Modeling and predicting the biofilm formation of Salmonella Virchow with respect to temperature and pH

Biofilm formation of Salmonella Virchow was monitored with respect to time at three different temperature (20, 25 and 27.5 °C) and pH (5.2, 5.9 and 6.6) values. As the temperature increased at a constant pH level, biofilm formation decreased while as the pH level increased at a constant temperature, biofilm formation increased. Modified Gompertz equation with high adjusted determination coefficient (Radj2) and low mean square error (MSE) values produced reasonable fits for the biofilm formation under all conditions. Parameters of the modified Gompertz equation could be described in terms of temperature and pH by use of a second order polynomial function. In general, as temperature increased maximum biofilm quantity, maximum biofilm formation rate and time of acceleration of biofilm formation decreased; whereas, as pH increased; maximum biofilm quantity, maximum biofilm formation rate and time of acceleration of biofilm formation increased. Two temperature (23 and 26 °C) and pH (5.3 and 6.3) values were used up to 24 h to predict the biofilm formation of S. Virchow. Although the predictions did not perfectly match with the data, reasonable estimates were obtained. In principle, modeling and predicting the biofilm formation of different microorganisms on different surfaces under various conditions could be possible

The potential of metering roundabouts: influence in transportation externalities

Roundabouts are increasingly being used on busy arterial streets for traffic calming purposes. However, if one roundabout leg is near a distribution hub, e.g. parking areas of shopping centers, the entry traffic volumes will be particularly high in peak hours. This paper investigated a partial-metering based strategy to reduce traffic-related costs in a corridor. Specifically, the resulting traffic performance, energy, environmental and exposure impacts associated with access roundabouts were studied in an urban commercial area, namely: a) to characterize corridor operations in terms of link-specific travel time, fuel consumption, carbon dioxide and nitrogen oxides emissions, and noise costs; b) to propose an optimization model to minimize above outputs; and c) to demonstrate the model applicability under different traffic demand and directional splits combinations. Traffic, noise and vehicle dynamics data were collected from a corridor with roundabouts and signalized intersections near a commercial area of Guimarães, Portugal. Microscopic traffic and emission modeling platforms were used to model traffic operations and estimate pollutant emissions, respectively. Traffic noise was estimated with a semi-dynamical model. Link-based cost functions were developed based on the integrated modeling structure. Lastly, a Sequential quadratic programming type approach was applied to find optimal timing settings. The benefit of the partial-metering system, in terms of costs, could be up to 13% with observed traffic volumes. The efficiency of the proposed system increased as entering traffic at the metered approaches increased (~7% less costs). The findings let one to quantify metering benefits near shopping areas

Average travel time estimations for urban routes that consider exit turning movements

This paper presents a methodology for real-time estimation of exit movement-specific average travel time on urban routes by integrating real-time cumulative plots, probe vehicles, and historic cumulative plots. Two approaches, component based and extreme based, are discussed for route travel time estimation. The methodology is tested with simulation and is validated with real data from Lucerne, Switzerland, that demonstrate its potential for accurate estimation. Both approaches provide similar results. The component-based approach is more reliable, with a greater chance of obtaining a probe vehicle in each interval, although additional data from each component is required. The extreme-based approach is simple and requires only data from upstream and downstream of the route, but the chances of obtaining a probe that traverses the entire route might be low. The performance of the methodology is also compared with a probe-only method. The proposed methodology requires only a few probes for accurate estimation; the probe-only method requires significantly more probes

Recent advances in genetics of lactic acid bacteria

Lactic acid bacteria (LAB) are a heterogeneous family of microorganisms that can ferment a variety of carbohydrates primarily into lactic acid (Carr et al. 2002). Most of the LAB belongs to the order of Lactobacillales, a group of mainly Gram-positive, anaerobic, non-sporulating and acidtolerant bacteria. Biochemically, LAB include both homofermenters and heterofermenters (Kleerebezem et al. 2003). The former group produces primarily lactic acid through carbohydrate fermentation, while the latter group yields a variety of fermentation by-products including lactic acid, acetic acid, ethanol, carbon dioxide and formic acid (Leroy and de Vuyst 2004). LAB can be sub-classifi ed into seven phylogenetic clades: Lactococcus, Enterococcus, Oenococcus, Pediococcus, Streptococcus, Leuconostoc and Lactobacillus. The defi nition of LAB is biological rather than taxonomical, i.e., the LAB do not comprise a monophyletic group of bacteria. Today, it is known that LAB play a crucial role in the world food supply by performing the main bioconversions in fermented dairy products, meats and vegetables. LAB are also used in the production of wine, coffee, silage, cocoa, sourdough and numerous indigenous food fermentations (Leroy and de Vuyst 2004). LAB are indigenous to food-related habitats including plant (fruits, vegetables and cereal grains) and milk environments. In addition, some LAB species are also member of the fl ora of the mouth, intestine and vagina of the mammalian (Vaughan et al. 2005). Isolates of the same species are often obtained from plant, dairy and animal habitats, implying widedistribution and specialized adaptation of these species to these diverse environments. © 2015 by Taylor & Francis Group, LLC

