Abstract
The use of antimicrobial photodynamic inactivation as a non-antibiotic alternative method to inactivate Acinetobacter baumannii was described in response to the ever-growing problem of antibiotic resistance. It was found that irradiation of the bacterial suspension for 10 min reduced the number of viable cells by approximately 99% and this energy fluence was considered to be sub-lethal phototherapy. The lethal dose of laser light (cell mortality about 99.9%) was 9.54 J cm−2, which corresponds to 30 min of irradiation. After a 15-fold phototherapy cycle, the tolerance to aPDT decreased, resulting in a decrease in the number of viable cells by 2.15 and 3.23 log10 CFU/ml units with the use of sub-lethal and lethal light doses, respectively. Multiple photosensitizations decreased the biofilm formation efficiency by 25 ± 1% and 35 ± 1%, respectively. No changes in antibiotic resistance were observed, whereas the cells were more sensitive to hydrogen peroxide. Metabolomic changes after multiple photosensitization were studied and 1H NMR measurements were used in statistical and multivariate data analysis. Many significant changes in the levels of the metabolites were detected demonstrating the response of A. baumannii to oxidative stress.
Highlights
The use of antimicrobial photodynamic inactivation as a non-antibiotic alternative method to inactivate Acinetobacter baumannii was described in response to the ever-growing problem of antibiotic resistance
Our studies were preceded by the determination of the dark antimicrobial activity of Methylene Blue (MB) on planktonic cells of A. baumannii and representative results obtained by BacTiter-GloTM Microbial Cell Viability Assay were collected in Fig. S1 (Supplementary Information)
Based on these results it was established that irradiation of the bacterial suspension for 10 min reduced the number of viable cells by approximately 99% (~ 2 log[10] unit reduction) and this energy fluence was considered to be sub-lethal phototherapy
Summary
The use of antimicrobial photodynamic inactivation as a non-antibiotic alternative method to inactivate Acinetobacter baumannii was described in response to the ever-growing problem of antibiotic resistance. Acinetobacter baumannii is a saprophytic bacterium, widely distributed in the natural environment, including water, soil, sewage and skin of animals and humans[4] In the past, it was considered a low-category pathogen but today this coccobacillus is one of the major pathogens responsible for causing nosocomial infections, especially in intensive care units (ICUs) worldwide. APDT is not a new technique as it has been used for over 1000 years in Egypt, India, and China[9], and today it has found application in periodontal infection, endodontic disinfection, and the treatment of localized infections from the dermatological o rigin[10,11] This treatment has a significant advantage over existing antimicrobial therapies as it is faster compared to other
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