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Bulgecin A as a β -lactam enhancer for carbapenem-resistant Pseudomonas aeruginosa and carbapenem-resistant Acinetobacter baumannii clinical isolates containing various resistance mechanisms

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ABSTRACT

Genetic screening of Pseudomonas aeruginosa (PSDA) and Acinetobacter baumannii (ACB) reveals genes that confer increased susceptibility to β-lactams when disrupted, suggesting novel drug targets. One such target is lytic transglycosylase. Bulgecin A (BlgA) is a natural product of Pseudomonas mesoacidophila and a lytic transglycosolase inhibitor that works synergistically with β-lactams targeting PBP3 for Enterobacteriaceae. BlgA also weakly inhibits di-Zn2+ metallo-β-lactamases like L1 of Stenotrophomonas maltophilia. We hypothesized that because of its unique mechanism of action, BlgA could restore susceptibility to carbapenems in carbapenem-resistant PSDA (CR-PSDA) and carbapenem-resistant ACB, as well as ACB resistant to sulbactam. A BlgA-containing extract was prepared using a previously published protocol. CR-PSDA clinical isolates demonstrating a variety of carbapenem resistance mechanisms (VIM-2 carbapenemases, efflux mechanisms, and AmpC producer expression) were characterized with agar dilution minimum inhibitory concentration (MIC) testing and polymerase chain reaction. Growth curves using these strains were prepared using meropenem, BlgA extract, and meropenem plus BlgA extract. A concentrated Blg A extract combined with low concentrations of meropenem, was able to inhibit the growth of clinical strains of CR-PSDA for strains that had meropenem MICs ≥8 mg/L by agar dilution, and a clinical strain of an OXA-24 producing ACB that had a meropenem MIC >32 mg/L and intermediate ampicillin/sulbactam susceptibility. Similar experiments were conducted on a TEM-1 producing ACB strain resistant to sulbactam. BlgA with ampicillin/sulbactam inhibited the growth of this organism. As in Enterobacteriaceae, BlgA appears to restore the efficacy of meropenem in suppressing the growth of CR-PSDA and carbapenem-resistant ACB strains with a variety of common carbapenem resistance mechanisms. BlgA extract also inhibits VIM-2 β-lactamase in vitro. BlgA may prove to be an exciting adjunctive compound to extend the life of carbapenems against these vexing pathogens.

No MeSH data available.


IC50 expressed as percent concentration of bulgecin A extract to inhibit VIM-2 β-lactamase hydrolysis activity.
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f4-dddt-10-3013: IC50 expressed as percent concentration of bulgecin A extract to inhibit VIM-2 β-lactamase hydrolysis activity.

Mentions: In order to demonstrate whether BlgA extract could inhibit VIM-2 MBL, we measured the IC50 of the extract expressed as a percent concentration for VIM-2 MBL of PSDA39 (Figure 4) using a kinetic assay (see the “Materials and methods” section). BlgA is hypothesized to bind in a reversible manner to di-Zn2+ MBLs27 by coordinating its GlcNAC sulfate group to the Zn2+ ions. The measured IC50 for our extract is 0.5%±0.1%. BlgA has an IC50 of 150 µM for the structurally similar L1 di-Zn2+ enzyme of S. maltophilia.27 A concentration of 10% BlgA extract was used in the growth inhibition experiments, or a 50-fold higher concentration in the medium, compared to the estimated IC50 % in the in vitro enzyme assay. So, it is reasonable to assume that some inhibition of the PSDA R96 strains is due to the activity of BlgA extract against VIM-2. Further studies with pure BlgA are needed to demonstrate this effect, as well as further characterization of strain 860, to determine whether efflux of BlgA may occur or if OprD loss plays a role in resistance to BlgA.


Bulgecin A as a β -lactam enhancer for carbapenem-resistant Pseudomonas aeruginosa and carbapenem-resistant Acinetobacter baumannii clinical isolates containing various resistance mechanisms
IC50 expressed as percent concentration of bulgecin A extract to inhibit VIM-2 β-lactamase hydrolysis activity.
© Copyright Policy
Related In: Results  -  Collection

License 1 - License 2
Show All Figures
getmorefigures.php?uid=PMC5036594&req=5

f4-dddt-10-3013: IC50 expressed as percent concentration of bulgecin A extract to inhibit VIM-2 β-lactamase hydrolysis activity.
Mentions: In order to demonstrate whether BlgA extract could inhibit VIM-2 MBL, we measured the IC50 of the extract expressed as a percent concentration for VIM-2 MBL of PSDA39 (Figure 4) using a kinetic assay (see the “Materials and methods” section). BlgA is hypothesized to bind in a reversible manner to di-Zn2+ MBLs27 by coordinating its GlcNAC sulfate group to the Zn2+ ions. The measured IC50 for our extract is 0.5%±0.1%. BlgA has an IC50 of 150 µM for the structurally similar L1 di-Zn2+ enzyme of S. maltophilia.27 A concentration of 10% BlgA extract was used in the growth inhibition experiments, or a 50-fold higher concentration in the medium, compared to the estimated IC50 % in the in vitro enzyme assay. So, it is reasonable to assume that some inhibition of the PSDA R96 strains is due to the activity of BlgA extract against VIM-2. Further studies with pure BlgA are needed to demonstrate this effect, as well as further characterization of strain 860, to determine whether efflux of BlgA may occur or if OprD loss plays a role in resistance to BlgA.

View Article: PubMed Central - PubMed

ABSTRACT

Genetic screening of Pseudomonas aeruginosa (PSDA) and Acinetobacter baumannii (ACB) reveals genes that confer increased susceptibility to β-lactams when disrupted, suggesting novel drug targets. One such target is lytic transglycosylase. Bulgecin A (BlgA) is a natural product of Pseudomonas mesoacidophila and a lytic transglycosolase inhibitor that works synergistically with β-lactams targeting PBP3 for Enterobacteriaceae. BlgA also weakly inhibits di-Zn2+ metallo-β-lactamases like L1 of Stenotrophomonas maltophilia. We hypothesized that because of its unique mechanism of action, BlgA could restore susceptibility to carbapenems in carbapenem-resistant PSDA (CR-PSDA) and carbapenem-resistant ACB, as well as ACB resistant to sulbactam. A BlgA-containing extract was prepared using a previously published protocol. CR-PSDA clinical isolates demonstrating a variety of carbapenem resistance mechanisms (VIM-2 carbapenemases, efflux mechanisms, and AmpC producer expression) were characterized with agar dilution minimum inhibitory concentration (MIC) testing and polymerase chain reaction. Growth curves using these strains were prepared using meropenem, BlgA extract, and meropenem plus BlgA extract. A concentrated Blg A extract combined with low concentrations of meropenem, was able to inhibit the growth of clinical strains of CR-PSDA for strains that had meropenem MICs ≥8 mg/L by agar dilution, and a clinical strain of an OXA-24 producing ACB that had a meropenem MIC >32 mg/L and intermediate ampicillin/sulbactam susceptibility. Similar experiments were conducted on a TEM-1 producing ACB strain resistant to sulbactam. BlgA with ampicillin/sulbactam inhibited the growth of this organism. As in Enterobacteriaceae, BlgA appears to restore the efficacy of meropenem in suppressing the growth of CR-PSDA and carbapenem-resistant ACB strains with a variety of common carbapenem resistance mechanisms. BlgA extract also inhibits VIM-2 β-lactamase in vitro. BlgA may prove to be an exciting adjunctive compound to extend the life of carbapenems against these vexing pathogens.

No MeSH data available.