The MICs of streptomycin for Salmonella isolates from swine and poultry were determined by a micro-broth dilution technique. The Salmonella isolates were recovered from the lymph nodes and cecal contents of market-age swine and from the cecal contents of poultry at the time of slaughter and were found by disk diffusion to be resistant to 10 μg of streptomycin. MIC testing was carried out with the Sensititre susceptibility system for streptomycin, which uses a microwell concentration gradient of 16 to 800 μg/ml. Results indicated that >80% of the swine isolates had MICs of ≤64 μg/ml, while 51% of poultry isolates exhibited MICs of ≥128 μg/ml. The highest MICs observed in swine and poultry were 256 and 800 μg/ml, respectively. Replicate tests performed on 12 of the isolates chosen at random indicated a 100% correlation between runs. Advantages of this system include easily read results and precoated wells. Disadvantages include the cost and the inability to test concentrations of streptomycin other than those in the wells. We found this micro-broth dilution commercial test kit to provide a relatively quick and easy testing procedure for the determination of streptomycin resistance in Salmonella.

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