Abstract:
Mycobacteria form lipid-rich biofilms that restrict the efficacy of antimicrobial chemotherapy, possibly
necessitating the use of lipophilic antibiotics. In the current study, the activity of one such agent,
clofazimine, against Mycobacterium tuberculosis and Mycobacterium smegmatis planktonic cells and
biofilms was investigated. Minimum inhibitory concentrations (MICs) of clofazimine were determined
for planktonic cultures, whilst minimum bactericidal concentrations (MBCs) were determined for
planktonic, biofilm-producing and biofilm-encased organisms using standard bacteriological proce-
dures. The effects of clofazimine on biofilm formation and the stability of pre-formed biofilm were
measured using a crystal violet-based spectrophotometric procedure. In the case of M. smegmatis,
clofazimine was found to be active against planktonic phase (MICs and MBCs of 2.5 mg/L and >20 mg/L,
respectively) and biofilm-producing organisms (MBC of 2.5 mg/L); clofazimine demonstrated greater
activity against M. tuberculosis, corresponding values of 0.06, 5 and 0.3 mg/L. Although clofazimine
inhibited biofilm production both by M. tuberculosis and M. smegmatis (P < 0.05 at 0.07 mg/L and
0.3 mg/L, respectively) and appeared to reduce the pre-formed M. tuberculosis biofilm, addition of
antimicrobial agent to pre-existing biofilm matrices failed to kill biofilm-encased organisms. In
conclusion, clofazimine is more effective against M. tuberculosis than against M. smegmatis, exhibiting
bactericidal activity both for actively growing and slowly replicating bacilli but not for non-replicating
organisms of both species.
