Bacteria-specific pro-photosensitizer kills multidrug-resistant Staphylococcus aureus and Pseudomonas aeruginosa

Thymoquinone as an electron transfer mediator to convert Type II photosensitizers to Type I photosensitizers

The development of Type I photosensitizers (PSs) is of great importance due to the inherent hypoxic intolerance of photodynamic therapy (PDT) in the hypoxic microenvironment. Compared to Type II PSs, Type I PSs are less reported due to the absence of a general molecular design strategy. Herein, we report that the combination of typical Type II PS and natural substrate carvacrol (CA) can significantly facilitate the Type I pathway to efficiently generate superoxide radical (O2-•). Detailed mechanism study suggests that CA is activated into thymoquinone (TQ) by local singlet oxygen generated from the PS upon light irradiation. With TQ as an efficient electron transfer mediator, it promotes the conversion of O2 to O2-• by PS via electron transfer-based Type I pathway. Notably, three classical Type II PSs are employed to demonstrate the universality of the proposed approach. The Type I PDT against S. aureus has been demonstrated under hypoxic conditions in vitro. Furthermore, this coupled photodynamic agent exhibits significant bactericidal activity with an antibacterial rate of 99.6% for the bacterial-infection female mice in the in vivo experiments. Here, we show a simple, effective, and universal method to endow traditional Type II PSs with hypoxic tolerance.

Photochemical Strategies toward Precision Targeting against Multidrug-Resistant Bacterial Infections

Infectious diseases pose a serious threat and a substantial economic burden on global human and public health security, especially with the frequent emergence of multidrug-resistant (MDR) bacteria in clinical settings. In response to this urgent need, various photobased anti-infectious therapies have been reported lately. This Review explores and discusses several photochemical targeted antibacterial therapeutic strategies for addressing bacterial infections regardless of their antibiotic susceptibility. In contrast to conventional photobased therapies, these approaches facilitate precise targeting of pathogenic bacteria and/or infectious microenvironments, effectively minimizing toxicity to mammalian cells and surrounding healthy tissues. The highlighted therapies include photodynamic therapy, photocatalytic therapy, photothermal therapy, endogenous pigments-based photobleaching therapy, and polyphenols-based photo-oxidation therapy. This comprehensive exploration aims to offer updated information to facilitate the development of effective, convenient, safe, and alternative strategies to counter the growing threat of MDR bacteria in the future.

Herbal Products-Powered Thermosensitive Hydrogel with Phototherapy and Microenvironment Reconstruction for Accelerating Multidrug-Resistant Bacteria-Infected Wound Healing

Wound healing and infection remain significant challenges due to the ineffectiveness against multidrug-resistant (MDR) bacteria and the complex oxidative wound microenvironments. To address these issues, thymoquinone-reinforced injectable and thermosensitive TQ@PEG-PAF-Cur hydrogels with dual functions of microenvironment reshaping and photodynamic therapy are developed. The hydrogel comprises natural compound thymoquinone (TQ) and poly (ethylene glycol)-block-poly (alanine-co-phenyl alanine) copolymers (PEG-PAF) conjugated with natural photosensitizer curcumin (Cur). The incorporation of TQ and Cur reduces the sol-to-gel transition temperature of TQ@PEG-PAF-Cur to 30°C, compared to PEG-PAF hydrogel (37°C), due to the formation of strong hydrogen bonding, matching the wound microenvironment temperature. Under blue light excitation, TQ@PEG-PAF-Cur generates significant amounts of reactive oxygen species such as H2O2, 1O2, and ·OH, exhibiting rapid and efficient bactericidal capacities against methicillin-resistant Staphylococcus aureus and broad spectrum β-lactamases Escherichia coli via photodynamic therapy (PDT). Additionally, Cur effectively inhibits the expressions of proinflammatory cytokines in skin tissue-forming cells. As a result, the composite hydrogel can rapidly transform into a gel to cover the wound, reshape the wound microenvironment, and accelerate wound healing in vivo. This collaborative antibacterial strategy provides valuable insights to guide the development of multifunctional materials for efficient wound healing.

