Monitoring Of Bacterial Growth Research Articles

Role of Denitrification in Selenite Reduction by Azospirillum brasilense with the Formation of Selenium Nanoparticles.

Many bacteria are capable of reducing selenium oxyanions, primarily selenite (SeO32-), in most cases forming selenium(0) nanostructures. The mechanisms of these transformations may vary for different bacterial species and have so far not yet been clarified in detail. Bacteria of the genus Azospirillum, including ubiquitous phytostimulating rhizobacteria, are widely studied and have potential for agricultural biotechnology and bioremediation of excessively seleniferous soils, as they are able to reduce selenite ions. Cultures of A.brasilense Sp7 and its derivatives (mutant strains) were grown on the modified liquid malate salt medium in the presence or absence of selenite. The following methods were used: spectrophotometric monitoring of bacterial growth; inhibition of glutathione (GSH) synthesis in bacteria by L-buthionine-sulfoximine (BSO); optical selenite and nitrite reduction assays; transmission electron microscopy of cells grown with and without BSO and/or selenite. In a set of separate comparative studies of nitrite and selenite reduction by the wild-type strain A.brasilense Sp7 and its three specially selected derivatives (mutant strains) with different rates of nitrite reduction, a direct correlation was found between their nitrite and selenite reduction rates for all the strains used in the study. Moreover, for BSO it has been shown that its presence does not block selenite reduction in A.brasilense Sp7. Evidence has been presented for the first time for bacteria of the genus Azospirillum that the denitrification pathway known to be inherent in these bacteria, including nitrite reductase, is likely to be involved in selenite reduction. The results using BSO also imply that detoxification of selenite through the GSH redox system (which is commonly considered as the primary mechanism of selenite reduction in many bacteria) does not play a significant role in A.brasilense. The acquired knowledge on the mechanisms underlying biogenic transformations of inorganic selenium in A.brasilense is a step forward both in understanding the biogeochemical selenium cycle and to a variety of potential nano- and biotechnological applications.

Phosphorylation-amplified synchronized droplet microfluidics sensitizes bacterial growth kinetic real-time monitoring

The necessity for rapid and accurate bacterial growth monitoring is imperative across various domains, including healthcare and environmental safety. We introduce the self-synchronized droplet-amplified electrical screening cytometry (SYNC) system, a novel meld of droplet microfluidics and electrochemical amplification tailored for precise bacterial growth kinetic monitoring. SYNC encapsulates single bacteria in picolitre droplets, enabling real-time, fluorescence-free electrochemical monitoring. A specially devised phosphorylation-amplified culture medium translates bacterial metabolic activity into discernible electrical impedance changes. The dual-channel design and a rail-based structure in SYNC facilitate parallel screening and self-synchronization of droplets, addressing the limitations of conventional impedance cytometry. SYNC showcases a 5-fold enhancement in detection sensitivity and reduces 50% of the detection time compared to traditional approaches. Notably, SYNC is pioneering in providing exact initial bacterial concentrations, achieve to 104 bacteria/ml, a capability unmatched by existing real-time techniques measuring electrochemical variations. Along with its robust performance, this earmarks SYNC as a powerful tool for applications such as antibiotic susceptibility testing, food quality monitoring, and real-time water bacteria monitoring, paving the way for enhanced microbial process management and infection control.

Mechanical and ex-vivo assessment of functionalized surgical sutures for bacterial infection monitoring

