Elizabeth Ohneck | Emory University (original) (raw)
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Papers by Elizabeth Ohneck
mBio, 2011
While horizontal gene transfer occurs frequently among bacterial species, evidence for the transf... more While horizontal gene transfer occurs frequently among bacterial species, evidence for the transfer of DNA from host to microbe is exceptionally rare. However, the recent report by Anderson and Seifert [mBio 2(1):e00005-11, 2011] provides evidence for such an event with the finding that 11% of Neisseria gonorrhoeae strains harbor a 685-bp sequence that is 98 to 100% identical to the human long interspersed nuclear element L1. While the function of this element in gonococci remains unclear, this finding significantly impacts our consideration of the coevolution of hosts and microbes, particularly that of humans and pathogens.
mBio, 2016
Staphylococcus aureus is a formidable human pathogen that uses secreted cytolytic factors to inju... more Staphylococcus aureus is a formidable human pathogen that uses secreted cytolytic factors to injure immune cells and promote infection of its host. Of these proteins, the bicomponent family of pore-forming leukocidins play critical roles in S. aureus pathogenesis. The regulatory mechanisms governing the expression of these toxins are incompletely defined. In this work, we performed a screen to identify transcriptional regulators involved in leukocidin expression in S. aureus strain USA300. We discovered that a metabolic sensor-regulator, RpiRc, is a potent and selective repressor of two leukocidins, LukED and LukSF-PV. Whole-genome transcriptomics, S. aureus exoprotein proteomics, and metabolomic analyses revealed that RpiRc influences the expression and production of disparate virulence factors. Additionally, RpiRc altered metabolic fluxes in the trichloroacetic acid cycle, glycolysis, and amino acid metabolism. Using mutational analyses, we confirmed and extended the observation t...
ABSTRACT The export action of efflux pumps is a nearly universal mechanism used by bacteria to es... more ABSTRACT The export action of efflux pumps is a nearly universal mechanism used by bacteria to escape the action of toxic compounds in their environment. Antimicrobials faced by bacteria include various biocides (natural or synthetic) and classical antibiotics used in therapy of infections. Certain efflux pumps also export antimicrobials produced by their hosts and this ability likely enhances the survival of the infecting pathogen, especially during early stages of infection when mediators of innate host defense normally function to reduce the microbial load. This review is concerned with the roles of efflux pumps produced by Neisseria gonorrhoeae in contributing to its resistance to antimicrobials used in therapy of infections or those that participate in innate host defense. Specific emphasis is placed on the genetic organization, transcriptional regulation and function of gonococcal efflux pumps. The major theme of this review is that in addition to their role in enhancing bacterial resistance to classical antibiotics and biocides, certain efflux pumps, such as those harbored by strict human pathogens like gonococci can also influence in vivo fitness and survival since they provide a mechanism to resist natural antimicrobials produced by their host.
ABSTRACT The export action of efflux pumps is a nearly universal mechanism used by bacteria to es... more ABSTRACT The export action of efflux pumps is a nearly universal mechanism used by bacteria to escape the action of toxic compounds in their environment. Antimicrobials faced by bacteria include various biocides (natural or synthetic) and classical antibiotics used in therapy of infections. Certain efflux pumps also export antimicrobials produced by their hosts and this ability likely enhances the survival of the infecting pathogen, especially during early stages of infection when mediators of innate host defense normally function to reduce the microbial load. This review is concerned with the roles of efflux pumps produced by Neisseria gonorrhoeae in contributing to its resistance to antimicrobials used in therapy of infections or those that participate in innate host defense. Specific emphasis is placed on the genetic organization, transcriptional regulation and function of gonococcal efflux pumps. The major theme of this review is that in addition to their role in enhancing bacterial resistance to classical antibiotics and biocides, certain efflux pumps, such as those harbored by strict human pathogens like gonococci can also influence in vivo fitness and survival since they provide a mechanism to resist natural antimicrobials produced by their host.
