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The impact of drug resistance on Mycobacterium tuberculosis physiology: what can we learn from rifampicin?

Koch A, Mizrahi V, Warner DF - Emerg Microbes Infect (2014)

Bottom Line: Although influenced by multiple factors, high-level resistance is often associated with mutations in target-encoding or related genes.Here, we examine evidence from diverse bacterial systems indicating very specific effects of rpoB polymorphisms on cellular physiology, and consider these observations in the context of Mtb.While our focus is on RIF, we also highlight results which suggest that drug-independent effects might apply to a broad range of resistance-associated mutations, especially in an obligate pathogen increasingly linked with multidrug resistance.

View Article: PubMed Central - PubMed

Affiliation: Medical Research Council/National Health Laboratory Service/University of Cape Town Molecular Mycobacteriology Research Unit, Department of Science and Technology/National Research Foundation Centre of Excellence for Biomedical Tuberculosis Research, Institute of Infectious Disease and Molecular Medicine and Department of Clinical Laboratory Sciences, University of Cape Town , Cape Town 7701, South Africa.

ABSTRACT
The emergence of drug-resistant pathogens poses a major threat to public health. Although influenced by multiple factors, high-level resistance is often associated with mutations in target-encoding or related genes. The fitness cost of these mutations is, in turn, a key determinant of the spread of drug-resistant strains. Rifampicin (RIF) is a frontline anti-tuberculosis agent that targets the rpoB-encoded β subunit of the DNA-dependent RNA polymerase (RNAP). In Mycobacterium tuberculosis (Mtb), RIF resistance (RIF(R)) maps to mutations in rpoB that are likely to impact RNAP function and, therefore, the ability of the organism to cause disease. However, while numerous studies have assessed the impact of RIF(R) on key Mtb fitness indicators in vitro, the consequences of rpoB mutations for pathogenesis remain poorly understood. Here, we examine evidence from diverse bacterial systems indicating very specific effects of rpoB polymorphisms on cellular physiology, and consider these observations in the context of Mtb. In addition, we discuss the implications of these findings for the propagation of clinically relevant RIF(R) mutations. While our focus is on RIF, we also highlight results which suggest that drug-independent effects might apply to a broad range of resistance-associated mutations, especially in an obligate pathogen increasingly linked with multidrug resistance.

No MeSH data available.


Related in: MedlinePlus

Schematic representation of RNAP structural elements including the RIF resistance determining region (RRDR). The cartoon showing the RNAP holoenzyme is adapted from Borukhuv and Nudler.17 Structural annotations have been simplified, and the promoter sequence has been excluded. The rpoB-encoded β subunit is highlighted in green. A yellow star represents the RNAP active site and a red circle denotes the RIF molecule which approaches within 12 Å of the active site,18 inhibiting transcription. Double-stranded DNA is represented by pink lines and, once unwound, only template DNA is shown, with the growing RNA chain colored in blue. The inset shows a simplified depiction of the RIF binding pocket.18 Amino acids that form hydrogen bonds with RIF are highlighted in blue and those that form van der Waals interactions are colored yellow; amino-acid numbering corresponds to that used for E. coli. Mutations identified in 11 of the 12 residues that surround the RIF binding pocket have been associated with RIF resistance, albeit at different frequencies18 (the sole amino acid, E565, which has not been associated with RIFR mutations is colored in grey). A schematic representation of the rpoB gene which encodes the β subunit of RNA polymerase is shown below the RNAP cartoon (adapted from Campbell et al.18). Amino-acid numbering is shown as dashed demarcations. The RRDR is highlighted in blue and the amino-acid sequence of the RRDR is magnified below. The alignment contains the amino-acid sequences of E. coli, T. aquaticus and M. tuberculosis. Amino acids that interact directly with RIF are indicated by circles and the colors correspond to the inset diagram. Circles highlighted in red indicate residues that are most frequently observed in RIFR isolates.18
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fig1: Schematic representation of RNAP structural elements including the RIF resistance determining region (RRDR). The cartoon showing the RNAP holoenzyme is adapted from Borukhuv and Nudler.17 Structural annotations have been simplified, and the promoter sequence has been excluded. The rpoB-encoded β subunit is highlighted in green. A yellow star represents the RNAP active site and a red circle denotes the RIF molecule which approaches within 12 Å of the active site,18 inhibiting transcription. Double-stranded DNA is represented by pink lines and, once unwound, only template DNA is shown, with the growing RNA chain colored in blue. The inset shows a simplified depiction of the RIF binding pocket.18 Amino acids that form hydrogen bonds with RIF are highlighted in blue and those that form van der Waals interactions are colored yellow; amino-acid numbering corresponds to that used for E. coli. Mutations identified in 11 of the 12 residues that surround the RIF binding pocket have been associated with RIF resistance, albeit at different frequencies18 (the sole amino acid, E565, which has not been associated with RIFR mutations is colored in grey). A schematic representation of the rpoB gene which encodes the β subunit of RNA polymerase is shown below the RNAP cartoon (adapted from Campbell et al.18). Amino-acid numbering is shown as dashed demarcations. The RRDR is highlighted in blue and the amino-acid sequence of the RRDR is magnified below. The alignment contains the amino-acid sequences of E. coli, T. aquaticus and M. tuberculosis. Amino acids that interact directly with RIF are indicated by circles and the colors correspond to the inset diagram. Circles highlighted in red indicate residues that are most frequently observed in RIFR isolates.18

