In vitro effectiveness of 455-nm blue LED to reduce the load of Staphylococcus aureus and Candida albicans biofilms in compact bone tissue

Effect of Nd:YAG Laser Irradiation on the Growth of Oral Biofilm

BACKGROUND

Oral microbiota comprises a wide variety of microorganisms. The purpose of this study was to evaluate the effects of Nd:YAG laser with a 1064 nm wavelength on the in vitro growth of Candida albicans, Candida glabrata, and Streptococcus mutans clinical strains, as well as their biofilm. The study also aimed to determine whether the parameters recommended for photobiomodulation (PBM) therapy, typically used for tissue wound healing, have any additional antibacterial or antifungal effects.

MATERIAL AND METHODS

Single- and dual-species planktonic cell solution and biofilm cultures of Streptococcus mutans, Candida albicans, and Candida glabrata were irradiated using an Nd:YAG laser (LightWalker; Fotona; Slovenia) with a flat-top Genova handpiece. Two test groups were evaluated: Group 1 (G-T1) exposed to low power associated parameters (irradiance 0.5 W/cm2) and Group 2 (G-T2) with higher laser parameters (irradiance 1.75 W/cm2). Group 3 (control) was not exposed to any irradiation. The lasers' effect was assessed both immediately after irradiation (DLI; Direct Laser Irradiation) and 24 h post-irradiation (24hLI) of the planktonic suspension using a quantitative method (colony-forming units per 1 mL of suspension; CFU/mL), and the results were compared with the control group, in which no laser was applied. The impact of laser irradiation on biofilm biomass was assessed immediately after laser irradiation using the crystal violet method.

RESULTS

Nd:YAG laser irradiation with photobiomodulation setting demonstrated an antimicrobial effect with the greatest immediate reduction observed in S. mutans, achieving up to 85.4% reduction at the T2 settings. However, the laser's effectiveness diminished after 24 h. In single biofilm cultures, the highest reductions were noted for C. albicans and S. mutans at the T2 settings, with C. albicans achieving a 92.6 ± 3.3% reduction and S. mutans reaching a 94.3 ± 5.0% reduction. Overall, the T2 settings resulted in greater microbial reductions compared to T1, particularly in biofilm cultures, although the effectiveness varied depending on the microorganism and culture type. Laser irradiation, assessed immediately after using the crystal violet method, showed the strongest biofilm reduction for Streptococcus mutans in the T2 settings for both single-species and dual-species biofilms, with higher reductions observed in all the microbial samples at the T2 laser parameters (p < 0.05) Conclusion: The Nd:YAG laser using standard parameters typically applied for wound healing and analgesic effects significantly reduced the number of Candida albicans; Candida glabrata; and Streptococcus mutans strains.

Reduction in Pathogenic Biofilms by the Photoactive Composite of Bacterial Cellulose and Nanochitosan Dots under Blue and Green Light

In this study, nanochitosan dots (ChiDs) were synthesized using gamma rays and encapsulated in bacterial cellulose (BC) polymer matrix for antibiofilm potential in photodynamic therapy. The composites were analyzed for structural changes using SEM, AFM, FTIR, XRD, EPR, and porosity measurements. Additionally, ChiD release was assessed. The results showed that the chemical composition remained unaltered, but ChiD agglomerates embedded in BC changed shape (1.5-2.5 µm). Bacterial cellulose fibers became deformed and interconnected, with increased surface roughness and porosity and decreased crystallinity. No singlet oxygen formation was observed, and the total amount of released ChiD was up to 16.10%. Antibiofilm activity was higher under green light, with reductions ranging from 48 to 57% under blue light and 78 to 85% under green light. Methicillin-resistant Staphylococcus aureus was the most sensitive strain. The new photoactive composite hydrogels show promising potential for combating biofilm-related infections.

