BackgroundThe composition of the gut microbiota has recently been associated with health and disease, particularly with obesity. Some studies suggested a higher proportion of Firmicutes and a lower proportion of Bacteroidetes in obese compared to lean people; others found discordant patterns. Most studies, however, focused on Americans or Europeans, giving a limited picture of the gut microbiome. To determine the generality of previous observations and expand our knowledge of the human gut microbiota, it is important to replicate studies in overlooked populations. Thus, we describe here, for the first time, the gut microbiota of Colombian adults via the pyrosequencing of the 16S ribosomal DNA (rDNA), comparing it with results obtained in Americans, Europeans, Japanese and South Koreans, and testing the generality of previous observations concerning changes in Firmicutes and Bacteroidetes with increasing body mass index (BMI).ResultsWe found that the composition of the gut microbiota of Colombians was significantly different from that of Americans, Europeans and Asians. The geographic origin of the population explained more variance in the composition of this bacterial community than BMI or gender. Concerning changes in Firmicutes and Bacteroidetes with obesity, in Colombians we found a tendency in Firmicutes to diminish with increasing BMI, whereas no change was observed in Bacteroidetes. A similar result was found in Americans. A more detailed inspection of the Colombian dataset revealed that five fiber-degrading bacteria, including Akkermansia, Dialister, Oscillospira, Ruminococcaceae and Clostridiales, became less abundant in obese subjects.ConclusionWe contributed data from unstudied Colombians that showed that the geographic origin of the studied population had a greater impact on the composition of the gut microbiota than BMI or gender. Any strategy aiming to modulate or control obesity via manipulation of this bacterial community should consider this effect.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-014-0311-6) contains supplementary material, which is available to authorized users.

The aim of this work was to examine a possible association between resistance of two Escherichia coli strains to high hydrostatic pressure and the susceptibility of their cell membranes to pressure-induced damage. Cells were exposed to pressures between 100 and 700 MPa at room temperature (approximately 20 degrees C) in phosphate-buffered-saline. In the more pressure-sensitive strain E. coli 8164, loss of viability occurred at pressures between 100 MPa and 300 MPa and coincided with irreversible loss of membrane integrity as indicated by uptake of propidium iodide (PI) and leakage of protein of molecular mass between 9 and 78 kDa from the cells. Protein release increased to a maximum at 400 MPa then decreased, possibly due to intracellular aggregation at the higher pressures. In the pressure-resistant strain E. coli J1, PI was taken up during pressure treatment but not after decompression indicating that cells were able to reseal their membranes. Loss of viability in strain J1 coincided with the transient loss of membrane integrity between approximately 200 MPa and 600 MPa. In E. coli J1 leakage of protein occurred before loss of viability and the released protein was of low molecular mass, between 8 and 11 kDa and may have been of periplasmic origin. In these two strains differences in pressure resistance appeared to be related to differences in the ability of their membranes to withstand disruption by pressure. However it appears that transient loss of membrane integrity during pressure can lead to cell death irrespective of whether cells can reseal their membranes afterwards.

A new primary model based on a thermodynamically consistent first-order kinetic approach was constructed to describe non-log-linear inactivation kinetics of pressure-treated bacteria. The model assumes a first-order process in which the specific inactivation rate changes inversely with the square root of time. The model gave reasonable fits to experimental data over six to seven orders of magnitude. It was also tested on 138 published data sets and provided good fits in about 70% of cases in which the shape of the curve followed the typical convex upward form. In the remainder of published examples, curves contained additional shoulder regions or extended tail regions. Curves with shoulders could be accommodated by including an additional time delay parameter and curves with tails shoulders could be accommodated by omitting points in the tail beyond the point at which survival levels remained more or less constant. The model parameters varied regularly with pressure, which may reflect a genuine mechanistic basis for the model. This property also allowed the calculation of (a) parameters analogous to the decimal reduction time D and z, the temperature increase needed to change the D value by a factor of 10, in thermal processing, and hence the processing conditions needed to attain a desired level of inactivation; and (b) the apparent thermodynamic volumes of activation associated with the lethal events. The hypothesis that inactivation rates changed as a function of the square root of time would be consistent with a diffusion-limited process.When microbes are exposed to lethal agents such as heat, gamma radiation, or chemical disinfectants, the concentration of surviving organisms decreases more or less exponentially with time. This behavior has been interpreted in two different ways. The first views the inactivation process as being similar to a first-order reaction such that lethal events occur at random over time within a population of cells that are similar in their susceptibility to the agent (6). The second interpretation, sometimes referred to as the "vitalist" approach, supposes that the observed differences in survival time are the result of differences in resistance among individual cells (41).The simple first-order model has been applied very successfully for many years in the food industry to define safe thermal processes for canned foods (38). For cells heated under isothermal conditions, a plot of the logarithm of the surviving fraction against time yields a straight line, and inactivation rates are expressed in terms of the decimal reduction time, or D value, which is the reciprocal of the specific inactivation rate at a particular temperature. The relationship between D value and temperature is given by the z value, which is the temperature increase needed to change the D value by a factor of 10. These two parameters are also used to describe microbial inactivation by UV or ionizing radiation. However, there are many exceptions to the simple first-order type kinetics, especially when cells are ex...

