Impact of antibiotic concentration gradients on nitrate reduction and antibiotic resistance in a microfluidic gradient chamber

Lang Zhou; Reinaldo E Alcalde; Jinzi Deng; Baltazar Zuniga; Robert A Sanford; Bruce W Fouke; Charles J Werth

doi:10.1016/j.scitotenv.2021.146503

Impact of antibiotic concentration gradients on nitrate reduction and antibiotic resistance in a microfluidic gradient chamber

Sci Total Environ. 2021 Jul 20:779:146503. doi: 10.1016/j.scitotenv.2021.146503. Epub 2021 Mar 17.

Authors

Lang Zhou¹, Reinaldo E Alcalde¹, Jinzi Deng², Baltazar Zuniga³, Robert A Sanford⁴, Bruce W Fouke⁵, Charles J Werth⁶

Affiliations

¹ Department of Civil, Architectural and Environmental Engineering, University of Texas at Austin, Austin, TX 78712, USA.
² Carl R. Woese Institute of Genomic Biology, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA.
³ College of Natural Sciences, University of Texas at Austin, Austin, TX 78712, USA.
⁴ Department of Geology, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA.
⁵ Carl R. Woese Institute of Genomic Biology, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA; Department of Geology, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA; Department of Microbiology, University of Illinois Urbana-Champaign, Urbana, IL 61801, USA.
⁶ Department of Civil, Architectural and Environmental Engineering, University of Texas at Austin, Austin, TX 78712, USA. Electronic address: werth@utexas.edu.

PMID: 34030234
DOI: 10.1016/j.scitotenv.2021.146503

Abstract

In order to explore the impact of antibiotics on the bacterial metabolic cycling of nitrate within contaminated soil and groundwater environments, we compared the effects of polymyxin B (PMB) and ciprofloxacin (CIP) concentration gradients on the distribution and activity of a wild type (WT) and a flagella deficient mutant (Δflag) of Shewanella oneidensis MR-1 in a microfluidic gradient chamber (MGC). Complementary batch experiments were performed to measure bacteriostatic versus bactericidal concentrations of the two antibiotics, as well as their effect on nitrate reduction. Prior work demonstrated that PMB disrupts cell membranes while CIP inhibits DNA synthesis. Consistent with these modes of action, batch results from this work show that PMB is bactericidal at lower concentrations than CIP relative to their respective minimum inhibitory concentrations (MICs) (≥5× MIC_PMB vs. ≥20× MIC_CIP). Concentration gradients from 0 to 50× the MIC of both antibiotics were established in the MGC across a 2-cm interconnected pore network, with nutrients injected at both concentration boundaries. The WT cells could only access and reduce nitrate in regions of the MGC with PMB at <18× MIC_PMB, whereas this occurred with CIP up to 50× MIC_CIP; and cells extracted from these MGCs showed no antibiotic resistance. The distribution of Δflag cells was further limited to lower antibiotic concentrations (≤1× MIC_PMB, ≤43× MIC_CIP) due to inability of movement. These results indicate that S. oneidensis access and reduce nitrate in bactericidal regions via chemotactic migration without development of antibiotic resistance, and that this migration is inhibited by acutely lethal bactericidal levels of antibiotics.

Keywords: Ciprofloxacin; Microfluidics; Nitrate reduction; Polymyxin B; Shewanella.

MeSH terms

Anti-Bacterial Agents* / toxicity
Ciprofloxacin / toxicity
Drug Resistance, Microbial / genetics
Microbial Sensitivity Tests
Microfluidics
Nitrates* / toxicity
Shewanella

Substances

Anti-Bacterial Agents
Nitrates
Ciprofloxacin

Supplementary concepts

Shewanella oneidensis