Growth Kinetic Parameters Research Articles

Effects of Different Nutritional Zinc Forms on the Proliferation of Beneficial Commensal Microorganisms

This study compared the minimal inhibition concentrations (MICs) and their effects on the growth kinetics of seven different types of zinc (Zn) compounds and Na2EDTA in the case of three typical commensal beneficial microorganisms (Bacillus subtilis, Lactococcus lactis, and Saccharomyces cerevisiae). The seven Zn compounds included ZnSO4, four Zn–amino acid chelates, and two Zn–EDTA complexes. Both MICs and growth kinetic parameters indicated that different microorganisms show different sensitivities; for example, B. subtilis, L. lactis, and S. cerevisiae were most sensitive to ZnSO4, Na2EDTA, and Zn(NH3)2(Gly)2, respectively. Both ZnEDTA and Zn(NH3)2(Lys)2 improved the growth rate of all beneficial commensal intestinal microorganisms at low concentrations (5–10 mg/L) and showed low toxicity towards all tested strains. At higher concentrations (100–500 mg/L), all compounds decreased the growth rate and increased the lag phase. In conclusion, both growth kinetic parameters and MICs tested effectively measured the inhibitory effects of the test materials; however, growth kinetics provides a more detailed picture of the concentration-dependent effects and those on the mechanisms of microbial growth inhibition.

Active and Intelligent Packaging for Enhancing Modified Atmospheres and Monitoring Quality and Shelf Life of Packed Gilthead Seabream Fillets at Isothermal and Variable Temperature Conditions.

The study investigated the effect of active modified atmosphere packaging (20% CO2–60% N2–20% O2) with CO2 emitters (MAP-PAD) and conventional MAP (MAP) on the quality and shelf-life of gilthead seabream fillets during chill storage, while the most appropriate enzymatic Time Temperature Integrators (TTI) were selected for monitoring their shelf-life at isothermal and variable temperature storage conditions (Teff = 4.8 °C). The concentration of CO2 and O2 in the headspace of the package, volatile compounds and of the microbial population were monitored during storage. The kinetic parameters for bacterial growth were estimated at 0–10 °C using the Baranyi growth model. The MAP-PAD samples presented significantly lower microbial growth rates and longer lag phases compared to the MAP samples, leading to significant shelf-life extension: 2 days of extension at 2.5 °C and 5 °C, while 50% extension at variable conditions (Teff = 4.8 °C). CO2 emitters in the package improved the chemical freshness (K-values) and volatile compounds (characterizing freshness). The responses of different enzymatic TTI were modeled as the function of enzyme concentration, temperature and storage time. The activation energy (Ea) ranged from 97 to 148 kJ mol−1, allowing the selection of appropriate TTIs for the shelf-life monitoring of each fish product: LP-150U for the MAP and M-25U for the MAP-PAD samples. The validation experiment at Teff = 4.8 °C confirmed the applicability of Arrhenius-type models, as well as the use of TTIs as effective chill chain management tools during distribution and storage.

Development of a New Modelling Approach and Performance Evaluation of Meta-heuristic Optimization Algorithms for the Prediction of Kinetic Growth Parameters for Pseudomonas spp. in Fish

The main aim of the current work was to build up a new mathematical modelling approach in predictive food microbiology field for the prediction of growth kinetics of microorganisms. For this purpose, the bacterial growth data of Pseudomonas spp. in whole fish (gilt-head seabream) subjected to isothermal and non-isothermal storage temperatures were collected from previously published growth curves. Maximum specific growth rate (1/h) and lag phase duration (h) were described as a function of storage temperature using the direct two-step, direct one-step and inverse dynamic modelling approaches based on various meta-heuristic optimization algorithms. The fitting capability of the modelling approaches and employed optimization algorithms was separately compared, and the one-step modelling approach for the direct methods and the Bayesian optimization method for the used algorithms provided the best goodness of fit results. These two were then further processed in validation step. The inverse dynamic modelling approach based on the Bayesian optimization algorithm yielded satisfactorily statistical indexes (1.02 > Bias factor > 1.09 and 1.07 > Accuracy factor > 1.13), which indicates it can be reliably used as an alternative way of describing the growth behaviour of Pseudomonas spp. in fish in a fast and efficient manner with minimum labour effort.

