Establishment and application of a novel fluorescence-based analytical method for the rapid detection of viable bacteria in different samples

Progress in methods for the detection of viable Escherichia coli

Escherichia coli (E. coli) is a prevalent enteric bacterium and a necessary organism to monitor for food safety and environmental purposes. Developing efficient and specific methods is critical for detecting and monitoring viable E. coli due to its high prevalence. Conventional culture methods are often laborious and time-consuming, and they offer limited capability in detecting potentially harmful viable but non-culturable E. coli in the tested sample, which highlights the need for improved approaches. Hence, there is a growing demand for accurate and sensitive methods to determine the presence of viable E. coli. This paper scrutinizes various methods for detecting viable E. coli, including culture-based methods, molecular methods that target DNAs and RNAs, bacteriophage-based methods, biosensors, and other emerging technologies. The review serves as a guide for researchers seeking additional methodological options and aiding in the development of rapid and precise assays. Moving forward, it is anticipated that methods for detecting E. coli will become more stable and robust, ultimately contributing significantly to the improvement of food safety and public health.

Illuminating Bacterial Contamination in Water Sources: The Power of Fluorescence-Based Methods

Bacterial contamination of water sources is a significant public health concern, and therefore, it is important to have accurate and efficient methods for monitoring bacterial concentration in water samples. Fluorescence-based methods, such as SYTO 9 and PI staining, have emerged as a promising approach for real-time bacterial quantification. In this review, we discuss the advantages of fluorescence-based methods over other bacterial quantification methods, including the plate count method and the most probable number (MPN) method. We also examine the utility of fluorescence arrays and linear regression models in improving the accuracy and reliability of fluorescence-based methods. Overall, fluorescence-based methods offer a faster, more sensitive, and more specific option for real-time bacterial quantification in water samples.

Advances in detection methods for viable Salmonella spp.: current applications and challenges

Salmonella is a common intestinal pathogen that can cause food poisoning and intestinal disease. The high prevalence of Salmonella necessitates efficient and sensitive methods for its identification, detection, and monitoring, especially of viable Salmonella. Conventional culture methods need to be more laborious and time-consuming. And they are relatively limited in their ability to detect Salmonella in the viable but non-culturable status if present in the sample to be tested. As a result, there is an increasing need for rapid and accurate techniques to detect viable Salmonella spp. This paper reviewed the status and progress of various methods reported in recent years that can be used to detect viable Salmonella, such as culture-based methods, molecular methods targeting RNAs and DNAs, phage-based methods, biosensors, and some techniques that have the potential for future application. This review can provide researchers with a reference for additional method options and help facilitate the development of rapid and accurate assays. In the future, viable Salmonella detection approaches will become more stable, sensitive, and fast and are expected to play a more significant role in food safety and public health.

Do the Culturable Microbial Groups Present in Cutaway Bogs Change According to Temporal Variation? Pilot Study Based on the Midlands in the Republic of Ireland

Cutaway peatlands in the midlands of the Republic of Ireland are rarely the focus of scientific studies. The soil quality and related microenvironment have been severely impacted by peat extraction. Returning them to a ‘near-natural state’ would require greater insights into this ecological niche. The current research took the initiative to study the microbiology of vast cutaway sites in the midlands of Ireland. Peat was collected over two seasons in January, February and April. Homogenised peat was aseptically cultured on a range of specific and non-specific culture media. Microbial enumeration, Gram staining and other microscopic observations of morphologically distinct microorganisms were performed. The total viable bacterial and fungal numbers were highest in February (1.33 × 105 CFU ml−1 and 5.93 × 106 CFU ml−1, respectively) and were lowest in April (1.14 × 103 CFU ml−1 and 5.57 × 106 CFU ml−1). Penicillium spp. and Trichoderma spp. were common in all the sites. The highest values of phosphate solubilisation index were recorded in peat collected in April (SI = 3.167 & 3.000). Overall, there is a statistically significant difference (p ≤ 0.0001) among the microbial numbers across the three months. This variation could be due to the temperature and pH differences across peat soil.

