In microorganisms, virulence encompasses traits that facilitate colonization, enable evasion of host defenses, and cause cellular or systemic damage. Virulence-associated factors are central to pathogenesis and may involve activation of stress responses, biofilm formation, and regulation of communication through quorum sensing systems. Because reactive oxygen species (ROS) generated during aPDT can damage proteins, lipids, and nucleic acids, it is reasonable to assume that such effects may alter components—particularly nucleic acids and proteins—linked to microbial virulence. Table 4 summarizes studies that have examined the impact of aPDT on virulence and virulence-associated factors.
Table 4. Overview of studies assessing the effects of aPDT on virulence and related determinants.
aPDT Conditions | Targeted microorganism(s) | Observation(s) | Reference |
TBO, Diode laser, 630 nm | E. coli and P. aeruginosa | Inhibition of protease activity and LPS LAL activity | |
MB, Diode laser, 665 nm | S. aureus | Inhibition of V8 protease, α- and β-hemolysin activity | |
MB, Diode Laser, 670 nm | Porphyromonas gingivalis | Decreased protease activity | |
MB, Diode laser, 630 nm, 3 cycles | S. aureus | Increased biofilm formation efficiency | |
Tetra-Py+-Me, LED, 380-700 nm, 10 cycles | S. aureus | No change in β-hemolysin, lipase, lecithinase, catalase, and bound coagulase activity, decreased activity of free coagulase and enterotoxins A and C. Reduction of the amount of active enterotoxins SE, A, and C | |
TBO, LED, 630 nm | A. baumannii | Decreased expression of genes involved in biofilm formation (csuE, epsA, abal, lpsB), metabolic modulations, and increased expression of genes involved in stress survival (dnaK, recA, blsA) | |
MB, Diode laser, 660 nm | E. faecalis | Decreased biofilm formation efficiency | |
TBO, Diode laser, 635 nm | |||
ICG, Diode laser, 810 nm | |||
PDZ, LED, 660 nm | C. albicans | No change in adherence and biofilm formation ability | |
5-ALA, LED, 630 nm | P. aeruginosa | Decreased expression of rhlA and lasB genes involved in virulence, and lasI, lasR, rhlI, and rhlR involved in QS | |
MB, LED, 660 nm | Serratia marcescens | Decreased production of prodigiosin and hemolysin activity. Reduced biofilm formation efficiency, swrR expression, and mobility at the phenotypical and transcriptional (flhD) levels | |
MB, Red laser light source | P. aeruginosa | Increased expression of the Las QS system and c-di-GMP signaling | |
TAPC, Halogen lamp, 350-800 nm | S. aureus | Decreased biofilm formation efficiency and modifications in biofilm architecture | |
ZnPPc4+, Halogen lamp, 350-800 nm | Decreased biofilm formation efficiency and modifications in biofilm architecture | ||
Cur, N.C., 405 nm | P. aeruginosa | Decreased expression of lasI, lasR, rhlI, and rhlR, involved in QS. Decreased biofilm formation efficiency | |
PhotoACTIVE®, Diode laser, 635 nm | Streptococcus mutans | Increased expression of the virulence factor-encoding gtfB gene, increased biofilm formation, and increased acid production | |
PDZ, LED, 660 nm | C. albicans
| Decreased expression of genes involved in adhesion and biofilm formation (ALS1, HWP1) and oxidative stress response (CAP1, CAT1, and SOD1) depending on the light fluence | |
Cur, LED, 450 nm | Decreased expression of genes involved in adhesion and biofilm formation (ALS1, HWP1) and oxidative stress response (CAP1, CAT1, and SOD1) depending on the light fluence | ||
