ARS | Publication request: DETERMINATION OF MINIMUM INHIBITORY CONCENTRATIONS OF STREPTOMYCIN FOR RESISTANT SALMONELLA ISOLATES IN SWINE AND POULTRY USING A MICRO-BROTH DILUTION SYSTEM

Submitted to: Journal of Food Protection
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 1, 2001
Publication Date: N/A

Interpretive Summary: The use of antibiotics in swine and poultry production has raised concerns that the bacteria once killed by the antibiotics may be developing resistance to them. The purpose of the present study was to determine the highest dose of the antibiotic streptomycin required to kill streptomycin- resistant Salmonella from poultry and swine. Results showed that 80% of the swine isolates were sensitive to 64 ug/ml streptomycin while 51% of poultry were sensitive to 128 ug/ml of streptomycin. These levels are much lower than currently recommended dosage rates for streptomycin in swine and poultry. Therefore, short-term administration of streptomycin should be effective for Salmonella control in these animals when used properly and according to label directions. In performing these assays, we used a commercially available test kit for streptomycin resistance, which we found to be reliable, reproducible and easy to run. However, using this commercial test kit is more expensive than other available methods.

Technical Abstract: The minimum inhibitory concentration (MIC) of streptomycin for Salmonella isolates from swine and poultry were determined utilizing a micro-broth dilution technique. The isolates were recovered from the lymph nodes and cecal contents of market-age swine and cecal contents of poultry at the time of slaughter and were found resistant by disk diffusion to 10 ug of streptomycin. MIC testing was carried out with the Sensititre susceptibility system for streptomycin which utilizes a micro-well concentration gradient of 16 to 800 ug/ml. Results indicated that over 80% of the swine isolates had MIC's of 64 ug/ml or less while 51% of poultry isolates exhibited a MIC of 128 ug/ml or greater. The highest MIC's observed in swine and poultry were 256 and 800 ug/ml, respectively. Replicate tests, performed on twelve of the isolates chosen at random, indicated a 100% correlation between runs. Advantages of this system include easily read results and pre-coated wells. Disadvantages include cost and inability to test concentrations of streptomycin other than those in the wells. This system also provides a convenient alternative to the classical broth dilution technique.