Surgical sutures are long-established medical devices that play an important role closing and healing damaged tissues and organs postoperatively. However, current commercial sutures are not able to detect infections at the wound site, which are quite frequent after surgery. In this work, we present mechanically stable smart sutures for the real-time monitoring of bacterial growth and biofilm formation. For this purpose, a conducting polymer named poly(3,4-ethylenedioxythiophene) (PEDOT), which is able to detect bacteria metabolites, was implemented as a coating onto commercial biostable sutures. A protecting hydrogel layer with adhesive properties, which was made of polydopamine-polyacrylamide (PDA-PAM), was used to prevent the detachment of the sensing coating of PEDOT upon looping and knotting the suture. The protective hydrogel preserved not only the knot mechanical properties of the suture but also the electrochemical response of the PEDOT-coating and, therefore, its ability to detect NADH from bacteria respiration. Ex-vivo assays using sutured swine intestine samples demonstrated that the suture with the PDA-PAM hydrogel layer detects the growth of bacteria in real tissues. As a proof of concept, sutures coated with PEDOT and protected with PDA-PAM were used to inhibit the local growth of bacteria in sutured intestines by applying controlled electrostimuli. Results evidenced that smart electro-responsive sutures can be used as multi-task devices focused on fighting bacterial infections, meaning not only monitoring but also hampering bacteria growth.

Development and evaluation of an artificial intelligence for bacterial growth monitoring in clinical bacteriology.

In clinical bacteriology laboratories, reading and processing of sterile plates remain a significant part of the routine workload (30%-40% of the plates). Here, an algorithm was developed for bacterial growth detection starting with any type of specimens and using the most common media in bacteriology. The growth prediction performance of the algorithm for automatic processing of sterile plates was evaluated not only at 18-24 h and 48 h but also at earlier timepoints toward the development of an early growth monitoring system. A total of 3,844 plates inoculated with representative clinical specimens were used. The plates were imaged 15 times, and two different microbiologists read the images randomly and independently, creating 99,944 human ground truths. The algorithm was able, at 48 h, to discriminate growth from no growth with a sensitivity of 99.80% (five false-negative [FN] plates out of 3,844) and a specificity of 91.97%. At 24 h, sensitivity and specificity reached 99.08% and 93.37%, respectively. Interestingly, during human truth reading, growth was reported as early as 4 h, while at 6 h, half of the positive plates were already showing some growth. In this context, automated early growth monitoring in case of normally sterile samples is envisioned to provide added value to the microbiologists, enabling them to prioritize reading and to communicate early detection of bacterial growth to the clinicians.

Contactless Electrical Sensor Based on Resonance Frequency for Real-Time Monitoring of Bacterial Growth

Contactless Electrical Sensor Based on Resonance Frequency for Real-Time Monitoring of Bacterial Growth

A Highly Integrated Lab-on-a-CMOS Platform for Real-Time Monitoring of E. Coli Growth Kinetics.

Existing miniaturized and cost-effective solutions for bacterial growth monitoring usually require offline incubators with constant temperature to culture the bio-samples prior to measurement. Such a separated sample preparation and detection scheme requires extensive human intervention, risks contamination, and suffers from poor temporal resolution. To achieve integrated sample preparation and real-time bacterial growth monitoring, this article presents a lab-on-a-CMOS platform incorporates an optical sensor array, temperature sensor array, micro-heaters, and readout circuits. Escherichia coli's (E. coli) optimum growth temperature of 37 °C is achieved through a heat regulation system consisting of two micro-heaters and an on-chip temperature sensor array. A photodiode array with an in-pixel capacitive trans-impedance amplifier to reduce inter-pixel cross-coupling is designed to extract the optical information during bacterial growth. To balance the footprint, power consumption, and quantization speed, a 10 b column successive-approximation register (SAR)/single-slope (SS) dual-mode analog-to-digital converter (ADC) is designed to digitize the temperature and optical signals. Fabricated in a standard 0.18 um CMOS process, the proposed platform can regulate the sample temperature to 37 +/- 0.2/0.3 °C within 32 mins. Enabled by an on-chip heat regulation system and photodetectors, the prototype demonstrates a real-time monitoring of bacterial growth kinetics and antibiotic responses. Minute-level temporal resolution is achieved as this proposed platform is free of extensive and time-consuming human intervention. The proposed platform can be viably used in contamination sensitive applications such as antibiotic tests, stem cell cultures, and organ-on-chips.

