Metals and antibiotics are common co-contaminants, and exposure to metals may co-select for antibiotic resistance genes (ARGs) by several mechanisms. The presence of heavy metals can act as a stressor, allowing for favorable conditions that are favorable for the development of AR. Due to the seriousness of the risks of ARG proliferation, the relative paucity of data on ARGs in reclaimed water for irrigation, the complex dynamics between ARGs and heavy metals present in the environment, and the necessity for increased water reuse, a detailed study in this area is warranted. The dynamics of and between ARGs, environmental heavy metal concentrations, the mobile genetic element (MGE) intI1, and the human-associated Bacteroidales marker HF183, as well as 16S rRNA are to be studied in the effluent of local northwest Mexican treatment systems as well as throughout reclaimed water distribution systems. The above will additionally be evaluated at the point of entry (POE) and point of use (POU) to the agricultural irrigation system at sites that: 1) have historically irrigated with reclaimed water, 2) have recently began irrigating with reclaimed water, and 3) irrigate using only fresh water from the aquifer. The Maneadero aquifer, our study cite, is one of four main sources of water for the city of Ensenada, Mexico. All wastewater receives secondary treatment and some of which is sent to the Maneadero agricultural valley. Reclaimed water from the two wastewater treatment plants (Naranjo and Maneadero), a holding tank, POU, and POE at 3 irrigation sites will contain a range of ARGs, intI1, HF183, and heavy metals versus well water used at the same irrigation sites. Specifically, different mixing regiments between reclaimed water and well water may result in water with fewer ARGs. qPCR (quantitative PCR) will be used for monitoring and quantification of all genes (blaSHV, sul1, sul2, tetA, tetW, vanA, blaTEM, and ermF) in this study, which will allow for sensitive detection of the targeted genes and the quantification of their relative abundance. Soil samples will also be digested according to EPA method 3050B and analyzed for heavy metals (Ag, Cd, Co, Cr, Cu, Ni, Pb, Mn, Zn) by ICP-OES.

Antibiotic resistance genes and heavy metal co-selection dynamics in reclaimed water for irrigation in northwest Mexico

2019 Fall National Meeting

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