Content uploaded by Dusan Milivojevic
Author content
All content in this area was uploaded by Dusan Milivojevic on Dec 28, 2015
Content may be subject to copyright.
Institute of Molecular
Genetics and Genetic
Engineering, University
of Belgrade, Belgrade,
Serbia
1Department of
Chemistry, Faculty of
Science, University of
Kragujevac,
Kragujevac, Serbia
2
Silver(I) and gold(III) complexes
with aromatic nitrogen-containing heterocycles:
Antimicrobial evaluation
Dusan R. Milivojevic , Nada D. Savic , Biljana Dj. Glisic , Tatjana Ilic Tomic , Milos I. Djuran , Branka Vasiljevic
1 1 1222
The major public health concern nowdays is antibiotic resistance.Therefore, finding new antimicrobial
agents is imperative. Some metals have been introduced as potential antimicrobial agents to treat a
variety of diseases and conditions [1,2].
The aim of this study was to compare antimicrobial potential of silver(I) and gold(III) complexes
against planktonic and biofilm growing pathogenic bacteria.
Methods: Five aromatic nitrogen-containing heterocycles (N-heterocycles), pyridazine, pyrimidine,
pyrazine, quinoxaline and phenazine, were used as ligands for the synthesis of silver(I) and gold(III)
complexes (Fig. 1). These Ag(I) and Au(III) complexes and inorganic salts (AgNO and K[AuCl ]) were
evaluated against a panel of microbial pathogens. Effect on planktonic bacterial growth was assessed
using standard broth microdilution assay, while the effect on biofilms was studied by crystal violet
staining and fluorescent microscopy.
Antimibrobial activity:
Silver(I) and gold(III) complexes showed
exellent antimicrobial activity (Table 1), with
Ag(I) complexes being more potent.
Table 1. Minimal inhibitory concentrations (MIC) in mg/ml
P. aeruginosa biofilm
disruption activity:
By influencing cell viability silver(I) and
gold(III) complexes inhibited Pseudomonas
aeruginosa biofilm formation and more
importantly disrupted preformed biofilms
(Fig.2).
40
60
80
100
120
Biofilm remained, %
*
20
0
Au1 Au2 Au3 Au4 Au5 K[AuCl ] DMF
Au(III) compound
40
60
80
100
120
Biofilm remained, %
*
20
0
Ag1 Ag2 Ag3 Ag4 Ag5 AgNO DMSO
Ag(I) compound
3
4
10µm
10µm
Ag1
DMSO control
Figure 2. Relative percentages showing
Pseudomonas aeruginosa PAO1 and P. aeruginosa
MD-49 biofilm disruption capabilities of the silver(I) and
gold(III) complexes. Relative percentages were
calculated upon comparing with the negative control
(DMSO and DMF). Values presented here are mean
values of four replicate wells of two independent
experiments. Following the treatments, biofilms were
visualized using fluorescence microscopy after
Live/Dead staining with SYTO9 (green) and propidium
iodide (red).
Genomic DNA interaction:
Most of the complexes exhibited marked ability
to interact with bacterial genomic DNA in vitro
(Fig. 3)
120
100
80
60
40
20
0
Relative luminescence, %
Au1 Au2 Au3 Au4 Au5 DMF M
120
100
80
60
40
20
0
Relative luminescence, %
Ag1 Ag2 Ag3 Ag4 Ag5 DMSO M
Au(III) complex
Ag(I) complex
Figure 3. In vitro intercalation ability of Ag(I) and Au(III) complexes to P. aeruginosa gDNA. Genomic DNA (200 ng) was
incubated with MIC concentrations of each complex at 37 C, pH 7.4 and visualized after ethidium bromide staining.
Conclusion: Both silver(I) and gold(III)
complexes containing N-heterocycles have
promising antimicrobial potential, however
Ag(I) complexes were more efficient against
various tested pathogens in comparison to
Au(III) complexes . Given that the resistance to
silver and gold ions is rare, the utilization of
these compounds could be an efficient strategy
to fight widespread difficult-to-treat bacterial
infections.
References:
[1] Glišic Dj B, Djuran, IM: Gold complexes as antimicrobial agents: an overview of different
biological activities in relation to the oxidation state of the gold ion and the ligand
structure. Dalton Trans, 2014, 43, 5950–5969
[2] Lemire AJ, Harrison JJ, Turner, JR:Antimicrobial activity of metals: mechanisms,
molecular targets and applications. Nat Rev Microbiol, 2013,11, 371–384
Contact:
Dusan Milivojevic e-mail: dusan.milivojevic@imgge.bg.ac.rs
N N
NN
Ag
O
O
N
Ag
O
O
NO
O
Ag1
N
Ag
N
N
Ag
N
NO3-
NO3-
Ag2
NAgNN N
NO3-
NO3-
Ag
Ag3
NAgNN N
NO3-
NO3-
Ag
Ag4
AgNNAg
O2NO
ONO2
Ag5
Au1 Au2
Au3 Au4 Au5 Figure 1. Ten different Ag(I) and
Au(III) complexes used in this study.
P 9B
o
34
P. aeruginosa PAO1
P. aeruginosa MD-49
Compound
Pseudomonas
aeruginosa
PAO1
Escherichia
coli
Staphylococcus
aureus
Lysteria
monocitogenes
Candida
albicans
Ag1
2.5± 0.1
7.8± 0.4
15.6 ± 0.4
7.8± 0.6
7.8± 0.5
Ag2
2.5 ±
0.1
7.8 ± 0.6
15.6 ± 0.5
7.8 ± 0.8
15.6 ± 0.8
Ag3
7.8 ±
0.5
15.6 ± 0.8
15.6 ± 0.2
7.8 ± 0.4
15.6 ± 0.6
Ag4
15.6 ±
0.5
15.6 ± 0.4
31.2 ± 0.5
7.8 ± 0.4
15.6 ± 0.6
Ag5
7.8 ±
4
15.6 ± 1
31.2 ± 2
15.6 ± 0.4
31.2 ± 0.9
AgNO3
3.1 ± 0.1
5 ± 0.2
2.5 ± 0.2
3.1 ± 0.2
50 ± 3
Au1
10 ±
1
15.6 ± 0.8
15.6 ± 0.4
100 ± 6
50 ± 0.8
Au2
15 ±
1
15.6 ± 0.8
15.6 ± 0.5
100 ± 8
200 ± 3
Au3
8 ±
0.5
16 ± 0.6
15.6 ± 0.2
100 ± 4
50 ± 0.6
Au4
12.5 ±
0.5
31.2 ± 0.4
15.6 ± 0.5
100 ± 4
250 ± 1
Au5
30 ±
4
62.5 ± 1
62.5 ± 2
100 ± 4
250 ± 4
K[AuCl4]
8 ±
0.5
31.2 ± 0.8
15.6 ± 0.4
100 ± 5
40 ± 0.5