Mycobacterium tuberculosis survival and biofilm formation studies: effect of d-amino acids, d-cycloserine and its components

d-amino acids play an important role in cell wall peptidoglycan biosynthesis. Mycobacterium tuberculosis d-amino acid oxidase deletion led to reduced biofilm-forming ability. Other recent studies also suggest that the accumulation of d-amino acids blocks biofilm formation and could also disperse pre-formed biofilm. Biofilms are communities of bacterial cells protected by extracellular matrix and harbor drug-tolerant as well as persistent bacteria. In Mycobacterium tuberculosis, biofilm formation or its inhibition by d-amino acids is yet to be tested. In the present study, we used selected d-amino acids to study their role in the prevention of biofilm formation and also if d-cycloserine’s activity was due to presence of d-Serine as a metabolite. It was observed that d-serine limits biofilm formation in Mycobacterium tuberculosis H37Ra (Mtb-Ra), but it shows no effect on pre-formed biofilm. Also, d-cycloserine and its metabolic product, hydroxylamine, individually and in combination, with d-Serine, limit biofilm formation in Mtb-Ra and also disrupts existing biofilm. In summary, we demonstrated that d-alanine, d-valine, d-phenylalanine, d-serine, and d-threonine had no disruptive effect on pre-formed biofilm of Mtb-Ra, either individually or in combination, and d-cycloserine and its metabolite hydroxylamine have potent anti-biofilm activity.