1. Introduction
Results
Further work
References
1. Cushnie, T.P.T. & Lamb, A.J., 2011. Recent Advances in Understanding the Antibacterial Properties of Flavonoids. International journal
of antimicrobial agents, 38(2), pp.99–107. Available at: http://www.ncbi.nlm.nih.gov/pubmed/21514796 [Accessed August 11, 2014].
2. Hadley, S., 2014. Resistant Gram-Positive Infections: Where Have We Been, Where Are We Now, and Where Are We Going? Clinical
therapeutics, 36(10), pp.1298–1302. Available at: http://www.ncbi.nlm.nih.gov/pubmed/25287699 [Accessed November 9, 2014].
3. Moodley, S., Koorbanally, N. a, Moodley, T., Ramjugernath, D. & Pillay, M., 2014. The 3-(4,5-Dimethylthiazol-2-Yl)-2,5-Diphenyl
Tetrazolium Bromide (MTT) Assay Is a Rapid, Cheap, Screening Test for the in Vitro Anti-Tuberculous Activity of Chalcones. Journal of
Microbiological Methods, 104, pp.72–8. Available at: http://www.ncbi.nlm.nih.gov/pubmed/24978593 [Accessed September 23, 2014].
4. Shlaes, D.M. & Spellberg, B., 2012. Overcoming the Challenges to Developing New Antibiotics. Current opinion in pharmacology, 12(5),
pp.522–6. Available at: http://www.ncbi.nlm.nih.gov/pubmed/22832234 [Accessed September 23, 2014].
5. Tseng, S.-H., Lee, C.-M., Lin, T.-Y., Chang, S.-C. & Chang, F.-Y., 2011. Emergence and Spread of Multi-Drug Resistant Organisms:
Think Globally and Act Locally. Journal of microbiology, immunology, and infection, 44(3), pp.157–65. Available at:
http://www.ncbi.nlm.nih.gov/pubmed/21524608 [Accessed November 15, 2014].
Conclusions
Further investigations will include assessing viability of Gram-negative
bacteria using MTT assay, testing the chalcone chemicals against clinical
isolates of MDRs and using scanning electron microscopy (SEM) to
demonstrate possible morphological changes to the cells of non-resistant
and MDR organisms. The molecular features of the compounds will be
validated by Infrared spectroscopy (IR) and nuclear resonance microscopy
(NMR).
Antimicrobial Activities of Novel Substituted Ferrocenyl
Chalcone Derivatives
Elecia Henrya
, Robert B Smithb
, Michael Collinsc
, Susan J Birda
, Pauline Gowlanda
, John P Cassellaa
a
School of Sciences, Staffordshire University, Stoke-on-Trent, Staffordshire, ST4 2DF, United Kingdom
b
School of Forensic and Investigative Sciences, University of Central Lancashire, Preston, Lancashire, PR1
2HE, United Kingdom
c
Chesterfield Royal Hospital NHS Foundation Trust, Calow, Chesterfield, Derbyshire, S44 5BL, United Kingdom
Materials & Method
Resistance to antibacterial drugs has increased and has quickly become a
cause for global concern (Tseng et al., 2011). Healthcare-acquired infections
(HCAI) are caused by multi-drug resistant bacteria (MDR) such as methicillin-
resistant Staphylococcus aureus (MRSA), vancomycin-resistant
Staphylococcus aureus (VRSA) and carbapenemase-producing
Enterobacteriaceae (CPE) (Hadley, 2014). Since drug efficacy and
development has decreased, new antibiotics are needed against these
pathogens (Shlaes & Spellberg, 2012). Chalcones are naturally-occurring
flavonoids that show favourable antibacterial activity, especially against MDRs
(Cushnie & Lamb, 2011). One type of chalcone that has gained attention from
researchers are ferrocenyl chalcones.This study has examined the
antibacterial activity in terms of the minimum inhibitory concentration (MIC) of
novel ferrocenyl chalcones with increasing chain lengths (Figure 1) against
non-resistant bacteria and possible mode of action against Gram-positive
bacteria using MTT (3-(4,5-Dimethylthiazol-2-yl)-2,5-Diphenyltetrazolium
Bromide) assay to measure cell viability (Moodley et al., 2014)
Figure 1 – Diagram of basic structure of chalcone followed by nitrogen substitution and alkyl
iodide addition in ring A, and a ferrocenyl group substitution on ring B.
Figure 2 – Example of 2-fold broth microdilution plate (nonyl chalcone) after incubation and
final mean ±SD cell density (log cfu/ml) vs nonyl chalcone concentration (mg/ml) (N=3).
Table 1 – Final MIC (mg/ml) of each
chalcone against non-resistant
S.aureus 8244, K.pneumoniae and
E.coli 9483.
MIC values (mg/ml)
Chalcone S.aureus 8244 K.pneumoniae E.coli 9483
Methyl 0.125 0.125 0.125
Ethyl 0.125 0.125 0.125
Propyl 0.125 0.125 0.125
Butyl 0.125 0.125 0.125
Pentyl 0.125 0.125 0.125
Hexyl 0.063 0.125 0.125
Heptyl 0.063 0.125 0.125
Octyl 0.063 0.125 0.125
Nonyl 0.063 0.125 0.125
Decyl 0.031 0.125 0.125
The increasing lipophilicity of the chalcone compounds completely
necessitated their being dissolved in 100%DMSO, which dissolves both
polar and non-polar compounds. It was also observed that the compounds
appeared to react with components of the plastic tubes, which caused the
chalcones to degrade from deep red to dark brown. This led to the use of 96-
wll plates for the determination of the MICs. The chalcone compounds with
longer alkyl chains (hexyl to decyl) showed lower MICs than those with
shorter chains and appeared to be more effective against Gram-positive
bacteria. The MTT assays as shown above indicate that for the hexyl to
decyl chalcones the potential mode of action is to inhibit respiration resulting
in cell death.
MIC values (mg/ml)
Chalcone K.kristinae E.faecalis Salmonella
Hexyl 0.016 0.063 0.125
Heptyl 0.031 0.063 0.125
Octyl 0.016 0.063 0.125
Nonyl 0.016 0.063 0.125
Decyl 0.008 0.063 0.125
Table 2 – Final MIC (mg/ml) of each
chalcone against non-resistant
K.kristinae, E.faecalis and Salmonella
spp.
Figure 3 – Example of MTT assay microplate (decyl chalcone) after incubation and final
mean dilution (±SD) of respiring cells (570nm) based on formazan product vs decyl chalcone
concentration (mg/ml) (N=3).
Fe
N+
O
A B
I
-
R
Substituted Ferrocenyl Chalcone
Fe
N+
O
A B
I
-
R
Substituted Ferrocenyl Chalcone
A B
O
Chalcone