Table 2 Effect of positively charged ligand-conjugated metal nanoclusters (NCs) towards gram-positive and gram-negative bacteria
From: Size and charge effects of metal nanoclusters on antibacterial mechanisms
Material | Target pathogens | Charge (zeta potential) | Results | Antibacterial mechanism | References | |
|---|---|---|---|---|---|---|
Gram-positive bacteria | Gram-negative bacteria | |||||
Gold nanoclusters (AuNCs)–DAMP | Staphylococcus aureus (ATCC29213) Methicillin-resistant S. aureus (MRSA) Vancomycin-resistant Enterococcus (VRE) | Escherichia coli (ATCC35218) Multidrug resistant (MDR) E. coli MDR Acetobacter baumannii MDR Pseudomonas aeruginosa MDR Klebsiella pneumoniae |  + 37.6 ± 1.1 mV | The antibacterial effect of AuNCs-DAMP widely ranges in gram-positive and gram-negative bacteria | Cell membrane damage | |
AuNCs-MUTAB | S. pneumoniae Bacillus subtilis Ent. Faecalis VRE | E. coli P. aeruginosa | Positive (not mentioned) | The antimicrobial effect of AuNCs-MUTAB showed broad-spectrum actions against both in gram-positive and gram-negative bacteria | Damage to the membrane integrity of bacteria | [116] |
Branched polyethyleneimine-functionalized silver nanoclusters (bPEI-AgNCs) | Amycolatopsis azurea MRSA (CD-489) E. faecalis (CD-746, CD-895) S. aureus (CD-1578) | P. aeruginosa (ATCC 19660, CD-1006, CD-23, CD-14) E. coli (CD-549, CD-2, CD-3) Ent. cloacae complex (CD-1412, CD-866) |  + 30 mV | bPEI-AgNCs selectively suppressed the growth of both gram-positive and gram-negative bacteria | Cell membrane disruption | [117] |
Prot/MTU-AuNCs | S. aureus | E. coli | Positive (not mentioned) | Prot/MTU-AuNCs showed an antimicrobial effect against both gram-positive and gram-negative bacteria | Cell membrane damage and reactive oxygen species (ROS) generation | [101] |
Peptide@AgNCs (KLA@AgNCs) | S. aureus | E. coli |  + 29.8 mV | The minimum inhibitory concentration (MIC) of KLA@AgNCs was determined in both gram-positive and gram-negative bacteria | Membrane integrity damage | [118] |
AuNCs decorated with amine-functionalized graphene oxide (Au-GO-NH2) nanosheets | S. aureus B. subtilis | E. coli P. aeruginosa |  + 10.4 ± 0.5 mV | Cell viability and MIC level of Au-GO-NH2 were better for gram-positive bacteria than gram-negative bacteria. But the growth curve for gram-negative bacteria was lower than for gram-positive bacteria | Bacteria were captured in a film, oxidative stress was produced, and photothermal ablation occurred | [119] |
Peptide-reduced gold nanoclusters (Au-HHC NCs) | S. aureus S. epidermidis | E. coli P. aeruginosa |  + 31.4 ± 5.7 mV | Au-HHC NCs (positive charge) exhibited higher antimicrobial activity than Au-HHC-CA NCs (negative charge). Au-HHC NCs showed low MICs toward gram-positive and gram-negative bacteria | Cell membrane disruption | [120] |
Positively charged ligand-conjugated metal NCs which showed better antibacterial effects against gram-positive bacteria than against gram-negative bacteria | ||||||
Quaternary ammonia (QA) salt-functionalized AuNCs (QA-AuNCs) | S. aureus MRSA | E. coli MDR E. coli | Positive (not mentioned) | QA-AuNCs had a striking antibacterial effect on gram-positive and gram-negative bacteria but were better for gram-positive bacteria | Membrane integrity, membrane permeability, and membrane potential damage | [113] |
Alkyl-thiolated zwitterionic and pyridinium ligands AuNCs | S. aureus MRSA | E. coli MDR P. aeruginosa MDR K. pneumoniae | Positive (not mentioned) | MIC levels of AuNCs were smaller for gram-positive bacteria than for gram-negative bacteria, at 8 µg/ml for S. aureus and MRSA, and 32 µg/ml for E. coli, P. aeruginosa, and K. pneumoniae | Adhesion and penetration of GNCs into the cell envelope | [109] |
Riboflavin-protected silver nanoclusters (RF@AgNCs) | S. aureus | E. coli |  + 0.283 mV | RF@AgNCs showed an antimicrobial effect on both gram-positive and gram-negative bacteria, but were better for gram-positive bacteria. Relative viabilities of S. aureus and E. coli treated with RF@AgNCs were 0.83% and 2.08% | Cell membrane damage | [121] |
AgNCs-GSH@chitosan | S. aureus B. subtilis | E. coli P. aeruginosa |  + 24.2 ± 4.7 mV | MIC levels of AgNCs-GSH@chitosan were smaller for gram-positive bacteria than for gram-negative bacteria, at 0.48 and 0.63 µM for S. aureus and B. subtilis, and 0.73 and 1.13 µM for E. coli and P. aeruginosa | ROS generation | [122] |
Positively charged ligand-conjugated metal NCs which showed better antibacterial effect against gram-negative bacteria than gram-positive bacteria | ||||||
Dpep-AgNCs | S. aureus | E. coli Shewanella oneidensis MR-1 | Positive (not mentioned) | Dpep-AgNCs had an antibacterial effect against both gram-positive and gram-negative bacteria but were better against gram-negative bacteria. MIC levels of Dpep-AgNCs for E. coli and She. oneidensis were 6.5 µM, but for S. aureus was 13 µM | Uptake and internalization of Ag ions; ROS generation | [80] |
4,6-diamino-2-pyrimidinethiol (DAPT)-modified AuNCs (DAPT-AuNCs) | S. aureus | E. coli |  + 14 mV | Via SEM imaging, DAPT-AuNCs more strongly damaged gram-negative bacteria than gram-positive bacteria, but the ROS generation level of gram-positive bacteria was higher than that of gram-negative bacteria | Cell membrane damage | [123] |