Can a 450 nm LED kill streptococcus?

Can a 450 nm LED kill streptococcus? And what is its effective kill rate against streptococci?

The bactericidal effect of 450 nm LED light on streptococci varies from species to species — there is no single, uniform answer.

Current research shows that 450 nm blue light is effective against some streptococci but has very little effect on others. The specific kill rates are as follows:

Streptococcus salivarius: a kill rate of about 52%. The study used specific parameters (an intensity of 10 mW/cm² and a total dose of 75.6 J/cm²).

Streptococcus agalactiae (Group B streptococcus): essentially no effect. Even though this bacterium contains pigments that can absorb blue light, 450 nm light cannot kill it effectively.

Streptococcus mutans: research shows that 450 nm blue light on its own has a limited effect; it generally needs to be combined with a photosensitizer (such as curcumin) in antimicrobial photodynamic therapy (aPDT) to enhance the bactericidal effect.

📌 Key premise: effectiveness depends heavily on the experimental conditions

The kill rate is not a fixed value; it depends heavily on the following variables:

l Light intensity and dose: intensity, irradiation time, and total energy (J/cm²) are critical.

l Bacterial state: planktonic (free-floating) bacteria vs. biofilm.

l Photosensitizer: whether a substance that enhances the light effect has been added.

In summary, it cannot be said across the board that a 450 nm LED effectively kills "streptococci." It has some effect on Streptococcus salivarius (about 52%), is basically ineffective against S. agalactiae, and its effect on other species also depends heavily on the specific experimental conditions.