In vitro and in vivo susceptibility of Salmonella spp. isolated from broiler chickens.

Salmonellosis is the most important zoonotic disease, causing diarrhea and systemic infections. Due to poor management in antibiotic consumption, microbial resistance has increased in the treatment of zoonotic diseases. This study was conducted to evaluate the antimicrobial susceptibility of Salmonella spp. isolated from day-old broiler chickens which were referred to a private laboratory in Mazandaran-a province in the north of Iran-from 2008 to 2010. After harvesting the samples from the yolk sac, liver, and intestine of chickens, intestinal samples were transferred to selenite F and then incubated at 43 °C for 12-16 h. A loopful from selenite F and samples of liver and yolk sac were streaked on XLD and S.S agars. After incubation, the suspected colonies were inoculated into TSI agar for biochemical confirmation. The disk diffusion method on Muller Hinton agar was used to determine the susceptibility to antimicrobial agents. Because of the predominant use of enrofloxacin, sulfadiazine + trimethoprim, and flumequine for controlling Salmonella and Escherichia coli infections in the first week of broilers brooding in Iran, these three antibiotics were used in the in vivo study. From day 2 and continuing for 4 days, antibiotics were administrated in water, and after 10 days, samples from the liver, heart, and intestine were taken for isolation of Salmonella. In antimicrobial resistant tests, the most susceptible antibiotics were chloramphenicol, cefotaxime, and sulfadiazine + trimethoprim. The antimicrobial resistance to enrofloxacin, flumequine, colistin, and neomycin were 6.6, 11.6, 21.6, and 33.3 %, respectively. The results showed that 12 parties of broiler chickens were infected with paratyphoid salmonellae and the in vivo study showed that enrofloxacin and sulfadiazine + trimethoprim had the best and the weakest performance, respectively.