Growth of Myriangium sp. in sabouraud medium: a new approach to the definition of kinetic parameters / Crescimento de Myriangium sp. em meio sabouraud: uma nova abordagem para a definição de parâmetros cinéticos

In this study, the yeast growth process was mathematically modeled and growth kinetic parameters were defined for two strains of Myriangium sp. (Y6511 and Y6512) in Sabouraud medium at temperatures of 26, 30 and 34 °C at time t varying from t0 = 0 h, tf = 36 h. Maximum cell concentrations were 30.50 g/L (Y6511 at 34°C) and 34.00 g/L (Y6512 at 34°C). The maximum specific growth rates calculated for strains Y6511 and Y6512 were respectively 0.30 and 0.28 h-1 in the growth condition at 26 °C after 11.5 h of growth (for Y6511) and 9.5 h of growth (for Y6512). Maximum biomass volumetric growth rates were 2.75 and 2.63 g/L.h for strains Y6511 and Y6512, respectively, at 26 °C. For strain Y6511, the unit increase in temperature (g/L.°C) raises the cell concentration to a maximum value of 0.27 g/L.°C in the process time of 9.55 h and temperature of 29.5 °C. Similarly, for strain Y6512, the unit increase in temperature raises the cell concentration to a maximum value of 0.45 g/L.°C in the process time of 7.35 h and temperature of 26.8 °C. The observed parameters can be used for the production of cell mass, in batch or continuous process, enzymes and other bioproducts of commercial interest.

Fertilization promotes microbial growth and minimum tillage increases nutrient-acquiring enzyme activities in a semiarid agro-ecosystem

Microorganisms respiratory and enzymatic activities provide sensitive indicators of changes in soil properties, such as those caused by interactive effects of tillage and fertilization regimes or other agricultural practices. However, the rapid, adaptive microbial growth, respiratory and enzymatic responses to changes in soil environments induced by specific agricultural practices are not well understood. Thus, to explore these adaptations we compared effects of contrasting environments on functional microbial traits (growth and enzyme kinetic parameters) in a Mediterranean agro-ecosystem. These environments differed in long-term disturbance (no, minimum, or conventional tillage), nitrogen-richness (fertilization with 90 kg N ha−1 versus no fertilization), and resource scarcity (increasing with soil depth in 0–30, 30–60 and 60–90 cm layers). Reducing soil disturbance from conventional to minimum tillage promoted microbial growth through shorter Tlag and larger active biomass fraction and induced increases in N- and P-acquiring enzyme activities by increasing nutrients limitation. Fertilization stimulated increases in fast-growing microorganisms with low substrate-affinity enzyme systems, microbial biomass, enzymatic activities, and turnover rates of soil organics. In contrast, increasing scarcity of resources with soil depth strongly reduced microbial biomass and activity. A lack of correlation between soil and enzymatic stoichiometric ratios raises concern regarding the applicability of eco-enzymatic stoichiometric indexes in Mediterranean agro-ecosystems. We conclude that decomposition and turnover of organic substrates under contrasting agricultural practices are mediated by microbial communities with distinct functional traits (active fraction, growth parameters) and enzyme properties (Vmax, Km), which need to be considered in smart land use regimes.

Fermentation of Habanero Pepper by Two Lactic Acid Bacteria and Its Effect on the Production of Volatile Compounds

Lactiplantibacillus plantarum is a lactic acid bacterium that grows in different environments; this ability arises due to the variability within the species, which may be influenced by their origin. On the other hand, habanero pepper (Capsicum chinense) from Yucatan, Mexico, is characterized by its unique sensory properties such as aroma and pungency and has an annual production of more than 5000 t in the Yucatan Peninsula. Thus, the purpose of this study was to compare L. plantarum from different isolation sources during habanero pepper fermentation. A 23 factorial design was made for the evaluation of the effect of two cultures a commercial (COM) and a wild (WIL) strain, in a habanero pepper puree medium (HPP); ripe and unripe peppers and different proportions of habanero pepper puree (40:60 or 60:40, HPP:water, w/w) were used to obtain the kinetic parameters of growth, lactic acid production, and volatile composition. The highest growth and lactic acid production were achieved in the 60:40 HPP:water, while WIL presented the major production of lactic acid. Characteristic volatiles in WIL fermentation were 2,3- butanedione, whereas in COM fermentation, they were limonene, cis-3-hexenyl hexanoate, and 1-hexanol. The association between COM and 1-hexanol was confirmed with principal component analysis (PCA).

