Alternative Evolutionary Pathways for Drug-Resistant Small Colony Variant Mutants in <italic toggle="yes">Staphylococcus aureus</italic>

ABSTRACT Staphylococcus aureus is known to generate small colony variants (SCVs) that are resistant to aminoglycoside antibiotics and can cause persistent and recurrent infections. The SCV phenotype is unstable, and compensatory mutations lead to restored growth, usually with loss of resistance. How...

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Autores principales:	Sha Cao, Douglas L. Huseby, Gerrit Brandis, Diarmaid Hughes
Formato:	article
Lenguaje:	EN
Publicado:	American Society for Microbiology 2017
Materias:	ATP experimental evolution growth compensation hemin biosynthesis menaquinone SrrAB Microbiology QR1-502
Acceso en línea:	https://doaj.org/article/2d9f917113e745adac96b3ae636a6375
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spelling	oai:doaj.org-article:2d9f917113e745adac96b3ae636a63752021-11-15T15:51:29ZAlternative Evolutionary Pathways for Drug-Resistant Small Colony Variant Mutants in <italic toggle="yes">Staphylococcus aureus</italic>10.1128/mBio.00358-172150-7511https://doaj.org/article/2d9f917113e745adac96b3ae636a63752017-07-01T00:00:00Zhttps://journals.asm.org/doi/10.1128/mBio.00358-17https://doaj.org/toc/2150-7511ABSTRACT Staphylococcus aureus is known to generate small colony variants (SCVs) that are resistant to aminoglycoside antibiotics and can cause persistent and recurrent infections. The SCV phenotype is unstable, and compensatory mutations lead to restored growth, usually with loss of resistance. However, the evolution of improved growth, by mechanisms that avoid loss of antibiotic resistance, is very poorly understood. By selection with serial passaging, we isolated and characterized different classes of extragenic suppressor mutations that compensate for the slow growth of small colony variants. Compensation occurs by two distinct bypass mechanisms: (i) translational suppression of the initial SCV mutation by mutant tRNAs, ribosomal protein S5, or release factor 2 and (ii) mutations that cause the constitutive activation of the SrrAB global transcriptional regulation system. Although compensation by translational suppression increases growth rate, it also reduces antibiotic susceptibility, thus restoring a pseudo-wild-type phenotype. In contrast, an evolutionary pathway that compensates for the SCV phenotype by activation of SrrAB increases growth rate without loss of antibiotic resistance. RNA sequence analysis revealed that mutations activating the SrrAB pathway cause upregulation of genes involved in peptide transport and in the fermentation pathways of pyruvate to generate ATP and NAD+, thus explaining the increased growth. By increasing the growth rate of SCVs without the loss of aminoglycoside resistance, compensatory evolution via the SrrAB activation pathway represents a threat to effective antibiotic therapy of staphylococcal infections. IMPORTANCE Small colony variants (SCVs) of Staphylococcus aureus are a significant clinical problem, causing persistent and antibiotic-resistant infections. However, SCVs are unstable and can rapidly evolve growth-compensated mutants. Previous data suggested that growth compensation only occurred with the loss of antibiotic resistance. We have used selection with serial passaging to uncover four distinct pathways of growth compensation accessible to SCVs. Three of these paths (reversion, intragenic suppression, and translational suppression) increase growth at the expense of losing antibiotic resistance. The fourth path activates an alternative transcriptional program and allows the bacteria to produce the extra ATP required to support faster growth, without losing antibiotic resistance. The importance of this work is that it shows that drug-resistant SCVs can evolve faster growth without losing antibiotic resistance.Sha CaoDouglas L. HusebyGerrit BrandisDiarmaid HughesAmerican Society for MicrobiologyarticleATPexperimental evolutiongrowth compensationhemin biosynthesismenaquinoneSrrABMicrobiologyQR1-502ENmBio, Vol 8, Iss 3 (2017)
institution	DOAJ
collection	DOAJ
language	EN
topic	ATP experimental evolution growth compensation hemin biosynthesis menaquinone SrrAB Microbiology QR1-502
