Microevolution In Staphylococcus Aureus: Does Exposure To Sub-Lethal Levels Of Cinnamon Bark Oil Lead To Changes In Antimicrobial Susceptibility?

The emergence of antibiotic-resistant and multi-drug resistant bacteria presents a growing global health issue recognized by the World Health Organization and the Centers for Disease Control and Prevention. Infections caused by drug-resistant bacteria are associated with longer hospital stays, higher treatments costs, and increased mortality compared to infections caused by antibiotic-susceptible pathogens. The global increase in antibiotic resistance is driven in part by the misuse and overuse of antibiotics in healthcare and agriculture. Staphylococcus aureus can infect humans and animals, and strains that are resistant to one or more antibiotics are common. Many plant essential oils have antimicrobial properties. Essential oils (EOs) are volatile liquids distilled from plant parts, and they contain a variety of organic compounds. Some EOs exhibit antibacterial, antiviral, and antifungal properties. Cinnamon bark oil (CBO) has been identified as one EO that has bacteriostatic, bactericidal, and anti-biofilm activities at low concentrations. Exposure to traditional antimicrobial compounds can select for resistant bacteria, although it is unclear if exposure to essential oils selects for resistance to essential oils or conventional antimicrobials. Building on prior experiments, I designed a study to evaluate the extent of resistance development among S. aureus isolates exposed to CBO in vitro. Three S. aureus isolates were serially exposed to half-minimum inhibitory concentration of CBO or penicillin in an agar dilution antimicrobial gradient exposure system, for 10 passages over forty days. Penicillin exposure induced greater reductions in susceptibility compared to CBO, and for both penicillin and CBO there was evidence of cross-resistance to the other antimicrobial. Compared to traditional antibiotics, cinnamon bark oil may exert less selective pressure on the antimicrobial susceptibility profile of bacterial pathogens, and therefore may provide a more sustainable option for treating and preventing infections. CBO may have applications in healthcare and agriculture, primarily as a topical antibiotic or antiseptic product. Replacing some antibiotics with CBO or other essential oils could slow the development of resistance to antimicrobials in bacterial populations