Solutions with metal nanoparticles and nanoparticle composites had strong in vitro activity against Gram-negative bacteria and may prevent the growth of multidrug-resistant Gram-negative colonizers in the lower respiratory tract for patients with chronic lung disease. These findings were published in the Journal of Microbiology, Immunology and Infection.

Clinical isolates of methicillin-resistant Staphylococcus aureus (MRSA), carbapenem-resistant Acinetobacter baumannii (CRAB), carbapenem-resistant Klebsiella pneumoniae (CRKP), Streptococcus pneumoniae, Haemophilus influenzae, and Pseudomonas aeruginosa were collected between 2019 and 2020 at the National Taiwan University Hospital. Between 2020 and 2021, isolates were randomly selected for an in vitro susceptibility study. The 5 evaluated solutions were chitosan-capped selenium nanoparticles (Se-NP), Silver nanoparticle (Ag-NP), and 3 composite nanoparticle solutions (ND50, NK99, and TPNT1). There were 50 clinical isolates of each pathogen included in the study, and the minimum inhibitory concentration (MIC) of the nanoparticle solutions against each isolate was determined via broth microdilution.

Among 50 CRKP isolates, 54% were carbapenemase-producing and 92% and 58% were susceptible to amikacin and tigecycline, respectively. For CRAB isolates, a MIC of 2 µg/mL or more was observed for colistin and tigecycline in 100% and 80% of the isolates, respectively. For P aeruginosa isolates, high susceptibility rates were observed fluoroquinolones (range, 90%-100%), third- and fourth-generation cephalosporins (range, 80%-90%), and piperacillin and tazobactam (range, 60%-70%). The H influenzae isolateswere highly susceptible to amoxicillin, clavulanate, and cephalosporins. Of the MRSA isolates, all were susceptible to vancomycin, daptomycin, and linezolid, and most were susceptible to fusidic acid (96%) and trimethoprim-sulfamethoxazole (75%). The S pneumoniae isolates were highly susceptible to vancomycin, levofloxacin, and moxifloxacin.


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In regard to Ag-NP, the MIC to neutralize 50% of bacteria (MIC50s) was less than 3.125 parts per million (ppm) for CRAB isolates, 25 ppm for CRKP isolates, and less than 3.125 ppm for P aeruginosa isolates. For Se-NP, the MIC50s was more than 50 ppm for isolates of CRAB, CRKP and P aeruginosa. For ND50, NK99, and TPNT1, the MIC50s were all one-eighth dilution for CRAB isolates; more than one-half dilution, one-half dilution, and one-half dilution for CRKP isolates; and more than one-half dilution, one-fourth dilution, and one-half dilution for P aeruginosa isolates, respectively.

For H influenzae isolates, the MIC50s was more than 3.125 ppm for Ag-NP and 12.5 ppm for Se-NP. Among all species, H influenzae was the most susceptible to Se-NP. Further analysis of H influezae isolates showed that the MICs of ND50 and NK99 were both more than one-half dilution, and the MIC50 and MIC90 of TPNT1 were both one-fourth dilution.

In regard to MRSA isolates, all were highly susceptible to the metal nanoparticles, with MIC50s of 50 ppm for Ag-NP, more than 50 ppm for Se-NP, more than one-half dilution for ND50, and one-half dilution for both NK99 and TPNT1. Similar results were observed for S pneumoniae isolates, with a MIC50s of more than 50 ppm for both Ag-NP and Se-NP, more than one-half dilution for ND50 and NK99, and one-half dilution for TPNT1.

The major limitation of this study was that all isolates were sourced from a single center.

According to the researchers, “metal nanoparticles and nanoparticle composites showed good in vitro activity against Gram-negative bacteria, including drug-resistant strains.” They concluded “further research is needed to explore the potential application of nanoparticles and nanoparticle composites as environmental disinfectants or therapeutic agents for multidrug-resistant organism-related infections.”

Reference

Huang Y-S, Wang J-T, Tai H-M, Chang P-C, Huang H-C, Yang P-C. Metal nanoparticles and nanoparticle composites are effective against Haemophilus influenzae, Streptococcus pneumoniae, and multidrug-resistant bacteria. J Microbiol Immunol Infect. 2022;S1684-1182(22)00071-8. doi:10.1016/j.jmii.2022.05.003