Evaluating the antibiotic resistance pattern of Salmonella isolated from a number of laying poultry flocks in the northwest of the country during 2021 and investigating its relationship with the performance of the mentioned farms

Infection with the Salmonella genus of bacteria causes chronic and acute diseases in poultry leading to significant economic losses to the poultry industry. The aim of the present study was to evaluate the antibiotic resistance pattern of Salmonella serotypes isolated from a number of laying poultry flocks in the northwest of the country and to investigate its relationship with the performance of those farms. Eighty samples were taken from 20 flocks suspected of salmonellosis .The samples were cultured in selective and differential cultures of Salmonella. After isolation of Salmonella serotypes, the antibiogram test was performed to determine the antibiotic sensitivity. In order to check the performance of suspicious flocks, the history of the flock was obtained and the amount of mortality and production drop was calculated by statistical methods.The results indicated that 40% of the flocks were positive in terms of the presence of Salmonella, with 30% of the flocks affected by Salmonella gallinarum, 5% by Salmonella enteritidis, and 5% by concurrent presence of both Salmonella enteritidis and Salmonella gallinarum. The highest antibiotic sensitivity of Salmonella serotypes was recorded from fosfomycin and danofloxacin with a frequency of 100% and soltrim with a frequency of 78.6%. The highest antibiotic resistance was observed against erythromycin with a frequency of 75% and chlortetracycline with a frequency of 53.6%. Based on the results, there was a statistically significant difference in  the amount of flock mortality and production drop between Salmonella negative and Salmonella positive herds (p<0.05). Also, more vigilant use of antibiotics is required due to the high levels of resistance shown by Salmonella against various antibiotic drugs.