Investigation of biofilm formation and clarithromycin susceptibility in Mycobacterium fortuitum isolates

Kurumanastırlı Berke, Investigation of Biofilm Formation and Clarithromycin Susceptibility in Mycobacterium fortuitum Isolates, Hacettepe University Faculty of Medicine, Department of Medical Microbiology, Thesis in Medical Microbiology, Ankara, 2024. Mycobacterium fortuitum is a rapid growing nontuberculous mycobacteria (NTM) species. This species which is very common in the environment, has been associated with nosocomial infections, especially in immunosuppressed patients. M. fortuitum can form biofilm on various surfaces (surgical instruments, implants, etc.). Biofilm is a surface formation consisting of a mucopolysaccharide layer and a population of microorganisms. Specialized cells within the biofilm which have high antimicrobial minimum inhibitory concentration (MIC) values may cause treatment failures. Mutations in the erm (39) gene have been associated with inducible macrolide resistance against clarithromycin, which is a member of the macrolide antibiotic group used in the treatment of M. fortuitum infections. In our study, we aimed to investigate clarithromycin susceptibility by standard broth microdilution method, biofilm formation and erm (39) gene mutations in 40 M. fortuitum isolates. While all isolates were found to be susceptible at the 72 nd hour, 65% of the isolates were reported as inducible macrolide resistance on day 14. The crystal violet method was used to investigate biofilm formation and two isolates (5%) were reported as "moderate biofilm positive" and 38 isolates (95%) as "weak biofilm positive". Mutations in the erm (39) gene were investigated using the Sanger sequencing method. The erm (39) gene was found positive in PCR in all isolates. There are a limited number of studies on susceptibility and biofilm testings of M. fortuitum in the world and in our country as well. Thanks to our findings, we aim to contribute to a more conscious and effective treatment principle in M. fortuitum infections.