Journal of bacteriology, 2015
Staphylococcus aureus is responsible for a large number of diverse infections worldwide. In order... more Staphylococcus aureus is responsible for a large number of diverse infections worldwide. In order to support its pathogenic lifestyle, S. aureus has to regulate the expression of virulence factors in a coordinated fashion. One of the central regulators of the S. aureus virulence regulatory networks is the transcription factor repressor of toxin (Rot). Rot plays a key role in regulating S. aureus virulence through activation or repression of promoters that control expression of a large number of critical virulence factors. However, the mechanism by which Rot mediates gene regulation has remained elusive. Here, we have determined the crystal structure of Rot and used this information to probe the contribution made by specific residues to Rot function. Rot was found to form a dimer, with each monomer harboring a winged helix-turn-helix (WHTH) DNA-binding motif. Despite an overall acidic pI, the asymmetric electrostatic charge profile suggests that Rot can orient the WHTH domain to bind...
Nature communications, 2014
Evasion of the host phagocyte response by Staphylococcus aureus is crucial to successful infectio... more Evasion of the host phagocyte response by Staphylococcus aureus is crucial to successful infection with the pathogen. γ-haemolysin AB and CB (HlgAB, HlgCB) are bicomponent pore-forming toxins present in almost all human S. aureus isolates. Cellular tropism and contribution of the toxins to S. aureus pathophysiology are poorly understood. Here we identify the chemokine receptors CXCR1, CXCR2 and CCR2 as targets for HlgAB, and the complement receptors C5aR and C5L2 as targets for HlgCB. The receptor expression patterns allow the toxins to efficiently and differentially target phagocytic cells. Murine neutrophils are resistant to HlgAB and HlgCB. CCR2 is the sole murine receptor orthologue compatible with γ-haemolysin. In a murine peritonitis model, HlgAB contributes to S. aureus bacteremia in a CCR2-dependent manner. HlgAB-mediated targeting of CCR2(+) cells highlights the involvement of inflammatory macrophages during S. aureus infection. Functional quantification identifies HlgAB an...
Molecular microbiology, 2014
Staphylococcus aureus has evolved as a pathogen that causes a range of diseases in humans. There ... more Staphylococcus aureus has evolved as a pathogen that causes a range of diseases in humans. There are two dominant modes of evolution thought to explain most of the virulence differences between strains. First, virulence genes may be acquired from other organisms. Second, mutations may cause changes in the regulation and expression of genes. Here we describe an evolutionary event in which transposition of an IS element has a direct impact on virulence gene regulation resulting in hypervirulence. Whole-genome analysis of a methicillin-resistant S. aureus (MRSA) strain USA500 revealed acquisition of a transposable element (IS256) that is absent from close relatives of this strain. Of the multiple copies of IS256 found in the USA500 genome, one was inserted in the promoter sequence of repressor of toxins (Rot), a master transcriptional regulator responsible for the expression of virulence factors in S. aureus. We show that insertion into the rot promoter by IS256 results in the derepres...
cdn.intechopen.com
In 2007 the Centers for Disease Control and Prevention placed Neisseria gonorrhoeae on the infamo... more In 2007 the Centers for Disease Control and Prevention placed Neisseria gonorrhoeae on the infamous “Super Bugs” list to highlight the high prevalence of strains resistant to relatively inexpensive antibiotics, such as penicillin, tetracycline and fluoroquinolones, ...