Strain wars 3: Differences in infectivity and pathogenicity between Delta and Omicron strains of SARS-CoV-2 can be explained by thermodynamic and kinetic parameters of binding and growth

In this paper, for the first time, empirical formulas have been reported of the Delta and Omicron strains of SARS-CoV-2. The empirical formula of the Delta strain entire virion was found to be CH1.6383O0.2844N0.2294P0.0064S0.0042, while its nucleocapsid has the formula CH1.5692O0.3431N0.3106P0.0060S0.0043. The empirical formula of the Omicron strain entire virion was found to be CH1.6404O0.2842N0.2299P0.0064S0.0038, while its nucleocapsid has the formula CH1.5734O0.3442N0.3122P0.0060S0.0033. Based on the empirical formulas, standard thermodynamic properties of formation and growth have been calculated and reported for the Delta and Omicron strains. Moreover, standard thermodynamic properties of binding have been reported for Wild type (Hu-1), Alpha, Beta, Gamma, Delta and Omicron strains. For all the strains, binding phenomenological coefficients and antigen-receptor (SGP-ACE2) binding rates have been determined and compared, which are proportional to infectivity. The results show that the binding rate of the Omicron strain is between 1.5 and 2.5 times greater than that of the Delta strain. The Omicron strain is characterized by a greater infectivity, based on the epidemiological data available in the literature. The increased infectivity was explained in this paper using Gibbs energy of binding. However, no indications exist for decreased pathogenicity of the Omicron strain. Pathogenicity is proportional to the virus multiplication rate, while Gibbs energies of multiplication are very similar for the Delta and Omicron strains. Thus, multiplication rate and pathogenicity are similar for the Delta and Omicron strains. The lower number of severe cases caused by the Omicron strain can be explained by increased number of immunized people. Immunization does not influence the possibility of occurrence of infection, but influences the rate of immune response, which is much more efficient in immunized people. This leads to prevention of more severe Omicron infection cases.

English

“Rabilé” is a popular traditional ferment in Burkina Faso, consisting mainly of yeasts. It is used as a food supplement or additive like Single Cell Protein (SCP). The present work focused on identifying yeast microbiota in local food, and studying their growth kinetic parameters. “Rabilé” sampling from the 13 regions of Burkina Faso was used to isolate yeast strains. Molecular methods, including PCR-RFLP, Sanger Sequencing, and Single Locus Analysis, were applied for strain identification. The kinetic parameters were determined in batch culture. The results show 390 isolates belonging to 12 species with a predominance of Saccharomyces cerevisiae, followed by Cutaneotrichosporon curvatus. Among the selected strains, S. cerevisiae OG22 and Kluyveromyces marxianus KY01 showed the highest maximum growth rate (0.566 and 0.568 h-1) concerning kinetic parameters. These results demonstrate that “Rabilé” is an important biotope of yeast strains, and could be a potential food supplement.   Key words: Yeast, Rabilé, traditional ferment, molecular identification, kinetic parameters.

Developing Microbial Co-Culture System for Enhanced Polyhydroxyalkanoates (PHA) Production Using Acid Pretreated Lignocellulosic Biomass.

