High-dose nitric oxide as a potential new therapeutic agent against Mycobacterium abscessus

Mycobacterium abscessus (MAB) is an emerging multidrug resistant nontuberculous mycobacterium (NTM) with high prevalence in cystic fibrosis (CF) patients and limited treatment options. High-dose NO has been shown to eradicate a variety of bacterial species in preclinical models. In this study, we investigate whether high-dose NO exhibits antibacterial activity against drug-resistant MAB clinical strain in vitro. A continuous horizontal-flow NO delivery device, previously described by Ghaffari et al., Nitric Oxide 12(2005), was used to deliver NO at specific doses. To validate the efficacy of the device, Pseudomonas aeruginosa (P. aeruginosa) and E. coli (DH5α), previously shown to be sensitive to NO, were treated at 200ppm NO. Next, MAB inoculated at 106 CFU/ml in 0.85% saline or Middlebrook 7H9 medium was treated with medical air (control), 250ppm, or 400ppm NO for up to 10hr. Viable bacteria were assessed through quantitative microbial cultures on 7H11 agar and CFU analyses. The minimum bactericidal concentration (MBC) was defined as NO concentration (ppm) x duration of exposure (hr) or Total ppm.h of NO required to achieve 99.9% bacterial kill. At 200ppm continuous NO exposure, a MBC of 800 ppm.h and 600 ppm.h was observed for P. aeruginosa and E. coli in saline, respectively. MAB in saline exhibited a MBC of 1500 ppm.h and 800 ppm.h at 250ppm and 400ppm continuous NO exposures, respectively. These findings demonstrate the in vitro potency of NO against drug-resistant MAB and suggest that evaluation of NO therapy as a potential antibacterial agent for infections caused by MAB is warranted.