Adsorption of gentamicin on surfactant-kaolinite and its antibacterial activity

Abstract

Kaolinite is a common component of soil. Negatively-charged kaolinite can act as an adsorbent material and it has the ability to adsorb antimicrobial agents. In this study, local natural kaolinite was used to adsorb gentamicin and cationic surfactant molecules. Gentamicin-loaded surfactant-kaolinite (GSK) was prepared firstly by the attachment of cationic surfactant 4.0 mM hexadecyltrimethyl ammonium (HDTMA) on raw kaolinite to produce surfactant-kaolinite (SK), which was then loaded with gentamicin sulphate (50 and 200 mg/L) to yield GSK. Gentamicin-loaded kaolinite (GK) was also prepared and compared. All samples were characterised by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and CHNS elemental analysis. The characterisation results proved that the framework structure of kaolinite was not disrupted after modification with antimicrobial agents. The antibacterial activity of the samples was tested against Gram-negative Escherichia coli (ATCC 11229) and Gram-positive Enterococcus faecalis (ATCC 29212) through disc diffusion technique (DDT). Based on the technique, raw kaolinite did not exhibit antibacterial activity but showed antibacterial activity when HDTMA and/or gentamicin was loaded on kaolinite. In addition, GSK showed better antibacterial activity compared to GK and performed better on Gram-positive bacteria compared to Gram-negative bacteria. As a conclusion, immobilisation of HDTMA on kaolinite proved that kaolinite can act as an adsorbent to adsorb antibiotics and it has the potential to be developed as an enhanced antimicrobial agent.