Initial Concentration Of Microorganisms Research Articles

Effects of the initial concentration of microorganisms on inactivation by ultrasonic cavitation

Ultrasonic sterilization is gaining progressively more attention for microbial sterilization without the drawbacks of heat, UV radiation, and chemical treatments. It is crucial to understand ultrasonic cavitation in heterogeneous media in order to disable microorganisms efficiently by ultrasound. In this study, the effect of initial bacterial concentration on the inactivation of Escherichia coli by ultrasonic cavitation was investigated over a wide range of frequencies. We found that the inactivation of microorganisms by ultrasound was frequency dependent, and the frequency dependence of the inactivation rate varied with the concentration. The results indicated that the strength of ultrasonic cavitation can vary with frequency and suggested that the mechanism of inactivation by ultrasound may vary with concentration.

1Pa4-4 Effects of the initial concentration of microorganisms on inactivation by ultrasonic cavitation

1Pa4-4 Effects of the initial concentration of microorganisms on inactivation by ultrasonic cavitation

Simulation of Methane Gas Production Process from Animal Waste in a Discontinuous Bioreactor

Due to the importance of environmental protection and the need to use new energy and alternative to conventional fuels, renewable energy has received much attention. Due to this necessity, a discontinuous bioreactor producing methane gas from animal waste has been modeled and simulated in this research. Monod kinetics was used to express the relationship between the growth rate of microorganisms and substrate concentration. The fourth-order Rong Kuta numerical method solved the substrate consumption and production of microorganisms and methane gas. The effect of the initial concentration of microorganisms on methane production has also been investigated. The initial concentrations of substrate and microorganisms are 74.51 g/L and 61.1 g/L, respectively. The results of this study showed that the mathematical model deviates about 53.8% from the laboratory data. According to the presented model, the amount of methane produced after 70 days is equal to 29.10 g/L. The decomposition rate of the substrate and methane gas production depends on the substrate's residence time. Increasing the initial concentration of microorganisms produces methane gas in less time. The amount of methane produced is independent of the initial concentration of microorganisms. The model presented in this study can predict the time required to perform the reaction, optimal bioreactor performance, design of relevant process equipment, and increase the scale of equipment, such as storage tank and proper control to produce high purity methane more volume. Suitable in bioreactors.

Gamma irradiation improves the microbiological safety and shelf-life of kimchi seasoning mixture

Kimchi seasoning is manufactured non-thermally without any additional decontamination step, resulting in possible microbiological growth and food safety issues. This study examines the effects of gamma irradiation on the microbiological and physicochemical characteristics of kimchi seasoning mixture during storage. Foodborne pathogens, i.e., Escherichia coli O157:H7 and Salmonella Typhimurium were inoculated into the seasoning mixture and irradiated at doses ranging from 0 to 10 kGy. Regardless of the microbial species, the number of microorganisms was adversely correlated with increasing gamma irradiation. The levels of E. coli O157:H7 and S. Typhimurium were reduced to below the detection limit (1 log CFU/g) after exposure to 5 kGy of gamma irradiation. The number of total aerobic and lactic acid bacteria decreased by 3.29 and 4.78 log CFU/g, respectively, after 10 kGy of gamma irradiation exposure. Changes in pH, acidity, reducing sugar content, and headspace gas concentrations were significantly delayed in irradiated kimchi seasoning mixtures (P < 0.05), whereas no significant difference was observed in color values between the irradiated and non-irradiated kimchi seasoning mixtures (P > 0.05). These results imply that gamma irradiation can enhance the microbiological safety and shelf-life of kimchi seasoning mixture, and decrease the initial concentration of microorganisms without adverse effects on quality.

Non-thermal atmospheric gas plasma for decontamination of sliced cheese and changes in quality.

The atmospheric-pressure non-thermal dielectric barrier discharge (DBD) plasma has recently emerged as an efficient decontamination method for the food safety enhancement. Thus the objective of this study was to evaluate the effectiveness of a simple DBD plasma treatment, with a relatively low-frequency power supply operating at 60 Hz, for microbial inactivation. A parametric study of operating conditions for bacterial inactivation was conducted using nutrient agar inoculated with Escherichia coli (2.28--6.28 log CFU/ml). The microbial log reduction was enhanced with increasing input power (30, 50, 70 W) and plasma exposure time (0, 1, 3, 5, 7 min). The inactivation effect was increased by decreasing inter-electrode gap (2, 1.5, 1 cm) and by reducing the initial microorganism concentration. Accordingly, a DBD plasma treatment at 50 W for 10 min could lead to complete killing of E. coli and partial inactivation of Listeria innocua on cheese (mean log reduction: 4.75 ± 0.02 and 0.72 ± 0.01, respectively). The decontamination efficacy of DBD plasma was affected by the types of microorganisms. The changes in hardness and color of cheese were unnoticeable after 10 min treatment with a power of 50 W. Overall, the results suggested that the DBD plasma can be potentially exploited to improve the food safety.

