Antimicrobial activity of carvacrol and thymol against Erwinia amylovora and Aspergillus ochraceus

Essential oils are naturally occurring terpenic mixtures with well known antimicrobial properties against some important plant pathogens. Plant secondary metabolites have potential in medical procedures and relevant applications in the cosmetic, food and pharmaceutical industries. The growing interest in the substitution of “traditional food preservatives” with “natural ones” fostered research on plant sources, with the aim of identifying new active compounds. On the other hand, prevention of fungal growth is becoming increasingly interesting in connection with the prevention of mycotoxin contamination in several foods, and these natural compounds represent possible alternatives to most food additives currently in use. Along these lines, the main objective of this study is to determine the inhibitory effects of carvacrol and thymol, the main components of the essential oils of oregano and thyme, on the growth of the causal agent of fire blight disease, Erwinia amylovora, and on that of the ochratoxigenic Aspergillus ochraceus that causes food spoilage. The antimicrobial activity was investigated by the disc diffusion and dilution (agar and broth) methods. The effects of the phenolis on the mold spore germination time and radial growth rates were also evaluated. Carvacrol and thymol showed antimicrobial activity against the micro-organisms tested. The effect of composition of media, exposure time, and other environmental factors (i.e. temperature, pH) on the antimicrobial activity was investigated. Finally, the present study evaluates whether these antimicrobial compounds may be suitable candidates to enhance the protection of pear plants damaged by hail wounds towards E. amylovora, and to inhibit ochratoxins production by A. ochraceus