Antibacterial Assessment of Oils from Four Plants Against Selected Gentamicin-Resistant Gram-Positive Bacteria

Abstract

Background: The continuous rise of the menace of antibiotic resistance in microorganisms remains a global health problem, and this places a significant burden on the effective management of infections caused by multiple-resistant species. Phytocompounds are being constantly assessed for bioactive components to discover new products. This study was designed to investigate the antibacterial activity of oils from four plants – sweet almond (SAO), avocado (AO), black seed (BSO), and coconut (CO) against gentamicin-resistant Gram-positive bacteria from environmental sources. Methods: Fifty-seven water and soil samples were collected, and gentamicin-resistant Gram-positive bacteria isolates were recovered and identified with the ABIS online Microbiology software. Antibiotic susceptibility testing was done using the Kirby-Bauer disc diffusion method and multiple antibiotic resistance indices (MARI) of isolates evaluated. The antibacterial activity of plant oils was evaluated with the agar well diffusion technique, and analyses of bioactive compounds in the oil samples using a gas chromatograph-mass spectrometer (GC-MS). Results: Altogether, 60 Gram-positive Gentamicin-resistant bacterial isolates were recovered. The isolates spanned 34 species belonging to 11 genera, namely Staphylococcus spp. (27), Bacillus spp. (18), Enterococcus spp. (2), Listeria spp. (2), Macrococcus spp. (3), Corynebacterium sp. (1), Lactobacillus sp. (1), Paenibacillus sp. (1), Rothia sp. (1), Salinicoccus sp. (1) and Streptococcus spp. (3). A high proportion of the isolates were resistant to erythromycin and oxacillin at 96.7%, and ampicillin at 86.7%. Meropenem was observed to be the most effective in-vitro. All isolates (100.0%) exhibited multidrug resistance and had MARI above 0.4. In undiluted forms, plant oils exhibited very low inhibitory activity against isolates but improved upon dilution of the plant oils in the order BSO > SAO > CO > AO. Conclusion: The extremely high levels of multidrug resistance suggest the rapid dissemination of antibiotic resistance traits in the community and are quite bothersome. The plant oils exhibited low antimicrobial activity, emphasising the need for a continuous search for bioactive compounds against multidrug-resistant pathogens. This study, therefore, recommends the in-vivo investigation of the plant oils and the possibility of a synergistic relation-ship of these plant oils with conventional antibiotics.