Disinfectant and antibiotic resistance in Mycobacterium abscessus water isolates

Abstract

Mycobacterium abscessus has been found in drinking water distribution systems worldwide, and infections have been increasing in frequency. The emergence of dominant circulating clones within clinical settings and during chronic disease has been considered a potential cause of the increasing frequency of disease. However, M. abscessus has been thought to be largely environmentally acquired, and how selective pressures in the environment may be influencing M. abscessus evolution has not previously been considered. This study aimed to investigate the disinfectant and antibiotic susceptibility of M. abscessus isolated from drinking water treated with both chlorine and chloramine in 2007, 2017-2018, and 2021-2022 as well as a laboratory evolution experiment. There was no trend in disinfectant or antibiotic resistance of water isolates over time, although there were significant differences between subspecies and dominant circulating clones. M. abscessus isolates were found to be significantly more susceptible to chloramine than chlorine, yet both MICs were greater than the concentrations used in water treatment. The laboratory evolution experiment resulted in a chlorine-resistant phenotype that was not a heritable genetic change. Exposure to chloramine resulted in decreased imipenem susceptibility without a change in chloramine susceptibility. Overall, the results of this study show that M. abscessus is highly resistant to disinfection, and exposure to disinfectants within drinking water distribution systems could influence antimicrobial susceptibility.IMPORTANCEMycobacterium abscessus causes significant disease and is present in drinking water distribution systems where it is exposed to chlorine and chloramine. In this study, M. abscessus drinking water isolates were highly resistant to both chlorine and chloramine, with significant differences within the M. abscessus group. A laboratory evolution experiment induced chlorine resistance, and exposure to chloramine resulted in decreased imipenem susceptibility. These results suggest that exposure to disinfectants within drinking water distribution systems could result in increased disinfectant and antibiotic resistance, potentially contributing to the increasing frequency of disease.

Keywords: antimicrobial resistance; chloramine; chlorine; disinfection; drinking water; nontuberculous mycobacteria.

Fig 1

Chlorine and chloramine susceptibility of M. abscessus isolated from Brisbane’s municipal water in 2007, 2017–2018, and 2021–2022. (A) Susceptibility over time. (B) Subspecies difference in susceptibility. The circled isolate is a DCC1, where all other Maa isolates were DCC5. * P < 0.05, **P < 0.01, and ***P < 0.001.

Fig 2

Growth of chlorine and chloramine evolved lines across six passages of the evolution experiment. The calculated CFU per milliliter from colony counts across two dilutions in duplicate for the biological triplicates of each condition presented as the mean and SD. (A) Control passaged in broth. (B) Chlorine passaged lines. (C) Chloramine passaged lines. Percentage growth was calculated as the mean CFU per milliliter divided by the mean CFU per milliliter of the control lines at the same passage. (D) Chlorine passaged lines. (E) Chloramine passaged lines. *P < 0.05, **P < 0.01, and ***P < 0.001.

Fig 3

Antimicrobial susceptibility testing results of the chlorine, chloramine, and imipenem passaged lines across passages 2, 4, and 6. Gray represents the control passaged lines susceptibility testing. All data are represented as the median and range of biological triplicate under each condition. (A) Chlorine. (B) Chloramine. *P < 0.05, **P < 0.01, ***P < 0.001, and ****P < 0.0001.

Fig 4

Method used for the evolution of antimicrobial resistance in an M. abscessus water isolate. The experiment was completed in biological triplicate. Created with BioRender.com.