In Vitro Bactericidal Effects of Photodynamic Therapy Combined with Four Tetracyclines against Clostridioides difficile KCTC5009 in Planktonic Cultures

Microscopy methods for Clostridioides difficile

Microscopic technologies including light and fluorescent, transmission electron microscopy (TEM), scanning electron microscopy (SEM), and cryo-electron microscopy have been widely utilized to visualize Clostridioides difficile at the molecular, cellular, community, and structural biology level. This comprehensive review summarizes the microscopy tools (fluorescent and reporter system) in their use to study different aspects of C. difficile life cycle and virulence (sporulation, germination) or applications (detection of C. difficile or use of antimicrobials). With these developing techniques, microscopy tools will be able to find broader applications and address more challenging questions to study C. difficile and C. difficile infection.

Antimicrobial Photodynamic Therapy Involving a Novel Photosensitizer Combined With an Antibiotic in the Treatment of Rabbit Tibial Osteomyelitis Caused by Drug-Resistant Bacteria

Osteomyelitis is deep tissue inflammation caused by bacterial infection. If such an infection persists, it can lead to dissolution and necrosis of the bone tissue. As a result of the extensive use of antibiotics, drug-resistant bacteria are an increasingly common cause of osteomyelitis, limiting the treatment options available to surgeons. Photodynamic antibacterial chemotherapy has attracted increasing attention as a potential alternative treatment. Its advantages are a broad antibacterial spectrum, lack of drug resistance, and lack of toxic side effects. In this study, we explored the impact of the new photosensitizer LD4 in photodynamic antimicrobial chemotherapy (PACT), both alone and in combination with an antibiotic, on osteomyelitis. A rabbit tibial osteomyelitis model was employed and microbiological, histological, and radiological studies were performed. New Zealand white rabbits (n = 36) were randomly divided into a control group, antibiotic group, PACT group and PACT + antibiotic group for treatment. In microbiological analysis, a reduction in bacterial numbers of more than 99.9% was recorded in the PACT group and the PACT + antibiotic group 5 weeks after treatment (p < 0.01). In histological analysis, repair of the damaged bone tissue was observed in the PACT group, and bone repair in the PACT + antibiotic group was even more significant. In radiological analysis, the X-ray Norden score showed that the severity of bone tissue defects or destruction followed the pattern: PACT + antibiotic group < PACT group < antibiotic group < control group.

Inactivation of Bacillus subtilis by Curcumin-Mediated Photodynamic Technology through Inducing Oxidative Stress Response

Photodynamic sterilization technology (PDT) is widely used in disease therapy, but its application in the food industry is still at the research stage because of the limitations of food-grade photosensitizers. Curcumin exhibits photosensitivity and is widely used as a food additive for its natural color. This study aimed to determine the effect of curcumin-mediated photodynamic technology (Cur-PDT) on Bacillus subtilis and to elucidate the anti-bacterial mechanism involved. First, the effects of curcumin concentration, duration of light irradiation, light intensity, and incubation time on the inactivation of B. subtilis were analyzed. It was found that Cur-PDT inactivated 100% planktonic cells with 50 μmol/L curcumin in 15 min (120 W). Then, the cell morphology, oxidation state and the expression of membrane structure- and DNA damage-related genes of B. subtilis vegetative cells were investigated under different treatment conditions. The membrane permeability of cells was enhanced and the cell membrane structure was damaged upon treatment with Cur-PDT, which were exacerbated with increases of treatment time and curcumin concentration. Meanwhile, the production of reactive oxygen species increased and the activities of the antioxidant enzymes SOD, GPX, and CAT decreased inside the cells. Furthermore, the Cur-PDT treatment significantly downregulated the mRNA of the membrane protein TasA and upregulated the DNA damage recognition protein UvrA and repair protein RecA of B. subtilis. These results suggested that curcumin-mediated PDT could effectively inactivate B. subtilis by inducing cell redox state imbalance, damaging DNA, and disrupting membrane structures.

Orange-red to NIR emissive carbon dots for antimicrobial, bioimaging and bacteria diagnosis

Antimicrobial photodynamic therapy (aPDT) has become a popular technology for the treatment of bacterial infections. The development of antimicrobial agents combining diagnosis and treatment remains a major challenge. Herein, curcumin carbon quantum dots (Cur-NRCQDs) with antibacterial and imaging effects were synthesized using a hydrothermal method. The fluorescence absorption range of the Cur-NRCQDs in aqueous solution was 555 to 850 nm, showing orange-red to near infrared (NIR) fluorescence, and its maximum emission wavelength was 635 nm. At the same time, Cur-NRCQDs improved the efficiency of Cur as the photosensitizer (PS), showed good storage and light stability, and enhanced the efficiency of reactive oxygen (ROS) generation and antibacterial activity. Under the irradiation of a xenon lamp, Cur-NRCQDs inactivated 100% Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) at concentrations of 10 and 15 μM, respectively. The possible reason for this was that under PDT, the ROS produced by the Cur-NRCQDs destroyed the integrity of the cell membrane, resulting in leakage of the contents. In addition, the Cur-NRCQDs showed good cell compatibility, as they can also enter bacteria and cells for imaging, so they can be employed for the detection of bacteria and cell tissues. Therefore, Cur-NRCQDs are an ideal candidate material for aPDT treatment and fluorescent bioimaging.

Antimicrobial Photodynamic Therapy Combined With Antibiotic in the Treatment of Rats With Third-Degree Burns

Cationic porphyrin conjugate, protoporphyrin IX-methyl ethylenediamine derivative (PPIX-MED) has a potent photosensitive antibacterial effect on clinically isolated bacteria, including methicillin-resistant Staphylococcus aureus, (MRSA), Escherichia coli, and Pseudomonas aeruginosa. This study investigated (i) the PPIX-MED-mediated antimicrobial photodynamic effect on these three species in vitro and (ii) the effect of antimicrobial photodynamic therapy (aPDT) combined with the use of an antibiotic on the healing in vivo of third-degree burns of rats with the wounds infected by these bacterial species. PPIX-MED exerted a potent inhibitory effect on the growth of the three bacterial species by producing reactive oxygen species when photoactivated. PPIX-MED-mediated antimicrobial photodynamic therapy (PPIX-MED-aPDT) had high bacterial photoinactivation ability in vitro, with a minimum inhibitory concentration of 15.6 μM PPIX-MED against each of the three types of bacteria and minimum bactericidal concentrations of 31.25 μM against MRSA and E. coli and 62.5 μM against P. aeruginosa. In rats with third-degree burns infected by a mixture of these bacteria, the bactericidal efficiency of PPIX-MED–aPDT-combined-with-antibiotic treatment was higher than that of antibiotic or aPDT treatment alone. This was confirmed by analysis of viable bacterial counts in wound tissue and blood. Enzyme-linked immunosorbent assay revealed that aPDT-combined-with-antibiotic treatment resulted in an obvious reduction in tumor necrosis factor-alpha and interleukin-6 levels compared with the no-treatment control group and the other treatment groups. Immunohistochemistry revealed that the expression of basic fibroblast growth factor and CD31 (a marker of neovascularization), expressed in burn wound tissue was higher in the aPDT-combined-with-antibiotic treatment group than in the other groups. PPIX-MED–aPDT has a promising bactericidal effect both in vitro and in vivo, and PPIX-MED–aPDT-combined-with-antibiotic treatment enhanced the healing of infected third-degree burns in rats.