Determination of live:dead bacteria as a function of antibiotic treatment

On the Use of the Intrinsic DNA Fluorescence for Monitoring Its Damage: A Contribution from Fundamental Studies

The assessment of DNA damage by means of appropriate fluorescent probes is widely spread. In the specific case of UV-induced damage, it has been suggested to use the emission of dimeric photoproducts as an internal indicator for the efficacy of spermicidal lamps. However, in the light of fundamental studies on the UV-induced processes, outlined in this review, this is not straightforward. It is by now well established that, in addition to photodimers formed via an electronic excited state, photoionization also takes place with comparable or higher quantum yields, depending on the irradiation wavelength. Among the multitude of final lesions, some have been fully characterized, but others remain unknown; some of them may emit, while others go undetected upon monitoring fluorescence, the result being strongly dependent on both the irradiation and the excitation wavelength. In contrast, the fluorescence of undamaged nucleobases associated with emission from ππ* states, localized or excitonic, appearing at wavelengths shorter than 330 nm is worthy of being explored to this end. Despite its low quantum yield, it is readily detected nowadays. Its intensity decreases due to the disappearance of the reacting nucleobases and the loss of exciton coherence provoked by the presence of lesions, independently of their type. Thus, it could potentially provide valuable information about the DNA damage induced, not only by UV radiation but also by other sanitizing or therapeutic agents.

A novel derivative synchronous fluorescence method for the rapid, non-destructive and intuitive differentiation of denitrifying bacteria

It is challenging to differentiate bacteria residing in the same habitat by direct observation. This difficulty impedes the harvest, application and manipulation of functional bacteria in environmental engineering. In this study, we developed a novel method for rapid differentiation of living denitrifying bacteria based on derivative synchronous fluorescence spectroscopy, as exemplified by three heterotrophic nitrification-aerobic denitrification bacteria having the maximum nitrogen removal efficiencies greater than 90%. The intact bacteria and their living surroundings can be analyzed as an integrated target, which eliminates the need for the complex pre-processing of samples. Under the optimal synchronous scanning parameter (Δλ = 40 nm), each bacterium possesses a unique fluorescence spectral structure and the derivative synchronous fluorescence technique can significantly improve the spectral resolution compared to other conventional fluorescence methods, which enables the rapid differentiation of different bacteria through derivative synchronous fluorescence spectra as fast as 2 min per spectrum. Additionally, the derivative synchronous fluorescence technique can extract the spectral signals contributed by bacterial extracellular substances produced in the biological nitrogen removal process. Moreover, the results obtained from our method can reflect the real-time denitrification properties of bacteria in the biological nitrogen removal process of wastewater. All these merits highlight derivative synchronous fluorescence spectroscopy as a promising analytic method in the environmental field.

Adsorption of antibiotics by bentonite-chitosan composite: Phenomenological modeling and physical investigation of the adsorption process

The increased use of antibiotics worldwide turned into a serious preoccupation due to their environmental and health impacts. Since the majority of antibiotic residuals are hardly eliminated from wastewater, based on usual methods, other treatments receive considerable attention. Adsorption is known as the most effective method of the treatment of antibiotics. In this paper, the adsorption isotherms of doripenem, ampicillin, and amoxicillin on bentonite-chitosan composite are determined at three temperatures, T = 303.15, 313.15 and 323.15 K, which are used to achieve a theoretical investigation of the removal phenomenon, based on a statistical physics theory. Three analytical models are utilized to describe the AMO, AMP, and DOR adsorption phenomena at the molecular level. From the fitting results, all antibiotic adsorption on a BC adsorbent is associated with the monolayer formation with one type of site. Concerning the number of adsorbed molecules per site (n), it is concluded that multi-docking (n < 1) and multi-molecular (n > 1) phenomena are feasible for AMO, AMP, and DOR adsorption on BC. The adsorption amounts at saturation of the BC adsorbent, deduced by the monolayer model, are found to be 70.4-88.0 mg/g for doripenem, 57.8-79.2 mg/g for ampicillin and 38.6-67.5 mg/g for amoxicillin indicating that the antibiotics adsorption performance of BC was greatly depended on temperature where the adsorption capacities increased with the increment of this operating variable. All adsorption systems are demonstrated by a calculation of the energy of adsorption, considering that the extrication of these pollutants implies physical interactions. The thermodynamic interpretation confirms the spontaneous and feasible nature of the adsorption of the three antibiotics on BC adsorbent. In brief, BC sample is regarded as a promising adsorbent to extract antibiotics from water and presents important potentials to be effected in wastewater handling at industrial level.

The effects of removing dead bacteria by propidium monoazide on the profile of salivary microbiome

Background

Oral microbiome played an important role in maintaining healthy state and might exhibit certain changes under circumstances of diseases. However, current microbiological research using sequencing techniques did not regard dead bacteria as a separate part, causing findings based on subsequent analyses on dynamic equilibrium and functional pathways of microbes somewhat questionable. Since treatment by propidium monoazide (PMA) was able to remove dead bacteria effectively, it would be worth studying how the sequencing results after PMA treatment differed from those focusing on the whole microbiota.

Methods

Unstimulated whole saliva samples were obtained from 18 healthy people from 3 age groups (children, adults, and the elderly). After removal of dead bacteria by propidium monoazide (PMA), changes in the profile of salivary microbiome were detected using 16S rRNA sequencing technology, and differences among age groups were compared subsequently.

Results

Dead bacteria accounted for nearly a half of the whole bacteria flora in saliva, while freezing had little effect on the proportion of deaths. After treatment with PMA, the numbers of OTUs reduced by 4.4–14.2%, while the Shannon diversity indices decreased significantly (P < 0.01). Only 35.2% of positive and 6.1% of negative correlations were found to be shared by the whole microbiota and that with dead bacteria removed. Differences in significantly changed OTUs and functional pathways among different age groups were also observed between the group of PMA and the control.

Conclusions

It was necessary to take the influence of living state of bacteria into account in analytic studies of salivary microbiome.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12903-021-01832-5.