Bactericidal and Antibiotic Synergistic Effect of Nanosilver Against Methicillin-Resistant Staphylococcus aureus

Silver Nanoparticle-Based Combinations with Antimicrobial Agents against Antimicrobial-Resistant Clinical Isolates

The increasing prevalence of antimicrobial-resistant (AMR) bacteria along with the limited development of antimicrobials warrant investigating novel antimicrobial modalities. Emerging inorganic engineered nanomaterials (ENMs), most notably silver nanoparticles (AgNPs), have demonstrated superior antimicrobial properties. However, AgNPs, particularly those of small size, could exert overt toxicity to mammalian cells. This study investigated whether combining AgNPs and conventional antimicrobials would produce a synergistic response and determined the optimal and safe minimum inhibitory concentration (MIC) range against several wild-type Gram-positive and -negative strains and three different clinical isolates of AMR Klebsiella pneumoniae. Furthermore, the cytotoxicity of the synergistic combinations was assessed in a human hepatocyte model. The results showed that the AgNPs (15-25 nm) were effective against Gram-negative bacteria (MIC of 16-128 µg/mL) but not Gram-positive strains (MIC of 256 µg/mL). Both wild-type and AMR K. pneumoniae had similar MIC values following exposure to AgNPs. Importantly, co-exposure to combinations of AgNPs and antimicrobial agents, including kanamycin, colistin, rifampicin, and vancomycin, displayed synergy against both wild-type and AMR K. pneumoniae isolates (except for vancomycin against AMR strain I). Notably, the tested combinations demonstrated no to minimal toxicity against hepatocytes. Altogether, this study indicates the potential of combining AgNPs with conventional antimicrobials to overcome AMR bacteria.

Nanosilver-Decorated Biodegradable Mesoporous Organosilica Nanoparticles for GSH-Responsive Gentamicin Release and Synergistic Treatment of Antibiotic-Resistant Bacteria

PURPOSE

Antibiotic-resistant bacteria are pathogens that have emerged as a serious public health risk. Thus, there is an urgent need to develop a new generation of anti-bacterial materials to kill antibiotic-resistant bacteria.

METHODS

Nanosilver-decorated mesoporous organosilica nanoparticles (Ag-MONs) were fabricated for co-delivery of gentamicin (GEN) and nanosilver. After investigating the glutathione (GSH)-responsive matrix degradation and controlled release of both GEN and silver ions, the anti-bacterial activities of Ag-MONs@GEN were systematically determined against several antibiotic-susceptible and antibiotic-resistant bacteria including Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus faecalis. Furthermore, the cytotoxic profiles of Ag-MONs@GEN were evaluated.

RESULTS

The GEN-loaded nanoplatform (Ag-MONs@GEN) showed glutathione-responsive matrix degradation, resulting in the simultaneous controlled release of GEN and silver ions. Ag-MONs@GEN exhibited excellent anti-bacterial activities than Ag-MONs and GEN alone via inducing ROS generation, especially enhancing synergetic effects against four antibiotic-resistant bacteria including Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Enterococcus faecalis. Moreover, the IC50 values of Ag-MONs@GEN in L929 and HUVECs cells were 313.6 ± 15.9 and 295.7 ± 12.3 μg/mL, respectively, which were much higher than their corresponding minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values.

CONCLUSION

Our study advanced the development of Ag-MONs@GEN for the synergistic and safe treatment of antibiotic-resistant bacteria.

Effect of silver nanoparticles on vancomycin resistant Staphylococcus aureus infection in critically ill patients

A prevalent increase in antimicrobial resistance represents a universal obstacle for the treatment of Staphylococcus aureus (S. aureus) infection, especially in critically ill patients. Silver nanoparticles are defined as broad spectrum bactericidal agents, which might be effective against vancomycin resistant S. aureus (VRSA). In this study, we examined the bactericidal efficacy of silver nanoparticles on VRSA in 150 blood and sputum samples isolated from intensive care patients. Methicillin resistant S. aureus (MRSA) isolates were identified in 83 samples, with an incidence of 55.3%. Meanwhile, VRSA isolates were found in 11 and 8 isolates (a total of 19 isolates out of 150) from sputum and blood samples, with an incidence of 14.67% and 10.67%, respectively, with a total incidence of 12.67%. Vancomycin intermediate S. aureus (VISA) isolates had an inhibitory zone ranging from 9 to 13 mm, which was found in 13 out of 19 isolates, whereas VRSA isolates had an inhibitory zone ranging from 0 to 6 mm, which was detected in 6 out of 19 isolates. The findings of this study confirm that silver nanoparticles are an effective treatment against VRSA.

Recent advances in Staphylococcus aureus infection: focus on vaccine development

Staphylococcus aureus normally colonizes the nasal cavity and pharynx. After breaching the normal habitat, the organism is able to cause a number of infections at any site of the body. The development of antibiotic resistance has created a global challenge for treating infections. Therefore, protection by vaccines may provide valuable measures. Currently, several vaccine candidates have been prepared which are either in preclinical phase or in early clinical phase, whereas several candidates have failed to show a protective efficacy in human subjects. Approaches have also been made in the development of monoclonal or polyclonal antibodies for passive immunization to protect from S. aureus infections. Therefore, in this review we have summarized the findings of recently published scientific literature to make a concise report.

