Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2004
Publication Date: 8/1/2004
Citation: Yildirim-Aksoy, M., Lim, C.E., Dowd, M., Wan, P., Klesius, P.H., Shoemaker, C.A. 2004. In vitro inhibitory effect of gossypol from gossypol-acetic acid, and (+)- and (-)-isomers of gossypol on the growth of Edwardsiella ictaluri. Journal of Applied Microbiology. 97(1):97-82. Interpretive Summary: Gossypol is a naturally occurring yellow pigment of cottonseed and it is suspected to have anti-microbial activities. Gossypol exists in the cotton plant as a mixture of two forms, (+)- and (-)-isomers, which have different toxic effects to microorganisms. Thus, this study was conducted to determine if gossypol and its forms would inhibit the growth of the catfish pathogen, Edwardsiella ictaluri. Inhibitory effect of gossypols was determined by inoculation of bacteria on plates containing various concentrations of gossypols and by a disk diffusion method. Bacterial recovery was determined by preincubation of E. ictaluri in medium containing various concentrations of gossypol and subsequent activation of bacteria by inoculating on gossypol-free plates. Levels of all forms of gossypol of 1.5 'g/ml significantly reduced the number of bacterial colonies and 3 'g/ml or higher completely inhibited the growth of E. ictaluri. Increasing concentrations of all forms of gossypol significantly prolonged the period of bacterial growth. Recovery of E. ictaluri was less than 50% for all three forms of gossypol at levels of 5 'g/ml. The bacterial recovery remained relatively constant (6.5%) at gossypol concentrations from 10 to 100 'g/ml. Complete killing of E. ictaluri could not be reached even at gossypol levels up to 100 'g/ml. This study showed that all forms of gossypol have anti-E. ictaluri activities. This therapeutic effect of gossypol against E. ictaluri may be useful in controlling Enteric Septicemia of Catfish (ESC).
Technical Abstract: This study was conducted to evaluate the toxic effect of racemic gossypol (gossypol-acetic acid), and (+)- and (-)-isomers of gossypol on the growth of Edwardsiella ictaluri. Methods and Results: Inhibitory effect of various concentrations of gossypol on the growth of E. ictaluri was determined. Bacterial recovery was performed by preincubation of bacteria in media containing various concentrations of gossypol and subsequent activation of bacteria by inoculating on gossypol-free plates. Concentrations of racemic gossypol, (+)-gossypol and (-)-gossypol of 1.5 'g ml-1 or higher significantly reduced the number of bacterial colonies compared to that of the control. The growth of E. ictaluri was completely inhibited on agar plates supplemented with 3 'g ml-1, regardless of the forms of gossypol. The inhibitory effect of (+)-gossypol was higher than that of (-)-gossypol or gossypol-acetic acid. Recovery of E. ictaluri was less than 50% for all three forms of gossypol at concentrations of 5 'g ml-1. Bacterial recovery remained relatively constant (6.5%) at gossypol concentrations from 10 to 100 'g ml-1. Complete killing of E. ictaluri was not reached at gossypol levels up to 100 'g ml-1. Conclusion: Gossypol-acetic acid, and (+)- and (-)-optical isomers have anti-bacterial effect against E. ictaluri. Results suggest the action is bacteriostatic rather than bactericidal. Significance and Impact of the study: The therapeutic effect of gossypol against E. ictaluri may be useful in controlling Enteric Septicemia of Catfish (ESC).