterial infections are one of the important causes of casualties and financial losses in the poultry industry. Despite the key role of antibiotics in the treatment of these infectious diseases, a significant increase in antibiotic resistance is considered a threat to societies. Several studies have investigated the antibiotic resistance levels of the different pathogenic bacterial strains in poultry. This study aimed to investigate the bacterial causes of death in chicken farms in Kazeroun City and also to evaluate the drug sensitivity of these bacterial strains.

The samples were obtained from the clinically-affected broiler chickens from 118 industrial poultry farms around Kazeroun City during 2021-2022. The samples were cultured on MacConkey agar and eosin methylene blue (EMB) agar culture media. Then, the antibiotic sensitivity of the samples that were positive for Escherichia coli was evaluated by different antibiotics (enrofloxacin, erythromycin, oxytetracycline, tylosin, gentamicin, doxycycline, danofloxacin, difloxacin, sultrim, florfenicol, flumequine, fosbac, chlortetracycline, colistin, lincospectin, and neomycin).

Among the 118 samples, 106 samples were positive for gram-negative bacteria. 100 of the 106 gram-negative samples were positive for Escherichia coli. All the Escherichia coli-positive samples were resistant to neomycin, chlortetracycline, flumoquine, gentamicin, and tylosin. Also, 99% and 97% of the Escherichia coli-positive samples were resistant to lincospectin and difloxacin, respectively. The highest antibiotic sensitivity of the samples was found to fosbac (94%) and Colistin (90%).

Due to the increase in resistance against common antibiotics, alternative methods are needed to slower drug resistance development and also reduce their resulting mortality. Biosecurity and using acidifiers and probiotics are among the ways to reduce bacterial infections and their need for antibiotic consumption.