Mentions: Comparative genomic analyses have established that high-level drug resistance in Mtb arises almost exclusively through chromosomal mutations in genes required for antibiotic action,10,11,12,13,14,15 that is, genes encoding the protein targets of the applied drugs, or the enzymes required for prodrug activation. Since antibiotics target essential cellular functions, it might be expected that resistance mutations in target-encoding genes will impact pathogenesis—a concept loosely captured in the term ‘fitness cost'.16 In turn, this raises fundamental questions regarding the ability of Mtb to harbour multiple drug resistance mutations while retaining the ability to infect, persist, and cause disease in its obligate human host. We are interested in RIF resistance (RIFR), which results primarily from single-nucleotide substitution mutations in a small region of rpoB, the gene encoding the β-subunit of the DNA-dependent RNA polymerase (RNAP) (Figure 1). Given the essentiality of RNAP for transcription, it appears likely that mutations in rpoB will have multiple effects on Mtb physiology in addition to RIFR. In this review, we summarize insights obtained from other bacterial systems into the structural and physiological consequences of rpoB mutations, and consider these observations in the context of the available evidence from Mtb. In addition, we assess the potential impact of RIFR on Mtb physiology and pathogenesis and discuss the possible consequences for the continued emergence of drug resistance in a pathogen that is uniquely adapted to human infection.19


The impact of drug resistance on Mycobacterium tuberculosis physiology: what can we learn from rifampicin?

Koch A, Mizrahi V, Warner DF - Emerg Microbes Infect (2014)

Schematic representation of RNAP structural elements including the RIF resistance determining region (RRDR). The cartoon showing the RNAP holoenzyme is adapted from Borukhuv and Nudler.17 Structural annotations have been simplified, and the promoter sequence has been excluded. The rpoB-encoded β subunit is highlighted in green. A yellow star represents the RNAP active site and a red circle denotes the RIF molecule which approaches within 12 Å of the active site,18 inhibiting transcription. Double-stranded DNA is represented by pink lines and, once unwound, only template DNA is shown, with the growing RNA chain colored in blue. The inset shows a simplified depiction of the RIF binding pocket.18 Amino acids that form hydrogen bonds with RIF are highlighted in blue and those that form van der Waals interactions are colored yellow; amino-acid numbering corresponds to that used for E. coli. Mutations identified in 11 of the 12 residues that surround the RIF binding pocket have been associated with RIF resistance, albeit at different frequencies18 (the sole amino acid, E565, which has not been associated with RIFR mutations is colored in grey). A schematic representation of the rpoB gene which encodes the β subunit of RNA polymerase is shown below the RNAP cartoon (adapted from Campbell et al.18). Amino-acid numbering is shown as dashed demarcations. The RRDR is highlighted in blue and the amino-acid sequence of the RRDR is magnified below. The alignment contains the amino-acid sequences of E. coli, T. aquaticus and M. tuberculosis. Amino acids that interact directly with RIF are indicated by circles and the colors correspond to the inset diagram. Circles highlighted in red indicate residues that are most frequently observed in RIFR isolates.18
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3975073&req=5