mBio, 2011
The MtrC-MtrD-MtrE multidrug efflux pump of Neisseria gonorrhoeae confers resistance to a diverse... more The MtrC-MtrD-MtrE multidrug efflux pump of Neisseria gonorrhoeae confers resistance to a diverse array of antimicrobial agents by transporting these toxic compounds out of the gonococcus. Frequently in gonococcal strains, the expression of the mtrCDE operon is differentially regulated by both a repressor, MtrR, and an activator, MtrA. The mtrR gene lies 250 bp upstream of and is transcribed divergently from the mtrCDE operon. Previous research has shown that mutations in the mtrR coding region and in the mtrR-mtrCDE intergenic region increase levels of gonococcal antibiotic resistance and in vivo fitness. Recently, a C-to-T transition mutation 120 bp upstream of the mtrC start codon, termed mtr 120 , was identified in strain MS11 and shown to be sufficient to confer high levels of antimicrobial resistance when introduced into strain FA19. Here we report that this mutation results in a consensus ؊10 element and that its presence generates a novel promoter for mtrCDE transcription. This newly generated promoter was found to be stronger than the wild-type promoter and does not appear to be subject to MtrR repression or MtrA activation. Although rare, the mtr 120 mutation was identified in an additional clinical isolate during sequence analysis of antibiotic-resistant strains cultured from patients with gonococcal infections. We propose that cis-acting mutations can develop in gonococci that significantly alter the regulation of the mtrCDE operon and result in increased resistance to antimicrobials. IMPORTANCE Gonorrhea is the second most prevalent sexually transmitted bacterial infection and a worldwide public health concern. As there is currently no vaccine against Neisseria gonorrhoeae, appropriate diagnostics and subsequent antibiotic therapy remain the primary means of infection control. However, the effectiveness of antibiotic treatment is constantly challenged by the emergence of resistant strains, mandating a thorough understanding of resistance mechanisms to aid in the development of new antimicrobial therapies and genetic methods for antimicrobial resistance testing. This study was undertaken to characterize a novel mechanism of antibiotic resistance regulation in N. gonorrhoeae. Here we show that a single base pair mutation generates a second, stronger promoter for mtrCDE transcription that acts independently of the known efflux system regulators and results in high-level antimicrobial resistance.
Antimicrobial agents and chemotherapy, 2015
The global consequence of drug efflux gene overexpression in bacteria has not been specifically a... more The global consequence of drug efflux gene overexpression in bacteria has not been specifically analyzed because strains showing high-level expression typically have mutations in genes encoding regulatory proteins that control other genes. Results from a transcriptional profiling study performed with a strain of Neisseria gonorrhoeae that is capable of high-level transcription of the mtrCDE efflux pump operon independently of control by cognate regulatory proteins revealed that its overexpression has ramifications for systems other than drug efflux.
mBio, 2011
While horizontal gene transfer occurs frequently among bacterial species, evidence for the transf... more While horizontal gene transfer occurs frequently among bacterial species, evidence for the transfer of DNA from host to microbe is exceptionally rare. However, the recent report by Anderson and Seifert [mBio 2(1):e00005-11, 2011] provides evidence for such an event with the finding that 11% of Neisseria gonorrhoeae strains harbor a 685-bp sequence that is 98 to 100% identical to the human long interspersed nuclear element L1. While the function of this element in gonococci remains unclear, this finding significantly impacts our consideration of the coevolution of hosts and microbes, particularly that of humans and pathogens.
mBio, 2016
Staphylococcus aureus is a formidable human pathogen that uses secreted cytolytic factors to inju... more Staphylococcus aureus is a formidable human pathogen that uses secreted cytolytic factors to injure immune cells and promote infection of its host. Of these proteins, the bicomponent family of pore-forming leukocidins play critical roles in S. aureus pathogenesis. The regulatory mechanisms governing the expression of these toxins are incompletely defined. In this work, we performed a screen to identify transcriptional regulators involved in leukocidin expression in S. aureus strain USA300. We discovered that a metabolic sensor-regulator, RpiRc, is a potent and selective repressor of two leukocidins, LukED and LukSF-PV. Whole-genome transcriptomics, S. aureus exoprotein proteomics, and metabolomic analyses revealed that RpiRc influences the expression and production of disparate virulence factors. Additionally, RpiRc altered metabolic fluxes in the trichloroacetic acid cycle, glycolysis, and amino acid metabolism. Using mutational analyses, we confirmed and extended the observation t...