Inhibitory effect of natural compounds on quorum sensing system in Pseudomonas aeruginosa: a helpful promise for managing biofilm community

Pseudomonas aeruginosa biofilm is a community of bacteria that adhere to live or non-living surfaces and are encapsulated by an extracellular polymeric substance. Unlike individual planktonic cells, biofilms possess a notable inherent resistance to sanitizers and antibiotics. Overcoming this resistance is a substantial barrier in the medical and food industries. Hence, while antibiotics are ineffective in eradicating P. aeruginosa biofilm, scientists have explored alternate strategies, including the utilization of natural compounds as a novel treatment option. To this end, curcumin, carvacrol, thymol, eugenol, cinnamaldehyde, coumarin, catechin, terpinene-4-ol, linalool, pinene, linoleic acid, saponin, and geraniol are the major natural compounds extensively utilized for the management of the P. aeruginosa biofilm community. Noteworthy, the exact interaction of natural compounds and the biofilm of this bacterium is not elucidated yet; however, the interference with the quorum sensing system and the inhibition of autoinducer production in P. aeruginosa are the main possible mechanisms. Noteworthy, the use of different drug platforms can overcome some drawbacks of natural compounds, such as insolubility in water, limited oral bioavailability, fast metabolism, and degradation. Additionally, drug platforms can deliver different antibiofilm agents simultaneously, which enhances the antibiofilm potential of natural compounds. This article explores many facets of utilizing natural compounds to inhibit and eradicate P. aeruginosa biofilms. It also examines the techniques and protocols employed to enhance the effectiveness of these compounds.

Antibacterial and Antibiofilm Effects of Photodynamic Treatment with Curcuma L. and Trans-Cinnamaldehyde against Listeria monocytogenes

Photodynamic inactivation (PDI) is a highly effective treatment that can eliminate harmful microorganisms in a variety of settings. This study explored the efficacy of a curcumin-rich extract, Curcuma L., (Cur)- and essential oil component, trans-cinnamaldehyde, (Ca)-mediated PDI against Listeria monocytogenes ATCC 15313 (Lm) including planktonic cells and established biofilms on silicone rubber (Si), polytetrafluoroethylene (PTFE), stainless steel 316 (SS), and polyethylene terephthalate (PET). Applying Ca- and Cur-mediated PDI resulted in planktonic cell reductions of 2.7 and 6.4 log CFU/cm2, respectively. Flow cytometric measurements (FCMs) coupled with CFDA/PI and TOTO®-1 staining evidenced that Ca- doubled and Cur-mediated PDI quadrupled the cell damage. Moreover, the enzymatic activity of Lm cells was considerably reduced by Cur-mediated PDI, indicating its superior efficacy. Photosensitization also affected Lm biofilms, but their reduction did not exceed 3.7 log CFU/cm2. Cur-mediated PDI effectively impaired cells on PET and PTFE, while Ca-mediated PDI caused no (TOTO®-1) or only slight (PI) cell damage, sparing the activity of cells. In turn, applying Ca-mediate PDI to Si largely diminished the enzymatic activity in Lm. SS contained 20% dead cells, suggesting that SS itself impacts Lm viability. In addition, the efficacy of Ca-mediated PDI was enhanced on the SS, leading to increased damage to the cells. The weakened viability of Lm on Si and SS could be linked to unfavorable interactions with the surfaces, resulting in a better effect of Ca against Lm. In conclusion, Cur demonstrated excellent photosensitizing properties against Lm in both planktonic and biofilm states. The efficacy of Ca was lower than that of Cur. However, Ca bears potent antibiofilm effects, which vary depending on the surface on which Lm resides. Therefore, this study may help identify more effective plant-based compounds to combat L. monocytogenes in an environmentally sustainable manner.

