D-Amino acids do no inhibit biofilm formation in Staphylococcus sp.

Abstract

D-amino acids are responsible for cell wall re-modelling in Staphylococcus and are capable of inhibition and mature biofilm disassembly. Staphylococcus aureus and Staphylococcus epidermidis are recognised as recurrent nosocomial pathogens and a common cause of biofilm-associated infections. The combination of amino acids used in the study consisted of d- and l- isomers of tyrosine, methionine, tryptophan and phenylalanine. A semiquantitative microplate crystal violet assay was used to assess the effect of amino acids on biofilm development. Biofilm viability staining using fluorescent microscopy was performed to assess the effect of the amino acid mixtures on biofilm development on submerged surfaces. None of the amino acids when tested individually or as a mixture could reduce biofilm formation. However, at the highest concentration tested 25 mmol 1−1 equimolar D-amino acid mixture of tryptophan, phenylalanine, tyrosine and methionine caused a considerable biofilm inhibition in three Staphylococcus strains. Microscopy analysis showed that initial surface attachment remained unaffected at 25 mmol 1−1 mixture of d-amino acids but bacteria did not proceed to form mature biofilms. This suggests inhibition of protein synthesis or a lack of polysaccharide extracellular adhesin formation as no aggregates were observed. The reported bioactivity of D-amino acid on biofilm development and disassembly has been conflictual. It has been established that D-amino acids are incorporated in the bacterial cell wall suggesting they play a role in the complexity of biofilm lifecycle. However, our study indicates that they play no direct role in the inhibition of biofilm formation in Staphylococcus.

Tryptophan interferes with the quorum sensing and cell surface hydrophobicity of Staphylococcus aureus: a promising approach to inhibit the biofilm development

“…The result showed no significant variation in the expression of 16S rRNA gene between the tryptophan treated and untreated cells (data not shown). In support of this observation, we noticed that under the influence of D-tryptophan, the production of PIA by S. aureus was reduced considerably that resulted in the inhibition of microbial biofilm formation (Szank et al 2019). It was observed that PIA could hold the complex biofilm matrix architecture efficiently (Vuong et al 2004).…”