Paola Minardi

Chemical Composition and Antimicrobial Activity of Essential Oils from Aerial Parts of Monarda didyma and Monarda fistulosa Cultivated in Italy

Abstract Monarda spp. are promising Lamiaceae due to essential oil (EO) composition and antimicrobial activity. To investigate these properties, Monarda didyma and M. fistulosa were grown for two years in two Italian sites for EO extraction (distillation), analysis (GC and GC/MS), and antimicrobial activity (microplate diffusion broth method). EO yield greatly increased from first to second year of cultivation (0.27 and 0.51% in 2013 and 2014, respectively), showing minor differences between M. didyma and M. fistulosa. Conversely, EO composition significantly varied between the two species and years. Of the fifteen major compounds identified, eight were shared by the two species. However, the amounts differed, especially in thymol (62 vs. 31% in M. didyma vs. M. fistulosa) opposed to α- and β-phellandrene (their average, 1% in M. didyma and 16% in M. fistulosa). An increase of thymol was observed between 2013 and 2014 in both species (average, +11%), reflecting juvenile plants showing only vegetative organs (2013) vs. fully flowered plants (2014). Despite such differences, EO’s from the two Monarda species exhibited a similar activity against pathogenic and non-pathogenic strains of fungi and bacteria from human, animal and plant source. In general, Monarda EO’s showed a lower minimum inhibitory concentration, i.e. a stronger activity, against pathogenic (Escherichia coli, Erwinia amylovora and Candida albicans) than beneficial microorganisms (Bifidobacterium animalis and Lactobacillus casei). The higher susceptibility of pathogenic microorganisms supports the use of Monarda EO’s as antimicrobial agents with a favourable profile of selectivity. Applications are envisaged in food preservation, plant protection and human health.

In vivo and in vitro effects of selected antioxidants on rabbit meat microbiota

The purpose of this study was to investigate the effect of dietary vitamin E or EconomasE™ supplementation on the growth of several background/pathogenic bacteria on rabbit carcasses and hamburgers during refrigerated storage. For 51days, 270 New Zealand rabbits received either a basal diet, or experimental diets enriched with 100 or 200mg/kg of vitamin E or EconomasE™. The bacteria studied were Salmonella, Listeria monocytogenes, Pseudomonas, Enterobacteriaceae, Escherichia coli, coagulase-positive staphylococci, plus both mesophilic and psychrotrophic aerobes. The growth of Listeria monocytogenes on contaminated patties was evaluated through a challenge test. The potential protective or antimicrobial effect of vitamin E or EconomasE™ on Listeria monocytogenes or Pseudomonas aeruginosa was assessed in vitro. Diet did not influence the concentrations of bacteria found on rabbit carcasses and developing on hamburgers. Vitamin E (in vivo and in vitro) and EconomasE™ in vivo had a protective antioxidant role, while EconomasE™ in vitro had strong antibacterial activity against Listeria monocytogenes, but not against Pseudomonas aeruginosa.

MOLECULAR ANALYSIS OF THE dspEF LOCUS IN ERWINIA AMYLOVORA WILD STRAINS OF NORTHERN ITALY

In the years following the severe 1997 epidemic in Emilia-Romagna (northern Italy), fire blight cases were mainly found on pear and the AFLP analysis showed that the E. amylovora (Ea) populations belonged to the same clone (Ea1994). From 1997 to 2001, there has been an increase in outbreaks on apple and hawthorn. The introduction of novel bacterial strains or the modification of virulence factors in the existing clonal populations was hypothesized, as well as the involvement of the dspEF locus of clone Ea1994 under immune pressure by different hosts. The AFLP analysis of serial isolates of Ea1994 during and after 6 passages on pear, apple and hawthorn showed the same genomic profiles. Modifications of the dspEF locus were investigated by means of dspE gene restriction analysis and of gene sequence analysis of dspF in 7 strains with virulence higher than Ea1994 and of the dspE gene of Ea1994. Restriction analysis revealed indistinguishable profiles, and sequence analysis showed that the sequences of the dspEF locus totally correlated (99.9- 100%) with those of Ea321, a North-American Ea strain. In the Po Valley the existence of more virulent strains and the increase of fire blight cases in apple do not seem attributable to changes in the dspEF locus. The results confirmed that the DspE effector and its chaperon DspF, are highly conserved. Thus, the increase of the fire blight cases on apple in this area might be the result of agronomic factors (i.e. higher plant density, new training forms, new cultivars more susceptible to fire blight, higher presence of 1-7 year plantings) associated with a higher inoculum potential in the environment.