Miniature Magnetic Resonance Imaging System for in situ Monitoring of Bacterial Growth and Biofilm Formation.

In situ monitoring of bacterial growth can greatly benefit human healthcare, biomedical research, and hygiene management. Magnetic resonance imaging (MRI) offers two key advantages in tracking bacterial growth: non-invasive monitoring through opaque sample containers and no need for sample pretreatment such as labeling. However, the large size and high cost of conventional MRI systems are the roadblocks for in situ monitoring. Here, we proposed a small, portable MRI system by combining a small permanent magnet and an integrated radio-frequency (RF) electronic chip that excites and reads out nuclear spin motions in a sample, and utilize this small MRI platform for in situ imaging of bacterial growth and biofilm formation. We demonstrate that MRI images taken by the miniature--and thus broadly deployable for in situ work--MRI system provide information on the spatial distribution of bacterial density, and a sequential set of MRI images taken at different times inform the temporal change of the spatial map of bacterial density, showing bacterial growth.

596. Image Sensor-based Real Time Monitoring of Bacterial Growth on Agar Plates

Abstract Background Agar plates are used to culture microorganisms and identify microbes. As the determination is made by a laboratory technician, the detection of bacterial growth on agar plate is highly depends on each microbiologist. Here, we developed a new thin-film transistor (TFT) image sensor for measuring transmitted light and calculating optical density (OD) to observe bacterial growth on agar plates. Methods The TFT image sensor consists of 4 image sensor arrays (271 x 436 pixels, pixel size = 80 μm) and flat surface illuminating module. Each pixel measures the intensity of light passing through the agar medium. Verification of the sensor performance was conducted using Enterobacter cloacae spread on agar medium, which is positioned between the sensor and the illuminating module, in an incubator for 18 hours at 37°C. The intensity of light was measured every 5 minutes from all pixels. For each pixel, the baseline intensity is defined as the average of first 10 frames (I0), and OD is calculated from the average intensity of three consecutive frames. Application for inhibition circle measurement was also conducted using Escherichia coli with two antibiotic discs (amoxicillin/clavulanic acid and ampicillin/sulbactam). Results Figure 1 shows the OD measured at the pixels in the high concentration area (blue) and single colony area (red) superimposed on the transmitted light image of the last frame. The time needed to detect rising of OD was significantly longer in the low concentration area compared to the high concentration area with exponential curve. As a direct application of the OD measurement, we attempted to predict bacterial growth. With the threshold set at OD=0.05 and TRUE growth defined as OD >0.1 at the last frame, the precision of the prediction was nearly 100% after 250 min in high concentration area (Figure 2). The decrease in precision after 650 min was due to very slow growth in these areas. Using the principle above, we successfully predict the inhibition circle diameter at a much earlier time (8.3 hours vs. 25 hours) as shown in Figure 3. Fig1 OD-PlotFigure 1.Growth curves measured at the pixels in the high concentration area (blue square) and single colony (red square) superimposed on the transmitted light image of the last frame. Fig2 predictionFigure 2.Bacterial growth prediction using optical density. Fig3 Inhibition circleFigure 3.Prediction of the inhibition circle created by two antibiotic discs (top/left: amoxicillin/clavulanic acid and bottom/right: ampicillin/sulbactam) using optical density measurements. Transmitted light image at 8.3 hrs. (A) and 25 hrs. (B). Predicted growth and binarized image from 8.3-hour data with measured diameter of each circle (C). Binarized image from 25-hour data with measured diameters (D). Conclusion The new TFT image sensor was able to measure bacterial growth on agar plates. By using the growth curve from each pixel, we were able to predict bacterial growth on agar plates and propose clinical applications such as inhibition circle measurement. Disclosures Masakazu Nakajima, B. Engineering, Soiken Holdings: Board Member|Welby Inc.: Board Member|Welby Inc.: Ownership Interest|Welby Inc.: Stocks/Bonds Goh Ohji, MD, PhD, CarbGeM: Advisor/Consultant|CarbGeM: Grant/Research Support