The current work studied four types of binary antagonist/pathogen bacterial culture system, in order to determine the effect of interaction between two strains of Lactobacillus plantarum and two food-borne pathogens, Listeria monocytogenes and Escherichia coli, in whole UHT milk at 37°C. To determine the type of interaction between the two bacterial populations in co-cultures and to evaluate the antagonistic activity of the lactic acid bacteria (LAB) on the pathogenic bacteria, the growth curves, the kinetic parameters, and the pH profiles of mono- and co-cultures were compared. The Lb. plantarum strains showed different bacteriocin-like inhibitory substance (BLIS) production, auto- and co-inducible. The antibacterial effect of neutralized supernatants of mono and co-cultures harvested at different times of incubation was assessed in order to establish the presence of bacteriocin-like inhibitory-substances (BLIS) and their possible relation to the growth inhibition of the pathogen. The LAB reduced the growth of Esch. coli and of List. monocytogenes by 4 and ∼5 log cycles, respectively and influenced other growth kinetic parameters, such as μ(max) and lag phase, in the different binary combinations. The growth of the LAB was not relevantly altered by simultaneous growth with the pathogenic strains showing an interaction of amensalism. The pattern of inhibition exerted by the LAB on the pathogens was different; Lb. plantarum LB279 inhibited the growth of List. monocytogenes more effectively than that of Esch. coli. The behaviour of Esch. coli in co-culture with Lb. plantarum WS4174 suggested the presence of metabolic crowding in the mechanism of growth suppression. This exploratory study showed the complexity and specific particularities of the inhibition phenomena between bacterial communities.

In this study the effect of refrigeration, abusive and optimum growth temperatures (5, 20, and 37C) on the dynamic of bacterial populations in pure and co-cultures was investigated. The antagonistic activity of two lactic acid bacteria (LAB) strains, with auto-and co-inducible bacteriocin-like inhibitory substance production, against Escherichia coli and Listeria monocytogenes was described and quantified through the comparison of the growth curves and the estimated kinetic parameters of pure and mixed cultures. The growth pattern of the bacterial binary systems studied showed that the mechanism of inhibition was complex and not attributable to one antagonist factor. Temperature had an effect on the spectrum of action and the level of inhibition of the growth of the pathogens by LAB. Low and suboptimal temperatures significantly reduced the antagonistic activity of the two LAB strains against the pathogenic bacteria. At refrigeration temperature only the growth of L. monocytogenes was inhibited by Lactobacillus plantarum WS4174. The results obtained show the importance of validating functionality of biological antimicrobial systems when used for biopreservation purposes under different application conditions. PRACTICAL APPLICATIONSConsumers demand the use of natural systems to provide safety foods with extended shelf life. Lactic acid bacteria (LAB) have demonstrated through thousands years their potential to control spoilage and pathogenic 1 Corresponding microorganisms and therefore suitable for biopreservation purposes. The antagonistic properties of LAB rely on the production of organic acids and antimicrobial peptides (bacteriocins) among other bioactive metabolites. However, there is need for more research in order to understand the mechanism of inhibition and to assess the effectiveness of LAB and/or of their growth-limiting metabolites under different conditions. LAB and their antimicrobial compounds, such as bacteriocins, are not necessarily functional in all food systems and environmental conditions. The present study shows how the fluctuation in bacteriocin-like inhibitory substances production and/or activity caused by temperature changes is reflected on the inhibition potential against Listeria monocytogenes and Escherichia coli. Effectiveness of biological control is essential for its safe and successful application on foods.