Investigation of Therapeutic and Possible Toxic Effects of Gentamicin and Enrofloxacin in Combination against Experimental Salmonella enteritidis Infection in Embryonated Eggs

The efficacy of the combination of gentamicin and enrofloxacin on the reduction of Salmonella enteritidis contamination rates in embryonated eggs that were experimentally infected was studied. In order to determine the optimum concentration of the combination for egg injection, the antibacterial activities of these antibiotics were tested in vitro against Salmonella enteritidis by the serial broth macrodilution method. The in vitro interaction test of gentamicin and enrofloxacin has indicated that these two antibacterial agents had an additive effect against Salmonella enteritidis. In order to examine the effect of the combination of gentamicin and enrofloxacin in vivo the eggs that were infected with Salmonella enteritidis by temperature-differential dipping were injected in vitro with a minimum inhibitory concentration (MIC) of gentamicin, enrofloxacin, or both drugs. The other two groups were used as positive and negative controls. After the incubation period, hatching was only observed from groups given the antibiotic among the groups infected with Salmonella enteritidis and the percentage of hatching was 35%, 52%, and, 65%in groups given gentamicin, enrofloxacin, or both drugs, respectively. Salmonella enteritidis was isolated from the visceral organs of these chicks after being necropsied following hatching. However, Salmonella enteritidis detection rates in the group treated with the combination was lower than in groups treated with either drug alone. On the other hand, pathologic findings in the combination group were virtually the same in the uninfected and untreated control. These results indicate the value of gentamicin and enrofloxacin in combination for controlling Salmonella enteritidis infection in experimentally infected eggs.