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Open AccessArticle

Essential Gene Clusters Involved in Copper Tolerance Identified in Acinetobacter baumannii Clinical and Environmental Isolates

1
Department of Microbiology and Parasitology, Faculty of Medical Science, Naresuan University, Phitsanulok 65000, Thailand
2
Department of Genetics and Genome Biology, University of Leicester, University Road, Leicester LE1 7RH, UK
3
Department of Microbiology and Immunology, Faculty of Tropical Medicine, Mahidol University, Bangkok 10400, Thailand
4
Mahidol-Oxford Tropical Medicine Research Unit, Faculty of Tropical Medicine, Mahidol University, Bangkok 10400, Thailand
*
Author to whom correspondence should be addressed.
Pathogens 2020, 9(1), 60; https://doi.org/10.3390/pathogens9010060
Received: 11 November 2019 / Revised: 10 January 2020 / Accepted: 13 January 2020 / Published: 15 January 2020
Copper is widely used as antimicrobial in agriculture and medicine. Copper tolerance mechanisms of pathogenic bacteria have been proven to be required for both copper tolerance and survival during bacterial infections. Here, we determined both copper-tolerant phenotype and genotype in A. baumannii originated from clinical and environmental samples. Using copper susceptibility testing, copper-tolerant A. baumannii could be found in both clinical and environmental isolates. Genotypic study revealed that representative copper-related genes of the cluster A (cueR), B (pcoAB), and D (oprC) were detected in all isolates, while copRS of cluster C was detected in only copper-tolerant A. baumannii isolates. Moreover, we found that copper-tolerant phenotype was associated with amikacin resistance, while the presence of copRS was statistically associated with blaNDM-1. We chose the A. baumannii strain AB003 as a representative of copper-tolerant isolate to characterize the effect of copper treatment on external morphology as well as on genes responsible for copper tolerance. The morphological features and survival of A. baumannii AB003 were affected by its exposure to copper, while whole-genome sequencing and analysis showed that it carried fourteen copper-related genes located on four clusters, and cluster C of AB003 was found to be embedded on genomic island G08. Transcriptional analysis of fourteen copper-related genes identified in AB003 revealed that copper treatment induced the expressions of genes of clusters A, B, and D at the micromolar level, while genes of cluster C were over-expressed at the millimolar levels of copper. This study showed that both clinical and environmental A. baumannii isolates have the ability to tolerate copper and carried numerous copper tolerance determinants including intrinsic copper tolerance (clusters A, B, and D) and acquired copper tolerance (cluster C) that could respond to copper toxicity. Our evidence suggests that we need to reconsider the use of copper in hospitals and other medical environments to prevent the selection and spread of copper-tolerant organisms. View Full-Text
Keywords: Acinetobacter baumannii; copper susceptibility; copper-related genes; whole-genome sequence analysis; gene expression Acinetobacter baumannii; copper susceptibility; copper-related genes; whole-genome sequence analysis; gene expression
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Thummeepak, R.; Pooalai, R.; Harrison, C.; Gannon, L.; Thanwisai, A.; Chantratita, N.; Millard, A.D.; Sitthisak, S. Essential Gene Clusters Involved in Copper Tolerance Identified in Acinetobacter baumannii Clinical and Environmental Isolates. Pathogens 2020, 9, 60.

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