Photodynamic therapy as a novel antimicrobial strategy against biofilm-based nosocomial infections: study protocols

Antibiotic Combination Therapy: A Strategy to Overcome Bacterial Resistance to Aminoglycoside Antibiotics

After the first aminoglycoside antibiotic streptomycin being applied in clinical practice in the mid-1940s, aminoglycoside antibiotics (AGAs) are widely used to treat clinical bacterial infections and bacterial resistance to AGAs is increasing. The bacterial resistance to AGAs is owed to aminoglycoside modifying enzyme modification, active efflux pump gene overexpression and 16S rRNA ribosomal subunit methylation, leading to modification of AGAs' structures and decreased concentration of drugs within bacteria. As AGAs's side effects and bacterial resistance, the development of AGAs is time-consuming and difficult. Because bacterial resistance may occur in a short time after application in clinical practice, it was found that the antibacterial effect of the combination was not only better than that of AGAs alone but also reduce the dosage of antibiotics, thereby reducing the occurrence of side effects. This article reviews the clinical use of AGAs, the antibacterial mechanisms, the molecular mechanisms of bacterial resistance, and especially focuses a recent development of the combination of AGAs with other drugs to exert a synergistic antibacterial effect to provide a new strategy to overcome bacterial resistance to AGAs.

Photodynamic therapy using methylene blue, combined or not with gentamicin, against Staphylococcus aureus and Pseudomonas aeruginosa

Antimicrobial photodynamic therapy (a-PDT), combined or not with antibiotics, constitutes a promising therapy for superficial infections caused by bacteria implicated in multidrug resistance processes. We compared the efficacy of aPDT using the photosensitizer methylene blue (MB), combined or not with the antibiotic gentamicin (GN), against Staphylococcus aureus and Pseudomonas aeruginosa. Different concentrations of MB (0.03-7000 μg/mL), with or without GN (1-20 μg/mL), were added to planktonic cultures or biofilms and the samples irradiated with a LED lamp (λ 625 nm, 7 mW/cm², 18 J/cm²). The number of viable bacteria in the samples and in corresponding nonirradiated controls was quantified by counting colony-forming units to evaluate the individual effects of MB, GN, and irradiation. MB-aPDT resulted in significant bacterial photoinactivation. The combination of GN and MB-aPDT exerted a synergistic bactericidal effect against planktonic cultures of S. aureus and P. aeruginosa. This combination did not significantly alter the photoinactivating effect of MB against S. aureus biofilms, but exerted a positive bactericidal effect against P. aeruginosa biofilms. These results underscore the need for further clinical studies of this therapeutic combination for the management of difficult-to-treat skin and mucous infections, especially those caused by P. aeruginosa.

Antimicrobial photodynamic activity of Rose Bengal, alone or in combination with Gentamicin, against planktonic and biofilm Staphylococcus aureus

Antimicrobial photodynamic therapy (aPDT) could constitute an alternative therapy to antibiotics especially against superficial infections caused by bacteria involved in multidrug resistance processes. The aim of this study is to compare the efficacy of aPDT using the photosensitizer rose bengal (RB), combined or uncombined with gentamicin (GN), against Staphylococcus aureus. Different concentrations of RB (ranging from 0.03 to 64 μg/ml) were added to S. aureus in water suspensions or forming biofilms in the absence or presence of GN (1-40 μg/ml) and the samples were irradiated (18 or 37 J/cm²). The number of viable bacteria was quantified by counting colony-forming units. RB-aPDT shows significant photoactivity. The combination of GN and RB-aPDT exerts a synergistic bactericidal effect against planktonic S. aureus. On the other hand, a synergistic effect is observed only when the maximum concentration tested of RB and GN was used in biofilm. According to these result the use of RB-aPDT alone or in combination with GN could be implemented against S. aureus.