Relationships between zinc and meropenem resistance in the natural environment and experimental bioreactors

Abstract

The efficacy of antibiotics is being challenged by the emergence of bacteria resistant to antibiotics (AR), both in natural and clinical settings. Antibiotics and associated AR can be transmitted and dispersed via environmental bacteria, however AR might also be conferred in situ, without antibiotic pressure. For example, release of metal-bearing wastes to natural environments can proliferate AR. An important case is the influence of zinc (Zn) contamination on environmental AR, which increased tetracycline and quinolone resistance in wastewater isolates. However, how Zn might influence AR to therapeutically critical carbapenem antibiotics, including meropenem is unknown, which fuelled this study. Here the percentage of total isolates resistant to Zn, meropenem and-or both, were compared and assessed in varied microbial communities from natural environments and bioreactors. Overall, Zn levels, and Zn and meropenem resistant isolates correlated in all settings. For example, the abundance of combined meropenem plus Zn resistant isolates was significantly higher in high Zn (South Tyne) versus low Zn (North Tyne) sediments, and correlated with soluble and total Zn levels (p-value < 0.010 and p-value < 0.050, respectively), implying that acquired Zn resistance might confer meropenem resistance to isolates. In parallel, batch reactors seeded with North and South Tyne sediments, and amended with 2.00 mg/L (low) and 100 mg/L (high) Zn (2 x 2 design), showed increased relative percent meropenem resistant isolates in reactors with high (South Tyne: 21.0%; North Tyne: 31.0%) versus low Zn (South Tyne: 17.0%; North Tyne: 14.0%), whereas, sediment source (South vs North Tyne) was not important. Further, sediment soluble Zn levels significantly correlated with meropenem resistant isolates in all reactors, suggesting that the observed meropenem resistance was a possible “side effect” of cellular defence against Zn toxicity. Similar results were seen in Zn and meropenem-amended rotating tubular reactors treating domestic wastewater. Reactors dosed with 2.00 mg/L meropenem plus 100 mg/L Zn showed combined resistance in 51.0% of reactor effluent isolates, whereas only 24.0% displayed combined resistance with amendments of 2.00 mg/L meropenem and 20.0 mg/L Zn. Overall, elevated Zn levels significantly increased Zn, meropenem and combined resistance in isolates from sediments, batch reactors and tubular reactors. Therefore, one can conclude Zn levels impact meropenem resistance, although evidence suggest meropenem resistance is most apparent when Zn is present and resistance can be lost when Zn is removed, suggesting cross resistance mechanisms.