“…This could be particularity related to the concentration of endogenous photosensitive substances (e.g., porphyrin and flavin derivatives), which may vary between bacterial strains of the same species. [6][7][8][9] Our results agree with other studies where aPDI/aBL therapies lead to the effective eradication of XDR Gram-negative bacteria in hospital-acquired infections, in addition to the synergistic activity that can be achieved by associating photoinactivation and clinical use of antimicrobials. 6,8,10,13 In fact, Wozniak et al 11,26 demonstrated the usefulness of the synergistic effect of different antibiotics (colistin, tetracyclines or imipenem), with sublethal doses of irradiation (63.6 J/cm 2 ) against XDR E. cloacae, K. pneumoniae and A. baumannii strains.…”