RESUMEN
A novel imaging-driven technique with an integrated fluorescence signature to enable automated enumeration of two species of cyanobacteria and an alga of somewhat similar morphology to one of the cyanobacteria is presented to demonstrate proof-of-concept that high accuracy, imaging-based, rapid water quality analysis can be with conventional equipment available in typical water quality laboratories-this is not currently available. The results presented herein demonstrate that the developed method identifies and enumerates cyanobacterial cells at a level equivalent to or better than that achieved using standard manual microscopic enumeration techniques, but in less time, and requiring significantly fewer resources. When compared with indirect measurement methods, the proposed method provides better accuracy at both low and high cell concentrations. It extends the detection range for cell enumeration while maintaining accuracy and increasing enumeration speed. The developed method not only accurately estimates cell concentrations, but it also reliably distinguishes between cells of Anabaena flos-aquae, Microcystis aeruginosa, and Ankistrodesmus in mixed cultures by taking advantage of additional contrast between the target cell and complex background gained under fluorescent light. Thus, the proposed image-driven approach offers promise as a robust and cost-effective tool for identifying and enumerating microscopic cells based on their unique morphological features.
Asunto(s)
Anabaena/citología , Chlorophyceae/citología , Fluorescencia , Microcystis/citología , Anabaena/química , Anabaena/crecimiento & desarrollo , Chlorophyceae/química , Chlorophyceae/crecimiento & desarrollo , Análisis Costo-Beneficio , Técnicas Microbiológicas/economía , Técnicas Microbiológicas/métodos , Microcystis/química , Microcystis/crecimiento & desarrollo , Reproducibilidad de los ResultadosRESUMEN
Basic oxygen furnace (BOF) slag media were studied as a potential treatment material in on-site sanitation systems. Batch and column studies were conducted to evaluate attenuation of the bacteriophage PR772 and 0.190 microm diameter microspheres by BOF media, and to delineate the relative contributions of two principle processes of virus attenuation: inactivation and attachment. In the batch studies, conducted at 4 degrees C, substantial inactivation of PR772 did not occur in the pH 7.6 and 9.5 suspensions. At pH 11.4, bimodal inactivation of PR772 was observed, at an initial rate of 2.1 log C/C(0) day(-1) for the first two days, followed by a much slower rate of 0.124 log C/C(0) day(-1) over the following 10 days. Two column studies were conducted at 4 degrees C at a flow rate of 1 pore volume day(-1) using two slag sources (Stelco, Ontario; Tubarão, Brazil) combined with sand and pea gravel. In both column experiments, the effluent microsphere concentration approached input concentrations over time (reductions of 0.1-0.2 log C/C(0)), suggesting attachment processes for microspheres were negligible. Removal of PR772 virus was more pronounced both during the early stages of the experiments, but also after longer transport times (0.5-1.0 log C/C(0)). PR772 reduction appeared to be primarily as a result of virus inactivation in response to the elevated pH conditions generated by the BOF mixture (10.6-11.4). On-site sanitation systems using BOF media should be designed to maintain sufficient contact time between the BOF media and the wastewater to allow sufficient residence time of pathogens at elevated pH conditions.
Asunto(s)
Bacteriófagos/fisiología , Saneamiento/métodos , Aguas del Alcantarillado/virología , Eliminación de Residuos Líquidos/métodos , Bacteriófagos/química , Bacteriófagos/aislamiento & purificación , Restauración y Remediación Ambiental , Filtración/métodos , Concentración de Iones de Hidrógeno , Cinética , Microesferas , Porosidad , Aguas del Alcantarillado/química , Acoplamiento Viral , Inactivación de VirusRESUMEN
Polystyrene latex microspheres are widely used as surrogates for biocolloid transport in porous media; however, relatively few studies directly compare microsphere transport with that of the microorganism it is intended to represent, particularly at the field scale. Here, we compared the transport behaviour of a bacterium (Escherichia coli RS2g; 1.2 microm in diameter) and three different sized microspheres (1.1, 3.9, and 4.8 microm in diameter) within undisturbed agricultural field soil following infiltration under partially saturated conditions. The soil contained significant macroporosity. A tension infiltrometer was used to control the application of a transport solution containing Brilliant Blue FCF dye to two plots. A >2 log reduction in the concentration of all colloids was observed from the soil surface to 5 cm depth in both plots. The concentration of colloids in the soil was generally proportional to the intensity of soil dye staining; however, both the E. coli RS2g bacterium and the 1.1 microm microspheres appeared to be transported deeper than the other colloids and the visible dye along root holes at the bottom of the profile in both plots. The similarities in size and zeta potential of the 1.1 microm microspheres and the E. coli RS2g likely contributed to that outcome. Colloid concentrations in dyed soil by depth were similar between the two plots, despite differences in soil properties and infiltration patterns. The properties of the colloids and macropore density were the most important factors affecting colloid transport. These results suggest that microspheres with size and surface properties similar to the microbe of interest are useful surrogates to trace potential pathways of transport in the subsurface.
