Susceptibility of Strains to Selected Natural Products and Frontline Antibiotics.

species have developed resistance to existing antibiotics. The development of alternative therapies is, therefore, a necessity. This study evaluates the susceptibility of strains to selected natural products (NPs) and frontline antibiotics. Two strains (ATCC 33560 and MT947450) and two strains (ATCC 33559 and MT947451) were used. The antimicrobial potential of the NPs, including plant extracts, essential oils, and pure phytochemicals, was evaluated by broth microdilution. The growth was measured by spectrophotometry and iodonitrotetrazolium chloride. Antibiotic resistance genes ((O) and A) were characterized at the molecular level. The minimum inhibitory concentrations (MICs) and the minimum bactericidal concentrations (MBCs) ranged from 25 to 1600 µg/mL. Cinnamon oil, (E)-Cinnamaldehyde, clove oil, eugenol, and baicalein had the lowest MIC and MBC values (25-100 µg/mL). MT947450 and MT947451 were sensitive to erythromycin and gentamicin but resistant to quinolones and tetracycline. Mutations in A and (O) genes from resistant strains were confirmed by sequencing. The findings show that NPs are effective against drug-sensitive and drug-resistant strains. The resistance to antibiotics was confirmed at phenotypic and genotypic levels. This merits further studies to decipher the action mechanisms and synergistic activities of NPs.