Identification of adsorption inhibition, restriction/modification and abortive infection type phage resistance systems in Lactococcus lactis strains

98 Lactococcus lactis strains were isolated from traditional fermented milk products in Turkey tested against 60 lactococcal lytic phages to determine their resistance levels. While 82 L. lactis strains were sensitive against lactic phages at different levels, 16 L. lactis strains showed resistance to all phages tested. Types of phage resistance among 16 L. lactis strains were identified as phage adsorption inhibition in eight strains, restriction/modification in six strains and abortive infection (heat sensitive phage resistance) in two strains, using three broad-spectrum phages Fpll 98-32, Fpld 67-42 and Fpld 67-44

Genetic analysis of bacteriocin production ability and phage adsorption inhibition type resistance system in six Lactococcus lactis strains

In this study, the phage adsorption inhibition type resistance system was investigated in 6 bacteriocin producing strains, Lactococcus lactis subsp. lactis BLL10, BLL27, BLL31, BLL84 and BLL90 and L. lactis subsp. cremoris BLC67. All six bacteriocin producing strains were determined to comprise phage adsorption inhibition type of resistance against three phages (Øpll98-28, Øpld67-41 and Øpld67-43). Genetic determinants of these two systems were also analysed in these strains. The bacteriocin production abilities and phage adsorption inhibition type resistance of these strains were found to be determined by 13.4 kb and 25.3 kb plasmids in BLL10; 9.5 kb and 30.1 kb plasmids in BLL27; 10.4 kb and 29.0 kb plasmids in BLL31; 23.4 kb and 19.0 kb plasmids in BLL84; 7.5 kb and 15.3 kb plasmids in BLL90, respectively. In BLC67, both characteristics were found to be determined by 31.3 kb plasmid. Conjugal mating experiments showed that 30.1 kb plasmid in BLL27, 29.0 kb plasmid in BLL31, 23.4 kb plasmid in BLL84 and 31.3 kb plasmid in BLC67 were conjugally transferable with the frequencies of 3.6×10−3, 8.2×10−4, 1.4×10−6 and 6.6×10−3, respectively

Use of RAPD-PCR, plasmid profiling, class 1 integron analysis, and antimicrobial resistance for molecular characterisation of Salmonella strains isolated from Turkey

Forty-one Salmonella strains, isolated from food samples collected from different parts of Turkey were characterized by various biochemical and genotypic tests. Among 41 isolates, 10 strains harboured at least one plasmid, sizes ranging from 3 kb to 400 kb. The antibiotic resistance profiles of Salmonella isolates were studied against 16 commonly used antibiotics. The highest level of resistance was observed against sulfonamide and neomycin, respectively. Moreover, resistance to multiple antibiotics (5) was also observed among 59% of isolates. Each isolate was also screened for the presence of class 1 integrons and nearly 88% of strains contained class 1 integron with different variable regions (VRs). Further examination of the Salmonella isolates was carried out by testing their clonal relation by RAPD-PCR analyses. With the amplification of primer P1254 the isolates classified into 15 groups and with primer P1283, they classified into 8 groups, on the basis of statistical analyses

Estimation of delays at traffic signals for variable demand conditions

This paper proposes a delay model for signalized intersections that is suitable for variable demand conditions. The model is applicable to the entire range of expected operations, including highly oversaturated conditions with initial queues at the start of the analysis period. The proposed model clarifies several issues related to the determination of the peak flow period, as well as the periods immediately preceding and following the peak. Separate formulas are provided for estimating delay in each of the designated flow periods as well as in the total flow period. Formulas are also provided to estimate the duration of the oversaturation period where applicable. The strength of the model lies in the use of simple rules for determining flow rates within and outside the peak, using the peak flow factor, a generalization of the well-known peak hour factor parameter. Simple rules are also provided for the identification of the location and duration of the peak flow period from observations of the demand profile. Such information is considered vital from an intersection design and evaluation viewpoint. Application of the model to a variety of operating conditions indicates that the estimated delay for vehicles arriving in the peak flow period is an acceptable predictor of the average delay incurred during the total flow period, even when oversaturation persists beyond the total flow period. On the other hand, the use of the average degree of saturation with no consideration of peaking can lead to significant underestimation of delay, particularly when operating at or near capacity conditions. These findings were confirmed by comparing the model results with other models found in the literature. The significant contribution of this work is not simply in the development of improved delay estimates, but, more important, in providing an integrated framework for an estimation process that incorporates (a) the peaking characteristics in the demand flow pattern, (b) the designation of flow-specific periods within the total flow period in accordance with the observed peaking and (c) the estimation of performance parameters associated within each flow period and in combination with other periods. A revised delay formula for the U.S. Highway Capacity Manual (HCM) is proposed. The revised formula has no constraints on the peak flow period degree of saturation, unlike the current HCM formula. It is also recommended that a simple formula for estimating the duration of oversaturation be used in conjunction with the revised delay formula.