2583. Antimicrobial Resistance Profile of Mycobacterium simiae and Treatment Trends from a Tertiary Care Center in Lebanon

BACKGROUND: Mycobacterium simiae is a rare non-tuberculous mycobacterium (NTM) that is most identified in some Middle Eastern countries. It is unclear why this NTM is geographically restricted. The pathogen can either be a mere colonizer or cause significant morbidity. Patients with M. simiae infection require prolonged treatment with a combination of 3 antimicrobials. Drug resistance among M. simiae isolates can complicate the course of treatment. However, the correlation between in vitro resistance and clinical response is unknown. We aimed to report the susceptibility profile of M. simiae isolates from our institution and the prescribed treatments. METHODS: We conducted a retrospective study of M. simiae isolates from the American University of Beirut Medical Center (AUBMC) over 19 years. All isolates were cultured at AUBMC using the Lowenstein-Jensen media and the BacT/ALERT system then referred for speciation and susceptibility testing at Mayo Clinic, MN, USA. RESULTS: We included 72 isolates that underwent susceptibility testing from 59 patients. Most isolates were obtained from sputum samples (61.1%) and the rest from bronchoalveolar lavages (BAL). The highest rates of susceptibility were to clarithromycin (84.7%) and amikacin (73.6%). All isolates were resistant to ciprofloxacin, streptomycin, doxycycline, and minocycline (Graph 1). Median minimal inhibitory concentrations (MIC) for clarithromycin and amikacin for susceptible isolates were 8 and 16 mcg/mL respectively. Clofazimine susceptibility was performed on only 16 isolates, 10 of which had an MIC ≤ 0.06 mcg/mL and the highest was 0.25 mcg/mL. Empiric antimicrobial therapy was given to 30% of patients but was inappropriate in 80% of cases. Targeted therapy was given to 40.9% of patients. Most received triple therapy with clarithromycin (95.8%) and clofazimine (41.7%) being the most common agents. The median duration of treatment was 12 months with the longest duration being 11 years. Microbiologic cure was achieved in 73.9% of the 23 patients who underwent repeated testing. Susceptibility of Mycobacterium simiae isolates according to the CLSI breakpoints. [Figure: see text] TMP-SMX, trimethoprim-sulfamethoxazole. *Clofazimine was not included in this graph as there is no consensus on breakpoints for susceptibility for NTM. All our isolates had MICs ≤ 0.25 mcg/mL which is lower than breakpoints used in other studies. CONCLUSION: M. simiae exhibits resistance to most available antimycobacterial agents. Further research is needed to understand resistance mechanisms of this organism and correlate in vitro and in vivo findings. DISCLOSURES: Souha S Kanj, MD, Gilead: Advisor/Consultant|Menarini: Advisor/Consultant|MSD: Advisor/Consultant|Pfizer: Advisor/Consultant