Isoniazid resistance of exponentially growing Mycobacterium smegmatis biofilm culture.

Biofilm growth of Mycobacterium smegmatis was found to be unaffected at an isoniazid concentration that inhibited growth of planktonic bacilli (i.e. at isoniazid minimum inhibitory concentration=10 microg ml(-1)). Significant growth (50% of drug-free control) of biofilms was observed at up to 40 microg ml(-1) and the MIC for biofilm growth showed an increase to up to 80 microg ml(-1) isoniazid. Thus, the biofilm growth modus appears to be a strategy for replicating bacilli to evade the onslaught of antibacterials.