ABSTRACT The export action of efflux pumps is a nearly universal mechanism used by bacteria to es... more ABSTRACT The export action of efflux pumps is a nearly universal mechanism used by bacteria to escape the action of toxic compounds in their environment. Antimicrobials faced by bacteria include various biocides (natural or synthetic) and classical antibiotics used in therapy of infections. Certain efflux pumps also export antimicrobials produced by their hosts and this ability likely enhances the survival of the infecting pathogen, especially during early stages of infection when mediators of innate host defense normally function to reduce the microbial load. This review is concerned with the roles of efflux pumps produced by Neisseria gonorrhoeae in contributing to its resistance to antimicrobials used in therapy of infections or those that participate in innate host defense. Specific emphasis is placed on the genetic organization, transcriptional regulation and function of gonococcal efflux pumps. The major theme of this review is that in addition to their role in enhancing bacterial resistance to classical antibiotics and biocides, certain efflux pumps, such as those harbored by strict human pathogens like gonococci can also influence in vivo fitness and survival since they provide a mechanism to resist natural antimicrobials produced by their host.
ABSTRACT The export action of efflux pumps is a nearly universal mechanism used by bacteria to es... more ABSTRACT The export action of efflux pumps is a nearly universal mechanism used by bacteria to escape the action of toxic compounds in their environment. Antimicrobials faced by bacteria include various biocides (natural or synthetic) and classical antibiotics used in therapy of infections. Certain efflux pumps also export antimicrobials produced by their hosts and this ability likely enhances the survival of the infecting pathogen, especially during early stages of infection when mediators of innate host defense normally function to reduce the microbial load. This review is concerned with the roles of efflux pumps produced by Neisseria gonorrhoeae in contributing to its resistance to antimicrobials used in therapy of infections or those that participate in innate host defense. Specific emphasis is placed on the genetic organization, transcriptional regulation and function of gonococcal efflux pumps. The major theme of this review is that in addition to their role in enhancing bacterial resistance to classical antibiotics and biocides, certain efflux pumps, such as those harbored by strict human pathogens like gonococci can also influence in vivo fitness and survival since they provide a mechanism to resist natural antimicrobials produced by their host.
Journal of bacteriology, 2015
Staphylococcus aureus is responsible for a large number of diverse infections worldwide. In order... more Staphylococcus aureus is responsible for a large number of diverse infections worldwide. In order to support its pathogenic lifestyle, S. aureus has to regulate the expression of virulence factors in a coordinated fashion. One of the central regulators of the S. aureus virulence regulatory networks is the transcription factor repressor of toxin (Rot). Rot plays a key role in regulating S. aureus virulence through activation or repression of promoters that control expression of a large number of critical virulence factors. However, the mechanism by which Rot mediates gene regulation has remained elusive. Here, we have determined the crystal structure of Rot and used this information to probe the contribution made by specific residues to Rot function. Rot was found to form a dimer, with each monomer harboring a winged helix-turn-helix (WHTH) DNA-binding motif. Despite an overall acidic pI, the asymmetric electrostatic charge profile suggests that Rot can orient the WHTH domain to bind...
Nature communications, 2014
Evasion of the host phagocyte response by Staphylococcus aureus is crucial to successful infectio... more Evasion of the host phagocyte response by Staphylococcus aureus is crucial to successful infection with the pathogen. γ-haemolysin AB and CB (HlgAB, HlgCB) are bicomponent pore-forming toxins present in almost all human S. aureus isolates. Cellular tropism and contribution of the toxins to S. aureus pathophysiology are poorly understood. Here we identify the chemokine receptors CXCR1, CXCR2 and CCR2 as targets for HlgAB, and the complement receptors C5aR and C5L2 as targets for HlgCB. The receptor expression patterns allow the toxins to efficiently and differentially target phagocytic cells. Murine neutrophils are resistant to HlgAB and HlgCB. CCR2 is the sole murine receptor orthologue compatible with γ-haemolysin. In a murine peritonitis model, HlgAB contributes to S. aureus bacteremia in a CCR2-dependent manner. HlgAB-mediated targeting of CCR2(+) cells highlights the involvement of inflammatory macrophages during S. aureus infection. Functional quantification identifies HlgAB an...
