Antimicrobial activity of resveratrol-derived monomers and dimers against foodborne pathogens.

Plant polyphenolic compounds are considered a promising source for new antibacterial agents. In this study, we evaluated the antimicrobial activity of a collection of resveratrol-derived monomers and dimers screened as single molecules against a panel of nine foodborne pathogens. The results demonstrated that two monomers (i.e., pterostilbene 2 and (E)-3-hydroxy-4',5-dimethoxystilbene 9) and three dimers (i.e., δ-viniferin 10, viniferifuran 14 and dehydro-δ-viniferin 15) were endowed with significant antibacterial activity against gram-positive bacteria. The exposure of gram-positive foodborne pathogens to 100 µg/mL of 2, 9 and 15 induced severe cell membrane damage, resulting in the disruption of the phospholipid bilayer. The most promising dimeric compound, dehydro-δ-viniferin 15, was tested against Listeria monocytogenes, resulting in a loss of cultivability, viability and cell membrane potential. TEM analysis revealed grave morphological modifications on the cell membrane and leakage of intracellular content, confirming that the cell membrane was the principal biological target of the tested derivative.

Chemical markers for the evaluation of raw material hygienic quality in egg products.

The aim of this research was to study uracil and lactic and acetic acids as chemical markers for hygienic quality evaluation of raw material in liquid pasteurized egg products. Uracil, absent in sound whole eggs, was formed in raw and pasteurized egg products as a consequence of high microbial contamination (>10(6) cfu/g) after a sufficient lag time, remaining stable at 4 degrees C but disappearing after 7 days of storage at 25 degrees C. Both lactic and acetic acids, starting from initial values of 1-7 mg/kg dry matter, presented trends similar to that of uracil; however, acetic acid never decreased during the storage of raw egg products. With few exceptions, all three metabolites were produced by Enterobacter cloacae, Escherichia coli, Morganella morganii, Serratia liquefaciens, Aeromonas hydrophyla, Pseudomonas fluorescens, Enterococcus avium, and Enterococcus faecalis, separately inoculated in whole egg samples. Uracil seems to be the most sensible marker, with a suggested limit corresponding to the detectable level.

Development of PCR assay to identify Pseudomonas fluorescens and its biotype.

The paper provides a simple protocol that uses the polymerase chain reaction to amplify a specific portion of the 16S gene, allowing the recognition of Pseudomonas fluorescens from other group I Pseudomonas. The amplified DNA patterns of 16S rRNA and ITS1, from the restriction fragment length polymorphisms VspI, HaeIII and TaqI digestion, produced band patterns that distinguished the biotypes of Ps. fluorescens. In addition to distinguishing the biotypes C and 3 we used a phenotypical method for levan production.

Development of genus/species-specific PCR analysis for identification of Carnobacterium strains.

Heterofermentative lactic acid bacteria belonging to the genus Carnobacterium are currently divided into seven different species, C. piscicola, C. mobile, C. gallinarum, C. inhibens, C. divergens, C. funditum, and C. alterfunditum. 16S rDNA-targeted PCR assay was carried out for the identification of the genus Carnobacterium. In addition, type strains of all Carnobacterium species were analyzed by 16S-23S rDNA intergenic spacer analysis in comparison with type strains of phylogenetically related lactic acid bacteria. These methods enabled the identification and the discrimination among Carnobacterium species and the other phylogenetically related lactic acid bacteria. Likewise, analogous results were obtained by restriction analysis of amplified 16S rDNA performed with HaeIII and HinfI as restriction enzymes.

Phenotypic and genotypic characterization of Enterococcus spp. of different origins.

Sixty-four strains of Enterococcus spp. of different origin were identified using traditional phenotypic, biochemical and cultural tests, together with molecular tests. API 20 STREP tests identified the species at a preliminary level, only one strain remaining unidentified. Strains belonging to the genus Enterococcus were tested with genus-specific primers, while species-level identification was carried out with the 16S-23S rDNA intergenic region (ITS) and species-specific primers for E. faecium and E. faecalis. Those strains found to be negative with the species-specific primers were subjected to 16S rDNA partial sequencing.

Reclassification of Lactobacillus maltaromicus (Miller et al. 1974) DSM 20342(T) and DSM 20344 and Carnobacterium piscicola (Collins et al. 1987) DSM 20730(T) and DSM 20722 as Carnobacterium maltaromaticum comb. nov.

Phenotypic and genotypic characterizations of Lactobacillus maltaromicus strains DSM 20342(T) and DSM 20344 provided evidence for the reclassification of this species in the genus Carnobacterium. Moreover, phenotypic and genotypic comparisons made between L. maltaromicus and Carnobacterium piscicola highlighted that these two species should be considered synonyms. For these reasons, the species Carnobacterium maltaromaticum comb. nov. (type strain DSM 20342(T) = ATCC 27865(T) = CCUG 30142(T) = CIP 103135(T) = JCM 1154(T) = LMG 6903(T) = NRRL B-14852(T)) is proposed to accommodate L. maltaromicus and C. piscicola.