OprF is a general outer membrane porin of Pseudomonas aeruginosa, a well-known human opportunistic pathogen associated with severe hospital-acquired sepsis and chronic lung infections of cystic fibrosis patients. A multiphenotypic approach, based on the comparative study of a wild-type strain of P. aeruginosa, its isogenic oprF mutant, and an oprF-complemented strain, showed that OprF is required for P. aeruginosa virulence. The absence of OprF results in impaired adhesion to animal cells, secretion of ExoT and ExoS toxins through the type III secretion system (T3SS), and production of the quorum-sensing-dependent virulence factors pyocyanin, elastase, lectin PA-1L, and exotoxin A. Accordingly, in the oprF mutant, production of the signal molecules N-(3-oxododecanoyl)-L-homoserine lactone and N-butanoyl-L-homoserine lactone was found to be reduced and delayed, respectively. Pseudomonas quinolone signal (PQS) production was decreased, while its precursor, 4-hydroxy-2-heptylquinoline (HHQ), accumulated in the cells. Taken together, these results show the involvement of OprF in P. aeruginosa virulence, at least partly through modulation of the quorum-sensing network. This is the first study showing a link between OprF, PQS synthesis, T3SS, and virulence factor production, providing novel insights into virulence expression.

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Screening of a library of Enterococcus faecalis insertional mutants allowed isolation of a mutant affected in tyramine production. The growth of this mutant was similar to that of the wild-type E. faecalis JH2-2 strain in Maijala broth, whereas high-performance liquid chromatography analyses showed that tyramine production, which reached 1,000 g ml ؊1 for the wild-type strain, was completely abolished. Genetic analysis of the insertion locus revealed a gene encoding a decarboxylase with similarity to eukaryotic tyrosine decarboxylases. Sequence analysis revealed a pyridoxal phosphate binding site, indicating that this enzyme belongs to the family of amino acid decarboxylases using this cofactor. Reverse transcription-PCR analyses demonstrated that the gene (tdc) encoding the putative tyrosine decarboxylase of E. faecalis JH2-2 is cotranscribed with the downstream gene encoding a putative tyrosine-tyramine antiporter and with the upstream tyrosyl-tRNA synthetase gene. This study is the first description of a tyrosine decarboxylase gene in prokaryotes.Biogenic amines in food result mainly from microbial activity due to amino acid decarboxylation (16,49). Histamine and tyramine have been the most studied biogenic amines due to the toxicological effects derived from their vasoactive and psychoactive properties. Histamine has been recognized as the causative agent of scromboid poisoning (histamine intoxication), whereas tyramine has been related to food-induced migraines and hypertensive crisis (39). Various tyramine concentrations have been found in many foods, including cheeses, drinks, and meat and fish products (30,44,45), and a dose of only 6 mg total tyramine intake may be dangerous for patients under antidepressive treatment who are receiving monoamine oxidase inhibitors (42). The formation of tyramine in foods depends on the concentration of free tyrosine and the presence of microorganisms having tyrosine decarboxylase activity. Many microorganisms could be implicated in tyramine production. For example, some bacteria belonging to the genera Enterococcus, Carnobacterium, and Lactobacillus have been found to be tyramine producers (5, 31, 35). However, while tyrosine decarboxylase enzymes have been well characterized in eukaryotes, for example, in parsley (Petroselinum crispum) and in Drosophila (24, 47), little is known about tyrosine decarboxylase in prokaryotes. Indeed, only a few reports have described physiological studies of the influence of some physicochemical factors, such as temperature, pH, NaCl, or tyrosine concentration, on tyramine production by Lactobacillus curvatus (46), Lactobacillus brevis (35), and Carnobacterium divergens (32). Tyrosine decarboxylase purification and characterization of the enzyme have been reported only for Enterococcus faecalis (previously called Streptococcus faecalis) (4) and for L. brevis IOEB 9809 and ATCC 367 (34, 36). These authors have shown that tyrosine decarboxylases in E. faecalis and L. brevis have an [␣2] dimmer structure with two subunits of approximately...

Lactic acid bacteria (LAB) are known for their biotechnological potential. Moreover, LAB are distinguished by amazing criteria: Adjusting the intestinal environment, inhibiting pathogenic microbes in the gastrointestinal tract, ability to reduce pathogen adhesion activity, improving the balance of the microbiota inside the intestine, capabilities of regulating intestinal mucosal immunity, and maintaining intestinal barrier function. The escalating number of research and studies about beneficial microorganisms and their impact on promoting health has attracted a big interest in the last decades. Since antiquity, various based fermented products of different kinds have been utilized as potential probiotic products. Nevertheless, the current upsurge in consumers’ interest in bioalternatives has opened new horizons for the probiotic field in terms of research and development. The present review aims at shedding light on the world of probiotics, a continuous story of astonishing success in various fields, in particular, the biomedical sector and pharmaceutical industry, as well as to display the importance of probiotics and their therapeutic potential in purpose to compete for sturdy pathogens and to struggle against diseases and acute infections. Shadows and future trends of probiotics use are also discussed.