In the growing polymer industry, the interest of researchers is captivated by bioplastics production with biodegradable and biocompatible properties. This study examines the polyhydroxyalkanoates (PHA) production performance of individual Lysinibacillus sp. RGS and Ralstonia eutropha ATCC 17699 and their co-culture by utilizing sugarcane bagasse (SCB) hydrolysates. Initially, acidic (H2SO4) and acidified sodium chlorite pretreatment was employed for the hydrolysis of SCB. The effects of chemical pretreatment on the SCB biomass assembly and its chemical constituents were studied by employing numerous analytical methods. Acidic pretreatment under optimal conditions showed effective delignification (60%) of the SCB biomass, leading to a maximum hydrolysis yield of 74.9 ± 1.65% and a saccharification yield of 569.0 ± 5.65 mg/g of SCB after enzymatic hydrolysis. The resulting SCB enzymatic hydrolysates were harnessed for PHA synthesis using individual microbial culture and their defined co-culture. Co-culture strategy was found to be effective in sugar assimilation, bacterial growth, and PHA production kinetic parameters relative to the individual strains. Furthermore, the effects of increasing acid pretreated SCB hydrolysates (20, 30, and 40 g/L) on cell density and PHA synthesis were studied. The effects of different cost-effective nutrient supplements and volatile fatty acids (VFAs) with acid pretreated SCB hydrolysates on cell growth and PHA production were studied. By employing optimal conditions and supplementation of corn steep liquor (CSL) and spent coffee waste extracted oil (SCGO), the co-culture produced maximum cell growth (DCW: 11.68 and 11.0 g/L), PHA accumulation (76% and 76%), and PHA titer (8.87 and 8.36 g/L), respectively. The findings collectively suggest that the development of a microbial co-culture strategy is a promising route for the efficient production of high-value bioplastics using different agricultural waste biomass.

Predicting B. cereus growth and cereulide production in dairy mix

This study aims to quantify growth and cereulide production by Bacillus cereus and their potential correlation in an intermediate dairy wet-mix. Systematic experiments were carried out using the emetic reference strain F4810/72 in the suboptimal range of temperature of 12 °C to 20 °C. Growth and cereulide kinetic parameters were estimated and the three parameters (i) time to first cereulide quantification (tcer), (ii) maximum specific growth rates (μmax) and (iii) cereulide production rates (k) were modelled as a function of temperature. As temperature increased, growth lag time and tcer were shorter while microbial increase and cereulide production happened earlier, and at higher rates. Maximum concentration of cells and maximum cereulide concentration proved to be temperature-independent, reaching the average values of 7.9 ± 0.3 log10(CFU/mL) and 2.6 ± 0.2 log10(ng.g−1) respectively. Moreover, the time to reach the widely used threshold of 5 log10CFU/mL (t5log) was tested against tcer, and this suggested that this threshold can be used with increased confidence at lower temperatures to assure toxin is not quantified in this matrix. The average tcer were equal to 314 h, 118 h, 73 h and 45 h for 12 °C, 15 °C, 18 °C and 20 °C respectively. A validation study was performed using independent data sets obtained with the same strain in other dairy matrices. The microbial growth models presented good predictive power even when extrapolated beyond the temperature range of construction. Nevertheless, the models proposed for prediction of toxin production over time presented limitations, especially for food matrices that deviate significantly from the original matrix for which the model was developed, making cereulide predictions less accurate. Our findings suggest that similar modelling approaches can be used to predict growth, time to first cereulide quantification as well as cereulide formation over time for a specific matrix, but that matrix-extrapolations are more suitable for growth than for cereulide.

Kinetic modeling of fungal biomass growth and lactic acid production in Rhizopus oryzae fermentation by using grape stalk as a solid substrate.