Photoinactivation of Yeast and Biofilm Communities of Candida albicans Mediated by ZnTnHex-2-PyP4+ Porphyrin

Candida albicans is the main cause of superficial candidiasis. While the antifungals available are defied by biofilm formation and resistance emergence, antimicrobial photodynamic inactivation (aPDI) arises as an alternative antifungal therapy. The tetracationic metalloporphyrin Zn(II) meso-tetrakis(N-n-hexylpyridinium-2-yl)porphyrin (ZnTnHex-2-PyP⁴⁺) has high photoefficiency and improved cellular interactions. We investigated the ZnTnHex-2-PyP⁴⁺ as a photosensitizer (PS) to photoinactivate yeasts and biofilms of C. albicans strains (ATCC 10231 and ATCC 90028) using a blue light-emitting diode. The photoinactivation of yeasts was evaluated by quantifying the colony forming units. The aPDI of ATCC 90028 biofilms was assessed by the MTT assay, propidium iodide (PI) labeling, and scanning electron microscopy. Mammalian cytotoxicity was investigated in Vero cells using MTT assay. The aPDI (4.3 J/cm²) promoted eradication of yeasts at 0.8 and 1.5 µM of PS for ATCC 10231 and ATCC 90028, respectively. At 0.8 µM and same light dose, aPDI-treated biofilms showed intense PI labeling, about 89% decrease in the cell viability, and structural alterations with reduced hyphae. No considerable toxicity was observed in mammalian cells. Our results introduce the ZnTnHex-2-PyP⁴⁺ as a promising PS to photoinactivate both yeasts and biofilms of C. albicans, stimulating studies with other Candida species and resistant isolates.

Photoinactivation of Catalase Sensitizes Candida albicans and Candida auris to ROS-Producing Agents and Immune Cells

Microbes have developed their own specific strategies to cope with reactive oxygen species (ROS). Catalase, a heme-containing tetramer expressed in a broad range of aerobic fungi, shows remarkable efficiency in degrading hydrogen peroxide (H2 O2 ) for fungal survival and host invasion. Here, it is demonstrated that catalase inactivation by blue light renders fungal cells highly susceptible to ROS attack. To confirm catalase as a major molecular target of blue light, wild type Candida albicans are systematically compared with a catalase-deficient mutant strain regarding their susceptibility to ROS through 410 nm treatment. Upon testing a wide range of fungal species, it is found that intracellular catalase can be effectively and universally inactivated by 410 nm blue light. It is also found that photoinactivation of catalase in combination with ROS-generating agents is highly effective in total eradication of various fungal species, including multiple Candida auris strains, the causative agent of the global fungal epidemic. In addition, photoinactivation of catalase is shown to facilitate macrophage killing of intracellular Candida albicans. The antifungal efficacy of catalase photoinactivation is further validated using a C. albicans-induced mouse model of skin abrasion. Taken together, the findings offer a novel catalase-photoinactivation approach to address multidrug-resistant Candida infections.

Characterization of Blue Light Treatment for Infected Wounds: Antibacterial Efficacy of 420, 455, and 480 nm Light-Emitting Diode Arrays Against Common Skin Pathogens Versus Blue Light-Induced Skin Cell Toxicity

Objective: To determine effective treatment strategies against bacterial infections of chronic wounds, we tested different blue light (BL)-emitting light-emitting diode arrays (420, 455, and 480 nm) against wound pathogens and investigated in parallel BL-induced toxic effects on human dermal fibroblasts. Background: Wound infection is a major factor for delayed healing. Infections with Pseudomonas aeruginosa and Staphylococcus aureus are clinically relevant caused by their ability of biofilm formation and their quickly growing antibiotics resistance. BL has demonstrated antimicrobial properties against various microbes. Methods: Determination of antibacterial and cell toxic effects by colony-forming units (CFUs)/biofilm/cell viability assays, and live cell imaging. Results: A single BL irradiation (180 J/cm²), of P. aeruginosa at both 420 and 455 nm resulted in a bacterial reduction (>5 log₁₀ CFU), whereas 480 nm revealed subantimicrobial effects (2 log₁₀). All tested wavelengths of BL also revealed bacteria reducing effects on Staphylococcus epidermidis and Escherichia coli (maximum 1-2 log₁₀ CFU) but not on S. aureus. Dealing with biofilms, all wavelengths using 180 J/cm² were able to reduce significantly the number of P. aeruginosa, E. coli, and S. epidermidis. Here, BL_420nm achieved reductions up to 99%, whereas BL_455nm and BL_480nm were less effective (60-83%). Biofilm-growing S. aureus was more BL sensitive than in the planktonic phase showing a reduction by 63-75%. A significant number of cell toxic events (>40%) could be found after applying doses (>30 J/cm²) of BL_420nm. BL_455nm showed only slight cell toxicity (180 J/cm²), whereas BL_480nm was nontoxic at any dose. Conclusions: BL treatment can be effective against bacterial infections of chronic wounds. Nevertheless, using longer wavelengths >455 nm should be preferred to avoid possible toxic effects on skin and skin cells. To establish BL therapy for infected chronic wounds, further studies concerning biofilm formation and tissue compatibility are necessary.