Molecular microbiology, 2014
Staphylococcus aureus has evolved as a pathogen that causes a range of diseases in humans. There ... more Staphylococcus aureus has evolved as a pathogen that causes a range of diseases in humans. There are two dominant modes of evolution thought to explain most of the virulence differences between strains. First, virulence genes may be acquired from other organisms. Second, mutations may cause changes in the regulation and expression of genes. Here we describe an evolutionary event in which transposition of an IS element has a direct impact on virulence gene regulation resulting in hypervirulence. Whole-genome analysis of a methicillin-resistant S. aureus (MRSA) strain USA500 revealed acquisition of a transposable element (IS256) that is absent from close relatives of this strain. Of the multiple copies of IS256 found in the USA500 genome, one was inserted in the promoter sequence of repressor of toxins (Rot), a master transcriptional regulator responsible for the expression of virulence factors in S. aureus. We show that insertion into the rot promoter by IS256 results in the derepres...
cdn.intechopen.com
In 2007 the Centers for Disease Control and Prevention placed Neisseria gonorrhoeae on the infamo... more In 2007 the Centers for Disease Control and Prevention placed Neisseria gonorrhoeae on the infamous “Super Bugs” list to highlight the high prevalence of strains resistant to relatively inexpensive antibiotics, such as penicillin, tetracycline and fluoroquinolones, ...
mBio, 2011
The MtrC-MtrD-MtrE multidrug efflux pump of Neisseria gonorrhoeae confers resistance to a diverse... more The MtrC-MtrD-MtrE multidrug efflux pump of Neisseria gonorrhoeae confers resistance to a diverse array of antimicrobial agents by transporting these toxic compounds out of the gonococcus. Frequently in gonococcal strains, the expression of the mtrCDE operon is differentially regulated by both a repressor, MtrR, and an activator, MtrA. The mtrR gene lies 250 bp upstream of and is transcribed divergently from the mtrCDE operon. Previous research has shown that mutations in the mtrR coding region and in the mtrR-mtrCDE intergenic region increase levels of gonococcal antibiotic resistance and in vivo fitness. Recently, a C-to-T transition mutation 120 bp upstream of the mtrC start codon, termed mtr 120 , was identified in strain MS11 and shown to be sufficient to confer high levels of antimicrobial resistance when introduced into strain FA19. Here we report that this mutation results in a consensus ؊10 element and that its presence generates a novel promoter for mtrCDE transcription. This newly generated promoter was found to be stronger than the wild-type promoter and does not appear to be subject to MtrR repression or MtrA activation. Although rare, the mtr 120 mutation was identified in an additional clinical isolate during sequence analysis of antibiotic-resistant strains cultured from patients with gonococcal infections. We propose that cis-acting mutations can develop in gonococci that significantly alter the regulation of the mtrCDE operon and result in increased resistance to antimicrobials. IMPORTANCE Gonorrhea is the second most prevalent sexually transmitted bacterial infection and a worldwide public health concern. As there is currently no vaccine against Neisseria gonorrhoeae, appropriate diagnostics and subsequent antibiotic therapy remain the primary means of infection control. However, the effectiveness of antibiotic treatment is constantly challenged by the emergence of resistant strains, mandating a thorough understanding of resistance mechanisms to aid in the development of new antimicrobial therapies and genetic methods for antimicrobial resistance testing. This study was undertaken to characterize a novel mechanism of antibiotic resistance regulation in N. gonorrhoeae. Here we show that a single base pair mutation generates a second, stronger promoter for mtrCDE transcription that acts independently of the known efflux system regulators and results in high-level antimicrobial resistance.
Antimicrobial agents and chemotherapy, 2015
The global consequence of drug efflux gene overexpression in bacteria has not been specifically a... more The global consequence of drug efflux gene overexpression in bacteria has not been specifically analyzed because strains showing high-level expression typically have mutations in genes encoding regulatory proteins that control other genes. Results from a transcriptional profiling study performed with a strain of Neisseria gonorrhoeae that is capable of high-level transcription of the mtrCDE efflux pump operon independently of control by cognate regulatory proteins revealed that its overexpression has ramifications for systems other than drug efflux.