Experimental Study on the Resistance of Synthetic Penicillin Solid Lipid Nanoparticles to Clinically Resistant Staphylococcus aureus

Abstract

Background: With the increasing resistance of antibiotics to bacteria, new and effective methods are needed to transform existing antibiotics to solve the problem of long development cycles for new drugs. The antibiotic nanodelivery system has proven to be a promising strategy.

Aim: The purpose of this study is to synthesize penicillin solid lipid nanoparticles (penicillin SLNs) to enhance the antibacterial activity of penicillin against drug-resistant Staphylococcus aureus.

Materials and methods: Penicillin SLNs were synthesized. And particle size, the polydispersity index (PI), and zeta potential (ZP) of penicillin SLNs were measured. The surface morphology of penicillin SLNs was observed using a transmission electron microscope.

Results: The particle size of penicillin SLNs is 112.3 ± 11.9 nm, the polydispersity index (PI) and zeta potential (ZP) of penicillin SLNs are 0.212 ± 0.03 and -27.6 ± 5.5 mV. The encapsulation efficiency and drug loading were 98.31 ± 1.2% and 4.98 ± 0.05 (%w/w), respectively. Penicillin SLNs had a more significant inhibitory effect on the growth of methicillin-sensitive Staphylococcus aureus (MSSA) after the drug and the bacteria were incubated for 12 hours. The number of MRSA colonies in the penicillin group increased after 12 hours, while the number of MRSA colonies in the penicillin SLNs group did not change significantly.

Conclusion: Penicillin SLNs enhance the ability of penicillin to enter cells and increase the concentration of penicillin in the cell and also extend the residence time of penicillin in the cell. Our findings indicated that penicillin SLNs enhance the inhibitory effect of penicillin on drug-resistant Staphylococcus aureus.

Figure 1

Penicillin SLNs. (a) Penicillin SLNs under a transmission electron microscope (TEM). (b) Penicillin SLNs particle size distribution diagram. Scar bar: 100 nm. Penicillin SLNs: penicillin solid lipid nanoparticles.

Figure 2

Differential scanning calorimetry result. A 2 mg sample of penicillin SLN, F68, and ATO was placed in an aluminum pan and sealed. Use an empty pot as a reference. ATO: Compritol 888 ATO; F68: Lutrol F68.

Figure 3

X-ray diffraction (XRD) patterns. A 2 mg sample of penicillin SLN, F68, and ATO was placed in an aluminum pan and sealed. Use an empty pot as a reference. The peaks of penicillin SLN, F68, and ATO were recorded by A Bruker D8 advanced diffractometer. ATO: Compritol 888 ATO; F68: Lutrol F68.

Figure 4

Drug release profile. 1 mg of penicillin SLNs, free penicillin was dissolved in 5 mL PBS buffer (0.1 mol/L) and subjected to dialysis. At a certain time point (0, 1, 2, 3, 4, 5, 7, 9, 11, 24, 48, and 72 h), the penicillin content was calculated, and the time-drug accumulation release curve was drawn.

Figure 5

The antibacterial curve of penicillin SLNs against MSSA (a) and MRSA (b). RAW264.7 cells were diluted to 10⁶ cells/well with DMEM complete medium without penicillin and streptomycin on a 24-well plate. The ratio of the added Staphylococcus aureus and RAW264.7 cells was 10 : 1, and the culture solution was aspirated after incubating for 1 hour. For MSSA, 1, 4, and 10 MIC penicillin solution was added. For MRSA, 1, 4, and 10 MIC penicillin SLNs suspension was added. A blank was used as control. After coincubating for 0, 12, 24, and 48 hours, the number of bacteria to draw an intracellular bacteriostasis curve was calculated, the vertical axis is the logarithmic value of the bacteria, and the horizontal axis is the time point. SA: Staphylococcus aureus; Penicillin SLNs: penicillin solid lipid nanoparticles; MSSA: methicillin-sensitive SA; MRSA: methicillin-resistant SA.