Blue and red light photoemitters as approach to inhibit Staphylococcus aureus and Pseudomonas aeruginosa growth

The ability of pathogenic bacteria acquire resistance to the existing antibiotics has long been considered a dangerous health risk threat. Currently, the use of visible light has been considered a new approach to treat bacterial infections as an alternative to antibiotics. Herein, we investigated the antimicrobial effect of two range of visible light, blue and red, on Staphylococcus aureus and Pseudomonas aeruginosa, two pathogenic bacterial commonly found in healthcare settings-acquired infections and responsible for high rate of morbidity and mortality. Bacterial cultures were exposed to blue or red light (470 nm and 660 nm) provided by light-emitting diodes - LED. The fluencies and irradiance used for blue and red light were 284.90 J/cm2, 13.19 mW/cm2 and 603.44 J/cm2, 27.93 mW/cm2 respectively. Different experimental approaches were used to determine the optimal conditions of light application. Only exposure to blue light for 6 hours was able to inhibit about 75% in vitro growth of both bacterial species after 24 hours. The surviving exposed bacteria formed colonies significantly smaller than controls, however, these bacteria were able to resume growth after 48 hours. Blue light was able to inhibit bacterial growth upon inoculation in both saline solution and BHI culture medium. We can conclude that blue light, but not red light, is capable of temporarily retarding the growth of gram negative and gram positive bacteria.

Photodynamic therapry with curcumin in the reduction of enterococcus faecalis biofilm in bone cavity: rMicrobiological and spectral fluorescense analysis

BACKGROUND

Antimicrobial photodynamic therapy (PDT) has emerged as a therapeutic strategy to conventional procedures using antibiotics.

OBJECTIVE

To evaluate the antimicrobial effectiveness of PDT using blue light emitting diode (LED) associated with curcumin on biofilms of Enterococcus faecalis in bovine bone cavities and also to analyze the presence of these biofilms through spectral fluorescence.

MATERIALS AND METHODS

Standardized suspensions of E. faecalis (ATCC 29212) were incubated in artificial bone cavities for 14 days at 36 °C ± 1 °C for biofilm formation. The test specimens were distributed among the four experimental groups (n = 10): L-C- (control), L + C- (LED for 5 min), L-C+ (curcumin for 5 min) and L + C+ (PDT). Aliquots were collected from the bone cavities after treatments and seeded on BHI agar for 24 h at 36 °C ± 1 °C for CFU count. Before and after each treatment the specimens were submitted to spectral fluorescence, whose images were compared in the Image J program. The log10 CFU/mL results were submitted to the Kruskal-Wallis test (5%) and the biofilm fluorescence spectroscopy results were submitted to the Wilcoxon test (5%).

RESULTS

All treatments presented statistical difference when compared to the control, and PDT was responsible for the largest reduction (1.92 log10 CFU/mL). There was a reduction in the fluorescence emitted after the treatments, with greater statistical difference in the PDT group.

CONCLUSION

PDT was efficient in the reduction of E. faecalis biofilms. In all groups post treatment there was a significant reduction of biofilms in the fluorescence spectroscopy images with greater reduction in the PDT group.

Staphylococcus aureus growth delay after exposure to low fluencies of blue light (470 nm)

Antibiotic resistance is one of the greatest challenges to treat bacterial infections worldwide, leading to increase in medical expenses, prolonged hospital stay and increased mortality. The use of blue light has been suggested as an innovative alternative to overcome this problem. In this study we analyzed the antibacterial effect of blue light using low emission parameters on Staphylococcus aureus cultures. In vitro bacterial cultures were used in two experimental approaches. The first approach included single or fractionated blue light application provided by LED emitters (470 nm), with the following fluencies: 16.29, 27.16 and 54.32 J/cm2. For the second approach a power LED (470 nm) was used to deliver 54.32 J/cm2 fractionated in 3 applications. Our results demonstrated that bacterial cultures exposed to fractionated blue light radiation exhibited significantly smaller sizes colonies than the control group after 24 h incubation, however the affected bacteria were able to adapt and continue to proliferate after prolonged incubation time. We could conclude that the hypothetical clinical use of low fluencies of blue light as an antibacterial treatment is risky, since its action is not definitive and proves to be ineffective at least for the strain used in this study.

