Growth of Salmonella enteritidis and Salmonella typhimurium in the presence of quorum sensing signalling compounds produced by spoilage and pathogenic bacteria.

The effect of acylated homoserine lactones (AHLs) and autoinducer-2 (AI-2) signalling compounds present in the cell-free culture supernatants (CFS), of Pseudomonas aeruginosa, Yersinia enterocolitica-like GTE 112, Serratia proteamaculans 00612, Y. enterocolitica CITY650 and Y. enterocolitica CITY844, on the growth of two Salmonella Enteritidis and two S.

Rapid monitoring of the spoilage of minced beef stored under conventionally and active packaging conditions using Fourier transform infrared spectroscopy in tandem with chemometrics.

Fourier transform infrared (FTIR) spectroscopy was exploited to measure biochemical changes within fresh minced beef in an attempt to rapidly monitor beef spoilage. Minced beef packaged either aerobically, under modified atmosphere and using an active packaging were held from freshness to spoilage at 0, 5, 10, and 15°C. Frequent FTIR measurements were collected directly from the sample surface using attenuated total reflectance, in parallel the total viable counts of bacteria, the sensory quality and the pH were also determined.

Insights into the role of quorum sensing in food spoilage.

Food spoilage is a consequence of the degrading enzymatic activity of some food-associated bacteria. Several proteolytic, lipolytic, chitinolytic, and pectinolytic activities associated with the deterioration of goods are regulated by quorum sensing, suggesting a potential role of such cell-to-cell communication in food spoilage. Here we review quorum sensing signaling molecules and methods of their detection and quantification, and we provide insights into the role of quorum sensing in food spoilage and address potential quorum sensing inhibitors that might be used as biopreservatives.

Analysis of tetracycline resistance tet(W) genes and their flanking sequences in intestinal Bifidobacterium species.

Objectives: The tet(W) gene provides tetracycline resistance to a wide range of anaerobic intestinal and ruminal bacteria, but little is known about the molecular organization of the tet(W) gene. The aim of this study was to gain new insights into the molecular organization of the tet(W) gene in bifidobacteria strains from humans.

Methods: A segment of DNA encompassing the whole tet(W) gene and its immediate upstream and downstream sequences was analysed in 10 representative strains of four Bifidobacterium species, of which two have been shown to be tetracycline-susceptible.

Two different tetracycline resistance mechanisms, plasmid-carried tet(L) and chromosomally located transposon-associated tet(M), coexist in Lactobacillus sakei Rits 9.

Lactobacillus sakei is extensively used as functional starter culture in fermented meat products. One of the safety criteria of a starter culture is the absence of potentially transferable antibiotic resistance determinants. However, tetracycline-resistant L.

Identification of tet(M) in two Lactococcus lactis strains isolated from a Spanish traditional starter-free cheese made of raw milk and conjugative transfer of tetracycline resistance to lactococci and enterococci.

Specific PCR and sequencing showed that a tet(M) gene was present in two tetracycline-resistant Lactococcus lactis strains isolated from a raw milk, starter-free cheese. Hybridisation experiments using as a probe an internal segment of the gene obtained by PCR associated tet(M) with plasmids of around the same size (30 kbp) in both strains. Molecular analysis of the tetracycline resistance loci, including the upstream and downstream regions of the genes, showed them to be identical to one other and to the tet(M) encoded by the conjugative transposon Tn916.

Molecular characterization of intrinsic and acquired antibiotic resistance in lactic acid bacteria and bifidobacteria.

The minimum inhibitory concentrations (MICs) of 6 different antibiotics (chloramphenicol, clindamycin, erythromycin, streptomycin, tetracycline and vancomycin) were determined for 143 strains of lactic acid bacteria and bifidobacteria using the Etest. Different MICs were found for different species and strains. Based on the distribution of these MIC values, most of the strains were either susceptible or intrinsically resistant to these antibiotics.

Acquired macrolide resistance in the human intestinal strain Lactobacillus rhamnosus E41 associated with a transition mutation in 23S rRNA genes.