Asunto(s)
Escherichia coli/aislamiento & purificación , Microesferas , Microbiología del Suelo , Contaminantes del Suelo/aislamiento & purificación , Agricultura , Coloides , Monitoreo del Ambiente , Escherichia coli/química , Cinética , Suelo , Contaminantes del Suelo/químicaRESUMEN
The disinfection effectiveness of three organic N-chloramines (chlorinated amino acids and peptides) on the bacteria Escherichia coli (E. coli) was investigated, including a more detailed study into the pH dependency of the disinfection effectiveness of N-chloroglycine. The organic N-chloramines were prepared by combining sodium hypochlorite with each amino acid or peptide (glycine, Ala-Ala and Arg-Gly-Asp-Ser), at a N:Cl molar ratio of 1:0.4, and then used to treat E. coli suspensions for 180 min. No evidence of inactivation was observed at pH 8.1 for any of the tested organic N-chloramines. At pH 6.0 and 6.9, E. coli inactivation with N-chloroglycine was characterized by an initial lag phase, during which little or no measurable inactivation occurred, followed by a pseudo-first-order inactivation. This is in accordance with other results in the literature and supports the two step microbial inactivation mechanism proposed by some authors. Inactivation rate coefficients (Chick-Watson and lag coefficients) were calculated by fitting the experimental data with the Rennecker-Mariñas model. pH-dependent inactivation kinetics were observed, with faster inactivation rates occurring at lower pH values, when temperature and chlorine-to-nitrogen ratio where kept constant. N-chloroglycine was determined to be the only contributor to the inactivation process in these experiments. The free chlorine contribution was considered to be negligible in all experiments due to its very low concentration. As well, given that the anionic form of N-chloroglycine is expected to be the single predominant species over the tested pH range, changes in residual N-chloroglycine speciation could not be responsible for the observed pH-dependency of E. coli inactivation. However, while pH stress was considered as a possible synergistic factor, no significant effect of pH stress on E. coli viability was observed at the tested pH levels.
Asunto(s)
Cloraminas/farmacología , Desinfección/métodos , Cloraminas/química , Cloro/análisis , Escherichia coli/efectos de los fármacos , Escherichia coli/aislamiento & purificación , Glicina/análogos & derivados , Glicina/química , Glicina/farmacología , Concentración de Iones de Hidrógeno/efectos de los fármacos , Viabilidad Microbiana/efectos de los fármacos , Modelos Químicos , Análisis de Regresión , SolucionesRESUMEN
Fluorescent microspheres are increasingly used in environmental studies to evaluate threats of viral and bacterial pathogens in drinking water and to investigate colloid-facilitated contaminant transport. A commonly accepted technique for the enumeration of viruses, bacteria, and virus- and bacteria-sized particles by microscopy involves a field-of-view (field) approach to estimate concentration. Few studies have focused on those factors that are most important in ensuring precise and accurate measures of concentration. Microsphere counts in suspensions of artificial groundwater and deionized water were contrasted in this study to gain a greater understanding of the effect of ionic strength and the presence of precipitates in groundwater matrices that can bias microsphere enumerations. To investigate microsphere enumeration with minimal bias from other factors, a commonly used standard method was used to prepare slides and enumerate microspheres, with particular care to randomly select fields for counting. A factorial experiment evaluated two factors, (1) the density of microspheres in each field and (2) the number of counts in an enumeration. Two parameters, relative standard deviation and percent error, were used to assess methodological precision and accuracy. Visual observations of the slides indicated that some biases, such as undulation in the filter membrane or bubble entrained in the mounting medium, create biases in microsphere enumeration. Additional biases were introduced by the presence of precipitates that form in artificial groundwater saturated with calcite. Microsphere density was found to be critical for ensuring methodological precision, whereas the total number of microspheres counted was essential to ensuring methodological accuracy. The results suggested that to minimize variability using the field approach, the enumeration of at least 350 microspheres and 25-40 microspheresfield (-1) is necessary.