RB, LED, 515 nm, 15 cycles | S. aureus | Decreased expression of the seb gene coding for a toxin | |
NMB, LED, 632 nm, 15 cycles | S. aureus | Decreased expression of the seb gene coding for a toxin | |
ICG, Diode laser, 810 nm | A. baumannii, P. aeruginosa, and S. aureus | Decreased expression of abaI, agrA, and lasI QS genes, and reduced biofilm formation ability | |
Cur, LED, 450 nm, 10 cycles | S. pyogenes | Decreased biofilm formation efficiency | |
MB, LED, 633 nm | C. albicans
| No change in biofilm formation in AIDS patients | |
KI, LED, 633 nm | |||
PDZ, LED, 660 nm, 5 cycles | C. albicans | In vivo decreased expression of virulence (ALS1, EFG1, LIP3), antioxidant (CAP1, SOD1), and ergosterol biosynthesis (ERG1, ERG3, ERG11, and ERG25) genes, increased expression of antioxidant gene CAT1, unchanged expression of virulence EFG1, and LIP3 genes | |
TMPyP, Diode laser, 445 nm | E. faecalis | Increased expression of genes involved in stress survival (dnaK, σV, relA) and virulence (ace, fsrC, gelE) | |
MB, Diode laser, 635nm, 15 cycles | A. baumannii | Decreased biofilm formation efficiency | |
TBO, N.C., 635 nm | S. aureus | Decreased biofilm formation efficiency | |
PDZ, LED, 660 nm, 10 cycles | C. albicans
| Increased expression of the SOD1 gene, involved in stress survival, reduced expression of the antioxidant CAP1 and ergosterol biosynthesis ERG11 genes | |
Cur, LED, 660 nm, 10 cycles | Reduced expression of the ERG11 gene involved in ergosterol biosynthesis | ||
TMAP4+, N.C. | E. coli, S. aureus | Decreased biofilm formation efficiency in mono- and dual-species biofilms | |
MB + KI, LED, 633 nm | C. albicans | No change in expression of the CAT1 gene involved in oxidative stress response, and the HWP1 gene involved in adhesion and biofilm formation | |
ZnPPc4+, Halogen lamp, 380-700, 10 cycles | S. aureus | Unchanged β-hemolysin, lipase, and lecithinase activity | |
PDZ, LED, 5 cycles | C. albicans | In vivo decreased expression of genes involved in stress survival and biofilm formation in the infected mice model | |
NMB, N.C., 632 nm | S. aureus
| Decreased SEA, SEB, SEC, and SED enterotoxins expression. Decreased superantigenic TSST-1 expression and activity. | |
RB, N.C., 515 nm | Decreased expression and activity of SEA, SEB, SEC, and SED enterotoxins. Decreased superantigenic TSST-1 expression and activity. Ex vivo decreased SEA enterotoxin transcript and protein levels. In vivo decreased SEA enterotoxin levels in infected mouse model. | ||
CDsGEN-IMP, UVA light, 320 nm | P. aeruginosa
| Decreased expression of QS (lasI, lasR, rhlI, and rhlR) and virulence (lasB, lasA, rhlA, and phzM) genes | |
Abbreviations: 5-ALA: 5-aminolevulinic acid; Cur: curcumin; c-di-GMP: cyclic diguanylate; ICG: indocyanine green, KI: potassium iodide; LAL: limulus amoebocyte lysate; LED: light-emitting diode; LPS: lipopolysaccharide; MB: methylene blue; NMB: new methylene blue; PDZ: Photodithazine®; QS: quorum-sensing; RB: rose bengal; SEA: staphylococcal enterotoxin A; SEB: staphylococcal enterotoxin B (SEB), SEC: staphylococcal enterotoxin C; SED: staphylococcal enterotoxin D; TAPC: 5,10,15,20‐tetrakis[4‐(3‐N,N‐dimethylaminopropoxy)phenyl]chlorin; TBO: toluidine blue; TMAP4+: 5,10,15,20-tetra(4-N,N,N-trimethylammoniophenyl)porphyrin; TMPyP: 5,10,15,20-tetrakis (1methyl-4-pyridinium) porphyrin tetra(p-toluenesulfonate); TSST-1: toxic shock syndrome toxin-1. | |||