Studying growth kinetics of microbial populations using information technology. Solving the Cauchy problem

The possibilities of information technologies in the study of growth dynamics and development of microbial populations have been shown. In the R programming language in the Jupyter Notebooks environment, a direct kinetic problem has been solved. Kinetic regularities of growth of microbial populations under periodic cultivation have been considered within the framework of an approximation based on numerical integration of velocity equations. The one-step Runge-Kutta method of the fourth order of accuracy has been used as a method for solving a differential equation with initial conditions (Cauchy problem). Initial conditions of the problem were: the number of time steps n=10,000; initial substrate concentration S0=1; the initial concentration of microorganisms has been considered in four variants: M0=0.01, M0=0.05, M0=0.1, M0=0.2, which correspond to 1%, 5%, 10%, 20% of the inoculum density accordingly; affinity ration of the substrate to microorganisms Ks=0.5. The use of modern information technologies in the analysis of microbial growth patterns is mainly determined by the capabilities of personal computers, software environments and shells. The potential of modern software in the implementation of applied engineering and research problems in solving ordinary differential equations describing the development and course of the microbial process over time has been presented.

Detection of bacterial contamination in platelet concentrates from Brazilian donors by molecular amplification of the ribosomal 16S gene.

The aim of our work was to establish a semi-automated high-throughput DNA amplification method for the universal screening of bacteria in platelet concentrates (PCs). Among cases of transfusion transmission of infectious agents, bacterial contamination ranks first in the number of events, morbidity and mortality. Transmission occurs mainly by transfused PCs. Automated culture is adopted by some blood banks for screening of bacterial contamination, but this procedure is expensive and has a relatively long turnaround time. PCs were spiked with suspensions of five different bacterial species in a final concentration of 1 and 10 colony-forming units (CFU) per millilitre. After incubation, the presence of bacteria was investigated by real-time polymerase chain reaction (PCR) and by the Enhanced Bacterial Detection System (eBDS, Pall) assay as a reference method. Real-time PCR amplification was performed with a set of universal primers and probes targeting the 16S rRNA gene. Co-amplification of human mitochondrial DNA served as an internal control. Using the real-time PCR method, it was possible to detect the presence of all bacterial species tested with an initial concentration of 10CFU mL-1 24 h after contamination, except for Staphylococcus hominis. The PCR assay also detected, at 24 h, the presence of Serratia marcescens and Enterobacter cloacae with an initial concentration of 1CFU mL-1 . The real-time PCR assay may be a reliable alternative to conventional culture methods in the screening of bacterial contamination of PCs, enabling bacterial detection even with a low initial concentration of microorganisms.

ПЕРСПЕКТИВЫ ИСПОЛЬЗОВАНИЯ КУЛЬТУРЫ LEUCONOSTOC LACTIS ДЛЯ УПРАВЛЯЕМОГО ПРОЦЕССА ФЕРМЕНТАЦИИ БЕЛОКОЧАННОЙ КАПУСТЫ НА ПРЕДВАРИТЕЛЬНОМ ЭТАПЕ ФЕРМЕНТАЦИИ

The work is dedicated to the research of the application of starter culture of lactic acid microorganisms of Leuconostoc lactis for the controlled fermentation of white cabbage during the pre-fermentation stage. In the present work the influence of key factors (initial quantity of inoculated culture and chemical composition of white-cabbage based model media) on the dynamics of culture development during the pre-fermentation stage is considered. The results of the research showed that when using Leuconostoc lactis culture, the reaching of the point of change of positive rates into negative ones, when comparing samples with low initial concentrations of microorganisms to samples with high initial concentrations, is approximately 1.5 times different. From the point of view of dynamics of the rate of change in the concentrations of microorganisms in model media with different chemical composition, the development of the culture does not depend on either the substrate composition, or the initial concentration of microorganisms since the index of comparison of rates of development of microorganisms in the process of cultivation in the base and modified model media, both in the case of low and high initial concentration of microorganisms, does not go beyond the zone of invariance of response except for two small areas. From the point of view of comparing the concentrations of microorganisms in different model media, by changing the composition of the medium we can influence the dynamics of the development of the culture, on condition that a low initial concentration of microorganisms is used. As a consequence, this makes sense for low-tonnage production, in which the medium heterogeneity will be small. In its turn, the possible expressed heterogeneity of the composition of the medium, occurring in different areas of volume, can affect the overall efficiency of the development of culture. At the same time, the high initial concentration of lactic acid microorganisms due to their established invariance is insensitive to similar conditions, which should positively influence the efficiency of large-capacity industrial production.

