Water treatment processes and antibiotic resistance

Abstract

This research aims to investigate the impact of adsorption onto granular activated carbon (GAC) on horizontal gene transfer (HGT) and the proliferation of antibiotic-resistant bacteria, in the presence and absence of antibiotics.

Surface properties of three widely used GACs were characterized, and their adsorption and desorption performance in removal of Rifampicin and Vancomycin from water were investigated. Their influence on the transfer of vancomycin resistance genes (vanA) from donor (MF06036Van) to recipient (MW01105Rif) Enterococcus faecalis strains was also evaluated. A GAC, preloaded with one or both antibiotics, was exposed to the donor and recipient strains to assess their effect on horizontal gene transfer (HGT). A method was developed to correlate bacterial spatial proximity and cell-to-cell contacts on the GAC surface with gene transfer frequency in scanning electron microscope (SEM) imagery.

 The results revealed that adsorbed antibiotics remained attached to the GAC either by diffusion into its mesopores or by forming (mainly reversible) bonds to the functional groups on its surface. A close association was observed between GACs’ mesopore width with adsorbate molecular size and its ability to remove and retain antibiotics from water. Adsorbed antibiotic molecules became partially desorbed from GAC by changes in operational conditions and GAC surface charges, and released to the ambient aqueous medium. Filtrasorb-400 with an average mesopore width of 4.14 nm effectively adsorbed vancomycin and rifampicin from water and retained them on its structure. Its desorption rates were 5.99% for vancomycin, and 2.53% for rifampicin after 1 h exposure. However, these values were 31.35% for vancomycin and 4.13% for rifampicin for Norit-PK1-3 with an average mesopore width of 2.02 nm. For Norit-RB4W with 3.65 nm mesopore width, desorption rates were 53.74% for vancomycin and 2.33% for rifampicin after 1 h exposure.

Regardless of different surface properties, all studied GACs accommodated bacterial attachment and facilitated HGT. For instance, loading 0.5 g Filtrasorb-400 to 5 mL growth media augmented the gene transfer frequency by more than 28,700 times, i.e. from 3.33×10-9 in the bulk sample to 9.55×10-5. The response patterns of HGT between bacteria to GAC-dose were similar between GAC types but varied in amplitude. At antibiotic level 0.1 MIC, transfer frequencies on GAC preloaded with antibiotics could significantly exceed those on GAC without antibiotics.

Thesis is embargoed until 31 May 2027

Date of Award	May 2025
Original language	English
Sponsors	Department for the Economy
Supervisor	Joerg Arnscheidt (Supervisor), Heather Coleman (Supervisor) & James Dooley (Supervisor)