Design of silver containing mesoporous bioactive glass-embedded polycaprolactone substrates with antimicrobial and bone regenerative properties

ObjectivesThe aim of the present study was to design, produce and characterize composite substrates consisting of different formulations of poly(ε-caprolactone) (PCL), as a polymer matrix, and silver-containing mesoporous bioactive glasses (Ag-MBGs) with improved properties for bone tissue engineering. MethodsAg-MBGs were synthesized by an evaporation-induced self-assembly process. Different polymer-to-particles weight ratios were considered (90/10, 80/20, 70/30 wt%). PCL/Ag-MBGs composites substrates were manufactured by melting and molding technique. The effect of Ag-MBGs embedded in the polymer matrix was investigated by morphological (field emission scanning electron microscopy (FE-SEM), SEM and contact angle measurement), structural/functional (small punch and tensile tests), antimicrobial, and in vitro biological analyses. ResultsThe obtained results highlighted that the inclusion of 10% by weight of Ag-MBGs improved the punching performances as well as the tensile Young’s modulus (from 350.3 ± 32.0 MPa for PCL to 473.5 ± 41.0 MPa), without negatively altering the tensile strength of the neat PCL. Indeed, small punch test findings indicated that, over a threshold concentration (10% by weight), the Ag-MBGs acted as "weak points", rather than reinforcement, because the mechanical properties of the composite substrates decreased. The bacterial growth monitoring showed a clear antimicrobial effect against both Gram-negative and Gram-positive, confirmed by reduced cell viability registered after 24 h (2 ×105 CFU/mL for P. aeruginosa and 2.3 ×105 CFU/mL for S. aureus). The results were confirmed in terms of adhesion and adherent growth, reduced at day 3 on PCL samples with 10% of Ag/MBGs. Furthermore, this formulation induced a significant inhibition zone (21 mm for P. aeruginosa, 23 mm for S. aureus). In vitro biological assays confirmed that all formulations of PCL/Ag-MBGs supported periodontal ligament stem cells’ viability and differentiation over time. Particularly, substrates with Ag-MBGs at a concentration of 10% and 20% by weight of Ag-MBGs provided higher values of the percentage of Alamar Blue reduction meanwhile, the highest Ag-MBGs concentration induced a higher expression of alkaline phosphatase activity. SignificanceAg-MBGs proved to be suitable candidates as filler at a specific threshold concentration (10% by weight), considering a compromise among physicochemical, antimicrobial, and pro-regenerative features. These findings provide useful data for the design and development of improved biomaterials with optimized properties, suggesting a potential application in maxillofacial bone and/or periodontal tissue repair.

Species-Level Monitoring of Key Bacteria in Fermentation Processes Using Single-Nucleotide Resolved Nucleic Acid Assays Based on CRISPR/Cas12.

Microorganisms can determine the flavor and quality of fermented food, such as Baijiu, which is produced via Daqu fermentation. Therefore, monitoring key microorganisms during fermentation is important for ensuring high-quality fermented food. Here, we report a single-nucleotide resolved nucleic acid assay based on the CRISPR/Cas12 system, enabling the quantification of Bacillus amyloliquefaciens, a key microorganism in Daqu fermentation at the species level. The assay employs an amplification-refractory mutation system derived from PCR to analyze minor genetic differences between different Bacillus species. The utilization of CRISPR/Cas12 further guaranties the specificity of identifying the PCR amplicon and enables the quantification of Bacillus amyloliquefaciens via end-measurement fluorescence. Compared to conventional qPCR, the assay allows for species-level detection of bacteria, thus enabling the precise detection of the Bacillus strain that yields high-level 2,3,5,6-tetramethylpyrazine. The assay promises the precise monitoring of bacterial growth and contribution to flavor during Daqu fermentation, thus facilitating fermented food quality control.