Using Hyperspectral Imaging to Quantify Phototrophic Biofilms on Granite

This paper reports a non-invasive method for in situ biofilm quantification based on the use of hyperspectral imaging to analyze a chromatically and texturally heterogeneous substrate as granite colonized by green algae and cyanobacteria. Biofilm-forming microorganisms were inoculated on granite blocks and incubated under laboratory conditions for 21 days. The intensity of the green stains formed on the granite surfaces differed depending on the initial concentration of microorganisms used. A biofilm quantification (BQ) index was computed to determine the level of colonization on the surfaces. The index was obtained by comparing the quotient of the reflectance of the green (G) and red (R) bands of each pixel of the hyperimage against a threshold value, fth. The optimal value of the threshold was determined by examining the linear correlation between the BQ index and the chlorophyll a extracted. The BQ results were then compared with the F0 and ΔE*ab parameters yielded by colour spectrophotometry and PAM fluorometry techniques and used as reference methodologies to quantify greening on stone surfaces. The BQ index showed a high level of consistency with all of the other parameters; it was linearly correlated with the chlorophyll a concentration, F0 andΔE*ab, with high coefficients of determination (r2 > 0.92) for the range from 1.87 to 5.69 µg chl a.cm-2. The strength of the BQ index lies in its double use as a biomarker of quantity and percentage cover, as well as its good performance under different conditions, ranging from initial phototrophic colonization and thin (young) biofilms covering 21.19% of the surface to profuse biological colonization covering 67.36% of the surface. Moreover, the proposed BQ index may be able to be used with other types of rock with less heterogeneous surfaces than granite.

Soy molasses as a fermentation substrate for the production of biosurfactant using Pseudomonas aeruginosa ATCC 10145.

Soy molasses is a product co-generated during soybean processing that has high production and low commercial value. Its use has great potential in fermentative processes due to the high concentration of carbohydrates, lipids and proteins. This study investigated the use of Pseudomonas aeruginosa to produce biosurfactants in a soy molasses-based fermentation medium. A central composite design (CCD) was prepared with two variables and three replicates at the central point to optimize the production of biosurfactant. The concentration of soy molasses had values between 29.3 and 170.7g/L and the initial concentration of microorganism varied between 0.2 and 5.8g/L. All the experiments were performed in duplicate on a shaker table at 30.0±1.0°C and 120rpm for 72h with samples taken every 12h. Thus, to validate the experiments, the values of 120g/L for the initial concentration of soy molasses and 4g/L for the initial concentration of microorganisms were used. In response, the following values were obtained at 48h of fermentation: surface tension of 31.9dyne/cm, emulsifying index of 97.4%, biomass concentration of 11.5g/L, rhamnose concentration of 6.9g/L and biosurfactant concentration of 11.70g/L. Further analysis was carried out for critical micelle concentration (CMC) which was obtained at approximately 80mg/L. The bands found in Fourier transform infrared spectroscopy analysis had characteristic glycolipids as reported in the literature. These values show a great potential for biosurfactant production using soy molasses as a substrate and bacteria of the species P. aeruginosa.

The Effect of High Voltage Electric Pulse Treatment Process on the Concentration of E. coli Bacteria in Water

Disinfection of water and water resources from E. coli pathogenic bacteria using high voltage electric pulse treatment is studied. The methods of determination of concentration of microorganisms prior to and after the pulse treatment process are shown. The experimental results are presented on the effect of different modes of the treatment (crown, electric spark discharges), the period of the treatment (the number of discharges), the electric parameters of a high voltage generator (voltage, polarity, charging capacitance), and the initial concentration of microorganisms on changes in their quantity after the electric pulse impact. It was found that the degree of inactivation depends greatly on the mode and time of treatment (number of discharges), as well as the initial concentration of the microorganisms. The data on the most efficient modes of the electropulse treatment of a water medium are presented.

