Can Gram-Negative Bacteria Develop Resistance to Antimicrobial Blue Light Treatment?

Area of Science:

• Microbiology
• Photomedicine
• Antimicrobial Resistance

Background:

• Antimicrobial blue light (aBL) is generally considered low risk for inducing bacterial resistance.
• Its multitarget mechanism is thought to prevent adaptation.
• However, the potential for tolerance development in Gram-negative bacteria requires investigation.

Purpose of the Study:

• To determine if Gram-negative bacteria can develop tolerance to aBL.
• To investigate the stability of any observed tolerance.
• To explore potential genetic mechanisms underlying aBL tolerance.

Main Methods:

• Exposure of *Escherichia coli*, *Klebsiella pneumoniae*, and *Pseudomonas aeruginosa* to aBL.
• Evaluation of bacterial survival and adaptation post-treatment.
• Analysis of *E. coli* mutants deficient in specific genes (*tolC*, *tolA*, *umuD*, *recA*) to identify tolerance mechanisms.

Main Results:

• Representative Gram-negative bacteria, including *E. coli*, *K. pneumoniae*, and *P. aeruginosa*, demonstrated the capacity to develop tolerance to aBL.
• The acquired tolerance was observed to be a stable characteristic.
• Mutant assays suggested potential roles for *tolC*, *tolA*, *umuD*, and *recA* in the development of aBL tolerance.

Conclusions:

• Gram-negative bacteria can develop stable tolerance to antimicrobial blue light (aBL).
• This finding challenges the assumption of low resistance risk associated with aBL.
• Further research into the identified genetic mechanisms is warranted to understand and potentially mitigate aBL tolerance.