Abstract
Mycobacterium abscessus and Mycobacterium chimaera are emerging opportunistic human pathogens causing chronic lung disease in both healthy and immunocompromised individuals. These nontuberculous mycobacteria (NTM) display distinct colony morphologies (rough and smooth), with the rough morphotype considered invasive and unable to form biofilms, whilst the smooth morphotype is non-invasive and biofilm-forming. The colony morphologies and biofilm formation contribute to persistent infections that are difficult to treat and exhibit increased resistance to antibiotics.
The question being addressed is whether the increased AMR and treatment time in NTM infection is due to lack of antibiotic penetration into these NTM biofilms.
In this project the incorporation of front-line antibiotics, clarithromycin (CLAR) and bedaquiline (BDQ) in the individual cells of NTMs (M. abscessus and M. chimaera) grown in biofilm was compared with planktonic growth. The minimum inhibitory concentration (MIC) and minimum biofilm eradication concentration (MBEC) of CLAR and BDQ was used to determine antibiotic susceptibility in both planktonic and biofilm growth. The results demonstrated that the MBEC of BDQ and CLAR was significantly higher (≥16 and 32 times, respectively) compared to the MICs of the NTM isolates, indicating reduced efficacy against biofilms.
Multimodal imaging techniques revealed that both M. abscessus and M. chimaera formed biofilms, regardless of colony morphotype and the morphological effects of the antibiotics on these biofilms were observed. Additionally, NanoSIMS tracked the penetration of BDQ and CLAR within NTM biofilms by analysing the ratio uptake of Br- ions in BDQ and isotopically labelled 13C2H compound in CLAR with organic elements in individual cells. This study revealed the biofilm morphology (specifically the rough morphotype) exhibited the least antibiotic penetration compared with the other NTM isolates. Understanding the biofilm characteristics that contribute to antibiotic resistance could lead to improved management of NTM lung disease.