Inactivation of Bioaerosol in Indoor Air by DC Corona Discharge

A novel DC corona discharge technology was applied on inactivation of bioaerosol in indoor air. A wide range of initial concentration of microorganisms (from 35×104 CFU/m3 to 3×106 CFU/m3) was tested to show excellent germicidal properties for its high inactivation efficiency. Over 99.997% of microbe into the reactor were inactivated at t=150s, EP 2kV/cm and initial population was 3.0×106 CFU/m3. The effects of active species produced by a DC corona discharge on the inactivation of a mixture of bacteria in flowing aerosol were proved. The active radicals like OH radical which acted on microbes in the way of direct oxidation were the most significant factors influencing the microbe inactive efficiency through the assessment of heat variety, ultraviolet emission and ozones generation. The active radicals generation in the process of sterilization can be simply controlled by regulating applied voltage before ozone generated. The results indicate that use DC corona discharge technology in the future application of indoor air decontamination.

Effect of recirculation and initial concentration of microorganisms on the disinfection kinetics of Escherichia coli

Disinfection studies with two pure strains of Escherichia coli ATCC 11229 and ATCC 15597 and real municipal wastewater were carried out at laboratory scale with a 10 W low pressure ultraviolet lamp in an ultraviolet (UV) disinfection system with recirculation of the liquid. A double first order kinetic model was established to fit the ultraviolet disinfection curves for the two microorganisms. This model implies that there are two subpopulations within the study population, one of which is sensitive to ultraviolet and another that is radiation-resistant. The kinetic model depends on the applied UV dose and is directly related to the initial bacterial concentration (N o). It was possible to establish relationships between the kinetic parameters of the equation and the initial concentration, and so to predict the disinfection curves. The kinetic model was successfully fitted to a real wastewater sample, with the final microbial disinfection predicted as a function of the UV dose and N o.

Effect of microorganisms during the initial coagulum maturation of Hevea natural rubber

AbstractThe involvement of microorganisms in the initial stage of maturation of natural rubber coagula was assessed with five latex treatments that varied in the initial quantity of microorganisms; the treatments ranged from latex added with an antimicrobial agent (3.4 × 104 CFU/mL) to strongly inoculated latex (2.4 × 107 CFU/mL). After 0–6 days of maturation, the obtained rubber was characterized with respect to its physical and structural properties. The Wallace plasticity (P0) and plasticity retention index (PRI) remained constant during maturation with the antibiotic‐added treatment. PRI decreased with the maturation time, and the rate was proportional to the initial microorganism concentration. P0 of all inoculated rubber increased for the first 2 days of maturation and decreased after 6 days of maturation. With respect to structural parameters, a higher initial microorganism content corresponded to a higher gel content and a lower weight‐average molar mass after maturation, drying, and storage. The inoculated rubber showed a stable value for the number‐average molar mass (Mn), in contrast to the noninoculated samples, for which an increase in Mn during maturation was observed. The quantity of microorganisms significantly affected the physical properties and structure of the processed dry rubber. The mechanisms occurring during the initial stage of maturation are complex, and microorganisms are involved not only in the increase in sensitivity to thermooxidation but also in the crosslinking phenomenon between isoprene chains. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010

Impulsive state feedback control of the microorganism culture in a turbidostat

In this paper, a mathematical model with the impulsive state feedback control is proposed for turbidostat system. The sufficient conditions of existence of order-1 and order-2 periodic solutions are obtained by the existence criteria of periodic solution of a general planar impulsive autonomous system. It is shown that the system either tends to a stable state or has a periodic solution, which depends on the feedback state and the initial concentration of microorganism and substrate. Finally, some discussions and numerical simulations are given.

Dynamic analysis of a turbidostat model with the feedback control

In this paper, a mathematical model with impulsive state feedback control is proposed for turbidostat system. The sufficient conditions of existence of positive order one periodic solution are obtained by using the existence criteria of periodic solution of a general planar impulsive autonomous system. It is shown that the system either tends to a stable state or has a periodic solution, which depends on the feedback state, the control parameter of the dilution rate and the initial concentration of microorganism and substrate. By investigating the periodic solution, the period and the initial point of the periodic solution are given. The results show that turbidostat with impulsive state feedback control tends to an order one periodic solution.

Analysis of methane biodegradation by Methylosinus trichosporium OB3b.

The microbial oxidation of methane in the atmosphere is performed by methanotrophic bacteria that use methane as a unique source of carbon and energy. The objective of this work consisted of the investigation of the best conditions of methane biodegradation by methanotrophic bacteria Methylosinus trichosporium OB3b that oxidize it to carbon dioxide, and the use of these microorganisms in monitoring methods for methane. The results showed that M. trichosporium OB3b was capable to degrade methane in a more effective way with an initial microorganism concentration of 0.0700 g.L-1, temperature of 30ºC, pH 6.5 and using 1.79 mmol of methane. In these same conditions, there was no bacterial growth when 2.69 mmol of methane was used. The specific rate of microorganism growth, the conversion factor, the efficiency and the volumetric productivity, for the optimized conditions of biodegradation were, respectively, 0.0324 h-1, 0.6830 gcells/gCH4, 73.73% and 2.7732.10-3 gcells/L.h. The final product of methane microbiological degradation, carbon dioxide, was quantified through the use of a commercial electrode, and, through this, the grade of methane conversion in carbon dioxide was calculated.