Photodynamic Therapy by Diaryl-Porphyrins to Control the Growth of Candida albicans

Candida albicans is an opportunistic pathogen that often causes skin infections such as oral thrush, nail fungus, athlete’s foot, and diaper rash. Under particular conditions, C. albicans alters the natural balance of the host microbiota, and as a result, the skin or its accessory structures lose their function and appearance. Conventional antimycotic drugs are highly toxic to host tissues, and long-lasting drug administration induces the arising of resistant strains that make the antimycotic therapy ineffective. Among new antimicrobial approaches to combine with traditional drugs, light-based techniques are very promising. In this study, a panel of dyes was considered for photodynamic therapy (PDT) applications to control the growth of the model strain C. albicans ATCC 14053. The chosen photosensitizers (PSs) belong to the family of synthetic porphyrins, and in particular, they are diaryl-porphyrins. Among these, two monocationic PSs were shown to be particularly efficient in killing C. albicans upon irradiation with light at 410 nm, in a light-dose-dependent manner. The elicited photo-oxidative stress induced the loss of the internal cellular architecture and death. The photodynamic treatment was also successful in inhibiting the biofilm formation of clinical C. albicans strains. In conclusion, this study supports the great potential of diaryl-porphyrins in antimicrobial PDT to control the growth of yeasts on body tissues easily reachable by light sources, such as skin and oral cavity.

Antimicrobial Blue Light Inactivation of Microbial Isolates in Biofilms

BACKGROUND AND OBJECTIVES

Biofilms cause more than 80% of infections in humans, including more than 90% of all chronic wound infections and are extremely resistant to antimicrobials and the immune system. The situation is exacerbated by the fast spreading of antimicrobial resistance, which has become one of the biggest threats to current public health. There is consequently a critical need for the development of alternative therapeutics. Antimicrobial blue light (aBL) is a light-based approach that exhibits intrinsic antimicrobial effect without the involvement of exogenous photosensitizers. In this study, we investigated the antimicrobial effect of this non-antibiotic approach against biofilms formed by microbial isolates of multidrug-resistant bacteria.

STUDY DESIGN/MATERIALS AND METHODS

Microbial isolates of Acinetobacter baumannii, Candida albicans, Escherichia coli, Enterococcus faecalis, MRSA, Neisseria gonorrhoeae, Pseudomonas aeruginosa, and Proteus mirabilis were studied. Biofilms were grown in microtiter plates for 24 or 48 hours or in the CDC biofilm reactor for 48 hours and exposed to aBL at 405 nm (60 mW/cm² , 60 or 30 minutes). The anti-biofilm activity of aBL was measured by viable counts.

RESULTS

The biofilms of A. baumannii, N. gonorrhoeae, and P. aeruginosa were the most susceptible to aBL with between 4 and 8 log₁₀ inactivation after 108 J/cm² (60 mW/cm² , 30 minutes) or 216 J/cm² (60 mW/cm² , 60 minutes) aBL were delivered in the microplates. On the contrary, the biofilms of C. albicans, E. coli, E. faecalis, and P. mirabilis were the least susceptible to aBL inactivation (-0.30, -0.24, -0.84, and -0.68 log₁₀ inactivation, respectively). The same aBL treatment in biofilms developed in the CDC biofilm reactor, caused -1.68 log₁₀ inactivation in A. baumannii and -1.74 and -1.65 log₁₀ inactivation in two different strains of P. aeruginosa.

CONCLUSIONS

aBL exhibits potential against pathogenic microorganisms and could help with the significant need for new antimicrobials in clinical practice to manage multidrug-resistant infections. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.

