Abstract
Bacterial biofilms are associated with 80–90% of infections. Within the biofilm, bacteria are refractile to antibiotics, requiring concentrations >1,000 times the minimum inhibitory concentration. Proteins, carbohydrates and DNA are the major components of biofilm matrix. Pseudomonas aeruginosa (PA) biofilms, which are majorly associated with chronic lung infection, contain extracellular DNA (eDNA) as a major component. Herein, we report for the first time that L-Methionine (L-Met) at 0.5 μM inhibits Pseudomonas aeruginosa (PA) biofilm formation and disassembles established PA biofilm by inducing DNase expression. Four DNase genes (sbcB, endA, eddB and recJ) were highly up-regulated upon L-Met treatment along with increased DNase activity in the culture supernatant. Since eDNA plays a major role in establishing and maintaining the PA biofilm, DNase activity is effective in disrupting the biofilm. Upon treatment with L-Met, the otherwise recalcitrant PA biofilm now shows susceptibility to ciprofloxacin. This was reflected in vivo, in the murine chronic PA lung infection model. Mice treated with L-Met responded better to antibiotic treatment, leading to enhanced survival as compared to mice treated with ciprofloxacin alone. These results clearly demonstrate that L-Met can be used along with antibiotic as an effective therapeutic against chronic PA biofilm infection.
Highlights
Most of the microorganisms form micro-colonies and produce extracellular matrix to form biofilm
Growth of Pseudomonas aeruginosa (PA) was unaffected in the presence of 0.5 μ M L-Met in Luria broth (Fig. S1a) as well as M9 minimal media (Fig. S1b) under shaking condition (180 rpm) at 37 °C suggesting that the decrease in biofilm formation was not a result of growth inhibition by L-Met
The inhibitory effect of mM concentrations of tryptophan on PA biofilm formation was observed in our study, a similar effect was exerted by L-Met at a much lower concentration[25] (Fig. 1b)
Summary
Most of the microorganisms form micro-colonies and produce extracellular matrix to form biofilm. While the composition of this extracellular matrix might vary slightly in different microbes, biofilms endow the bacteria a unique resistance against antibiotics and other anti-microbial agents This reduced susceptibility may be due to the presence of extracellular polymer matrix which acts as a physical barrier to diffusion (intrinsic) or due to the transfer of extrachromosomal DNA from resistant organisms to susceptible organisms (acquired)[1]. In a mouse model of chronic PA lung infection, L-Met treatment in combination with antibiotics could rescue the mice whereas antibiotic therapy alone was ineffective To our knowledge, this is the first report demonstrating the therapeutic potential of L-Met through its inhibitory effect on the formation and maintenance of PA biofilm
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