Rapid effective treatment of waxy oily sludge using a method of dispersion combined with biodegradation in a semi-fluid state

Waxy oily sludge (WOS) from petrochemical enterprises has complex components and difficult treatment. Long-term large-scale stacking has seriously threatened human health and the ecological environment. In this paper, a new rapid and effective treatment method combining dispersion and biodegradation in a semi-fluid state was developed for the WOS. The degradation mechanism of the WOS in the bioreactor was preliminarily discussed. The component analysis results showed that the compounds with large molecular weight (M ≥ 282) in the WOS accounted for more than 50%. Among all microbial consortiums, the treatment effect of the consortium FF: NY3 = 9: 1 was the best for treating the crude oil in WOS, which was significantly different from that of a single strain (p < 0.05). Under the optimal nitrogen source NH₄NO₃ and the concentration of rhamnolipid, the developed high-efficiency microbial consortium (FF: NY3 = 9:1) could remove 85% of the total hydrocarbon pollutants in the 20 L semi-fluid bioreactor within 9 days. The degradation characteristics of WOS components in the bioreactor showed that the developed consortium has good degradation ability for n-alkanes (about 90%), middle- (77.35%)/long-chain (72.66%) isomeric alkanes, alkenes (79.12%), alicyclic hydrocarbons (78.9%) and aromatic hydrocarbons (62.78%). The kinetic analysis results indicated that, in comparison, the middle-chain n-alkanes, middle-chain isomeric saturated alkanes, alkenes, and alicyclic hydrocarbons were most easily removed. The removal rates of long-chain n-alkanes, long-chain isomeric saturated alkanes, and aromatic hydrocarbons were relatively low. The biological toxicity test showed that the germination rate of wheat seeds in treated waxy sludge was Significantly higher than that in untreated waxy sludge (p < 0.01). These results suggest that the new method developed in this paper can treat refractory WOS quickly and effectively. This method lays the foundation for the pilot-scale treatment of the semi-fluid bioreactor.

Rapid Ultrasensitive and High-Throughput Bioburden Detection: Microfluidics and Instrumentation

Contamination detection often requires lengthy culturing steps to detect low-level bioburden. To increase the rate of detection and decrease the limit of detection (LOD), a system featuring microfluidics and a multichannel fluorometer has been developed. The eight-channel fluorometer enables parallel testing of multiple samples with the LOD as low as <1 cfu/mL. This low-cost system utilizes the slope of fluorescence intensity that serves as the criterion for bioburden detection. The redox indicator dye resazurin is used to monitor the presence of viable cells in this study and is reduced to resorufin with a high quantum yield at 585 nm. The sample under investigation is spiked with resazurin and loaded in a special-design microfluidic cassette, and the rate of change is observed via the fluorometer. The method was validated using primary Escherichia coli culture in comparison with a spectrophotometer which served as the gold standard. An optimized assay based on Luria-Bertani medium was developed. The impact on the assay sensitivity based on incubation and filtration steps was also explored. The assay is shown to pick up inadvertent contamination from test tubes and pipette tips showing its applicability in real-world settings. The data analysis demonstrated a comparable performance of the multichannel fluorometer vis-a-vis the conventional plate reader. The multichannel system is shown to detect bioburden presence in as low as 20 s for bacterial concentrations ≥5 cfu/mL after 6 h of incubation. Considering its portability, low cost, simplicity of operation, and relevant assay sensitivity, the system is well positioned to detect low-level bioburden in the laboratory, pharmaceutical, and field settings.

A simple colorimetric method for viable bacteria detection based on cell counting Kit-8

In this study, Cell Counting Kit-8 (CCK-8) was introduced to detect the concentration of live bacteria for the first time depending on the redox reaction between CCK-8 solution and dehydrogenase. CCK-8 solution can be reduced to form water soluble orange-yellow formazan by the dehydrogenase present in bacterial cells, and the concentration of live bacteria is proportional to the absorbance value of formazan at 450 nm. Based on this principle, Staphylococcus aureus and Escherichia coli were chosen as the model bacteria. The optimal detection conditions were investigated and a good linear relationship was obtained in the concentration range from 2.600 × 10² to 1.160 × 10⁹ CFU mL^-1 with a linear equation of Y = 0.06305 log₁₀ X-0.1153 (X in CFU mL^-1, R² = 0.9747) for S. aureus and 9.750 × 10² to 6.000 × 10⁸ CFU mL^-1 with a linear equation of Y = 0.06122 log₁₀ X-0.1358 (X in CFU mL^-1, R² = 0.9958) for E. coli. The CCK-8 based viable bacteria detection method can be completed within 2 h with a wide bacterial detection concentration range. Satisfactory results were obtained when applied to an actual sample analysis and there is a good consistency between the proposed CCK-8 based method and the traditional plate counting method. More importantly, this method can realize the one-time detection of a large number of samples with high sensitivity, which suggests its great potential in high-throughput bacterial detection.