Susceptibility of Staphylococcus aureus to porphyrin-mediated photodynamic antimicrobial chemotherapy: an in vitro study

The ability of Staphylococcus aureus to develop multidrug resistance is well documented, and the antibiotic resistance showed by an increasing number of bacteria has shown the need for alternative therapies to treat infections, photodynamic therapy (PDT) being a potential candidate. The aim of this study was to determine the effect of photodynamic therapy as a light-based bactericidal modality to eliminate Staphylococcus aureus. The study investigated a technique based on a combination of light and a photosensitizer that is capable of producing oxidative species to induce a cytotoxic effect. A Staphylococcus aureus suspension was exposed to a light emitting diode (LED) emitting at 628 nm, 14.6 mW/cm(2), and energy density of 20J/cm(2), 40J/cm(2), or 60 J/cm(2) in the presence of different porphyrin concentrations (PhotogemA (R)). Three drug concentrations were employed: 12 mu l/ml, 25 mu l/ml, and 50 mu l/ml. The treatment response was evaluated by the number of bacterial colony forming units (CFU) after light exposure. The results indicated that exposure to 60 J/cm(2) eliminated 100% (10 log(10) scales) of bacteria, on average. The best PDT response rate to eliminate Staphylococcus aureus was achieved with exposure to LED light in combination with the photosensitizer at concentrations ranging from 25 mu l/ml to 50 mu l/ml. These data suggest that PDT has the potential to eliminate Staphylococcus aureus in suspension and indicates the necessary drug concentration and light fluency.

The Challenges of Antimicrobial Resistance in Brazil

Brazil is a country with continental proportions with high geographic and economic diversity. Despite its medical centers of excellence, antimicrobial resistance poses a major therapeutic challenge. Rates of methicillin-resistant Staphylococcus aureus are up to 60% and are related to an endemic Brazilian clone. Local resistance to vancomycin in Enterococci was first related to Enterococcus faecalis, which differs from European and American epidemiology. Also, local Klebsiella pneumoniae and Escherichia coli isolates producing extended-spectrum beta-lactamases have a much higher prevalence (40%-50% and 10%-18%, respectively). Carbapenem resistance among the enterobacteriaceae group is becoming a major problem, and K. pneumoniae carbapenemase isolates have been reported in different states. Among nonfermenters, carbapenem resistance is strongly related to SPM-1 (Pseudomonasaeruginosa) and OXA-23 (Acinetobacter baumannii complex) enzymes, and a colistin-only susceptible phenotype has also emerged in these isolates, which is worrisome. Local actions without loosing the global resistance perspective will demand multidisciplinary actions, new policies, and political engagement.

Fungicidal effect of photodynamic therapy against fluconazole-resistant Candida albicans and Candida glabrata

P>Although photodynamic therapy (PDT) has shown great promise for the inactivation of Candida species, its effectiveness against azole-resistant pathogens remains poorly documented. This in vitro study describes the association of Photogem (R) (Photogem, Moscow, Russia) with LED (light emitting diode) light for the photoinactivation of fluconazole-resistant (FR) and American Type Culture Collection (ATCC) strains of Candida albicans and Candida glabrata. Suspensions of each Candida strain were treated with five Photogem (R) concentrations and exposed to four LED light fluences (14, 24, 34 or 50 min of illumination). After incubation (48 h at 37 degrees C), colonies were counted (CFU ml-1). Single-species biofilms were generated on cellulose membrane filters, treated with 25.0 mg l-1 of Photogem (R) and illuminated at 37.5 J cm-2. The biofilms were then disrupted and the viable yeast cells present were determined. Planktonic suspensions of FR strains were effectively killed after PDT. It was observed that the fungicidal effect of PDT was strain-dependent. Significant decreases in biofilm viability were observed for three strains of C. albicans and for two strains of C. glabrata. The results of this investigation demonstrated that although PDT was effective against Candida species, fluconazole-resistant strains showed reduced sensitivity to PDT. Moreover, single-species biofilms were less susceptible to PDT than their planktonic counterparts.

Chemiluminescence as a PDT light source for microbial control

The photodynamic therapy (PDT) is a combination of using a photosensitizer agent, light and oxygen that can cause oxidative cellular damage. This technique is applied in several cases, including for microbial control. The most extensively studied light sources for this purpose are lasers and LED-based systems. Few studies treat alternative light sources based PDT. Sources which present flexibility, portability and economic advantages are of great interest. In this study, we evaluated the in vitro feasibility for the use of chemiluminescence as a PDT light source to induce Staphylococcus aureus reduction. The Photogem (R) concentration varied from 0 to 75 mu g/ml and the illumination time varied from 60 min to 240 min. The long exposure time was necessary due to the low irradiance achieved with chemiluminescence reaction at mu W/cm(2) level. The results demonstrated an effective microbial reduction of around 98% for the highest photosensitizer concentration and light dose. These data suggest the potential use of chemiluminescence as a light source for PDT microbial control, with advantages in terms of flexibility, when compared with conventional sources. (C) 2011 Elsevier B.V. All rights reserved.