Development of a new medium for rapid antibiotic susceptibility testing of enteric bacteria.

Many rapid antibiotic susceptibility tests that have been developed so far cannot be used widely, particularly in developing countries, because of their many difficulties and disadvantages. A simplified method has been developed for disc diffusion agar antimicrobial testing of enteric bacteria which gives the result in 4,5-5,5 hours, easy to perform and inexpensive. The procedure is based on the principle of using phenol red as an indicator in a medium called M. This method depends upon the mechanism which detects the acid formed by the bacteria, by the change of the color of the pH indicator in the medium. The susceptibility of 271 different isolates of enteric bacteria (E. coli, Klebsiella and Enterobacter) to Ampicillin, Aztreonam, Sulbactam/Ampicilin, Amikacin, Gentamicin, Trimethoprim-Sulfamethoxazole, Ceftazidim, Ciprofloxacin, Piperacilin-Tazobactam, Imipenem, Cefuroxime and Nalidixic acid is examined by this new "Rapid Color Change Test". The procedure was run in paralel with conventional disc diffusion agar techniques. Most of the errors were minor. But the minor error rate, major error rate, and very major error rate for all bacterial isolates tested were 4.2%, 0.6% ve 0.8% respectively. And the overall agreement between two methods has been found to be 95.1 percent. The modified agar diffusion method (M medium) for rapid antimicrobial susceptibility testing of individual enteric bacteria isolates (E. coli, Klebsiela and Enterobacter) was found to be superior to the conventional agar diffusion method since it was easier to read and required considerably less set up time.