Rapid assessment of antibiotic susceptibility using a fully 3D-printed impedance-based biosensor

The sustained misuse and overuse of antibacterial agents is accelerating the emergence of antimicrobial resistance (AMR), which is becoming one of the major threats to public health. Abuse of antibiotics drives spontaneous evolution, bacterial mutation, and exchange of resistant genes through lateral gene transfer. Mitigating the worldwide impact of AMR requires enhanced antibiotic stewardship through faster diagnostic testing. In this work, we aim to tackle this issue via development of a fully 3D-printed electrochemical, gel-modified biosensor for rapid bacterial growth monitoring. By using electrochemical impedance spectroscopy, we have successfully identified growth profiles and confirmed antibiotic susceptibility of two ESKAPE pathogens, Escherichia coli and Pseudomonas aeruginosa, following overnight culture it was possible to determine antibiotic sensitivity in 90 min, altogether faster than the 24–48 h current gold standard of culture-based antimicrobial susceptibility testing with significant scope for optimisation. Results show a clear distinction between growth profiles in the presence and absence of amoxicillin, gentamicin, and fosfomycin, therefore demonstrating a rapid, cost-efficient platform for phenotypic antibiotic susceptibility testing within clinically relevant concentration ranges for conditions such as urinary tract infections and pneumonia.

Real-Time Detection of the Bacterial Biofilm Formation Stages Using QCM-Based Sensors

Bacterial biofilms are a major cause of harm related to medical infections and biofouling. Thus, 80% of total infections are caused by biofilm-forming microorganisms. Consequently, knowledge of biofilm formation stages is crucial to develop effective treatments to prevent their formation in medical implants, tools, and devices. For this purpose, quartz crystal microbalance (QCM) sensors are becoming a good alternative to analytical methods for the real-time monitoring of bacterial growth in liquid media culture. In a previous paper, the authors described an affordable multi-channel measurement instrument based on QCM sensors. However, in order to validate its correct operation, complementary experimental measurements based on bacterial biofilm growth were performed. In this work, the experimental measurements that allow the identification of the different biofilm formation stages are described. The results obtained are discussed.

Time to positivity of blood culture as a prognostic marker in predicting the clinical outcome of blood stream infection

Automated blood culture systems provide continuous monitoring of bacterial growth, and time to positivity (TTP), may be used as good tool for diagnosis of blood stream infections. Objective of the study was to document bacterial profile and their susceptibility pattern and to evaluate the association between the TTP and clinical outcome in patients with BSIs. A cross-sectional study was conducted (after obtaining waiver of consent from institute ethics committee), on 75 patients with positive blood culture. Laboratory data such as TTP, bacterial pathogen isolated from positive blood cultures and their susceptibility pattern, clinical parameters such as demographic characteristics, source of BSIs, severity of infection as per various clinical scores were analysed for patients with TTP ≤10 hours and > 10 hours using univariate analysis. was the commonest gram-negative bacterial isolate (33.3%), and Staphylococcus aureus was the commonest gram-positive bacterial isolate (22.2%). Antimicrobial resistance rate in GNB was very high for cefotaxime (57%), ciprofloxacin (44%) and among gram-positive bacterial isolates was high for clindamycin (56.5%), and cefotaxime (50%). In the study, median TTP was 13 hours and short TTP of ≤10h was observed for , and . There were statistically significant differences observed for end stage renal disease, diabetes association and neutropenia patients with short TTP. Time to positivity is a useful tool for to-measure laboratory prognostic factor for patients with bacteremia. However, further studies with larger sample size, may be required to define its usefulness and the optimal cut-off points.

