Gentamicin loaded PLA Microspheres Susceptibility against Staphylococcus aureus and Escherichia coli by Kirby-Bauer and Micro-dilution Methods

Poly(lactic) acid (PLA) microspheres is well known as a drug carrier in drug delivery system. This is due to PLA's versatility and easily custom-made based on specific applications. In this study, gentamicin with different wt% (0.125,0.25 and 0.375) was encapsulated within PLA microspheres for drug release application which further tested using Agar Well Diffusion (Kirby-Bauer) and Minimum Inhibitory Concentration (MIC) methods. The study was conducted to determine the effectiveness of gentamicin delivery from PLA microspheres to inhibit the growth of Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) and determine the MIC value of gentamicin for both strains. For Kirby-Bauer assay, the diameter for zone of inhibition was measured and compared for each wt% of gentamicin used while for MIC, the result was determined based on the lowest concentration of gentamicin works to kill S. aureus and E. coli. The higher the wt% of gentamicin loaded into PLA microspheres, the larger the diameter for zone of inhibition was obtained, with the highest diameter at 0.375 wt% (2.3 cm for S. aureus and 2.5 cm for E. coli). While, MIC value for both strains tested was at 0.002 mg/mL of gentamicin. The study showed that entrapment of gentamicin in the PLA microspheres is released in a controlled and sustained manners which effective to kill bacterial strains as the release is significantly above the MIC value.