Synthesis and evaluation of novel pleuromutilin derivatives targeting the 50S ribosomal subunit for antibacterial ability

Multidrug-resistant bacteria, particularly methicillin-resistant Staphylococcus aureus, have become a major global public health concern. Therefore, developing new antibiotics that do not possess cross-resistance for the currently available antibiotics is critical. Herein, we synthesized a novel class of pleuromutilin derivatives containing substituted triazine with improved antibacterial activity. Among these derivatives, 6d, which contains 4-dimethylamino-1,3,5-triazine in the side chain of pleuromutilin, exhibited highly promising antimicrobial activity and mitigated antibiotic resistance. The high antibacterial potency of 6d was further supported by docking model analysis and green fluorescent protein inhibition assay. Additionally, cytotoxicity and acute oral toxicity evaluation and in vivo mouse systemic infection experiments revealed that 6d possessed tolerable toxicity and promising therapeutic efficacy.

Visualization and elimination of polymicrobial biofilms by a combination of ALA-carvacrol-blue light

Chronic wound infections caused by multidrug-resistant (MDR) bacteria are one of the serious threats to public health due to limited therapeutic options and lengthy care. This investigation combines 5-aminolevulinic acid (ALA), blue light (BL), and phytochemical carvacrol, named ABC cocktail or trio-therapy, to efficiently eliminate wound-related MDR pathogens. Both planktonic cells and biofilms of blue light-refractory Escherichia (E.) coli and Klebsiella (K.) pneumoniae succumbed to the trio-therapy partly due to porphyrin accumulations following ALA incubation. ALA either alone or alongside carvacrol could vigorously trigger bursts of reactive oxygen species (ROS) upon blue light irradiation in K. pneumoniae, but not in mammalian cells. The robust antimicrobial activity was extended to polymicrobial biofilms composed of five MDR pathogens (Staphylococcus aureus, E. coli, K. pneumoniae, Acinetobacter baumannii, and Pseudomonas aeruginosa) in vitro and in vivo. Strikingly, polymicrobial biofilm in mouse wounds became readily visible in the presence of ALA owing to the increasing generation of porphyrins that exhibited bright red fluorescence in response to blue light. Thus, ALA not only enhances killing efficacy, but also helps to pinpoint the infections for guiding debridement, precise phototherapy, and timely assessment of treatment effectiveness. Featuring a broadened antimicrobial spectrum and advantages of bacterial/biofilm imaging, the trio-therapy can be used either alone or adjunctive to other wound management modalities to effectively combat MDR bacteria in wounds.

Blue light potentiates safety and bactericidal activity of p-Toluquinone

Fewer antibiotics are available for effective management of bacterial infections to date owing to increasing multiple-drug resistance (MDR). Here, we expand our early success in combination of 405 nm blue light irradiation with phenolic compounds to sufficiently kill blue light-refractory MDR Escherichia coli (E. coli). p-Toluquinone (p-TQ) alongside blue light inactivated 7.3 log₁₀E. coli within 6 min, whereas either alone was totally ineffective. A similar killing efficacy was attained with four other pathogens commonly seen in hospital-acquired infections and Enterococcus faecalis (Ef) that don't produce porphyrins-like molecules. The combinatory therapy prevented recurrence of E. coli infection in skin scratch wounds of murine. The bactericidal activity was ascribed to reactive oxygen species (ROS) generation triggered by blue light-mediated excitation of p-TQ, which is less likely to induce resistance because of multi-targeted and non-specific nature of ROS. Remarkably, toxic p-TQ became harmless to mammalian cells after brief exposure to blue light while retaining its bactericidal activity. The opposite effect of blue light on p-TQ activity unravels a novel, simple strategy to detoxify p-TQ and its combination with blue light as a safe and efficacious bactericidal modality for managing MDR bacterial infections.