Fluorescence spectroscopy of Candida albicans biofilms in bone cavities treated with photodynamic therapy using blue LED (450 nm) and curcumin

Fluorescence spectroscopy may assisst in the diagnosis and control of infectious processes associated with bone lesions of the oral cavity. The aim of this study was to analyze, through fluorescence spectroscopy, Candida albicans biofilms formed in artificial bone cavities treated with photodynamic therapy (PDT) mediated with 450-nm blue light-emitting diode (LED) and curcumin. Another aim of this study was to analyze the existence of a correlation between the effectiveness of the photodynamic treatments and the fluorescence spectroscopy images. Artificial bone lesions (n = 40) were made in bovine bones and inoculated with standard suspensions of Candida albicans (ATCC 18804) for biofilm formation (14 days / 36 °C ± 1 °C). The 40 specimens were distributed among four experimental groups (n = 10): L-C- (control), L + C- (LED for 5 min), L-C+ (curcumin for 5 min), and L + C+ (PDT). Aliquots of 100 μL were collected from the bone cavities after treatments and were seeded in duplicate on Sabouraud dextrose agar for 24 h at 36 °C ± 1 °C and the colony-forming units (CFU/ mL) were counted. Before and after each treatment, the specimens were subjected to spectral fluorescence and the images were compared using the Image J program. The log₁₀ CFU/mL were compared with Kruskal-Wallis and Dunn's Multiple Comparison post-test (significance level at 0.05). The fluorescence histogram values before and after treatment were compared using Wilcoxon test (95%).The correlation between Candida albicans log₁₀ CFU/mL and the number of the fluorescence red pixels spectroscopy was verified using Spearman correlation test. The reduction of Candida albicans log₁₀ CFU/mL in the L + C+ (PDT) group was the most relevant and the fluorescence spectroscopy was correlated to the microbiological result. It was concluded that there was a consistency between the number of Candida albicans log₁₀ CFU/mL and the red pixel data of the fluorescence images, demonstrating that the fluorescence diagnostic device reflects the true microbiological condition of Candida albicans biofilms in the bone cavities during the pre-treatment and post-treatment, thus providing the clinician the ability to dynamically, simply, and instantaneously verify the performance of the treatment used.

Photoinactivation of ESKAPE pathogens: overview of novel therapeutic strategy

The emergence of antimicrobial drug resistance requires development of alternative therapeutic options. Multidrug-resistant strains of Enterococcus spp., Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumanii, Pseudomonas aeruginosa and Enterobacter spp. are still the most commonly identified antimicrobial-resistant pathogens. These microorganisms are part of the so-called 'ESKAPE' pathogens to emphasize that they currently cause the majority of hospital acquired infections and effectively 'escape' the effects of antibacterial drugs. Thus, alternative, safer and more efficient antimicrobial strategies are urgently needed, especially against 'ESKAPE' superbugs. Antimicrobial photodynamic inactivation is a therapeutic option used in the treatment of infectious diseases. It is based on a combination of a photosensitizer, light and oxygen to remove highly metabolically active cells.

Effects of Nd:YAG laser irradiation on the growth of Candida albicans and Streptococcus mutans: in vitro study

The purpose of this study was to evaluate the effects of Nd:YAG laser with flat-top handpiece on the in vitro growth of Candida albicans and Streptococcus mutans. The incidence of C. albicans (opportunistic commensal) and S. mutans (facultatively anaerobic) infections is increasing, despite available treatments. Cultures of Streptococcus mutans and Candida albicans were irradiated using Nd:YAG laser (LightWalker, Fotona) with flat-top handpiece (Genova, LightWalker, Fotona) at the following parameters: group G1: 0.25 W, 10 Hz, 15 s, 3 J and group G2: 1 W, 10 Hz, 60s, 59 J. The results were evaluated directly and 24 h after irradiation using a quantitative culture method (estimation of colony-forming units in 1 ml of suspension, cfu/ml), and microscopic analysis with Janus green stain and compared with control group in which laser was not applied. C. albicans was reduced by 20 up to 54% for G1, and for G2 by 10 up to 60% directly after the application. The cfu/ml values for S. mutans decreased by 13% (p = 0.1771) for G1 and 89% (p < 0.0001) for G2. In both test groups 24 h after the application, the number of colony-forming units decreased by 15–46% for G1 and by 15–64% for G2. The arrested cell division, increasing the surface area and increasing the number of metabolically inactive cells, were observed in morphometric analysis. Macroscopic and microscopic analyses revealed a reduction in cell number and a significant decrease of cell metabolism after laser application for both C. albicans and S. mutans.

