RESEARCH HIGHLIGHTS
ANTIMICROBIALS
Targeting of C. difficile made easy oral administration of Av‑CD291.2 completely prevented C. difficile colonization
Clostridium difficile infection (CDI) is an urgent public health threat, particularly in nosocomial settings as the bacterium flourishes in the gut following antibiotic-induced disruption of the healthy microbiota. Treatment of C. difficile with traditional antibiotics is problematic owing to this off-target effect, and it is often unsuccessful because the pathogen produces spores that are recalcitrant to drugs, which results in high rates of relapsing infection. Now, a new study describes the development of a modified bacteriocin that specifically targets and kills C. difficile vegetative cells and blocks the shedding of spores from infected mice. Bacteriocins, which are anti microbial peptides produced by certain bacteria, can have either narrow or broad activity spectra. Diffocins are R-type bacteriocins that are produced by C. difficile and specifically kill other C. difficile strains; their contractile myophagelike needle structure pierces the target bacterial cell, thereby dissipating the membrane
potential. Killing is dependent on binding of the specific diffocin receptor-binding protein (RBP) to unique cell surface receptors on target cells. As naturally occuring diffocins that target C. difficile RT027 strains (which are predominant and associated with severe infections) are thermally unstable and/or acid labile, Gebhart et al. designed a modified diffocin with a novel and stable RBP. Reasoning that recently acquired prophages are likely to encode proteins that bind to existing cell surface receptors, the authors began by searching C. difficile prophage loci for potential RBP genes and identified the ptsM gene (which encodes the phage tail structure protein) in the phi027 prophage locus of a targeted RT027 strain. Replacement of the RBP of an existing diffocin with the ptsM gene generated a modified bacteriocin (termed Avidocin (Av)-CD291.1), which was also engineered to encode the cognate baseplate attachment proteins for PtsM to promote stability and proper functioning of the new RBP. A second construct, termed Av‑CD291.2, was also generated that contained chaperone proteins for PtsM assembly. In vitro bactericidal assays showed that both Av‑CD291.1 and Av‑CD291.2 killed vegetative cells of all 16 RT027 strains that were
tested, and pharmacokinetic studies in mice revealed that Av‑CD291.2 is stable in drinking water and during passage through the gut. Using a mouse model, it was found that oral administration of Av‑CD291.2 completely prevented C. difficile colonization of the gut, and spore transmission studies showed that faecal shedding of spores was also blocked. Furthermore, 16S rRNA sequencing of faecal DNA from treated and untreated mice indicated that Av‑CD291.2 did not alter the abundance or diversity of the gut microbiota; consistent with this, the authors reported that Av‑CD291.2 treatment did not disrupt natural colonization resistance to C. difficile or vancomycin-resistant Enterococcus faecium. This proof-of-concept study highlights the potential of modified bacteriocins as prophylatic agents for specific targeting of major nosocomial pathogens and provides strong motivation for continued development of these compounds for the management of CDI in humans. Christina Tobin Kåhrström ORIGINAL RESEARCH PAPER Gebhart, D. et al. A modified R-type bacteriocin specifically targeting Clostridium difficile prevents colonization of mice without affecting gut microbiota diversity. mBio 6, e02368‑14 (2015) FURTHER READING Cotter, P. D., Ross, R. P. & Hill, C. Bacteriocins — a viable alternative to antibiotics? Nature Rev. Microbiol. 11, 95–105 (2013)
NPG
NATURE REVIEWS | MICROBIOLOGY
VOLUME 13 | MAY 2015 © 2015 Macmillan Publishers Limited. All rights reserved
ANTIMICROBIALS
Targeting of C. difficile made easy oral administration of Av‑CD291.2 completely prevented C. difficile colonization
Clostridium difficile infection (CDI) is an urgent public health threat, particularly in nosocomial settings as the bacterium flourishes in the gut following antibiotic-induced disruption of the healthy microbiota. Treatment of C. difficile with traditional antibiotics is problematic owing to this off-target effect, and it is often unsuccessful because the pathogen produces spores that are recalcitrant to drugs, which results in high rates of relapsing infection. Now, a new study describes the development of a modified bacteriocin that specifically targets and kills C. difficile vegetative cells and blocks the shedding of spores from infected mice. Bacteriocins, which are anti microbial peptides produced by certain bacteria, can have either narrow or broad activity spectra. Diffocins are R-type bacteriocins that are produced by C. difficile and specifically kill other C. difficile strains; their contractile myophagelike needle structure pierces the target bacterial cell, thereby dissipating the membrane
potential. Killing is dependent on binding of the specific diffocin receptor-binding protein (RBP) to unique cell surface receptors on target cells. As naturally occuring diffocins that target C. difficile RT027 strains (which are predominant and associated with severe infections) are thermally unstable and/or acid labile, Gebhart et al. designed a modified diffocin with a novel and stable RBP. Reasoning that recently acquired prophages are likely to encode proteins that bind to existing cell surface receptors, the authors began by searching C. difficile prophage loci for potential RBP genes and identified the ptsM gene (which encodes the phage tail structure protein) in the phi027 prophage locus of a targeted RT027 strain. Replacement of the RBP of an existing diffocin with the ptsM gene generated a modified bacteriocin (termed Avidocin (Av)-CD291.1), which was also engineered to encode the cognate baseplate attachment proteins for PtsM to promote stability and proper functioning of the new RBP. A second construct, termed Av‑CD291.2, was also generated that contained chaperone proteins for PtsM assembly. In vitro bactericidal assays showed that both Av‑CD291.1 and Av‑CD291.2 killed vegetative cells of all 16 RT027 strains that were
tested, and pharmacokinetic studies in mice revealed that Av‑CD291.2 is stable in drinking water and during passage through the gut. Using a mouse model, it was found that oral administration of Av‑CD291.2 completely prevented C. difficile colonization of the gut, and spore transmission studies showed that faecal shedding of spores was also blocked. Furthermore, 16S rRNA sequencing of faecal DNA from treated and untreated mice indicated that Av‑CD291.2 did not alter the abundance or diversity of the gut microbiota; consistent with this, the authors reported that Av‑CD291.2 treatment did not disrupt natural colonization resistance to C. difficile or vancomycin-resistant Enterococcus faecium. This proof-of-concept study highlights the potential of modified bacteriocins as prophylatic agents for specific targeting of major nosocomial pathogens and provides strong motivation for continued development of these compounds for the management of CDI in humans. Christina Tobin Kåhrström ORIGINAL RESEARCH PAPER Gebhart, D. et al. A modified R-type bacteriocin specifically targeting Clostridium difficile prevents colonization of mice without affecting gut microbiota diversity. mBio 6, e02368‑14 (2015) FURTHER READING Cotter, P. D., Ross, R. P. & Hill, C. Bacteriocins — a viable alternative to antibiotics? Nature Rev. Microbiol. 11, 95–105 (2013)
NPG
NATURE REVIEWS | MICROBIOLOGY
VOLUME 13 | MAY 2015 © 2015 Macmillan Publishers Limited. All rights reserved