Restriction fragment length polymorphism and DNA sequencing of polymerase chain reaction (PCR) products showed that a Lactobacillus rhamnosus strain of human origin resistant to macrolides, from which no resistance determinants have been detected by specific PCR and microarray screening, contained a heterozygous A-->G transition mutation at position 2058 (Escherichia coli numbering) of its 23S rRNA genes.

Recent advances in the use of intrinsic fluorescence for bacterial identification and characterization.

Live bacteria contain a variety of intracellular biomolecules that have specific excitation and emission wavelength spectra characterizing their intrinsic fluorescence. This paper reviews recent developed methods using bacterial intrinsic fluorescence for identification and characterization purposes. Potential applications of such methods at the industrial level are also addressed.

Selection criteria for lactic acid bacteria to be used as functional starter cultures in dry sausage production: An update.

Lactic acid bacteria (LAB) have long been used as starter cultures in the production of fermented dry sausages and other meat-derived commodities. These cultures are generally designed to meet food safety, shelf-life, technological effectiveness and economic feasibility criteria. Besides all these traditional properties, novel starter cultures should take into account the risks posed by the formation of biogenic amines in food, and the development and spreading of bacterial resistance to antibiotics.

Antibiotic resistance in non-enterococcal lactic acid bacteria and bifidobacteria.

Over the last 50 years, human life expectancy and quality of life have increased dramatically due to improvements in nutrition and the use of antibiotics in the fight against infectious diseases. However, the heyday of antibiotic treatment is on the wane due to the appearance and spread of resistance among harmful microorganisms. At present, there is great concern that commensal bacterial populations from food and the gastrointestinal tract (GIT) of humans and animals, such as lactic acid bacteria (LAB) and bifidobacteria, could act as a reservoir for antibiotic resistance genes.

Reagentless identification of human bifidobacteria by intrinsic fluorescence.

A new identification method for bifidobacteria species from the human gastrointestinal tract was developed based on the measurement and statistical analysis of the intrinsic fluorescence of aromatic amino acids (AAA) and nucleic acids (NA), following their excitation at 250 nm. The model was constructed by recording the fluorescence spectra of 53 Bifidobacterium strains of 10 different species, including the corresponding type strains, and validated by analyzing the spectra data from nine further problem strains. Principal components analysis (PCA) and factorial discriminant analysis (FDA) of the results showed the technique to distinguish between the isolates at the species level; the Bifidobacterium pseudolongum subspecies (globosum and pseudolongum) could also be distinguished.

Molecular analysis of a chromosome-carried erm(B) gene and its flanking insertion points in Lactobacillus johnsonii G41.

An erm(B) gene carried on the Lactobacillus johnsonii G41 chromosome and the upstream and downstream regions were fully sequenced. Apparently, a 1,495-bp segment of pRE25 from Enterococcus faecalis carrying the erm(B) gene became inserted, by an unknown mechanism, into the L. johnsonii chromosome.

Molecular analysis of tet(W) gene-mediated tetracycline resistance in dominant intestinal Bifidobacterium species from healthy humans.

tet(W) was found responsible for tetracycline resistance (MICs, 4 to > or =32 microg ml(-1)) in dominant bifidobacterial species from the gastrointestinal tracts of healthy humans. The gene from Bifidobacterium longum H66 proved to be identical over a 2.6-kbp region to the recently described tet(W) determinant of Butyrivibrio fibrisolvens.

Fluorescence spectroscopy: a rapid tool for assessing tetracycline resistance in Bifidobacterium longum.

The tetracycline uptake kinetics of 35 Bifidobacterium longum strains isolated from the human gastrointestinal tract were examined by fluorescence spectroscopy, and the suitability of the technique as a screening tool of tetracycline resistance or susceptibility was determined. The strains were first grouped into three classes based on their corresponding minimum inhibitory concentrations (MICs) of tetracycline, as established by the microdilution method: susceptible (MICs or=32 microg mL(-1)). The kinetics of tetracycline uptake for the strains in each resistance group were then analyzed over a 20 min period by fluorescence spectroscopy (absorbance wavelength 524 nm, excitation wavelength 400 nm) in a buffer system containing 100 microg mL(-1) tetracycline.