Rapid and real-time monitoring of bacterial growth against antibiotics in solid growth medium using a contactless planar microwave resonator sensor

Infection diagnosis and antibiotic susceptibility testing (AST) are pertinent clinical microbiology practices that are in dire need of improvement, due to the inadequacy of current standards in early detection of bacterial response to antibiotics and affordability of contemporarily used methods. This paper presents a novel way to conduct AST which hybridizes disk diffusion AST with microwave resonators for rapid, contactless, and non-invasive sensing and monitoring. In this research, the effect of antibiotic (erythromycin) concentrations on test bacterium, Escherichia coli (E. coli) cultured on solid agar medium (MH agar) are monitored through employing a microwave split-ring resonator. A one-port microwave resonator operating at a 1.76 GHz resonant frequency, featuring a 5 mm2 sensitive sensing region, was designed and optimized to perform this. Upon introducing uninhibited growth of the bacteria, the sensor measured 0.005 dB/hr, with a maximum change of 0.07 dB over the course of 15 hours. The amplitude change decreased to negligible values to signify inhibited growth of the bacteria at higher concentrations of antibiotics, such as a change of 0.005 dB in resonant amplitude variation while using 45 µg of antibiotic. Moreover, this sensor demonstrated decisive results of antibiotic susceptibility in under 6 hours and shows great promise to expand automation to the intricate AST workflow in clinical settings, while providing rapid, sensitive, and non-invasive detection capabilities.

Surface-Enhanced Raman Spectroscopy of Bacterial Metabolites for Bacterial Growth Monitoring and Diagnosis of Viral Infection.

Bacterial metabolites are intermediate products of bacterial metabolism and their production reflects metabolic activity. Herein, we report the use of surface-enhanced Raman spectroscopy (SERS) for detection of both volatile and nonvolatile metabolites and the application of this approach for bacterial growth quantification and diagnosis of viral infection. The time-dependent SERS signal of the volatile metabolite dimethyl disulfide in the headspace above bacteria growing on an agar plate was detected and quantified. In addition, SERS signals arising from the plate reflected nutrient consumption and production of nonvolatile metabolites. The measurement of metabolite accumulation can be used for bacterial quantification. In the presence of bacteriophage virus, bacterial metabolism is suppressed, and the relative decrease in SERS intensity reflects the initial virus concentration. Using multivariate analysis, we detect viral infection with a prediction accuracy of 93%. Our SERS-based approach for metabolite production monitoring provides new insights toward viral infection diagnosis.

Nanotheranostic Interface Based on Antibiotic-Loaded Conducting Polymer Nanoparticles for Real-Time Monitoring of Bacterial Growth Inhibition.

Conducting polymers have been increasingly used as biologically interfacing electrodes for biomedical applications due to their excellent and fast electrochemical response, reversible doping-dedoping characteristics, high stability, easy processability, and biocompatibility. These advantageous properties can be used for the rapid detection and eradication of infections associated to bacterial growth since these are a tremendous burden for individual patients as well as the global healthcare system. Herein, a smart nanotheranostic electroresponsive platform, which consists of chloramphenicol (CAM)-loaded in poly(3,4-ethylendioxythiophene) nanoparticles (PEDOT/CAM NPs) for concurrent release of the antibiotic and real-time monitoring of bacterial growth is presented. PEDOT/CAM NPs, with an antibiotic loading content of 11.9± 1.3% w/w, are proved to inhibit the growth of Escherichia coli and Streptococcus sanguinis due to the antibiotic release by cyclic voltammetry. Furthermore, in situ monitoring of bacterial activity is achieved through the electrochemical detection of β-nicotinamide adenine dinucleotide, a redox active specie produced by the microbial metabolism that diffuse to the extracellular medium. According to these results, the proposed nanotheranostic platform has great potential for real-time monitoring of the response of bacteria to the released antibiotic, contributing to the evolution of the personalized medicine.

Fluorescein Derivatives as Fluorescent Probes for pH Monitoring along Recent Biological Applications.

