Susceptibility Testing of Mycobacterium frederiksbergense Strains Isolated from Alfalfa Plants against Antibacterial Compounds

Mycobacteria constitute vast population of bacteria that are found in animals, plants and outer environments. Tuberculosis mycobacteria are a group that causes very dangerous diseases for human and animals. Nontuberculous mycobacteria are mainly environmental and are pathogenic in certain circumstances. There are reports of finding mycobacteria in plant tissues, which can be effective to survey in case of different infectious disease issues. In a previous study, we found mycobacteria strains in alfalfa vascular tissues and identified them to species level using 16S rRNA gene sequence analysis, causing some symptoms in plant tissues and aerial parts. As these rapidly growing mycobacteria (RGM) have the potential to cause opportunistic infections in human tissues, one of the most important issues for dealing with these agents is to find the best and most effective drug to treat them. Here, we conducted some assays to investigate the MIC of 7 antibiotics and two antibacterial agents against eight Mycobacterium frederiksbergense alfalfa isolated strains, in order to find the susceptible and resistant ones. We performed susceptibility testing based on broth microdilution method using Mueller hinton broth as the medium used. Results were different among the strains and different resistant and susceptible reactions were observed among different strains against each drug tested, but ethambutol resulted in similar high MIC for all of them. This variability could be attributed to many factors, such as plant tissue composition and developmental stage from which the strains have been isolated, existence and nature of drug targets and other factors such as test conditions and environmental causes. These results can bring us some insights into design and develop new drugs for treating these kinds of organisms, based on the variations in susceptibility reactions and the plant composition effect on them. Corresponding author. M. Mousaviehzadeh, S. Sardari