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United States Department of Agriculture

Agricultural Research Service

Title: Determination of Minimum Inhibitory Concentrations of Streptomycin for Resistant Salmonella Isolates and Evaluation of a Micro-Broth Dilution System

item Farrington, Leigh - TEXAS A&M UNIVERISTY
item Harvey, Roger
item Droleskey, Robert
item Stanker, Larry

Submitted to: American Association of Veterinary Laboratory Diagnosticians
Publication Type: Proceedings
Publication Acceptance Date: June 1, 1999
Publication Date: N/A

Technical Abstract: We conducted an experiment to determine the minimum inhibitory concentration (MIC) of streptomycin for 56 Salmonella isolates by utilizing a micro-broth dilution technique. The Salmonella isolates were recovered from the lymph nodes and cecal contents of market-age swine at the time of slaughter and were found resistant by disk diffusion to 10ug of fstreptomycin. MIC testing was carried out with the Sensititre susceptibility system for streptomycin which utilizes a microwell concentration gradient of 16 to 800ug/mL. We found that over 80% of the isolates had MICs of 64ug/mL or less of streptomycin. Over 37% of these had MICs of 16ug/mL or less. The highest MIC, observed in about 2% of the isolates, was 256ug/mL of streptomycin. Replicate tests, performed on twelve of the isolates chosen at random, indicated a 100% correlation between runs. Advantages of this system include easy to read results and precoated wells. Disadvantages include cost and inability to test concentrations of streptomycin other than those in wells. We found the Sensititre susceptibility system to be a relatively quick and easy testing procedure that allows for a more accurate determination of streptomycin resistance in Salmonella than that by the disk diffusion method. This system also provides a convenient alternative to the classical broth dilution technique.

Last Modified: 4/22/2015
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