Evaluation of Plasmid Content and Tetracycline Resistance Conjugative Transfer in Enterococcus italicus Strains of Dairy Origin

Biofunctional attributes and storage study of milk fermented by Enterococcus italicus

Lactic acid bacteria are probiotics in the intestines and have been widely used as natural antioxidants in the food industry. In this study, Enterococcus italicus FM5 with strong antioxidant ability was isolated from fresh milk. The safety evaluation showed that E. italicus FM5 was sensitive to ampicillin, chloramphenicol, erythromycin, vancomycin, rifampicin, and tetracycline, and was not hemolytic. Meanwhile, the whole genome information and biofunctional attributes of this strain were determined and analyzed. Subsequently, E. italicus FM5 was co-cultured with traditional yogurt starters (Streptococcus thermophilus and Lactobacillus bulgaricus) to make fermented milk. The results showed that the addition of E. italicus FM5 could improve the oxygen free radical scavenging ability of the fermented milk, and the scavenging rates of DPPH, ABTS, OH-, and O2- radicals reaching up to 95.54 %, 88.35 %, 93.65 %, and 60.29 %, respectively. Furthermore, the addition of E. italicus FM5 reduced the curd time and improved the water holding capacity of the fermented milk. Besides, the growth of Lb. bulgaricus was significantly promoted when co-cultured with E. italicus FM5, thus the survival cells were increased compared with the traditional fermentation processes. Therefore, this study emphasized the potential to manufacture fermented milk by the co-cultivation of E. italicus with traditional yogurt starters.

Genomic analysis reveals the biotechnological ability of Enterococcus italicus to produce glutathione

Through the analysis of the recently available genome shotgun sequence of Enterococcus italicus DSM 15952T type strain (Accession PRJNA61487, ID 61487), we found the presence of a gene encoding a bifunctional enzyme, termed γ-GCS-GS or GshF, involved in glutathione production and not influenced by feedback inhibition. The gshF gene exhibited high nucleotide and amino acid sequence similarity to other reported sequences from the Enterococcus genus and was constitutively expressed both in osmotic shock or in common cultural conditions. Several experimental studies concerning the culture medium, physiological stress, cell extract obtainment, and scaling-up showed that in selected conditions E. italicus was able to accumulate up to 250 μM of intracellular glutathione, which represented the main thiol group present into the cells. This is the first report regarding the production of glutathione by E. italicus, a species that could be used as a safe adjunct culture for glutathione-enriched dairy foods.

Genotypic intraspecies heterogeneity of Enterococcus italicus: data from dairy environments

The diversity of a collection of 19 Enterococcus italicus strains isolated from different dairy sources was explored using a molecular polyphasic approach, comprising random amplification of polymorphic DNA (RAPD-PCR), repetitive element PCR (REP-PCR), plasmid profiling and ribotyping. The data obtained showed a high-level of biodiversity, not always correlated to the niche of isolation. Particularly, REP-PCR with primer BOXA1R and plasmid profiling allowed the best discrimination at strain level. Exploiting the genome shotgun sequence of the type strain of the species, available in public database, genes related to insertion sequences present on enterococcal Pathogenic Islands (ISEf1, IS905), determinants related to virulence factors (codifying for hemolysin and cell wall surface proteins), exogenously DNA (conjugal transfer protein, replication plasmid protein, pheromone shutdown protein, phage integrase/recombinase) and penicillin binding proteins system were detected. The presence of most of these genes seemed a common genetic trait in the Enterococcus genus, sur gene (cell wall surface protein) was only detected in strains of E. italicus. To our knowledge, this is the first time that specific primers, with the expection of the species-specific probe targeted to 16S rRNA gene, have been designed for this species.

Antibiotic resistance determinants in the interplay between food and gut microbiota

A complex and heterogeneous microflora performs sugar and lactic acid fermentations in food products. Depending on the fermentable food matrix (dairy, meat, vegetable etc.) as well as on the species composition of the microbiota, specific combinations of molecules are produced that confer unique flavor, texture, and taste to each product. Bacterial populations within such “fermented food microbiota” are often of environmental origin, they persist alive in foods ready for consumption, eventually reaching the gastro-intestinal tract where they can interact with the resident gut microbiota of the host. Although this interaction is mostly of transient nature, it can greatly contribute to human health, as several species within the food microbiota also display probiotic properties. Such an interplay between food and gut microbiota underlines the importance of the microbiological quality of fermented foods, as the crowded environment of the gut is also an ideal site for genetic exchanges among bacteria. Selection and spreading of antibiotic resistance genes in foodborne bacteria has gained increasing interest in the past decade, especially in light of the potential transferability of antibiotic resistance determinants to opportunistic pathogens, natural inhabitants of the human gut but capable of acquiring virulence in immunocompromised individuals. This review aims at describing major findings and future prospects in the field, especially after the use of antibiotics as growth promoters was totally banned in Europe, with special emphasis on the application of genomic technologies to improve quality and safety of fermented foods.

Regulation of bacterial conjugation: balancing opportunity with adversity

Conjugative plasmids are involved in the dissemination of important traits such as antibiotic resistance, virulence determinants and metabolic pathways involved in adapting to environmental niches, a process termed horizontal or lateral gene transfer. Conjugation is the process of transferring DNA from a donor to a recipient cell with the establishment of the incoming DNA and its cargo of genetic traits within the transconjugant. Conjugation is mediated by self-transmissible plasmids as well as phage-like sequences that have been integrated into the bacterial chromosome, such as integrative and conjugative elements (ICEs) that now include conjugative transposons. Both conjugative plasmids and ICEs can mediate the transfer of mobilizable elements by sharing their conjugative machinery. Conjugation can either be induced, usually by small molecules or peptides or by excision of the ICE from the host chromosome, or it can be tightly regulated by plasmid- and host-encoded factors. The transfer potential of these transfer regions depends on the integration of many signals in response to environmental and physiological cues. This review will focus on the mechanisms that influence transfer potential in these systems, particularly those of the IncF incompatibility group.