A historical legacy of antibiotic utilization on bacterial seed banks in sediments

Laura Madueño,Helmut Bürgmann,Pilar Junier,Sevasti Filippidou,Christophe Paul,Zhanna Bayrychenko,Karin Beck,Gilbert Greub,Thomas Junier

doi:10.7717/peerj.4197

Abstract

The introduction of antibiotics for both medical and non-medical purposes has had a positive effect on human welfare and agricultural output in the past century. However, there is also an important ecological legacy regarding the use of antibiotics and the consequences of increased levels of these compounds in the environment as a consequence of their use and disposal. This legacy was investigated by quantifying two antibiotic resistance genes (ARG) conferring resistance to tetracycline (tet(W)) and sulfonamide (sul1) in bacterial seed bank DNA in sediments. The industrial introduction of antibiotics caused an abrupt increase in the total abundance of tet(W) and a steady increase in sul1. The abrupt change in tet(W) corresponded to an increase in relative abundance from ca. 1960 that peaked around 1976. This pattern of accumulation was highly correlated with the abundance of specific members of the seed bank community belonging to the phylum Firmicutes. In contrast, the relative abundance of sul1 increased after 1976. This correlated with a taxonomically broad spectrum of bacteria, reflecting sul1 dissemination through horizontal gene transfer. The accumulation patterns of both ARGs correspond broadly to the temporal scale of medical antibiotic use. Our results show that the bacterial seed bank can be used to look back at the historical usage of antibiotics and resistance prevalence.

Highlights

The use of antibiotics to treat infectious diseases represents one of the major scientific achievements of the 20th century
antibiotic resistance genes (ARG) in seed bank DNA was measured by quantifying the number of copies of genes conferring resistance to tetracycline (tet (W) gene) and sulfonamide, two commonly reported antibiotics detected in environmental settings (Davies & Davies, 2010)
ARG quantification was standardized to DNA yield instead of number of 16S rRNA gene copies given the changes in community composition over time, and the variable number of copies of this molecular marker in different taxonomic groups (Lee, Bussema & Schmidt, 2009)

Summary

Introduction

The use of antibiotics to treat infectious diseases represents one of the major scientific achievements of the 20th century. Most of the antibiotics used today are chemical derivatives of small bioactive molecules that might perform a multitude of functions (Taylor, Verner-Jeffreys & Baker-Austin, 2011). In nature these molecules are thought to be produced at very low concentrations (Martinez, 2008), and for example, a study conducted at sub-inhibitory concentrations with erythromycin and rifampicin has shown that this low concentrations of antibiotics can modulate growth and bacterial metabolism (Goh et al, 2002). Antibiotics can be expected to modulate microbial interactions and regulate the dynamics of microbial communities (Martinez, 2008)

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Results

Discussion

Conclusion