Microcalorimetry: a novel method for detection of microbial contamination in platelet products

Measuring heat from replicating microorganisms in culture may be a rapid, accurate, and simple screening method for platelets (PLTs). Microcalorimetry for detection of microorganisms in in vitro contaminated PLT products was evaluated. Staphylococcus epidermidis, Staphylococcus aureus, Streptococcus sanguinis, Escherichia coli, Propionibacterium acnes, and Candida albicans were inoculated in single-donor apheresis PLTs to achieve target concentrations of 10(5), 10(3), 10, or 1 colony-forming units (CFU) per mL of PLTs. Contaminated PLTs in growth medium were incubated at 37 degrees C for 5 days in a calorimeter. Positivity was defined as heat flow of at least 10 microW above the lowest value of the power-time curve. With microcalorimetry, inocula of 10 CFUs per mL PLTs could be detected with the following detection times: S. epidermidis (31.65 hr), S. aureus (24.24 hr), S. sanguinis (7.82 hr), E. coli (7.53 hr), P. acnes (73.57 hr), and C. albicans (43.77 hr). The detection time was less than 4 hr at 10(5) CFUs per mL PLTs for S. aureus, S. sanguinis, and E. coli. Noncontaminated PLTs remained negative. The total heat ranged from 2.8 (S. sanguinis) to 8.3 J (E. coli). The shape of the power-time curve was species-specific and independent from the initial concentration of microorganisms. The detection limit of microcalorimetry was 1 to 10 CFUs per mL PLTs. Microcalorimetry is a promising novel method for detection of contaminated PLTs. Applying this method to all PLT products could reduce the frequency of transfusion-related sepsis and prolong the shelf life of PLTs.

Redox potential measurement as a rapid method for microbiological testing and its validation for coliform determination

The redox potential is one of the most complex indicators of the physiological state of microbial cultures and its measurement could be a useful tool for the qualitative and quantitative determination of the microbial contamination. During the bacterial growth, the redox potential of the medium decreases. The shape of the redox potential curve is characteristic on the type of microorganism, and the rate of the change (d E/d t) is proportional to the living cell concentration. Defining the time required to reach a significant change in redox potential as Time to Detection (TTD), similarly to the impedimetric measurements, a strict linear correlation could be established between the TTD and the logarithm of the initial concentration of microorganisms. On the base of this calibration curve, the determination of living cell concentration could be simplified. For the experiments, a computer-controlled multi-channel measuring system and software was developed by the authors. The redox potential measurement method was tested and validated for the determination of coliform bacteria. The results have proved the high efficiency and reliability of the new method.

Batch mixed culture of Chlorella vulgaris using settled and diluted piggery waste

A study of the effect of the initial concentration of settled piggery wastewater in the range from 250 to 1100 mg COD/l on a mixed culture of Chlorella vulgaris and bacteria was carried out using 1-l batch culture bottles. COD removals and microorganisms concentrations increased with the time in a range of initial substrate concentrations from 250 to 800 mg COD/l. Nevertheless, when the initial substrate concentration increased to 1100 mg COD/l, the COD removal and microorganism concentrations decreased considerably, showing the occurrence of an inhibition phenomenon. The specific growth rates of the exponential phases obtained for each initial concentration of substrate were determined and verified by the utilization of a modified logistic model applied to total chlorophyll (∑C) and volatile suspended solids (VSS) concentrations, indirect measurements of the concentrations of microalgae and total microorganisms, respectively. A strong relationship between the ratio of the initial substrate concentration and the initial concentration of microorganisms S 0/ X 0 ( B X ) and the specific growth rate expressed in ∑C and VSS was found. Process inhibition was observed for B X values of 100 mg COD/mg ∑C and 4.8 mg COD/mg VSS, respectively. The values of μ max were found to be 0.050 h −1 (1.20 d −1) for microalgae and 0.044 h −1 (1.06 d −1) for total microorganisms. The maximum value of the observed yield ( Y obs. max. ) was determined with respect to microalgae and was equal to 0.088 mg ∑C/mg COD.