Impact of Fertilizing With Raw or Anaerobically-Digested Sewage Sludge on the Abundance of Antibiotic-Resistant Coliforms, Antibiotic Resistance Genes and Pathogenic Bacteria in Soil, and on Vegetables at Harvest.

Rahube, T.O., Marti, R., Scott, A., Tien, Y.C., Murray, R.L., Sabourin, L., Zhang, Y., Duenk, P.W., Lapen, D.R., and Topp, E. (2014). "Impact of Fertilizing With Raw or Anaerobically-Digested Sewage Sludge on the Abundance of Antibiotic-Resistant Coliforms, Antibiotic Resistance Genes and Pathogenic Bacteria in Soil, and on Vegetables at Harvest.", Applied and Environmental Microbiology, 80(22), pp. 6898-6907. doi : 10.1128/AEM.02389-14  Access to full text

Abstract

The consumption of crops fertilized with human waste represents a potential route of exposure to antibiotic resistant fecal bacteria. The present study evaluated the abundance of bacteria and antibiotic resistance genes using both culture-dependent and molecular methods. Various vegetables (lettuce, carrots, radish and tomatoes) were sown into field plots fertilized inorganically or with Class B biosolids, or with untreated municipal sewage sludge and harvested when of marketable quality. Analysis of viable pathogenic bacteria or antibiotic-resistant coliform bacteria on plate counts did not reveal significant treatment effects of fertilization with Class B biosolids or untreated sewage sludge on the vegetables. Numerous targeted genes associated with antibiotic resistance and mobile genetic elements were detected by PCR in soil and on vegetables at harvest from plots that received no organic amendment. However, in the season of application, vegetables harvested from plots treated with either material carried gene targets not detected in the absence of amendment. Several gene targets evaluated using qPCR were considerably more abundant on vegetables harvested from sewage sludge-treated plots compared to controls in the season of application, whereas vegetables harvested the following year revealed no treatment effect. Overall, results of the present study suggest that producing vegetable crops in ground fertilized with human waste without appropriate delay or pre-treatment will result in an additional burden of antibiotic resistance genes on the harvested crops. Managing human exposure to antibiotic resistance genes carried in human waste must be undertaken through judicious agricultural practice.

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