Asociación en un mismo plásmido de blaVIM-1 y qnrS2 en Klebsiella pneumoniae y Klebsiella oxytoca aisladas en Sevilla / Combination of blaVIM-1 and qnrS2 on the same plasmid in Klebsiella oxytoca and Klebsiella pneumoniae isolates in Seville

Introducción: La resistencia combinada a quinolonas y (..) (AU)

Background: Combined resistance to quinolones and (..) (AU)

[Combination of bla(VIM-1) and qnrS2 on the same plasmid in Klebsiella oxytoca and Klebsiella pneumoniae isolates in Seville]. / Asociación en un mismo plásmido de bla(VIM-1) y qnrS2 en Klebsiella pneumoniae y Klebsiella oxytoca aisladas en Sevilla.

BACKGROUND: Combined resistance to quinolones and ß-lactams is common in Enterobacteriaceae. The appearance in enterobacteria coding for metallo-ß-lactamases and determinants of plasmid-mediated quinolone resistance are an emerging problem in our country. METHODS: The susceptibility was determined by E-test. The resistance genes were detected by PCR and the corresponding plasmids were characterised. RESULTS: This study describes 2 strains (1 Klebsiella oxytoca, 1 Klebsiella pneumoniae) carrying the genes qnrS2 and blaVIM-1 in a transferable plasmid of 70-Kb isolated in surveillance cultures at the University Hospital Virgen Macarena in Seville. CONCLUSION: This is the first combination of qnrS2 and bla(VIM-1) on the same non-typeable plasmid isolated in our centre.

Genetic characterization of an extended-spectrum AmpC cephalosporinase with hydrolysing activity against fourth-generation cephalosporins in a clinical isolate of Enterobacter aerogenes selected in vivo.

BACKGROUND: Extended-spectrum AmpC cephalosporinases (ESACs) have been reported in Enterobacteriaceae, Pseudomonas aeruginosa and Acinetobacter baumannii. Here, we characterize a new AmpC variant presenting a broadened substrate activity towards fourth-generation cephalosporins, selected in vivo following cefepime treatment for Enterobacter aerogenes. METHODS: Two consecutive clonally related isolates of E. aerogenes were evaluated. Screening for ESAC production was performed using plates containing 200 mg/L cloxacillin. MICs were determined by microdilution (CLSI guidelines). bla(AmpC) genes were cloned into a pCR-Blunt II-TOPO vector and expressed in Escherichia coli. The ampC genes were cloned into vector pGEX-6P-1 for protein purification. RESULTS: Isolate Ea595 was resistant to two fourth-generation cephalosporins, cefepime and cefpirome; using plates containing cloxacillin, susceptibility to ceftazidime and cefepime was restored, suggesting overproduction of the ESAC ß-lactamase. Sequencing identified a new AmpC ß-lactamase variant presenting one amino acid substitution, Val291Gly, inside the H-10 helix. Recombinant plasmids harbouring this ESAC ß-lactamase conferred a broadened resistance profile to cefepime and cefpirome, with resistance levels increasing from 16- to 32-fold in E. coli. AmpC-Ea595 hydrolysed ceftazidime, cefepime and cefpirome at high levels, presenting a lower K(m) and enabling us to classify the enzyme as an ESAC. Homology modelling suggested that the size of the active site could have increased. CONCLUSIONS: We characterized an ESAC ß-lactamase selected in vivo and conferring a high level of resistance to fourth-generation cephalosporins in E. aerogenes. The broadened spectrum was caused by a new modification to the H-10 helix, which modified the active site.

Predictive analysis of transmissible quinolone resistance indicates Stenotrophomonas maltophilia as a potential source of a novel family of Qnr determinants.

BACKGROUND: Predicting antibiotic resistance before it emerges at clinical settings constitutes a novel approach for preventing and fighting resistance of bacterial pathogens. To analyse the possibility that novel plasmid-encoded quinolone resistance determinants (Qnr) can emerge and disseminate among bacterial pathogens, we searched the presence of those elements in nearly 1000 bacterial genomes and metagenomes. RESULTS: We have found a number of novel potential qnr genes in the chromosomes of aquatic bacteria and in metagenomes from marine organisms. Functional studies of the Stenotrophomonas maltophilia Smqnr gene show that plasmid-encoded SmQnr confers quinolone resistance upon its expression in a heterologous host. CONCLUSION: Altogether, the data presented in our work support the notion that predictive studies on antibiotic resistance are feasible, using currently available information on bacterial genomes and with the aid of bioinformatic and functional tools. Our results confirm that aquatic bacteria can be the origin of plasmid-encoded Qnr, and highlight the potential role of S. maltophilia as a source of novel Qnr determinants.

[Activity and penetration of linezolid and vancomycin against Staphylococcus epidermidis biofilms]. / Actividad y permeabilidad de linezolid y vancomicina en biocapas de Staphylococcus epidermidis.

INTRODUCTION: The activity and capacity for penetration of linezolid and vancomycin were comparatively evaluated against Staphylococcus epidermidis biofilms. METHODS: The activity of linezolid versus vancomycin was assessed against 24-hour S. epidermidis biofilms developed on silicon catheters. Penetration of the two antimicrobial agents was measured in biofilms developed on polycarbonate membrane filters. Penetration and activity were comparatively tested using S. epidermidis, slime-producing and non-slime-producing strains. RESULTS: The activity of linezolid against S. epidermidis biofilms was significantly greater than that of vancomycin for both strains. Neither antimicrobial completely eradicated bacterial survival in 24-hour biofilms. Linezolid penetration in biofilms was greater than that of vancomycin for both S. epidermidis strains. CONCLUSIONS: Linezolid showed higher in vitro activity than vancomycin against S. epidermidis biofilms on silicone catheters. This effect may be due to the capability of linezolid to cross the bacterial biofilm.