Separation of Escherichia coli from natural samples for identification of sources and microcosm inoculation
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ENVIRONMENTAL MICROBIOLOGY - SHORT COMMUNICATION
Separation of Escherichia coli from natural samples for identification of sources and microcosm inoculation Marcos Tavares Carneiro 1,2
&
Daniel Vidal Perez 3 & Renato Castiglia Feitosa 2
&
Julio Cesar Wasserman 4,5
Received: 29 November 2019 / Accepted: 3 September 2020 # Sociedade Brasileira de Microbiologia 2020
Abstract Obtaining uncultured Escherichia coli from natural waters is an important step in the study of microbes in the environment, which are critical for bacterial decay and microbial source tracking. The quality of the samples used can influence the assays, because high contaminant concentrations, differing cell ages, and physiologic states can impair results. The proposed separation is based on a three-step filtration method applied to replicates of seven samples from a sewage plant affluent, collected in different periods. Aliquots of the leachate were inoculated into microcosms, aiming to observe the cultivability of the cells. The assay resulted in colimetry values ranging between 104 and 105 cells. In the leachate, averages of 1.05% of total coliforms and 1.10% of Escherichia coli were recovered from original samples. Although enduring unfavorable temperatures, salinities, and nutritional conditions, the inoculated microcosm populations grew approximately 310 times after 24 h. The final leachate contained cultivable cells in appropriate physiological states and quantities for inoculum in microcosm sets. The bacteria obtained from the leachate were also appropriate for surveys of microbial source tracking, because, in the developed procedure, organisms were separated from contaminants, while cell concentrations were sufficient for inocula. Keywords Escherichia coli . Wastewater . Microbial source tracking . Bacteria decay . Wild strains
Introduction Applying cultured bacteria inoculum in vitro microbiological studies can directly influence the results of the assays, because the gene expression can be very different from natural ones. This topic is particularly critical in both (a) environmental
Responsible Editor: Vania M.M. Melo * Julio Cesar Wasserman [email protected] 1
Programa de Pós-Graduação em Sistemas de Gestão Sustentáveis, Escola de Engenharia UFF, Niterói, Brazil
2
Departamento de Saneamento, Escola Nacional de Saúde Pública, FIOCRUZ, Rio de Janeiro, Brazil
3
EMBRAPA-Solos, Rio de Janeiro, Brazil
4
Network for the Environment and Sustainable Development and Post-Graduation Program in Geochemistry, University Federal Fluminense, Niterói, Brazil
5
Network for the Environment and Sustainable Development, Institute of Geosciences, Av Litorânea, s/n, Boa Viagem, Niterói, RJ CEP 24.210-346, Brazil
bacterial decay studies and (b) contamination source studies (microbial source tracking, MST) [1–3]: In decay studies, the culture of the samples alters the gene expression of the bacteria, because culture phase transitions induce pre-adaptations to osmotic shock, including variations in temperature, salinity, solar radiation, and
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