Cheese aroma is the result of the perception of a large number of molecules belonging to different chemical classes. The volatile compounds involved in the soft cheese flavor have received a great deal of attention. However, there has been less work concerning the volatile compounds in the soft smear-ripened cheeses than in the mold-ripened cheeses. This paper reviews the components that contribute to the characteristic flavor in the soft cheeses such as surface-ripened, Camembert-type, and Blue cheeses. The sensory properties and quantities of the molecules in the different cheeses are discussed.

Escherichia coli LR05, in addition to producing MccB17, J25, and D93, secretes microcin L, a newly discovered microcin that exhibits strong antibacterial activity against related Enterobacteriaceae, including Salmonella enterica serovars Typhimurium and Enteritidis. Microcin L was purified using a two-step procedure including solid-phase extraction and reverse-phase C 18 high-performance liquid chromatography. A 4,901-bp region of the DNA plasmid of E. coli LR05 was sequenced revealing that the microcin L cluster consists of four genes, mclC, mclI, mclA, and mclB. As bacterial resistance to currently used antibiotics is increasing, new pathogenic agents are discovered, and traditional bacterial diseases reappear, increased efforts to search for new antibiotics are needed. Over the past 40 years, research has been restricted largely to improving those well-known compound classes that are active against a standard set of drug targets. As no new classes of antibiotic have been discovered, such insufficient chemical variability exists that there is a potential for serious escalation in clinical microbe resistance. Numerous living organisms are able to produce a variety of ribosomally synthesized antibacterial peptides or proteins involved in their innate defense against microorganisms. During the past 15 years, these compounds have attracted considerable attention, offering many exciting possibilities for the future of antibiotics, in the face of current declining efficacy of conventional treatment (20,22). Of the bacteriocins produced by bacteria, many direct activity against pathogens and, in particular, food-borne microorganisms, such as the grampositive bacterium Listeria monocytogenes (7, 10) and gramnegative bacteria Salmonella enterica and Escherichia coli (34,40).Microcins are secreted by members of the Enterobacteriaceae family, in particular strains of E. coli. They constitute a class of low-molecular-mass peptides (Ͻ10 kDa) that exhibit a narrow antimicrobial spectrum of activity directed against bacterial species phylogenetically related to the producing strains (33). To protect itself, the microcin-producing bacterium exhibits immunity to the action of its own microcin. Recent developments in the biochemical characterization and mode of action allowed us to propose a classification of these peptides into two classes (17, 36). Class I, which includes to date microcins B17, C7, D93, and J25, encompasses peptides with molecular mass below 5 kDa that are highly posttranslationally modified. These microcins display a range of unrelated chemical structures, which in turn results in a variety of action mechanisms (9). Class II includes microcins E492, H47, V, most likely microcin 24, and now microcin L. This second group is more homogeneous and shares several common structural properties with class IIa gram-positive bacteriocins: size ranging from 7 to 10 kDa, absence of modified amino acids, and presence of a consensus motif. Additionally, they are synthesized as precursor peptides with a double-glycine type ...

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The inhibitory activities of known microcins were evaluated against some diarrheagenic Escherichia coli strains. Some antibacterial properties of microcin J25, the most active one, were studied. A rapid two-step purification was performed. The MIC and the minimum bactericidal concentration of J25 against E. coli O157:H7 were 1 and 100 g ml ؊1 , respectively. A 10 4 -CFU ml ؊1 contamination by this strain was destroyed in milk and meat extract by 6.25 g of J25 ml؊1 and in half-diluted egg yolk by 50 g of J25 ml ؊1.Diarrheagenic Escherichia coli (DEC) strains are currently associated with food-related illnesses (13). The notorious DEC serotype O157:H7 has been the cause of several large foodrelated epidemics in Europe, North America, and Japan, mostly after consumption of meat or dairy products (9). Physicochemical (3,4,7) and biological (2, 8) methods for the control of DEC have been described, mainly with E. coli O157:H7 as the target strain.Microcins and colicins are classical bacteriocins produced by Enterobacteriaceae that inhibit E. coli and closely related strains (12). Unlike most colicins, microcins are secreted peptides with low molecular masses (Ͻ10 kDa). Their synthesis is nonlethal for the producing strains and not mediated by conditions inducing the SOS system (12). Because of their small size, they are resistant to some proteases and fairly thermostable. So far, six microcins have been described, namely, B17 (19), C7 (6), D93 (10), E492 (18), H47 (5), and J25 (1); colicin V (Col V) can also be considered a microcin (12).The objective of the present study was to evaluate the inhibitory activity of microcins, particularly J25, against DEC strains. Our results showed that all the tested strains were inhibited by at least two microcins. The antagonistic activity of purified microcin J25, the most active one under our experimental conditions, was evaluated. This microcin is a cyclic peptide of 21 unmodified amino acid residues (1) which apparently block cell division (15). The operon coding for production, export, and immunity was recently described (16,17).Bacterial strains, preservation, and growth conditions. Microcin producers were recombinant E. coli strains (MC 4100 for B17, C7, and Col V; VCS 257 for E492; RYC 1000 for H47; and KI 3110 for J25), with each strain harboring the genes required for synthesis, export, and immunity for a single microcin. Producers of B17, C7, E492, J25, and Col V were supplied by F. Moreno (Unidad de Genetica Molecular, Hospital Ramon y Cajal, Madrid, Spain), and the producer of H47 was supplied by M. Laviña (Instituto de Investigaciones Biologicas Clemente Estable, Ministerio de Educacion y Cultura, Montevideo, Uruguay). DEC strains were six collection strains purchased from Institut Pasteur (Paris, France), named CIP 52.168, CIP 52.170, CIP 52.172, CIP 62.23, CIP 62.24, and CIP 103.571 (respective serotypes: O111:H12, O55:H6, O26:H11, O119, O125, and O157:H7) and nine clinical isolates obtained from different patients with acute diarrhea, which were serotypes O26, O55...

For the first time, microcin-producing strains showing inhibitory activities against enteropathogen Salmonella enteritidis were isolated from poultry intestinal contents. Among the numerous strains isolated, two strains of Escherichia coli, named J02 and J03, showing the greatest activities against S. enteritidis, were studied. Biochemical tests and purification identified the main antagonist compound produced as microcin J25. In order to evaluate the protective potential of E. coli J02 and J03 against S. enteritidis infection, the ability of these strains to inhibit growth of S. enteritidis was investigated in mixed culture. A strong antagonist activity was obtained with a preculture phase of the active strain in minimal medium before incubation with S. enteritidis. In a bioreactor experiment simulating the chicken gastric and intestinal tract environment, a mixture of the two strains E. coli J02 and J03, provided an enhanced inhibitory effect. Microcinogenic strain activities were not affected by bile, pancreatic enzymes addition, or acidic conditions. These results suggest the relevant role of microcin-producing microorganisms in microbial intestinal ecology. To conclude, this study shows that microcin J25 strains could exert a beneficial protective effect against S. enteritidis growth in situ.