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Beta-Lactamase Repressor BlaI Modulates Staphylococcus aureus Cathelicidin Antimicrobial Peptide Resistance and Virulence.

Pence MA, Haste NM, Meharena HS, Olson J, Gallo RL, Nizet V, Kristian SA - PLoS ONE (2015)

Bottom Line: Through screening a transposon library in S. aureus Newman for susceptibility to cathelicidin antimicrobial peptide, we discovered BlaI as a novel cathelicidin resistance factor.Additionally, through integrational mutagenesis in S. aureus Newman and MRSA Sanger 252 strains, we confirmed the role of BlaI in resistance to human and murine cathelidicin and showed that it contributes to virulence in human whole blood and murine infection models.We further demonstrated that BlaI could be a target for innate immune-based antimicrobial therapies; by removing BlaI through subinhibitory concentrations of 6-aminopenicillanic acid, we were able to sensitize S. aureus to LL-37 killing.

View Article: PubMed Central - PubMed

Affiliation: Biomedical Sciences Graduate Program, University of California San Diego, La Jolla, CA, United States of America; Department of Pediatrics, School of Medicine, University of California San Diego, La Jolla, CA, United States of America.

ABSTRACT
BlaI is a repressor of BlaZ, the beta-lactamase responsible for penicillin resistance in Staphylococcus aureus. Through screening a transposon library in S. aureus Newman for susceptibility to cathelicidin antimicrobial peptide, we discovered BlaI as a novel cathelicidin resistance factor. Additionally, through integrational mutagenesis in S. aureus Newman and MRSA Sanger 252 strains, we confirmed the role of BlaI in resistance to human and murine cathelidicin and showed that it contributes to virulence in human whole blood and murine infection models. We further demonstrated that BlaI could be a target for innate immune-based antimicrobial therapies; by removing BlaI through subinhibitory concentrations of 6-aminopenicillanic acid, we were able to sensitize S. aureus to LL-37 killing.

No MeSH data available.


Related in: MedlinePlus

Effect of blaI on the cathelicidin susceptibility of S. aureus.(A, B) S. aureus Newman and (C, D) MRSA252 WT, blaI mutant or complemented mutant strains were incubated with CRAMP or LL-37 and the numbers of surviving CFUs were determined at the indicated time points. Samples were run in triplicate, and average CFU/mL values ± SD for one representative experiments of at least two performed for each data set is shown on a log scale. *, p<0.05; **, p<0.01, ***, p<0.001.
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pone.0136605.g002: Effect of blaI on the cathelicidin susceptibility of S. aureus.(A, B) S. aureus Newman and (C, D) MRSA252 WT, blaI mutant or complemented mutant strains were incubated with CRAMP or LL-37 and the numbers of surviving CFUs were determined at the indicated time points. Samples were run in triplicate, and average CFU/mL values ± SD for one representative experiments of at least two performed for each data set is shown on a log scale. *, p<0.05; **, p<0.01, ***, p<0.001.

Mentions: We next performed killing kinetics with cathelicidin AMPs. Compared to their respective S. aureus Newman and MRSA252 WT strains, the blaI mutants were found to be more susceptible to the murine cathelicidin CRAMP and human LL-37 with their CFU concentrations being approximately 0.5 logs lower compared to the respective WT strains after 1–2 hours of co-incubation with the cathelicidins (Fig 2A–2D). The difference in AMP susceptibility between the Newman and MRSA252 WT and their respective blaI mutants was observed for both stationary and exponential phase cells (data not shown) indicating that the phenotype was growth phase-independent. Despite the fact that expression of BlaI in trans on plasmid pBlaI did not fully abolish the increased beta-lactamase activity (see above), the S. aureus Newman blaI mutant expressing pBlaI showed WT levels for both CRAMP and LL-37 resistance indicating functional complementation of blaI in terms of cathelicidin susceptibility (Fig 2A and 2B). Additionally, no differences in cathelicidin killing as compared to the MRSA252 WT strain were observed for a blaZ mutant in this strain background (data not shown) further ensuring that the cathelicidin susceptibility phenotype of the blaI mutant was specific to the blaI gene.