Comparison Therapeutic Effects of Ciprofloxacin, Silver Nanoparticles and Their Combination in the Treatment of Pseudomonas keratitis in Rabbit: An Experimental Study

Pseudomonas aeruginosa is one of the most common causes of keratitis. The current study was done to evaluate the therapeutic effects of antibacterial combinations with Silver nanoparticles (Ag-NPs) and Ciprofloxacin in experimental Pseudomonas keratitis. Sixty four New Zealand rabbits were prepared. All rabbits were randomly categorized into eight groups (each group containing eight rabbits): Control +, Control -, Ciprofloxacin, Ag-NPs, Ciprofloxacin plus Betamethasone, Ag-NPs plus Betamethasone, Ciprofloxacin plus Ag-NPs, and Ciprofloxacin plus Ag-NPs plus Betamethasone. Twelve hours after bacterial inoculation into the cornea, the eyes were examined daily to evaluate the number of days of ocular discharge and blepharospasm. Also, after 108 and 204 h, first grading of corneal opacity was done and then four rabbits of each groups were euthanized for bacterial count. The results showed that the means of days of blepharospasm, ocular discharge, and bacterial counts (log CFU mL^-1) were significantly different in the treatment groups at 108 and 204 h (P <0.0005, ANOVA). According to Tukey's test, Ciprofloxacin plus Ag-NPs plus Betamethasone group was significantly less than Control +, Ag-NPs, and Ag-NPs plus Betamethasone groups for these variables (P < 0.05). The mean rank of opacity scores was significantly different between treatment groups (P = 0.01, Kruskal-Wallis). Mann-Whitney U-test revealed that Ciprofloxacin plus Ag-NPs plus Betamethasone group had significantly better score than Control +, Ag-NPs, and Ag-NPs plus Betamethasone groups (P < 0.05). It seems Ag-NPs can be an appropriate adjuvant for Ciprofloxacin, but due to the results they can't be an alternative for Ciprofloxacin to treat Pseudomonas keratitis.

Augmented antibacterial activity of ampicillin with silver nanoparticles against methicillin-resistant Staphylococcus aureus (MRSA)

At present, including failed attempts, it takes about 15 years and costs totaling up to $2.6 billion to take a promising new compound from laboratory to the market. Increasing drug resistance among microbial pathogens has led to a growing interest in exploring novel methods to enhance the efficacy of existing drugs. Combination therapies involving two or more known antimicrobial methods, particularly those involving nanoparticles for combating the clinical problems associated with antibiotic resistance, have been garnering interest. In the current study, we determined whether a combination therapy involving silver nanoparticles, which are known for their antimicrobial activity, and the widely used antibiotic ampicillin can be effective against methicillin-resistant Staphylococcus aureus (MRSA). In the presence of sub-lethal dose of silver nanoparticles, ampicillin was found to be effective against MRSA. Indeed, the results show that silver nanoparticles and ampicillin act synergistically, with the effect being more pronounced when a lower concentration of ampicillin is present. When present at a higher concentration, ampicillin coats the silver nanoparticle, preventing the direct interaction of nanoparticles and bacteria. This study discusses the possible applications of combination antimicrobial therapies involving silver nanoparticles for therapeutic treatments.

A combination of silver nanoparticles and visible blue light enhances the antibacterial efficacy of ineffective antibiotics against methicillin-resistant Staphylococcus aureus (MRSA)

Background

Silver nanoparticles (AgNPs) are potential antimicrobials agents, which can be considered as an alternative to antibiotics for the treatment of infections caused by multi-drug resistant bacteria. The antimicrobial effects of double and triple combinations of AgNPs, visible blue light, and the conventional antibiotics amoxicillin, azithromycin, clarithromycin, linezolid, and vancomycin, against ten clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA) were investigated.

Methods

The antimicrobial activity of AgNPs, applied in combination with blue light, against selected isolates of MRSA was investigated at 1/2–1/128 of its minimal inhibitory concentration (MIC) in 24-well plates. The wells were exposed to blue light source at 460 nm and 250 mW for 1 h using a photon emitting diode. Samples were taken at different time intervals, and viable bacterial counts were determined. The double combinations of AgNPs and each of the antibiotics were assessed by the checkerboard method. The killing assay was used to test possible synergistic effects when blue light was further combined to AgNPs and each antibiotic at a time against selected isolates of MRSA.

Results

The bactericidal activity of AgNPs, at sub-MIC, and blue light was significantly (p < 0.001) enhanced when both agents were applied in combination compared to each agent alone. Similarly, synergistic interactions were observed when AgNPs were combined with amoxicillin, azithromycin, clarithromycin or linezolid in 30–40 % of the double combinations with no observed antagonistic interaction against the tested isolates. Combination of the AgNPs with vancomycin did not result in enhanced killing against all isolates tested. The antimicrobial activity against MRSA isolates was significantly enhanced in triple combinations of AgNPs, blue light and antibiotic, compared to treatments involving one or two agents. The bactericidal activities were highest when azithromycin or clarithromycin was included in the triple therapy compared to the other antibiotics tested.

Conclusions

A new strategy can be used to combat serious infections caused by MRSA by combining AgNPs, blue light, and antibiotics. This triple therapy may include antibiotics, which have been proven to be ineffective against MRSA. The suggested approach would be useful to face the fast-growing drug-resistance with the slow development of new antimicrobial agents, and to preserve last resort antibiotics such as vancomycin.