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.

The biochemical basis for the acquired or natural resistance of various gram-positive organisms to glycopeptides was studied by high-pressure liquid chromatographic analysis of their peptidoglycan UDPMurNAc-peptide precursors. In all cases, resistance was correlated with partial or complete replacement of the C-terminal D-Ala-D-Ala-containing UDP-MurNAc-pentapeptide by a new precursor with a modified C terminus. Nuclear magnetic resonance analysis by sequential assignment showed that the new precursor encountered in Enterococcus faecium D366, a strain belonging to the VANB class, which expresses low-level resistance to vancomycin, was UDP-MurNAc-L-Ala--y-D-Glu-L-Lys-D-Ala-D-lactate, identical to that previously found in the VANA class, which expresses high-level resistance to vancomycin. High-pressure liquid chromatographic analyses, composition determinations, and digestion by R39 D,D-carboxypeptidase demonstrated the exclusive presence of the new precursor in LactobaciUlus casei and Pediococcus pentosaceus, which are naturally highly resistant to glycopeptides. The low-level natural resistance of Enterococcus gaUlinarum to vancomycin was found to be associated with the synthesis of a new precursor identified as a UDP-MurNAcpentapeptide containing a C-terminal D-serine. The distinction between low and high levels of resistance to glycopeptides appeared also to depend on the presence or absence of a substantial residual pool of a D-Ala-D-Ala-containing UDP-MurNAc-pentapeptide.Glycopeptides are very important antibiotics widely used against gram-positive organisms in the clinical setting. Their mechanism of action is based essentially on their capacity to bind specifically to the D-alanyl-D-alanine C terminus of the disaccharide pentapeptide (24), which is the structural monomer unit of cell wall peptidoglycan (27). The formation of such a complex inhibits peptidoglycan synthesis by interfering with the transglycosylation and transpeptidation reactions leading to nascent peptidoglycan (27). It was previously assumed that except under very abnormal growth conditions (15), the Dalanyl-D-alanine terminal dipeptide was a feature present in the precursors of the peptidoglycans of all bacteria (28). Recently, clinical isolates of enterococci which have acquired resistance to glycopeptides (19,29,34) have been separated into two major classes, VANA and VANB. In the VANA class, the genes responsible for the resistance are plasmid borne and lead to inducible cross-resistance between vancomycin and teicoplanin (5, 29). In the VANB class, the resistance genes are chromosome borne and associated with inducible resistance to vancomycin only (34). There is a third class, designated VANC, which corresponds to natural resistance to vancomycin and to which Enterococcus gallinarum belongs (30,33 N-acetyldepsipeptide (10). Taking into account all of these results, we were prompted to investigate (i) whether the biochemical basis of the glycopeptide resistance in the VANB class resembles that of VANA and (ii) whether the presence o...

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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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Three flavonoids which promoted Escherichia coli topoisomerase IV-dependent DNA cleavage were isolated from cottonseed flour and identified as quercetin 3-O-␤-D-glucose-[1,6]-O-␣-L-rhamnose (rutin), quercetin 3-O-␤-D-galactose-[1,6]-O-␣-L-rhamnose, and quercetin 3-O-␤-D-glucose (isoquercitrin). The most active one (rutin) also inhibited topoisomerase IV-dependent decatenation activity (50% inhibitory concentration, 64 g/ml) and induced the SOS response of a permeable E. coli strain. Derivatives of quercetin glycosylated at position C-3 were shown to induce two site-specific DNA cleavages of pBR322 DNA, which were mapped by DNA sequence analysis to the gene encoding resistance to tetracycline. Cleavage at these sites was hardly detectable in cleavage reactions with quercetin or fluoroquinolones. None of the three flavonoids isolated from cottonseeds had any stimulatory activity on E. coli DNA gyrase-dependent or calf thymus topoisomerase IIdependent DNA cleavage, and they were therefore specific to topoisomerase IV. These results show that selective inhibitors of topoisomerase IV can be derived from the flavone structure. This is the first report on a DNA topoisomerase inhibitor specific for topoisomerase IV.

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