fig1: Schematic representation of RNAP structural elements including the RIF resistance determining region (RRDR). The cartoon showing the RNAP holoenzyme is adapted from Borukhuv and Nudler.17 Structural annotations have been simplified, and the promoter sequence has been excluded. The rpoB-encoded β subunit is highlighted in green. A yellow star represents the RNAP active site and a red circle denotes the RIF molecule which approaches within 12 Å of the active site,18 inhibiting transcription. Double-stranded DNA is represented by pink lines and, once unwound, only template DNA is shown, with the growing RNA chain colored in blue. The inset shows a simplified depiction of the RIF binding pocket.18 Amino acids that form hydrogen bonds with RIF are highlighted in blue and those that form van der Waals interactions are colored yellow; amino-acid numbering corresponds to that used for E. coli. Mutations identified in 11 of the 12 residues that surround the RIF binding pocket have been associated with RIF resistance, albeit at different frequencies18 (the sole amino acid, E565, which has not been associated with RIFR mutations is colored in grey). A schematic representation of the rpoB gene which encodes the β subunit of RNA polymerase is shown below the RNAP cartoon (adapted from Campbell et al.18). Amino-acid numbering is shown as dashed demarcations. The RRDR is highlighted in blue and the amino-acid sequence of the RRDR is magnified below. The alignment contains the amino-acid sequences of E. coli, T. aquaticus and M. tuberculosis. Amino acids that interact directly with RIF are indicated by circles and the colors correspond to the inset diagram. Circles highlighted in red indicate residues that are most frequently observed in RIFR isolates.18
Mentions: Comparative genomic analyses have established that high-level drug resistance in Mtb arises almost exclusively through chromosomal mutations in genes required for antibiotic action,10,11,12,13,14,15 that is, genes encoding the protein targets of the applied drugs, or the enzymes required for prodrug activation. Since antibiotics target essential cellular functions, it might be expected that resistance mutations in target-encoding genes will impact pathogenesis—a concept loosely captured in the term ‘fitness cost'.16 In turn, this raises fundamental questions regarding the ability of Mtb to harbour multiple drug resistance mutations while retaining the ability to infect, persist, and cause disease in its obligate human host. We are interested in RIF resistance (RIFR), which results primarily from single-nucleotide substitution mutations in a small region of rpoB, the gene encoding the β-subunit of the DNA-dependent RNA polymerase (RNAP) (Figure 1). Given the essentiality of RNAP for transcription, it appears likely that mutations in rpoB will have multiple effects on Mtb physiology in addition to RIFR. In this review, we summarize insights obtained from other bacterial systems into the structural and physiological consequences of rpoB mutations, and consider these observations in the context of the available evidence from Mtb. In addition, we assess the potential impact of RIFR on Mtb physiology and pathogenesis and discuss the possible consequences for the continued emergence of drug resistance in a pathogen that is uniquely adapted to human infection.19

Bottom Line: Although influenced by multiple factors, high-level resistance is often associated with mutations in target-encoding or related genes.Here, we examine evidence from diverse bacterial systems indicating very specific effects of rpoB polymorphisms on cellular physiology, and consider these observations in the context of Mtb.While our focus is on RIF, we also highlight results which suggest that drug-independent effects might apply to a broad range of resistance-associated mutations, especially in an obligate pathogen increasingly linked with multidrug resistance.

View Article: PubMed Central - PubMed

Affiliation: Medical Research Council/National Health Laboratory Service/University of Cape Town Molecular Mycobacteriology Research Unit, Department of Science and Technology/National Research Foundation Centre of Excellence for Biomedical Tuberculosis Research, Institute of Infectious Disease and Molecular Medicine and Department of Clinical Laboratory Sciences, University of Cape Town , Cape Town 7701, South Africa.

ABSTRACT
The emergence of drug-resistant pathogens poses a major threat to public health. Although influenced by multiple factors, high-level resistance is often associated with mutations in target-encoding or related genes. The fitness cost of these mutations is, in turn, a key determinant of the spread of drug-resistant strains. Rifampicin (RIF) is a frontline anti-tuberculosis agent that targets the rpoB-encoded β subunit of the DNA-dependent RNA polymerase (RNAP). In Mycobacterium tuberculosis (Mtb), RIF resistance (RIF(R)) maps to mutations in rpoB that are likely to impact RNAP function and, therefore, the ability of the organism to cause disease. However, while numerous studies have assessed the impact of RIF(R) on key Mtb fitness indicators in vitro, the consequences of rpoB mutations for pathogenesis remain poorly understood. Here, we examine evidence from diverse bacterial systems indicating very specific effects of rpoB polymorphisms on cellular physiology, and consider these observations in the context of Mtb. In addition, we discuss the implications of these findings for the propagation of clinically relevant RIF(R) mutations. While our focus is on RIF, we also highlight results which suggest that drug-independent effects might apply to a broad range of resistance-associated mutations, especially in an obligate pathogen increasingly linked with multidrug resistance.

No MeSH data available.


Related in: MedlinePlus