Novel approach to quorum quenching: rational design of antibacterials in combination with hexahistidine-tagged organophosphorus hydrolase.

N-acyl homoserine lactones (AHLs) are quorum sensing (QS) signal molecules used by most Gram-negative pathogenic bacteria. In this article the lactonase activity of the preparations based on hexahistidine-tagged organophosphorus hydrolase (His6-OPH) towards AHLs was studied. Initially, three of the most interesting ß-lactam antibiotics were selected from seven that were trialed during molecular docking to His6-OPH. Combinations of antibiotics (meropenem, imipenem, ceftriaxone) and His6-OPH taken in the native form or in the form of non-covalent enzyme-polyelectrolyte complexes (EPCs) with poly(glutamic acid) or poly(aspartic acid) were obtained and investigated. The lactonase activity of the preparations was investigated under different physical-chemical conditions in the hydrolysis of AHLs [N-butyryl-D,L-homoserine lactone, N-(3-oxooctanoyl)-D,L-homoserine lactone, N-(3-oxododecanoyl)-L-homoserine lactone]. An increased efficiency of catalytic action and stability of the lactonase activity of His6-OPH was shown for its complexes with antibiotics and was confirmed in trials with bacterial strains. The broadening of the catalytic action of the enzyme against AHLs was revealed in the presence of the meropenem. Results of molecular docking of AHLs to the surface of the His6-OPH dimer in the presence of antibiotics allowed proposing the mechanism of such interference based on a steric repulsion of the carbon chain of hydrolyzed AHLs by the antibiotics bounded to the enzyme surface.

Cefditoren versus ceftazidime in inducer-substrate combinations for the evaluation of AmpC production in a disc approximation test

Objetivo: Evaluar el cefditoren en combinaciones inductor-substrato para la detección de inducción de AmpC.Métodos: 100 aislados clínicos (25 P. aeruginosa, 25 E.cloacae, 14 M. morganii, 13 S. marcescens, 12 C. freundii,7 P. rettgeri, and 4 E. aerogenes) se ensayaron por el métodode disco Kirby-Bauer utilizando discos de cefditoren yceftazidima como substratos y de cefditoren e imipenemcomo inductores.Resultados: Ninguna cepa mostró inducción de AmpCcon la combinación cefditoren-ceftazidima como inductorsubstrato.La combinación de imipenem-cefditoren comoinductor-substrato no fue adecuada para evaluar las cepasde P. aeruginosa ya que no hubo halo de inhibición alrededordel disco de cefditoren. En las enterobacterias que sepudieron evaluar (por presentar halo de inhibición alrededordel substrato), se detectó AmpC inducible en 48 de 63(76.2%) con cefditoren, y en 33 de 68 (48.5%) de los aisladoscon ceftazidima como substrato. Se detectó un númerosignificantivamente (p= 0.013) mayor de productores deAmpC con cefditoren que con ceftazidima (76.2% vs.48.5%), debido a las diferencias encontradas en E. cloacae(72.8% vs. 21.7%; p= 0.0009) y S. marcescens (100% vs.54.5%; p= 0.03). Las reducciones medias del diámetro alrededorde los discos del substrato fueron mayores para cefditoren(4.17 mm) que para ceftazidima (3.79 mm), alcanzandosignificación estadística (p<0.05) en proteáceasindol-positivo: M. morganii (5.32 mm vs. 3.92 mm) y P.rettgeri (3.47 mm vs. 2.64 mm).Conclusión: Cefditoren no presentó capacidad de inducción, y utilizado como substrato (con imipenem comoinductor) ofreció una tasa de detección de AmpC inducibleen enterobacterias superior de la de la combinación imipenem-ceftazidima, principalmente en Enterobacter spp. ySerratia spp., con mayores reducciones del diámetro enproteáceas indol-positivo(AU)

Objective: To evaluate cefditoren in inducer-substratecombinations to screen for AmpC induction.Methods: 100 clinical isolates (25 P. aeruginosa, 25 E.cloacae, 14 M. morganii, 13 S. marcescens, 12 C. freundii, 7 P.rettgeri, and 4 E. aerogenes) were tested by the Kirby-Bauerdisc approximation method using cefditoren and ceftazidimediscs as substrates, and cefditoren and imipenem discs asinducers.Results: None of the strains showed induction of AmpCwith cefditoren-ceftazidime as inducer-substrate combination.Imipenem-cefditoren as inducer-substrate combination wasnot useful for evaluating strains of P. aeruginosa since noinhibition zones surrounding the cefditoren disc were found.Among evaluable enterobacteria (those showing substrateinhibition zone), inducible Amp C was detected in 48 out of 63(76.2%) with cefditoren, and in 33 out of 68 (48.5%) isolateswith ceftazidime as substrate. Significantly (p= 0.013) highernumber of AmpC producers were detected with cefditorenversus ceftazidime (76.2% vs. 48.5%), due to the differencesfound for E. cloacae (72.8% vs. 21.7%; p= 0.0009) and S.marcescens (100% vs. 54.5%; p= 0.03). Higher meanreductions of diameters around substrate discs were found forcefditoren (4.17 mm) vs. ceftazidime (3.79 mm), reachingstatistical significance (p<0.05) for indol-positive proteae: M.morganii (5.32 mm vs. 3.92 mm) and P. rettgeri (3.47 mm vs.2.64 mm).Conclusion: Cefditoren showed no induction capability,and when used as substrate (with imipenem as inducer) itoffered detection rates of AmpC inducible enterobacteriahigher than the imipenem-ceftazidime combination, mainly forEnterobacter spp. and Serratia spp., with higher diameterreductions for indol-positive proteae(AU)

Xanthoradones, new potentiators of imipenem activity against methicillin-resistant Staphylococcus aureus, produced by Penicillium radicum FKI-3765-2: I. Taxonomy, fermentation, isolation and biological properties.

The fungal strain FKI-3765-2, identified as Penicillium radicum, was found to produce potentiators of imipenem activity against methicillin-resistant Staphylococcus aureus (MRSA). Two new compounds, designated xanthoradones A and B, were isolated from the fermentation broth of the producing strain by solvent extraction, octadecyl silyl column chromatography and preparative HPLC. Xanthoradones A and B potentiated imipenem activity against MRSA by decreasing the MIC value of imipenem from 16 microg ml(-1) to 0.060 and 0.030 microg ml(-1), respectively.