The usefulness of wastewater-based epidemiology (WBE) was proven during the COVID-19 pandemic, and the role of environmental monitoring of emerging infectious diseases has been recognized. In this study, the prevalence of carbapenem-resistant Enterobacterales (CRE) in Japanese environmental samples was measured in the context of applying WBE to CRE. A total of 247 carbapenem-resistant isolates were obtained from wastewater, treated wastewater, and river water. Treated wastewater was shown to be an efficient target for monitoring CRE. The results of the isolate analysis showed that WBE may be applicable to Escherichia coli-carrying New Delhi metallo-β-lactamase (NDM)-type carbapenemase, the Enterobacter cloacae complex and Klebsiella pneumoniae complex-carrying IMP-type carbapenemase. In addition, a certain number of CRE isolated in this study carried Guiana extended spectrum (GES)-type carbapenemase although their clinical importance was unclear. Only a few isolates of Klebsiella aerogenes were obtained from environmental samples in spite of their frequent detection in clinical isolates. Neither the KPC-type, the oxacillinase (OXA)-type nor the VIM-type of carbapenemase was detected in the CRE, which reflected a low regional prevalence. These results indicated the expectation and the limitation of applying WBE to CRE.

Contamination with 2,4,6-trichloroanisole (TCA) often causes taste and odor (T&O) problems in drinking water due to its low odor threshold concentration. Microbial O-methylation of the precursor 2,4,6-trichlorophenol (TCP) would be the dominant mechanism for TCA formation. Simple and rapid measurement of TCP in the low concentration range is necessary to control the problems induced by TCA. In this study, the combination of microbial conversion and instrumental analysis was proposed as a method of TCP quantification. Fungi and bacteria were isolated from various water samples and examined for their ability to produce TCA from TCP. As a result, a strain exhibiting quantitative TCA production and a high growth rate was obtained and named Mycolicibacterium sp. CB14. The conversion rate of TCP to TCA by this strain was found to be high and stable (85.9 ± 5.3%), regardless of the applied TCP concentration, although within the range of 0.1–10 µg/L. The limits of detection and quantification for TCP by this proposed method were determined to be 5.2 ng/L and 17.3 ng/L, respectively. By improving the methods, Mycolicibacterium sp. CB14 could be used for the quantification of TCP at very low concentration levels, which is sufficient to manage the T&O problem caused by TCA.

MBRs (Membrane bioreactors) have been increasingly employed for municipal and industrial wastewater treatment in the last decades for their small footprint and excellent effluent quality. However, microorganisms are often detected in the permeates of microfiltration (MF) membranes even with small pore sizes. Coliform bacteria are known for indicating the potential presence of pathogenic bacteria that cause infectious disease such as bacteremia, respiratory tract infections, and urinary tract infections. Thus, the retention of coliform bacteria by membrane processes is important when the membrane process is utilized in water reclamation. In this study, a microbial community of coliform bacteria in the permeates of MF membranes with different pore sizes (0.2, 0.4, and 0.8 µm) was identified. The results showed that the dominant coliform bacteria changed from Enterobacter spp. and Citrobacter spp. in the activated sludge to Enterobacter spp. and Klebsiella spp. in the permeate of MF membranes, while some pieces of membranes showed complete retention. The bacterial regrowth on the surface of the piping system on the permeate side could be a significant factor contributing to the frequent and exclusive detection of Enterobacter spp. and Klebsiella spp. in the case of membranes with small pore size (0.2 and 0.4 µm) after a long continuous filtration time. To indicate the public health-related risk of treated wastewater by MF, Escherichia coli may not be a suitable indicator species because E. coli is relatively retentive in MF compared to other coliforms.

Heterotrophic microorganism Escherichia coli LS5218 was cultured with flesh green alga Chlamydomonas reinhardtii C-9: NIES-2235 as a nutrient supplier. In order to evaluate the cell response of Escherichia coli with Chlamydomonas reinhardtii, Escherichia coli was evaluated with microbial methods and comprehensive gene transcriptional analyses. Escherichia coli with Chlamydomonas reinhardtii showed a specific growth rate (µ_max) of 1.04 ± 0.27, which was similar to that for cells growing in Luria–Bertani medium (µ_max = 1.20 ± 0.40 h⁻¹). Furthermore, comparing the cellular responses of Escherichia coli in a green-algae-containing medium with those in the Luria–Bertani medium, transcriptomic analysis showed that Escherichia coli upregulated gene transcription levels related to glycolysis, 5-phospho-d-ribosyl-1-diphosphate, and lipid synthesis; on the other hand, it decreased the levels related to lipid degradation. In particular, the transcription levels were increased by 103.7 times on pgm (p * < 0.05 (p = 0.015)) in glycolysis, and decreased by 0.247 times on fadE (p * < 0.05 (p = 0.041)) in lipolysis. These genes are unique and could regulate the direction of metabolism; these responses possibly indicate carbon source assimilation as a cellular response in Escherichia coli. This paper is the first report to clarify that Escherichia coli, a substance-producing strain, directly uses Chlamydomonas reinhardtii as a nutrient supplier by evaluation of the cellular responses analyzed with microbial methods and transcriptome analysis.

Escherichia coli is an important indicator microorganism of fecal contamination in water. However, routine government monitoring often fails to capture the actual state of pollution, because E. coli concentrations in urban rivers are highly variable. This study presents a case study on factors influencing E. coli concentrations in an urban river draining a fully sewered area. An approximately 70-fold higher concentration compared with the average dry-weather concentration (1.9 CFU/mL) was observed under wet-weather conditions, probably due to the effects of combined sewer overflows. A very short survival of E. coli (less than one day) was expected in the unfiltered overlying water, due to the contributions of bacteriophages, protozoan predation, and bacterial competition, whereas a longer survival was expected in the sediment. Such a short survival may be a characteristic of the target watershed, where treated wastewater accounted for approximately 75% of the total flow. The highly variable antimicrobial resistance among E. coli populations under dry-weather conditions was possibly caused by the regrowth of a limited number of E. coli individuals in the sediment. Rising temperatures due to global warming are expected to decrease the concentration of E. coli in the target watershed, where E. coli populations are strongly suppressed by predation and competition.