spellingShingle	ATP experimental evolution growth compensation hemin biosynthesis menaquinone SrrAB Microbiology QR1-502 Sha Cao Douglas L. Huseby Gerrit Brandis Diarmaid Hughes Alternative Evolutionary Pathways for Drug-Resistant Small Colony Variant Mutants in <italic toggle="yes">Staphylococcus aureus</italic>
description	ABSTRACT Staphylococcus aureus is known to generate small colony variants (SCVs) that are resistant to aminoglycoside antibiotics and can cause persistent and recurrent infections. The SCV phenotype is unstable, and compensatory mutations lead to restored growth, usually with loss of resistance. However, the evolution of improved growth, by mechanisms that avoid loss of antibiotic resistance, is very poorly understood. By selection with serial passaging, we isolated and characterized different classes of extragenic suppressor mutations that compensate for the slow growth of small colony variants. Compensation occurs by two distinct bypass mechanisms: (i) translational suppression of the initial SCV mutation by mutant tRNAs, ribosomal protein S5, or release factor 2 and (ii) mutations that cause the constitutive activation of the SrrAB global transcriptional regulation system. Although compensation by translational suppression increases growth rate, it also reduces antibiotic susceptibility, thus restoring a pseudo-wild-type phenotype. In contrast, an evolutionary pathway that compensates for the SCV phenotype by activation of SrrAB increases growth rate without loss of antibiotic resistance. RNA sequence analysis revealed that mutations activating the SrrAB pathway cause upregulation of genes involved in peptide transport and in the fermentation pathways of pyruvate to generate ATP and NAD+, thus explaining the increased growth. By increasing the growth rate of SCVs without the loss of aminoglycoside resistance, compensatory evolution via the SrrAB activation pathway represents a threat to effective antibiotic therapy of staphylococcal infections. IMPORTANCE Small colony variants (SCVs) of Staphylococcus aureus are a significant clinical problem, causing persistent and antibiotic-resistant infections. However, SCVs are unstable and can rapidly evolve growth-compensated mutants. Previous data suggested that growth compensation only occurred with the loss of antibiotic resistance. We have used selection with serial passaging to uncover four distinct pathways of growth compensation accessible to SCVs. Three of these paths (reversion, intragenic suppression, and translational suppression) increase growth at the expense of losing antibiotic resistance. The fourth path activates an alternative transcriptional program and allows the bacteria to produce the extra ATP required to support faster growth, without losing antibiotic resistance. The importance of this work is that it shows that drug-resistant SCVs can evolve faster growth without losing antibiotic resistance.
format	article
author	Sha Cao Douglas L. Huseby Gerrit Brandis Diarmaid Hughes
author_facet	Sha Cao Douglas L. Huseby Gerrit Brandis Diarmaid Hughes
author_sort	Sha Cao
title	Alternative Evolutionary Pathways for Drug-Resistant Small Colony Variant Mutants in <italic toggle="yes">Staphylococcus aureus</italic>
title_short	Alternative Evolutionary Pathways for Drug-Resistant Small Colony Variant Mutants in <italic toggle="yes">Staphylococcus aureus</italic>
title_full	Alternative Evolutionary Pathways for Drug-Resistant Small Colony Variant Mutants in <italic toggle="yes">Staphylococcus aureus</italic>
title_fullStr	Alternative Evolutionary Pathways for Drug-Resistant Small Colony Variant Mutants in <italic toggle="yes">Staphylococcus aureus</italic>
title_full_unstemmed	Alternative Evolutionary Pathways for Drug-Resistant Small Colony Variant Mutants in <italic toggle="yes">Staphylococcus aureus</italic>
title_sort	alternative evolutionary pathways for drug-resistant small colony variant mutants in <italic toggle="yes">staphylococcus aureus</italic>
publisher	American Society for Microbiology
publishDate	2017
url	https://doaj.org/article/2d9f917113e745adac96b3ae636a6375
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Alternative Evolutionary Pathways for Drug-Resistant Small Colony Variant Mutants in <italic toggle="yes">Staphylococcus aureus</italic>

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