This work proposes the use of grape stalk, a residue from the wine industry, as a solid substrate for R. oryzae NCIM 1299 fermentation to obtain lactic acid. The use of filamentous fungi on grape stalk as a fermentative solid substrate has not been studied yet making this study an innovative research work. Grape Stalk was chemically characterized, and according to its properties, it was deemed as an innovative material with great potential to be used as a fermentation substrate. R. oryzae growth kinetic determination needs the measurement of the biomass dry weight of fungus versus time, but the filamentous fungi penetration into the solid substrate makes the quantitative biomass removal from the substrate practically impossible. Therefore, fungal growth on membrane experiment was performed making gravimetric quantification of fungal biomass feasible. Two mediums were used comparatively, potato dextrose agar and a medium designed with agar and grape stalk for 5 days at 30 °C and 50%RH. Logistic, First Order and First Order Plus Dead Time models were used to model biomass growth, where these last two models have not been previously used for microbial kinetics studies. Growth kinetic parameters ( X max , μ max , T p and T 0 ) were found for all models and the First Order model showed the best fit with an R 2 equal to 91.84%. The Luedeking-Piret model was used to model lactic acid production and provided the parameters Y p/x and m p , with an R 2 equal to 90.05%. The kinetic parameters found here are also of great interest for further bioreactor designs. • Grape stalk was characterized as a fungal fermentation substrate. • Grape stalk, raw material in fungal fermentation trials for Lactic acid production. • Cell biomass and lactic acid production kinetic modeling by membrane experiments. • First Order model for fungal biomass growth showed best data fitting. • The Luedeking Piret model parameters were obtained for Lactic Acid production.

Phenol biodegradation by plant growth promoting bacterium, S. odorifera: kinetic modeling and process optimization.

One of the main organic pollutants that could result from industrial products and chemical transformations is phenol. In the current study, the kinetics of Serratia odorifera, which was isolated from arable soil, was studied by growing it on broth minimal medium spiked with phenol as only carbon source and energy. The newly isolated plant growth-promoting bacterium (PGPB), S. odorifera, was used for the first time for phenol biodegradation. The growth kinetics parameters (phenol-dependent) including maximum specific growth rate (μmax), half-saturation coefficient (Ks), and the Haldane's growth kinetics inhibition coefficient (Ki), were tested via Haldane inhibition model and resulted on the 0.469 (h -1), 26.6 (mgL-1), and 292 (mgL-1), respectively. The sum of squared error (SSR) of 4.89 × 10-3 was fitted to the experimental data by Haldane equation. The results of phenol biodegradation were fitted into the modified Gombertz model. The increase of phenol concentrations led to increases in both the rate of phenol biodegradation and lagging time. The optimal phenol biodegradation and bacterial growth obtained by S. odorifera, were at 28°C incubation temperature and a pH of 7.0. The pathway of phenol biodegradation by S. odorifera was proposed in the current study to provide a new insight into synchronization of phenol biodegradation and plant growth-promoting bacteria. This may play an important role in remediation of phenol-contaminated soil besides promoting the plant growth, thus lessening the plant stress.

Anaerobic Treatment for Palm Oil Mill Effluent Using Covered In-the Ground Anaerobic Reactor (CIGAR)

Wastewater from crude palm oil mills contains high organic matter, which potentially produces biogas through anaerobic digestion processes. The design and operation of an anaerobic bioreactor require a good understanding of the reaction kinetic in the bioreactor. This study aimed to evaluate the biogas production from POME and to determine the kinetic parameters of microbial growth and the substrate utilization rates in a CIGAR. An experiment was conducted using a 5-m3 bioreactor with a working volume of 4.4 m3. Wastewater from the Bekri palm oil mill was stored in a 5-m3 tank. After stabilization, the wastewater was loaded into the reactor at a rate of 100 to 250 L/d, corresponding to a COD loading rate of 1.373-3.097 kg·m-3.d-1, and an HRT of 18-44 days. Monod, Contois, Moser, and Shuler kinetic models were evaluated. The results showed that the Shuler model performed best for microbial activities, while the first order reaction model performed best for the substrate utilization kinetic. The maximum specific growth rate (μmax) for the Shuler model was 0.052 d-1 and the saturation constant (Kso) was 0.119. The maximum substrate utilization rate constant (ks) was 2.183 d-1 and biomass yield (Yx/s) 0.024 kg/kg. The maximum average efficiency of anaerobic degradation (34.4%) occurred at a feeding rate of 100 L/d with methane yield of 0.120 Nm3/kg of removed COD. This value is relatively low compared to the maximum potential of 0.350 Nm3/kg CODr.