Potential of hydrogen (pH) is one of the most relevant parameters characterizing aqueous solutions. In biology, pH is intrinsically linked to cellular life since all metabolic pathways are implicated into ionic flows. In that way, determination of local pH offers a unique and major opportunity to increase our understanding of biological systems. Whereas the most common technique to obtain these data in analytical chemistry is to directly measure potential between two electrodes, in biological systems, this information has to be recovered in-situ without any physical interaction. Based on their non-invasive optical properties, fluorescent pH-sensitive probe are pertinent tools to develop. One of the most notorious pH-sensitive probes is fluorescein. In addition to excellent photophysical properties, this fluorophore presents a pH-sensitivity around neutral and physiologic domains. This review intends to shed new light on the recent use of fluorescein as pH-sensitive probes for biological applications, including targeted probes for specific imaging, flexible monitoring of bacterial growth, and biomedical applications.

Rapid automated system for bacteriophage virulence and antibiotic synergy testing – The ‘phago-antibiogram’

Background: The global emergence of multidrug resistant bacteria in the context of desiccating antimicrobial drug pipeline has led to resurgent interest in bacteriophage therapy (BT) to treat serious bacterial infections. Phages are highly specific at the species and strain level and measurement of the bacterial host range plays an important role in utilizing the phage as antimicrobials. We have developed a highly efficient high-throughput method utilizing a liquid handling robot to prepare 96-well plates carrying the targeted organisms in liquid broth and bacteriophage in a gradient across the rows. We also determined antibiotic synergy using the same method adding the antibiotics in fixed concentration to detect phage-antibiotic synergism (PAS). Methods and materials: The 96-well microtiter plates were prepared on Eppendorf epMotion 5075 liquid handling robot for high throughput testing containing LB broth, target bacterial isolates, serial dilutions of phage concentration and fixed concentrations of antibiotics (1/4 MIC). The plates were incubated at 37 °C for 18 h with orbital shaking in SpectraMax iD5 microplate reader with bacterial kinetics monitored every 30 min. Results: The automated plate assay correctly determined the phage virulence in majority of cases. The plaque assay tended to indicate greater phage sensitivity. Continued monitoring of bacterial growth allowed for determining the occurrence of bacterial resistance development over continued phage exposure. Phage combination with imipenem and ciprofloxacin exhibited synergistic activity and delayed the appearance of resistant mutants. Conclusion: Our method produced reproducible results in good agreement with the reference plaque assay for phage virulence determination and can also give valuable data about synergistic activity with different antimicrobial drugs.

Predictive Growth Model of Listeria monocytogenes Under Fluctuating Temperature Conditions in Pasteurized Milk by Using Real-Time Polymerase Chain Reaction.

The aim of this study was to evaluate the application of real-time polymerase chain reaction (PCR)-based quantification as a rapid and accurate tool for the monitoring and prediction of Listeria monocytogenes growth in pasteurized milk under constant and fluctuating temperature conditions. The growth of L. monocytogenes was monitored under constant temperature conditions at 4°C, 10°C, 15°C, 20°C, and 35°C. High correlation was obtained between the bacterial growth rate and incubation temperature, where the R2 of the slope of the square root model was calculated to be 0.993 and 0.996 for real-time PCR and the conventional culture method, respectively. Moreover, the obtained maximum specific growth rate (μmax) data plots were correlated with 188 L. monocytogenes μmax data points from the existing model according to ComBase database, with an R2 of 0.961 for real-time PCR and of 0.931 for the conventional culture method. The growth models were examined under three different patterns of fluctuating temperature conditions ranging from 2°C to 30°C. The prediction results fell within ±20% of the relative error zone, showing that real-time PCR quantification could be used for fast, sensitive, and specific bacterial growth monitoring with high-throughput results. Real-time PCR should be considered a promising option and powerful tool for the construction of a bacterial growth prediction model for safety risk analysis in the dairy industry.

Volatile organic compounds fingerprinting in faeces and urine of Alzheimer's disease model SAMP8 mice by headspace-gas chromatography-ion mobility spectrometry and headspace-solid phase microextraction-gas chromatography-mass spectrometry

Volatile organic compounds fingerprinting in faeces and urine of Alzheimer's disease model SAMP8 mice by headspace-gas chromatography-ion mobility spectrometry and headspace-solid phase microextraction-gas chromatography-mass spectrometry