Antifungal Compounds against Candida Infections from Traditional Chinese Medicine

Infections caused by Candida albicans, often refractory and with high morbidity and mortality, cause a heavy burden on the public health while the current antifungal drugs are limited and are associated with toxicity and resistance. Many plant-derived molecules including compounds isolated from traditional Chinese medicine (TCM) are reported to have antifungal activity through different targets such as cell membrane, cell wall, mitochondria, and virulence factors. Here, we review the recent progress in the anti-Candida compounds from TCM, as well as their antifungal mechanisms. Considering the diverse targets and structures, compounds from TCM might be a potential library for antifungal drug development.

Reduced methicillin-resistant Staphylococcus aureus biofilm formation in bone cavities by photodynamic therapy

Photodynamic Therapy (PDT) is a promising alternative for the treatment of infectious bone lesions in the oral cavity. The objective of this study was to evaluate the antimicrobial effectiveness of PDT using blue LED associated with curcumin in methicillin-resistant Staphylococcus aureus biofilms (MRSA) in bovine bone cavities by fluorescence spectroscopy. Standardized suspensions of MRSA culture were inoculated into bone lesions to form biofilm. Forty bone species were distributed in three distinct groups: L-C- (control); L + C- (LED for 5 min); L-C+ (curcumin incubation for 5 min) and L + C+ (PDT). Aliquots of 100 μL were collected from the bone cavities after the treatments and were cultived in BHI for 24 h at 36 °C ± 1 and bacterial colonies counting were performed. Statistical analysis were performed using the paired t-test and analysis of variance (ANOVA) for the variables studied.

RESULTS

The control and PDT groups presented statistically significant differences (p < 0.001). It was possible to reduce 3.666 log10 CFU/mL of MRSA and a reduction in the fluorescence emitted after the treatments was observed. The MRSA reduction in biofilms by PDT was the most efficient treatmnent. There was a significant reduction of biofilms in the L + C- and non-PDT groups by fluorescence spectroscopy images.

Antimicrobial blue light inactivation of pathogenic microbes: State of the art

As an innovative non-antibiotic approach, antimicrobial blue light in the spectrum of 400-470nm has demonstrated its intrinsic antimicrobial properties resulting from the presence of endogenous photosensitizing chromophores in pathogenic microbes and, subsequently, its promise as a counteracter of antibiotic resistance. Since we published our last review of antimicrobial blue light in 2012, there have been a substantial number of new studies reported in this area. Here we provide an updated overview of the findings from the new studies over the past 5 years, including the efficacy of antimicrobial blue light inactivation of different microbes, its mechanism of action, synergism of antimicrobial blue light with other angents, its effect on host cells and tissues, the potential development of resistance to antimicrobial blue light by microbes, and a novel interstitial delivery approach of antimicrobial blue light. The potential new applications of antimicrobial blue light are also discussed.

In Vivo Investigation of Antimicrobial Blue Light Therapy for Multidrug-resistant Acinetobacter baumannii Burn Infections Using Bioluminescence Imaging

Burn infections continue to be an important cause of morbidity and mortality. The increasing emergence of multidrug-resistant (MDR) bacteria has led to the frequent failure of traditional antibiotic treatments. Alternative therapeutics are urgently needed to tackle MDR bacteria. An innovative non-antibiotic approach, antimicrobial blue light (aBL), has shown promising effectiveness against MDR infections. The mechanism of action of aBL is not yet well understood. It is commonly hypothesized that naturally occurring endogenous photosensitizing chromophores in bacteria (e.g., iron-free porphyrins, flavins, etc.) are excited by aBL, which in turn produces cytotoxic reactive oxygen species (ROS) through a photochemical process. Unlike another light-based antimicrobial approach, antimicrobial photodynamic therapy (aPDT), aBL therapy does not require the involvement of an exogenous photosensitizer. All it needs to take effect is the irradiation of blue light; therefore, it is simple and inexpensive. The aBL receptors are the endogenous cellular photosensitizers in bacteria, rather than the DNA. Thus, aBL is believed to be much less genotoxic to host cells than ultraviolet-C (UVC) irradiation, which directly causes DNA damage in host cells. In this paper, we present a protocol to assess the effectiveness of aBL therapy for MDR Acinetobacter baumannii infections in a mouse model of burn injury. By using an engineered bioluminescent strain, we were able to noninvasively monitor the extent of infection in real time in living animals. This technique is also an effective tool for monitoring the spatial distribution of infections in animals.