Characterisation of the Plasmid Encoded AdeRS and AdeABC Variants Involved in Antibiotic Resistance

Abstract

Antibiotic resistance is a global concern and is promoted by various types of bacterial efflux systems. One known efflux system expressed by the Acinetobacter genus is the chromosomally encoded AdeABC pump which works in conjunction with the regulatory system AdeRS. Recently, plasmid encoded variants of the adeRS and adeABC have been identified and it is thought that these may pose similar or higher threats as the previously identified efflux system. It has been suggested that these variants may be more transmissible being that they are plasmid encoded and also have been found in varying genetic environments and adjacent to transposons, indicating mobilization. In addition, it has been proposed that the plasmid encoded AdeRS variants may promote expression of chromosomally encoded AdeABC.
The aim of this study was therefore to characterise the function of the plasmid encoded adeRS and adeABC variants identified in two different Acinetobacter species. In order to do this, Acinetobacter shuttle vectors had to be developed, two containing both the adeRS and adeABC gene variants from each of the species and two containing only the adeRS, this to examine the genes within this genus. Resistance assays were intended to be used to study resistance and substrate specificity of the expressed efflux system and RT-qPCR to examine gene expression.
Construction of Acinetobacter shuttle vectors did not go as anticipated, only one of the plasmids comprising an adeRS variant was successfully produced, which made gene characterisation difficult. However, an E. coli strain was instead transformed with genes of interest as an alternative method to study resistance phenotypes of the expressed efflux system. Results from these assays displayed similar resistance phenotypes as to a reference, indicating that the efflux system may not have been well expressed or functional in the heterologous host and using an Acinetobacter species could be better.
More research should be conducted to further enhance the knowledge in the characteristics of the plasmid encoded adeRS and adeABC genes since this could contribute to infection controls and development of novel antimicrobials.

Popular Abstract

A Global Threat
Antimicrobial resistance (AMR) is a well-known global concern and a highly recurrent issue due to
bacteria’s ability to continuously develop and evolve resistant genes. In 2019, 1.27 million deaths were
caused by various AMR infections and it is predicted that by 2050 this number will increase to 10 million
deaths per year (UNEP, 2024). In addition, the World Health Organization (WHO) has listed AMR
infections as one of the top threats to global health, affecting people across the world at all income levels
(UNEP, 2024).
AMR arises from global misuse and overuse of antimicrobials in health care and agriculture.
Bacteria have various mechanisms to become resistant to antimicrobials and one of these include the
export of drugs out of the cell which is achieved using different types of efflux systems. Efflux systems
comprise efflux pumps which sit within the bacterial cell walls and work by transporting antimicrobials
from the inside of the cell out to the external media, consequently making the drugs useless. Also part of
the efflux system are regulatory systems which control the efflux pumps by sensing changes in the
environment, such as presence of various drugs, and then activating or deactivating the pumps.
Recently, new variants of a previously identified efflux system called AdeABC/AdeRS have been
found within a bacterial genus called Acinetobacter. These new variants have been located on genetic
elements referred to as plasmids which may be an indication of them being more transmissible than the
previously identified systems and could hence potentially promote AMR further. In order to combat
AMR, we need to extend our knowledge about the cause and spread about the various resistance
mechanisms used by bacteria and for that reason, this study aimed to characterise these new variants of
efflux systems. For this to be possible, genetic material containing the efflux systems had to be developed
which could be further used to analyze the function of the systems in the bacteria that they originated
from, Acinetobacter. Developing this genetic material proved to be more complicated than anticipated and
only some of the material was successfully produced in the course of this study, making characterisation
of the efflux systems difficult. However, the produced material can be used for future research. In
addition, AMR conferred by one of the efflux systems was examined using a more easily manipulated
bacterium than what Acientobacter is. Although results indicated that the efflux system may have lacked
compatibility with this bacterium and characterisation in Acinetobacter would most likely give more
adequate results, this could be important to know for future studies.
Further research into how efflux systems work, what drugs they respond to, how they cooperate,
and whether they can be altered, could potentially help in the research and development of new
antimicrobials as well as preventing the spread of AMR.

• author: Axelsson, Sagalin
• supervisor: Magnus Carlquist; Karl Hassan; Varsha Naidu
• organization: Applied Microbiology
• alternative title: Karaktärisering av de plasmidkodade AdeRS- och AdeABC-varianterna som är involverade i antibiotikaresistens
• course: KMBM05 20241
• year: 2024
• type: H2 - Master's Degree (Two Years)
• subject: Technology and Engineering
• keywords: Efflux pumps, transport proteins, AdeABC, AdeRS, antibiotic resistance, applied microbiology
• language: English
• id: 9163365
• date added to LUP: 2024-06-17 12:21:46
• date last changed: 2024-06-17 12:21:46