Oregano Oil and Harmless Blue Light to Synergistically Inactivate Multidrug-Resistant Pseudomonas aeruginosa

Blue light (BL) at 405 nm and oregano essential oil (OEO) have shown bactericidal activity by its own. Here, we demonstrated that the two synergistically killed multidrug-resistant (MDR) Pseudomonas aeruginosa (Pa). Pa ATCC19660 and HS0065 planktonic cells and mature biofilms were reduced by more than 7 log₁₀ after treatment by BL combined with OEO, in sharp contrast to no significant bacterial reduction with the monotreatment. The duo also sufficiently eliminated acute or biofilm-associated infection of open burn wounds in murine without incurring any harmful events in the skin. The synergic bactericide was attributed mainly to the ability of OEO to magnify cytotoxic reactive oxygen species (ROS) production initiated by BL that excited endogenous tetrapyrrole macrocycles in bacteria while completely sparing the surrounding tissues from the phototoxic action. OEO ingredient analysis in combination with microbial assays identified carvacrol and its isomer thymol to be the major phytochemicals that cooperated with BL executing synergic killing. The finding argues persuasively for valuable references of carvacrol and thymol in assessing and standardizing the bactericidal potential of various OEO products.

Prevalence, antimicrobial resistance profile, and characterization of multi-drug resistant bacteria from various infected wounds in North Egypt

Multi-drug resistant (MDR) bacteria associated with wounds are extremely escalating. This study aims to survey different wounds in Alexandria hospitals, North Egypt, to explore the prevalence and characteristics of MDR bacteria for future utilization in antibacterial wound dressing designs. Among various bacterial isolates, we determined 22 MDR bacteria could resist different classes of antibiotics. The collected samples exhibited the prevalence of mono-bacterial infections (60%), while 40% included poly-bacterial species due to previous antibiotic administration. Moreover, Gram-negative bacteria showed dominance with a ratio of 63.6%, while Gram-positive bacteria reported 36.4%. Subsequently, the five most virulent bacteria were identified following the molecular approach by 16S rRNA and physiological properties using the VITEK 2 automated system. They were deposited in GenBank as Staphylococcus haemolyticus MST1 (KY550377), Pseudomonas aeruginosa MST2 (KY550378), Klebsiella pneumoniae MST3 (KY550379), Escherichia coli MST4 (KY550380), and Escherichia coli MST5 (KY550381). In terms of isolation source, S. haemolyticus MST1 was isolated from a traumatic wound, while P. aeruginosa MST2 and E. coli MST4 were procured from hernia surgical wounds, and K. pneumoniae MST3 and E. coli MST5 were obtained from diabetic foot ulcers. Antibiotic sensitivity tests exposed that K. pneumoniae MST3, E. coli MST4, and E. coli MST5 are extended-spectrum β-lactamases (ESBLs) bacteria. Moreover, S. haemolyticus MST1 belongs to the methicillin-resistant coagulase-negative staphylococcus (MRCoNS), whereas P. aeruginosa MST2 exhibited resistance to common empirical bactericidal antibiotics. Overall, the study provides new insights into the prevalent MDR bacteria in Egypt for further use as specific models in formulating antibacterial wound dressings.

Reversal of Polymicrobial Biofilm Tolerance to Ciprofloxacin by Blue Light plus Carvacrol

Chronic wound infections are often caused by multi-species biofilms and these biofilm-embedded bacteria exhibit remarkable tolerance to existing antibiotics, which presents huge challenges to control such infections in the wounds. In this investigation, we established a polymicrobial biofilm composed of P. aeruginosa, S. aureus, K. pneumoniae, and A. baumannii. We tested a cocktail therapy comprising 405-nm blue light (BL), carvacrol (Ca), and antibiotics on the multispecies biofilm. Despite the fact that all strains used to form the biofilm were susceptible to ciprofloxacin (CIP) in planktonic cultures, the biofilm was found to withstand ciprofloxacin as well as BL-Ca dual treatment, mainly because K. pneumoniae outgrew and became dominant in the biofilm after each treatment. Strikingly, when ciprofloxacin was combined with BL-Ca, the multispecies biofilms succumbed substantially and were eradicated at an efficacy of 99.9%. Mechanistically, BL-Ca treatment increased membrane permeability and potentiated the anti-biofilm activity of ciprofloxacin, probably by facilitating ciprofloxacin’s entrance of the bacteria, which is particularly significant for K. pneumoniae, a species that is refractory to either ciprofloxacin or BL-Ca dual treatment. The results suggest that bacterial membrane damage can be one of the pivotal strategies to subvert biofilm tolerance and combat the recalcitrant multispecies biofilms.