Graphene Oxide Nanosheets with Efficient Antibacterial Activity Against Methicillin-Resistant Staphylococcus aureus (MRSA)

Photothermal and natural activity-based synergistic antibacterial effects of Ti3C2Tx MXene-loaded chitosan hydrogel against methicillin-resistant Staphylococcus aureus

Methicillin-resistant Staphylococcus aureus (MRSA) has strong resistance to antibiotic therapy. In this regard, developing antibiotic-free antibacterial agents is of great significance to treat MRSA infections. Herein, we loaded Ti₃C₂T_x MXene nanomaterial in the non-crosslinked chitosan (CS) hydrogel. The obtained MX-CS hydrogel is expected to not only adsorb MRSA cells via CS-MRSA interactions, but also gather the MXene-induced photothermal hyperthermia, achieving the efficient and intensive anti-MRSA photothermal therapy. As a result, under NIR irradiation (808 nm, 1.6 W/cm², 5 min), MX-CS showed a greater photothermal effect than MXene alone did (30 μg/mL, 49.9 °C for MX-CS and 46.5 °C for MXene). Importantly, MRSA cells were rapidly adsorbed on MX-CS hydrogel (containing 30 μg/mL MXene) and completely inhibited (99.18 %) under NIR irradiation for 5 min. In contrast, MXene (30 μg/mL) and CS hydrogel alone only inhibited 64.52 % and 23.72 % MRSA, respectively, significantly lower than the inhibition caused by MX-CS (P < 0.001). Interestingly, when the hyperthermia was depleted by a 37 °C water bath, the bacterial inhibition rate of MX-CS significantly decreased to 24.65 %. In conclusion, MX-CS hydrogel has a remarkable synergistic anti-MRSA activity by gathering MRSA cells and MXene-induced hyperthermia, and may have great potentials in treating MRSA-infected diseases.

Ti3C2Tx MXene loaded with indocyanine green for synergistic photothermal and photodynamic therapy for drug-resistant bacterium

Infections caused by antibiotic-resistant bacteria are a critical threat to human health. Considering the difficulties and time-consuming nature of synthesizing new antibiotics, it is of great significance and importance to develop the antibiotic-independent antibacterial approaches against drug-resistant bacteria. Nanomaterials-based photothermal therapy (PTT) and photodynamic therapy (PDT) have attracted much attention due to their broad-spectrum bactericidal activity, low toxicity, and drug-free feature. In this work, we loaded indocyanine green (ICG) on the Ti₃C₂T_x MXene nanosheets (454 nm) so as to combine the photothermal effect of MXene with the photodynamic effect of ICG. Without near-infrared (NIR) irradiation, MXene (20 μg/mL), ICG (5 μg/mL) or ICG-loaded MXene (ICG-MXene) showed no significant antibacterial activity against methicillin-resistant Staphylococcus aureus (MRSA). Under NIR, however, the viability loss of MRSA remarkably increased to 45% for MXene, 66% for ICG and 100% for ICG-MXene. We further found that the great anti-MRSA activity of ICG-MXene under NIR was attributed to the combination of photothermal effect of MXene (high temperature) and photodynamic effect of ICG (high level of reactive oxygen species). Our findings indicate that MXene can be used as both the photothermal agent and the carrier of photosensitizers to achieve the synergistic PTT/PDT therapy for bacterial infections.

Enhanced antibacterial activity of Rosehip extract-functionalized Mg(OH)2 nanoparticles: An in vitro and in vivo study

The development of nanoparticles as antimicrobial agents against pathogenic bacteria has emerged as one of the leading global healthcare challenges. In this study, Mg(OH)₂ NPs with controlled morphology and nanometric size, using two distinct counterions, chloride or nitrate, have been synthesized using Rosehip (RH) extract that has privileges beyond conventional chemical and physical methods. Various physicochemical techniques were used to characterize the RH-functionalized Mg-based NPs. They exhibited a spherical shape with a diameter of ~10 nm, low crystallinity compared to non-functionalized NPs, high polyphenol content, and negative zeta potential in three different media (H₂O, TSB, and cell medium). The resulting RH-functionalized Mg-based NPs also exhibited an increased antibacterial activity against Gram-positive (S. Epidermis and S. aureus) and Gram-negative (E. Coli) bacteria compared to those prepared in pure water (0 % RH), an effect that was well evident with low NPs contents (250 μg/mL). A preliminary attempt to elucidate their mechanism of action revealed that RH-functionalized Mg-based NPs could disrupt cellular structures (bacterial cell wall and cytoplasmic membrane) and damage the bacterial cell, as confirmed by TEM imaging. Noteworthy is that Mg-based NPs exhibited higher toxicity to bacteria than to eukaryotic cells. More significantly, was their enhanced in vivo efficacy in a Galleria mellonella invertebrate animal model, when infected with S. aureus bacteria. Overall, our findings indicate that well-engineered Rosehip magnesium-based nanoparticles can be used as a green non-cytotoxic polyphenolic source in different antibacterial applications for the biomedical industry.