ФИЗИОЛОГИЯ И ПАТОЛОГИЯ МИТОЗА ПРИ ИЗУЧЕНИИ КИНЕТИЧЕСКИХ ПОКАЗАТЕЛЕЙ РОСТА НОВООБРАЗОВАНИЙ ЭПИТЕЛИАЛЬНОГО ПРОИСХОЖДЕНИЯ

This article presents results of a study of proliferative activity of moderately differentiated tubulopapillary adenocarcinoma in the mammary gland of cats. The studies were carried out on the basis of Interdepartment Scientific Center of Veterinary Medicine of Ulyanovsk State Agrarian University. Pathological material was obtained by excisional biopsy in accordance with the rules for taking biomaterial for histological studies. The biopsy material was freed from formalin by rinsing in tap water for 12 ... 24 hours. Slices of 20 ... 30 µm thick were obtained using a freezing microtome MZ-2. The preparations were stained with hematoxylin and eosin according to the standard technique. The parameter of mitotic activity of tumor tissue, the mitotic index, was calculated as the number of mitoses per 1000 cells of the tumor parenchyma, measured in the areas with the highest proliferative activity of the neoplasm on the periphery of the tumor node. Cell nuclei in a state of physiological rest, as well as at the stages of mitosis and apoptosis, clearly visible on photographs of the microscope visual fields, were marked in a graphic editor and counted using the ImageJ program. Based on the data of histological diagnostics of biopsy material slices, such kinetic parameters of tumor growth as mitotic activity were studied - the mitotic index, the number of mitoses in the field of view, the proportion and types of pathologies of cell division, and the cell loss factor, numerically measured in the form of the apoptotic index were calculated. Based on the obtained data, a characteristic was given of the growth rate and invasiveness of this neoplasm of epithelial origin, as well as a prognosis of metastatic activity, the risk of recurrence and the likelihood of complete morphological regression of tumor tissue after radiation and chemotherapy.

Accounting for the Presence of Molecular Clusters in Modeling and Interpreting Nucleation and Growth.

The effect of molecular cluster formation on the estimation of kinetic parameters for primary nucleation and growth in different systems has been studied using computationally generated data and three sets of experimental data in the literature. It is shown that the formation of molecular clusters decreases the concentration of monomers and hence the thermodynamic driving force for crystallization, which consequently affects the crystallization kinetics. For a system exhibiting a strong tendency to form molecular clusters, accounting for cluster formation in a kinetic model is critical to interpret kinetic data accurately, for instance, to estimate the specific surface energy γ from a set of primary nucleation rates. On the contrary, for a system with negligible cluster formation, a consideration of cluster formation does not affect parameter estimation outcomes. Moreover, it is demonstrated that using a growth kinetic model that accounts for cluster formation allows the estimation of γ from typical growth kinetic data (i.e., de-supersaturation profiles of seeded batch crystallization), which is a novel method of estimating γ developed in this work. The applicability of the novel method to different systems is proven by showing that the estimated values of γ are closely comparable to the actual values used for generating the kinetic data or the corresponding estimates reported in the literature.

A novel coconut-malt extract medium increases growth rate of morels in pure culture

Morels are gourmet wild edible mushrooms that can grow on several substrates with significant growth rate variations. Such variations have hindered the development of a standardized culture media to promote morel’s sustainable production. The aim of this study is developing a novel culture media that takes advantage of coconut water as a complementary component of culture media. Coconut water has been extensively used as a growth-promoting component for plant tissue cultures; however, its application as component of fungi cultivation medium has not been fully developed. This study confirms that coconut water can be efficiently used as culture media component for morels using a kinetic characterization. Morchella sp. kinetic growth is evaluated in different cultures: agar, malt extract agar (MEA), lactose, coconut water (15%) and combinations of them. Kinetic growth parameters (lag phase, λ and maximum specific growth rate, µmax) are estimated using primary modeling methods. Among the selected models, the best fit is achieved using Baranyi’s model. A significant increase from 15.8% to 43.4% of the µmax values was observed when culture media (agar, lactose, MEA) is supplemented with coconut water. The largest values of µmax are obtained in MEA-coconut cultures (21.13 ± 0.43–22.57 ± 0.35). Micro-sclerotia and late sclerotia are observed in all cultures containing coconut water justifying the development of a feasible and cost-effective way of culturing morels. The results demonstrate that coconut water can be used for formulation of standard media for morel cultivation leading to a cheap alternative to produce dense mycelium and promote sclerotia formation.

