No abstract

Grapevine trunk diseases (GTDs) are a major threat to the wine and grape industry. The aim of the study was to investigate the antifungal activity against Neofusicoccum parvum, Diplodia seriata, and Botryosphaeria dothidea of ε-polylysine, chitosan oligomers, their conjugates, Streptomyces rochei and S. lavendofoliae culture filtrates, and their binary mixtures with chitosan oligomers. In vitro mycelial growth inhibition tests suggest that the efficacy of these treatments, in particular those based on ε-polylysine and ε-polylysine:chitosan oligomers 1:1 w/w conjugate, against the three Botryosphaeriaceae species would be comparable to or higher than that of conventional synthetic fungicides. In the case of ε-polylysine, EC90 values as low as 227, 26.9, and 22.5 µg·mL−1 were obtained for N. parvum, D. seriata, and B. dothidea, respectively. Although the efficacy of the conjugate was slightly lower, with EC90 values of 507.5, 580.2, and 497.4 µg·mL−1, respectively, it may represent a more cost-effective option to the utilization of pure ε-polylysine. The proposed treatments may offer a viable and sustainable alternative for controlling GTDs.

This study aimed to investigate the effect of sub-minimum inhibitory concentrations (sub-MICs) of three food-grade biocides (benzalkonium chloride -BZK-, trisodium phosphate -TSP-, and sodium hypochlorite -SHY-) on Salmonella biofilms. The structural parameters and bacterial viability of the biofilms formed by a S. Typhimurium isolate from poultry was investigated by means of confocal laser scanning microscopy after staining with SYTO9 and propidium iodide. The MIC values for Salmonella cells before exposure to subinhibitory concentrations of biocides were 8.0 μg/mL (BZK), 18.0 mg/mL (TSP), and 6.0 mg/mL (SHY). The cultures exhibited a stable acquired tolerance to BZK and SHY. The maximum concentrations of biocides that allowed bacterial growth after several passages through gradually higher concentrations of such compounds were 30.4 μg/mL (BZK) and 10.1 mg/mL (SHY). The architecture and viability of S. Typhimurium biofilms varied in response to sub-MICs of different biocides. Previous adaptation to SHY enhanced (p < 0.001) biofilm formation (average biovolume in the observed field -14,161 μm-: 139,856.15 ± 155,213.27 μm) relative to unexposed cells (53,779.05 ± 55,535.62 μm) and cells previously exposed to BZK (58,216.97 ± 58,644.45 μm) or TSP (30,052.13 ± 28,290.56 μm). This was particularly marked when biofilm was grown in the absence of biocides or in the presence of sub-MICs of SHY. The highest percentage of dead cells was shown by biofilms formed by cultures previously exposed to TSP relative to the other conditions tested (34.08% ± 13.74% vs. 23.70% ± 16.16%; p < 0.001). The importance of maintaining higher than MICs of SHY during sanitizing procedures to fight foodborne infections by Salmonella biofilms is highlighted.

The hygiene status of raw chicken-meat preparations from retail outlets in North-Western Spain was investigated. Microbial counts (aerobic plate counts (APCs), psychrotrophs, Enterobacteriaceae, fecal coliforms, enterococci, pseudomonads, fluorescent pseudomonads, yeasts and molds, and Staphylococcus aureus) were determined for minced meat, hamburgers, nuggets, white sausages, red sausages, escalope, and roll-ups. S. aureus isolates were tested for susceptibility to twenty antimicrobials of veterinary and human clinical significance (disc diffusion method, CLSI). Average microbial loads (log10 cfu/g) ranged from 2.63 ± 0.80 (enterococci) to 6.66 ± 1.09 (psychrotrophs). Average APCs (6.44 ± 1.16 log10 cfu/g) were regarded as acceptable according to EU microbiological criteria. The type of product had an influence (P < 0.05) on microbial loads, samples of escalope showing the highest counts for most microbial groups. Two-thirds (66.7%) of the samples tested harbored S. aureus. All the S. aureus isolates were multi-resistant (to between three and fifteen antibiotics). The greatest prevalence of resistance was shown for ampicillin, oxacillin, penicillin G, ceftazidime, and nalidixic acid. The results of this study show that poultry-based meat preparations present high microbial loads and are a major reservoir of antibiotic-resistant S. aureus strains. This highlights the need for correct handling of such foodstuffs with a view to reducing risks to consumers.

In the work presented herein, we analyze the efficacy of three basic substances that comply with European Regulation (EC) No 1107/2009, namely chitosan, horsetail (Equisetum arvense L.) and nettle (Urtica dioica L.), for the control of grapevine trunk diseases (GTDs) in organic farming. The E. arvense and U. dioica aqueous extracts, prepared according to SANCO/12386/2013 and SANTE/11809/2016, have been studied by gas chromatography–mass spectrometry (GC-MS), identifying their main active constituents. The three basic substances, either alone or in combination (forming conjugate complexes), have been tested in vitro against eight Botryosphaeriaceae species, and in vivo, in grafted plants artificially inoculated with Neofusicoccum parvum and Diplodia seriata. A clear synergistic behavior between chitosan and the two plant extracts has been observed in the mycelial growth inhibition tests (resulting in EC90 values as low as 208 μg·mL−1 for some of the isolates), and statistically significant differences have been found in terms of vascular necroses lengths between treated and non-treated plants, providing further evidence of aforementioned synergism in the case of D. seriata. The reported data supports the possibility of extending the applications of these three basic substances in Viticulture beyond the treatment of mildew.