Evaluating the role of efflux pumps in bacterial disinfectant resistance
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Date
2022
Authors
Staats, Gunther Johann
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Journal ISSN
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Publisher
University of the Free State
Abstract
The global rise of antibiotic resistance could lead to the advent of a post-antibiotic era, where disinfectants and biosecurity will be vital parts to control microbial proliferation. The SARS-CoV-2 pandemic has shown how important proper biosecurity and disinfection protocols are to control disease outbreaks. Disinfectant resistance has the potential to alter every aspect of disease control, as this phenomenon impacts human life from food security to healthcare systems. Antimicrobial resistance at its core originates from the presence and regulation of specific genes within the genome of a microorganism able to combat/resist specific action of an antimicrobial. This study focuses on investigating whether specific resistance determinants are responsible for the insusceptibility of a highly resistant isolate, Serratia sp. HRI. This isolate has high levels of disinfectant resistance; therefore, it provides an opportune chance to study if a specific mechanism is responsible. To achieve this the genomes of the Serratia sp. HRI and its closest related type strain were investigated for efflux pump genes. The efflux pump genes were predicted using an automatic annotation pipeline. The predictions revealed a plethora of resistance efflux genes mostly harbouring multidrug functioning. Additionally, disinfectant-specific efflux pump genes were identified (emrE, sugE, qacA, qacE, and ssmE). Susceptibility testing using three disinfectants revealed how the resistance levels between the two Serratia isolates differed. Further investigation using efflux pump inhibitors (EPIs) showed how specific families of efflux pumps confer resistance in both isolates. Time-kill analyses over an extended period showed how Serratia sp. HRI tolerates long-term disinfection. Using EPI reserpine, the efflux pump activity was determined during long-term disinfection. The results showed that concentration-dependent recruitment of efflux pumps was seen by Serratia sp. HRI. At low disinfectant concentrations, another mechanism was responsible for the survivability of the bacteria. Using liquid chromatography with tandem mass spectrometry it was established that disinfectant levels introduced with Serratia sp. HRI decreased over time. Suggesting that the HRI isolate has some mechanism to alter the structure of the disinfectant, such as metabolism or degradation pathways. This work highlights the role of efflux pumps in disinfectant resistance and the potential of other mechanisms to be involved. Future research will include gene deletion and expression studies to fully determine the efflux pump reliance for disinfectant resistance. The work completed in this thesis added to the knowledge of efflux-mediated disinfectant resistance. This work also highlighted the potential role of metabolism/degradation in resistance to low-level disinfection.
Description
Dissertation (M.Sc.(Microbiology ))--University of the Free State, 2022