Comparison of the antibacterial activity of chelating agents using the agar diffusion method

Authors: Hinton Jr, Arthur; Ingram, Kimberly

Submitted to: International Journal of Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/24/2010
Publication Date: 11/29/2010
Citation: Hinton Jr, A., Ingram, K.D. 2010. Comparison of the antivacterial activity of chelating agents using the agar diffusion method. International Journal of Poultry Science. 9:1023-1026.

Interpretive Summary: EDTA (ethylenediaminetetraacetic acid) and EDDS (ethylenediaminedisuccinic acid) are both chelating agents that can bind minerals that produce water hardness. By binding these minerals, chelators reduce water hardness and increase the ability of soaps and detergents to remove dirt and debris during washing. EDTA is a synthetic, non-biodegradable chelator; and EDDS is a natural, biodegradable chelator. In this study, experiments were conducted to examine the ability these chelating agents to kill bacteria associated with poultry processing. Five concentrations of each chelating agent were placed into wells in agar media that had been inoculated with bacteria found on processed poultry. The agar plates were then incubated for 18-24 hours to permit bacteria in the agar to grow. After incubation, agar plates were examined for zones of inhibition of bacterial growth around the agar wells that had been filled with EDTA or EDDS. Results indicated that EDTA could inhibit growth of all 7 bacteria used in the study while EDDS could inhibit growth of 2 of these bacteria. Furthermore, the size of the zones of inhibition was larger around wells that contained higher concentrations of the chelators than around wells that contained lower concentrations of the chelating agents. The addition of these chelating agents to formulations of sanitizers used in poultry processing may improve the ability of the sanitizers to wash away microorganisms on chicken carcasses, and findings from this study indicate that EDTA and EDDS may also reduce contamination by killing microorganisms on the carcass.

Technical Abstract: The agar diffusion assay was used to examine antibacterial activity of 2 metal chelators. Concentrations of 0 to 40 mM of ethylenediaminetetraacetic acid (EDTA) and ethylenediamine-N,N’-disuccinic acid (EDDS) were prepared in 1.0 M potassium hydroxide (KOH). The pH of the solutions was adjusted to 11.0 with citric acid. Wells in agar media seeded with bacterial isolates were filled with the solutions containing the chelators. Agar plates were incubated at 35oC for 18-24 h, and zones of inhibition around the agar wells were measured. Results indicated that 10 mM EDTA produced significant (P < 0.05) zones of inhibition of Acinetobacter calcoaceticus, Enterococcus faecalis, Escherichia coli, Listeria monocytogenes, Pseudomonas aeruginosa, and Staphylococcus simulans growth, while 20 mM of EDTA produced significant (P < 0.05) zones of inhibition of Salmonella Typhimurium. Increases in the concentration of EDTA added to agar wells generally produced significantly increases in the size of zones of inhibition. EDDS only inhibited growth of A. calcoaceticus and P. aeruginosa. Significant (P < 0.05) zones of inhibition of both isolates were produced by 10 mM of EDDS, and significantly larger zones were produced by higher concentrations of EDDS, although intrazonal growth of A. calcoaceticus was present in all zones of inhibition of this isolate. The addition of these chelators to formulations of sanitizers used in poultry processing may improve the ability of sanitizers to wash away microorganisms on processed carcasses, but findings from this study indicate that these chelators also possess antimicrobial activity that may aid in reducing contamination of carcasses.