Submitted to: Journal of Food Protection
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/25/2009
Publication Date: 2/20/2010
Citation: Ravishankar, S., Zhu, L., Reyna-Granados, J., Law, B., Joens, L., Friedman, M. 2010. Carvacrol and cinnamaldehyde inactivate antibiotic-resistant Salmonella enterica in buffer and on celery and oysters. Journal of Food Protection. 73(2)234-240. Interpretive Summary: Salmonella enterica on contaminated foods is one of the leading causes of gastrointestinal foodborne illness. The emergence of antibiotic resistant strains of this pathogen is of concern to food processors, including the produce, poultry, and oyster industries. To help overcome this problem, we are participating in collaborative studies with colleagues at the Department of Veterinary Science and Microbiology at the University of Arizona in Tucson on new ways to inactivate antibiotic resistant foodborne pathogens with the aid of safe, food-compatible, plant-derived compounds and plant extracts. In the present study, we screened 23 Salmonella isolates for resistance against the following 7 antibiotics: amoxicillin/clavulanic, ampicillin, cefoxitin, chloramphenicol, streptomycin; trimethoprim/sulfamethoxazole, and tetracycline. Two resistant and two susceptible strains from this group were each exposed to the following plant compounds: carvacrol, the main ingredient in oregano plant essential oil, and cinnamaldehyde, the main ingredient in cinnamon plant essential oil. Both carvacrol and cinnamaldehyde inactivated both antibiotic resistant and nonresistant Salmonella strains in solution and on two foods, celery and oysters. The present study with Salmonella extends our previous study on the inactivation of antibiotic-resistant Campylobacter jejuni strains published in 2008 in the Journal of Food Protection, Volume 71, pages 1145-1149.
Technical Abstract: Salmonella enterica is one of the leading causes of gastrointestinal foodborne illness. The emergence of antibiotic resistant strains of this pathogen is of concern to food processors, including the produce, poultry, and oyster industries. The objective of this research was to identify the potential antimicrobial activities of two plant-derived compounds, cinnamaldehyde and carvacrol, against antibiotic resistant strains of S. enterica in phosphate buffer (PBS) and on contaminated celery and oysters. Twenty thee isolates were screened for resistance to 7 antibiotics. Two resistant and two susceptible strains were chosen for the study. Different concentrations of cinnamaldehyde and carvacrol (0.1, 0.2, 0.3 and 0.4% v/v) were added to cultures of S. enterica with populations of 104 CFU/ml. These were mixed well and incubated at 37°C. Samples were taken at 0, 1, 5 and 24 h diluted, plated for enumeration, incubated at 37°C and counted after 24-48 h. Both cinnamaldehyde and carvacrol showed complete inactivation of S. enterica in PBS at 0.3 and 0.4% concentrations at all time points tested. No survivors were detected at 5 h of sampling with 0.2% concentration of both antimicrobials. Cinnamaldehyde at 0.1% showed no survivors after 5 or more hours, while survivors were seen for some strains with 0.1% carvacrol. These results and additional data based on dipping celery and oysters contaminated with ~ 7 logs CFU in 1% solutions of the antimicrobials for 10 min or 1 h followed by storage for 3 d at 4°C suggest that carvacrol and cinnamaldehyde have the potential to inactivate antibiotic-resistant S. enterica in liquid and solid foods at concentrations of 0.1% and higher.