A mathematical model to predict the antilisteria bioprotective effect of Latilactobacillus sakei CTC494 in vacuum packaged cooked ham

Biopreservation is a strategy that has been extensively covered by the scientific literature from a variety of perspectives. However, the development of quantitative modelling approaches has received little attention, despite the usefulness of these tools for the food industry to assess the performance and to set the optimal application conditions. The objective of this study was to evaluate and model the interaction between the antilisteria strain Latilactobacillus sakei CTC494 (sakacin K producer) and Listeria monocytogenes in vacuum-packaged sliced cooked ham. Cooked ham was sliced under aseptic conditions and inoculated with L. monocytogenes CTC1034 and/or L. sakei CTC494 in monoculture and coculture at 10:10, 10:103 and 10:105 cfu/g ratios of pathogen:bioprotective cultures. Samples were vacuum packaged and stored at isothermal temperature (2, 5, 10 and 15 °C). The growth of the two bacteria was monitored by plate counting. The Logistic growth model was applied to estimate the growth kinetic parameters (N0, λ, μmax, Nmax). The effect of storage temperature was modelled using the hyperbola (λ) and Ratkowsky (μmax) models. The simple Jameson-effect model, its modifications including the Ncri and the interaction γ factor, and the predator-prey Lotka Volterra model were used to characterize the interaction between both microorganisms. Two additional experiments at non-isothermal temperature conditions were also carried out to assess the predictive performance of the developed models through the Acceptable Simulation Zone (ASZ) approach. In monoculture conditions, L. monocytogenes and L. sakei CTC494 grew at all temperatures. In coculture conditions, L. sakei CTC494 had an inhibitory effect on L. monocytogenes by lowering the Nmax, especially with increasing levels of L. sakei CTC494 and lowering the storage temperature. At the lowest temperature (2 °C) L. sakei CTC494 was able to completely inhibit the growth of L. monocytogenes when added at a concentration 3 and 5 Log higher than that of the pathogen. The inhibitory effect of the L. sakei CTC494 against L. monocytogenes was properly characterized and modelled using the modified Jameson-effect with interaction γ factor model. The developed interaction model was tested under non-isothermal conditions, resulting in ASZ values ≥83%. This study shows the potential of L. sakei CTC494 in the biopreservation of vacuum-packaged cooked ham against L. monocytogenes. The developed interaction model can be useful for the industry as a risk management tool to assess and set biopreservation strategies for the control of L. monocytogenes in cooked ham.

Comparison on the Growth Heterogeneity of Vibrio parahaemolyticus Coupled with Strain Source and Genotype Analyses in Different Oligotrophic Conditions

Vibrio parahaemolyticus is an important foodborne pathogen in aquatic products that can survive long term in an oligotrophic environment and maintain pathogenicity. In this study, the growth curves of 38 strains of V. parahaemolyticus (pathogenic and environmental strains) under different oligotrophic conditions (tryptone soy broth [TSB] and TSB medium diluted 2, 4, and 6 times) were simulated and their growth heterogeneities were compared. The growth kinetic parameters (maximum specific growth rate and lag time) were calculated by the modified Gompertz model. The results showed that oligotrophic conditions affected the growth variability of strains, and the coefficient of variation of all strains reached the maximum in the 4-fold dilution of TSB. Under different oligotrophic conditions, the lag time of the pathogenic strains was shorter than that of the environmental strains, whereas the maximum specific growth rate of the environmental strains was greater. This indicated that pathogenic strains were more adaptable to the nutrient-deficient environment. The analysis of different genotypes revealed that the strains with genotype tlh+/tdh+/trh- showed greater growth variability in oligotrophic environments. These results provided theoretical support for the accuracy of the risk assessment of aquatic products.

