Enhancing efficacy of existing antibacterials against selected multiple drug resistant bacteria using cinnamic acid-coated magnetic iron oxide and mesoporous silica nanoparticles

Abstract

Developing new antibacterial drugs by using traditional ways is insufficient to meet existing challenges; hence, new strategies in the field of antibacterial discovery are necessary. An alternative strategy is to improve the efficacy of currently available antibiotics. Herein, the antibacterial efficacy of drugs (Cefixime, Sulfamethoxazole, and Moxifloxacin) and drug-loaded cinnamic acid-coated magnetic iron oxide and mesoporous silica nanoparticles (NPs) was elucidated versus Gram-negative bacteria (Pseudomonas aeruginosa, Klebsiella pneumoniae, neuropathogenic Escherichia coli K1 and Serratia marcescens) and Gram-positive bacteria (Methicillin-resistant Staphylococcus aureus (MRSA), Streptococcus pyogenes, Streptococcus pneumoniae, and Bacillus cereus). NPs were synthesized by co-precipitation and the Stöber method, and characterized by Fourier transform-infrared spectroscopy, Zetasizer, and Atomic force microscopy. Lactate dehydrogenase (LDH) assays were accomplished to determine drug cytotoxicity against human cells. Spherical NPs in the range of 118-362 nm were successfully synthesized. Antibacterial assays revealed that drugs conjugated with NPs portray enhanced bactericidal efficacies against multiple drug resistant bacteria compared to the drugs alone. Of note, Cefixime-conjugated NPs against Escherichia coli K1 and Methicillin- resistant Staphylococcus aureus, resulted in the complete eradication of all bacterial isolates tested at significantly lower concentrations compared to the antibiotics alone. Likewise, conjugation of Moxifloxacin resulted in the complete elimination of E. coli K1 and MRSA. Of note, nano-formulated drugs presented negligible cytotoxicity against human cells. These results depict potent, and enhanced efficacy of nano-formulated drugs against medically important bacteria and can be used as alternatives to current antibiotics. Future in vivo studies and clinical studies are warranted in prospective years to realize these expectations.

Keywords: Antibiotic resistance; MBC; cytotoxicity; drug discovery; infectious diseases; magnetic nanoparticles; mic; multi-drug resistance; nanotechnology.

Scheme 1.

Synthetic scheme of MNPs, APT-MNPs and CA-MNPs

Figure 1.

A. FTIR spectra of MNPs, APT-MNPs, CA and CA-MNPs, b. FTIR spectra of CA-MNPs, CEF and CEF-CA-MNPs

Scheme 2.

Synthetic scheme of MSN, APT-MSN and Nap-MSN

Scheme 3.

Synthetic scheme of Mn-CHI, MSN, APT-MSN and Mn-CHI-MSN

Figure 2.

A. FTIR spectra of MSN, APT-MSN and Nap-MSN. b. FTIR spectra Nap-MSN, Sul-Nap-MSN and Sul

Figure 3.

A. FTIR spectra of CHI, Mn-CHI and Mn-CHI-MSN. b. FTIR spectra of Mn-CHI-MSN, Mox-Mn-CHI-MSN and Mox

Figure 4.

Atomic force microscopic images CA-MNPs, CEF-CA-MNPs, Na-MSN, Sul-Nap-MSN, Mn-CHI-MSN and Mox-Mn-CHI-MSN showing nearly spherical morphology

Figure 5.

Cumulative release profile of CEF-CA-MNPs, Sul-Nap-MSN and Mox-Mn-CHI-MSN at pH 4.0 and pH 7.4

Figure 6.

Magnetic iron oxide and silica based NPs loaded with various drugs presented essential antibacterial activity against Gram-negative pathogenic bacteria. Briefly, bacteria (1 × 10⁶) were incubated with different drugs conjugated with ZnO-NPs and nanoparticle alone at 37°C for 2 h. Next, the cultures were ten-fold serially diluted and plated onto the nutrient agar plates and the plates were incubated for overnight at 37°C and counted the viable bacterial colonies on the following day. For negative control, bacteria were incubated in PBS alone whereas for positive control gentamicin (100 µg/mL) was used. The data are expressed as the means ± standard errors from several independent experiments performed in duplicate where (*) represent when P ≤ 0.05

Figure 7.

Magnetic iron oxide and silica based NPs loaded with different drugs eradicated Gram-positive pathogenic bacteria. Briefly, NPs and drug conjugates were mixed with test bacteria at 37°C for 2 h. After this, cultures were serially diluted and plated on nutrient agar plates. The plates were incubated for overnight at 37°C and subsequently viable bacteria were counted. For controls, bacteria incubated alone in PBS and with gentamicin (100 µg/mL) was used as negative and positive controls, respectively. The data are expressed as the means ± standard errors from several independent experiments performed in duplicate where (*) represent when P ≤ 0.05

Figure 8.

Magnetic iron oxide and silica based NPs loaded with different drugs revealed negligible cytotoxic effects against HeLa cell lines. Human cells were grown in 96 well plate up to 80–90% confluency as discussed in material and methods. Next, cells monolayer was challenged with NPs, drugs and drugs-NPs combinations for 24 h at 37°C in humidified conditions with 5% CO₂. Cells alone in RPMI was taken as negative control. The data are presented as mean ± standard error of three times independent experiments performed in duplicates. Data was analyzed using Graph Pad Prism software (8.0.2)