Biofilms of Pathogenic Nontuberculous Mycobacteria Targeted by New Therapeutic Approaches

Abstract

Microbial infections of the cornea are potentially devastating and can result in permanent visual loss or require vision-rescuing surgery. In recent years, there has been an increasing number of reports on nontuberculous mycobacterial infections of the cornea. Challenges to the management of nontuberculous mycobacterial keratitis include delayed laboratory detection, low index of clinical suspicion, poor drug penetration, slow response to therapy, and prolonged use of antibiotic combinations. The ability of nontuberculous mycobacteria to evade the host immune response and the ability to adhere and to form biofilms on biological and synthetic substrates contribute to the issue. Therefore, there is an urgent need for new antimicrobial compounds that can overcome these problems. In this study, we evaluated the biofilm architectures for Mycobacterium chelonae and Mycobacterium fortuitum in dynamic flow cell chamber and 8-well chamber slide models. Our results showed that mycobacterial biofilms were quite resistant to conventional antibiotics. However, DNase treatment could be used to overcome biofilm resistance. Moreover, we successfully evaluated a new antimicrobial compound (AM-228) that was effective not only for planktonic mycobacterial cells but also for biofilm treatment and was compared favorably with the most successful “fourth-generation” fluoroquinolone, gatifloxacin. Finally, a new treatment strategy emerged: a combination of DNase with an antibiotic was more effective than an antibiotic alone.

Identification of Bicarbonate as a Trigger and Genes Involved with Extracellular DNA Export in Mycobacterial Biofilms

“…hominissuis tolerance of the antimicrobials. Since that report, another study also recently described effective cotreatment of M. chelonae and M. fortuitum biofilms with DNase I and antimicrobial agents (24), further demonstrating the importance of eDNA in NTM biofilms.…”

Curcumin, an antibiotic resistance breaker against a multiresistant clinical isolate of Mycobacterium abscessus

“…For the assessment of biofilm‐forming ability, M. abscessus 29904 was grown for 3–4 days in supplemented Middlebrook broth, standardized to 1 × 10 6 colony forming units/ml at optical density (OD) 600 = 0.1 (Aung et al, ), inoculated (200 μL) in 96‐well, flat–bottomed, sealed polystyrene plates, and incubated for 2, 4, and 8 days at 37 °C (Hall‐Stoodley & Lappin‐Scott, ). Biofilm formation was evaluated by measuring the biomass at each time point (Di Giulio, Traini, Sinjari, Nostro, Caputi, & Cellini ); after removing the planktonic phase, wells were washed with PBS, dried, and stained with 0.1% safranin solution (1 min).…”

Atypical Mycobacterial Keratitis: A Negligent and Emerging Thread for Blindness

“…Studies have shown that M. fortuitum and M. chelonae readily form drug-resistant biofilms, irregular finger-like projections and microcolonies (Figure-2), suggesting a probable cause of poor treatment compliance to conventional antibiotics 48 . Studies have concluded that there is a significant eDNA release with M. fortuitum and chelonae biofilms, which protect the organisms from the antibiotics: however, adding DNase can boost the efficacy of available antibiotics 33,48,49 .…”

“…Studies have shown that M. fortuitum and M. chelonae readily form drug-resistant biofilms, irregular finger-like projections and microcolonies (Figure-2), suggesting a probable cause of poor treatment compliance to conventional antibiotics 48 . Studies have concluded that there is a significant eDNA release with M. fortuitum and chelonae biofilms, which protect the organisms from the antibiotics: however, adding DNase can boost the efficacy of available antibiotics 33,48,49 . There was a pioneer report to show that AMB keratitis is a biofilm mode of growth in an experimental mouse keratitis model and suggested that poor clinical outcomes of AMB infections might be due to its presence of biofilm matrix causing a barrier for antibiotic penetration and resistance 33 .…”

“…Studies suggest that eDNA can increase gene expressions which could lead to antimicrobial resistance 46 . There were reports shown that eDNA is a major component of the mycobacterial biofilm matrix and DNase 1 aids the efficacy of antibiotics in treating infections in in vitro 48,49 .…”