Insulin modulation of microbial biofilm formation in response to various amino acids

The focus of this report is to assess the role that amino acids, together with insulin, play in adherence to plastic and latex under various temperatures and bacterial growth stages. Various gram-negative bacteria were grown in minimal medium to either logarithmic (log) or stationary (stat) growth phase. The adherence of washed cells to plastic or latex was determined using multiwell plates or 6-mm latex squares at 22°C or 37°C in a buffer containing physiological insulin levels (20 or 200 μU/ml), with and without the amino acids tested (10−1 to 10−3 M). The controls were buffer alone, insulin alone, and amino acid alone. Only seven of the 20 amino acids tested modulated adherence to plastic and/or latex. No global pattern based on the amino acid structure was evident. Insulin did not affect adherence in the presence of alanine, valine, aspartic acid, glutamine, and lysine. Arginine (Arg; 10−1 to 10−2 M) inhibited adherence to latex (but not plastic) and dispersed preformed biofilms for all organisms except Acinetobacter baumannii. At a biofilm-permissive Arg concentration (10−3 M), insulin (200 µU) restored the inhibitory effect of Arg. These findings may provide insights into material composition modifications that could have clinical and industrial applications.