ANALYSIS OF DIESEL SPILL BIOREMEDIATION BY BACTERIAL ISOLATES IN BATCH CULTURE USING MONOD AND HALDANE KINETIC MODEL

The unintended oil spills from oil tankers, transportation and storage facilities, leads to petroleum hydrocarbon pollution that causes adverse effects on the air, water and soil environment. Bioremediation using indigenous microorganisms has become a promising tool for effective mineralization of toxic contaminants into harmless end products. In this study, bioremediation of petroleum contaminated soil was carried out in a batch scale using Staphylococcus, Pseudomonas, Micrococcus, Escherichia, Acinetobacter, Bacillus, Corynebacterium, Salmonella and Klebsiella species, all isolated from petroleum hydrocarbon contaminated soil. The effect of 1 to 10% v/v diesel concentrations on the growth and biodegradation rate of all selected nine isolates was studied and specific growth rates (μh -1) were calculated. The initial rate of growth and biodegradation of nine isolates increased correspondingly with the diesel concentration up to 5% (v/v), but further increase in diesel concentration resulted in a slight decrease in the rate of biodegradation. Diesel is known to be an inhibitory substrate. Both Monod and Haldane kinetic models were useful for the evaluation of the growth kinetic parameters (μmax, Ks, Ki). It was found that the Monod model was able to express the growth parameters up to 5% v/v diesel. However, Haldane model effortlessly fitted with the experimental data for increase in the diesel i.e. over 6 % v/v diesel. These results showed that the diesel oil degraders were able to utilize a considerably high concentration of diesel and could be very effective in diesel biodegradation for restoration of contaminated sites.

Formation <i>in vitro</i> of colistin resistance in carbapenem-resistant Gram-negative bacteria and its biological cost

Introduction. The spread of resistance to carbapenems among gram-negative bacteria have led to an increase in the consumption of polymyxins and the emergence of certain strains resistant to them. Polymyxin resistance is mainly associated with mutations in chromosomal genes. The development of mutational resistance to antibiotics can lead to a decrease in the viability of bacteria; which is manifested by an increase in the duration of the cell cycle; a decrease in virulence and competitive fitness.The purpose of the study was to assess in vitro the intensity of the formation of colistin resistance in carbapenemresistant clinical isolates of gram-negative bacteria; the stability of the formed emerged resistance and its biological cost.Materials and methods. For 46 strains of Klebsiella pneumoniae; 77 strains of Pseudomonas aeruginosa and 42 strains of Acinetobacter baumannii; real time polymerase chain reaction (PCR) was used to detect the genes of carbapenemases; the minimum inhibitory concentrations (MIC) of meropenem and colistin were determined by broth microdilution method. The selection of resistant subpopulations on Muller–Hinton agar with the addition of 16 mg/l colistin was carried out. For colistin-resistant mutants and their isogenic sensitive strains; the kinetic parameters of growth in broth culture were determined. Incubation and result recording were performed on an Infinite M200 microplate reader for 18.5 hours at 35°C with measurement of light scatter in the wells every 15 minutes.Results. The production of carbapenemases MBL VIM in P. aeruginosa; MBL NDM; KPC and OXA-48 in K. pneumoniae; OXA-23 and OXA-40 in A. baumannii was observed. All strains were sensitive to colistin (MIC varied from 0.062 to 2 mg/l). The colony growth on a selective medium with16 mg/l colistin was observed for 97.8% of K. pneumoniae strains; 16.9% of P. aeruginosa strains; and 61.9% of A. baumannii strains. The mutational nature of colistin resistance was confirmed for 21.7% of K. pneumoniae strains. For colistin-resistant mutants of K. pneumoniae; a significant increase in the duration of the lag phase (Tlag) was observed: 225.6 ± 7.037 min in the wild-type susceptible strains and 245.5 ± 8.726 in resistant mutants; p = 0.037. The indicators of the doubling time of the number of microbial cells in the exponential growth phase (Tdoubling) and the area under the bacterial growth curve did not differ significantly.Conclusion. A high frequency of formation of colistin resistance in vitro in carbapenemase-producing strains of K. pneumoniae was observed. The absence of significant changes in the kinetics of microbial growth in resistant strains makes it possible to predict the further spread of mutational resistance to colistin; as well as its preservation in microbial populations of K. pneumoniae even in the case of limiting the use of this antibiotic.