Size-dependent photothermal antibacterial activity of Ti3C2Tx MXene nanosheets against methicillin-resistant Staphylococcus aureus

Developing antibiotics-independent antibacterial materials is of great importance for combating drug-resistant bacteria, such as methicillin-resistant Staphylococcus aureus (MRSA). MXene (transition metal carbides and nitrides), a class of novel 2D nanomaterials, has shown great potentials in biomedical areas. However, the effect of MXene size on its properties and bioactivity is still unknown. Herein, we report for the first time that the antibacterial photothermal therapy efficacy of Ti₃C₂T_x MXene nanosheets is size-dependent. Three MXene suspensions with small size of 196 nm (MX-s), medium size of 347 nm (MX-m) and large size of 497 nm (MX-l) were prepared via ultrasonication. Upon NIR irradiation for 5 min, the temperature of MXene suspensions (10 μg/mL) increased to 64, 60 and 56 °C for MX-s, MX-m and MX-l, respectively. Accordingly, the viability loss of MRSA induced by MX-s, MX-m and MX-l under NIR was 93%, 69% and 56%, respectively. The in vivo study in the MRSA-infected mouse model showed that the photothermal therapy efficacy of MX-s was comparable to that of the positive control vancomycin. This is the first report on the size-dependent photothermal effect and photothermal antibacterial activity of MXene, which may guide the development of MXene-based therapeutics in the future. In addition, the drug-free antibacterial therapy has great implications for the treatment of antibiotics-resistant bacteria infections.

Bacterial outer membrane vesicles as potential biological nanomaterials for antibacterial therapy

Antibiotic therapy is one of the most important approaches against bacterial infections. However, the improper use of antibiotics and the emergence of drug resistance have compromised the efficacy of traditional antibiotic therapy. In this regard, it is of great importance and significance to develop more potent antimicrobial therapies, including the development of functionalized antibiotics delivery systems and antibiotics-independent antimicrobial agents. Outer membrane vesicles (OMVs), secreted by Gram-negative bacteria and with similar structure to cell-derived exosomes, are natural functional nanomaterials and known to play important roles in many bacterial life events, such as communication, biofilm formation and pathogenesis. Recently, more and more reports have demonstrated the use of OMVs as either active antibacterial agents or antibiotics delivery carriers, implying the great potentials of OMVs in antibacterial therapy. Herein, we aim to provide a comprehensive understanding of OMV and its antibacterial applications, including its biogenesis, biofunctions, isolation, purification and its potentials in killing bacteria, delivering antibiotics and developing vaccine or immunoadjuvants. In addition, the concerns in clinical use of OMVs and the possible solutions are discussed. STATEMENT OF SIGNIFICANCE: The emergence of antibiotic-resistant bacteria has led to the failure of traditional antibiotic therapy, and thus become a big threat to human beings. In this regard, developing more potent antibacterial approaches is of great importance and significance. Recently, bacterial outer membrane vesicles (OMVs), which are natural functional nanomaterials secreted by Gram-negative bacteria, have been used as active agents, drug carriers and vaccine adjuvant for antibacterial therapy. This review provides a comprehensive understanding of OMVs and summarizes the recent progress of OMVs in antibacterial applications. The concerns of OMVs in clinical use and the possible solutions are also discussed. As such, this review may guide the future works in antibacterial OMVs and appeal to both scientists and clinicians.

Enhanced Antibacterial Activity of Indocyanine Green-Loaded Graphene Oxide via Synergistic Contact Killing, Photothermal and Photodynamic Therapy

Methicillin-resistant Staphylococcus aureus (MRSA) has become a serious threat to human's health. Recently, photodynamic/photothermal therapy (PDT/PTT) has emerged as promising strategies against antibiotics-resistant pathogens due to their broad antibacterial spectrum and negligible resistance. In this work, the photosensitizer indocyanine green (ICG) was loaded on graphene oxide (GO) nanosheets with good encapsulation efficiency high to 92.31%. Under near-infrared (NIR) irradiation, the anti-MRSA efficiency of GO (20 μg/ml), ICG (5 μg/ml) and ICG-GO (5 μg/ml-20 μg/ml) was 33.76%, 40.15% and 99.86%, respectively. We further showed that NIR irradiation mildly increased the temperature to 43.1 °C for ICG-GO, and lead to the highest reactive oxygen species (ROS) generation (316.51% and 157.11% compared to ICG alone and GO alone). In conclusion, ICG-GO has a great potential for antibacterial treatment due to its synergistic contact killing, photothermal and photodynamic activity.