Beta-Lactamase Repressor BlaI Modulates Staphylococcus aureus Cathelicidin Antimicrobial Peptide Resistance and Virulence.

Pence MA, Haste NM, Meharena HS, Olson J, Gallo RL, Nizet V, Kristian SA - PLoS ONE (2015)

Effect of blaI on the cathelicidin susceptibility of S. aureus.(A, B) S. aureus Newman and (C, D) MRSA252 WT, blaI mutant or complemented mutant strains were incubated with CRAMP or LL-37 and the numbers of surviving CFUs were determined at the indicated time points. Samples were run in triplicate, and average CFU/mL values ± SD for one representative experiments of at least two performed for each data set is shown on a log scale. *, p<0.05; **, p<0.01, ***, p<0.001.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4549145&req=5

pone.0136605.g002: Effect of blaI on the cathelicidin susceptibility of S. aureus.(A, B) S. aureus Newman and (C, D) MRSA252 WT, blaI mutant or complemented mutant strains were incubated with CRAMP or LL-37 and the numbers of surviving CFUs were determined at the indicated time points. Samples were run in triplicate, and average CFU/mL values ± SD for one representative experiments of at least two performed for each data set is shown on a log scale. *, p<0.05; **, p<0.01, ***, p<0.001.
Mentions: We next performed killing kinetics with cathelicidin AMPs. Compared to their respective S. aureus Newman and MRSA252 WT strains, the blaI mutants were found to be more susceptible to the murine cathelicidin CRAMP and human LL-37 with their CFU concentrations being approximately 0.5 logs lower compared to the respective WT strains after 1–2 hours of co-incubation with the cathelicidins (Fig 2A–2D). The difference in AMP susceptibility between the Newman and MRSA252 WT and their respective blaI mutants was observed for both stationary and exponential phase cells (data not shown) indicating that the phenotype was growth phase-independent. Despite the fact that expression of BlaI in trans on plasmid pBlaI did not fully abolish the increased beta-lactamase activity (see above), the S. aureus Newman blaI mutant expressing pBlaI showed WT levels for both CRAMP and LL-37 resistance indicating functional complementation of blaI in terms of cathelicidin susceptibility (Fig 2A and 2B). Additionally, no differences in cathelicidin killing as compared to the MRSA252 WT strain were observed for a blaZ mutant in this strain background (data not shown) further ensuring that the cathelicidin susceptibility phenotype of the blaI mutant was specific to the blaI gene.

Bottom Line: Through screening a transposon library in S. aureus Newman for susceptibility to cathelicidin antimicrobial peptide, we discovered BlaI as a novel cathelicidin resistance factor.Additionally, through integrational mutagenesis in S. aureus Newman and MRSA Sanger 252 strains, we confirmed the role of BlaI in resistance to human and murine cathelidicin and showed that it contributes to virulence in human whole blood and murine infection models.We further demonstrated that BlaI could be a target for innate immune-based antimicrobial therapies; by removing BlaI through subinhibitory concentrations of 6-aminopenicillanic acid, we were able to sensitize S. aureus to LL-37 killing.

View Article: PubMed Central - PubMed

Affiliation: Biomedical Sciences Graduate Program, University of California San Diego, La Jolla, CA, United States of America; Department of Pediatrics, School of Medicine, University of California San Diego, La Jolla, CA, United States of America.

ABSTRACT
BlaI is a repressor of BlaZ, the beta-lactamase responsible for penicillin resistance in Staphylococcus aureus. Through screening a transposon library in S. aureus Newman for susceptibility to cathelicidin antimicrobial peptide, we discovered BlaI as a novel cathelicidin resistance factor. Additionally, through integrational mutagenesis in S. aureus Newman and MRSA Sanger 252 strains, we confirmed the role of BlaI in resistance to human and murine cathelidicin and showed that it contributes to virulence in human whole blood and murine infection models. We further demonstrated that BlaI could be a target for innate immune-based antimicrobial therapies; by removing BlaI through subinhibitory concentrations of 6-aminopenicillanic acid, we were able to sensitize S. aureus to LL-37 killing.

No MeSH data available.


Related in: MedlinePlus