Reporting antimicrobial susceptibilities and phenotypes of resistance to vancomycin in vancomycin-resistant Enterococcus spp. clinical isolates: A nationwide proficiency study / Informe de sensibilidad antimicrobiana y fenotipos de resistencia a vancomicina en aislados clínicos de Enterococcus spp. resistentes a vancomicina: estudio multicéntrico nacional

Introduction: The ability of Spanish microbiology laboratories to (a) determine antimicrobial susceptibility (AS), and (b) correctly detect the vancomycin resistance (VR) phenotype in vancomycin-resistant Enterococcus spp. (VRE) was evaluated. Methods: Three VRE isolates representing the VanA (E. faecium), VanB (E. faecium) and VanC (E. gallinarum) VR phenotypes were sent to 52 laboratories, which were asked for: (a) AS method used; (b) MICs of ampicillin, imipenem, vancomycin, teicoplanin, linezolid, daptomycin, ciprofloxacin, levofloxacin and quinupristin–dalfopristin, and high-level resistance to gentamicin and streptomycin; (c) VR phenotype. Results: (a) The most frequently used system was MicroScan; (b) according to the system, the highest percentage of discrepant MICs was found with gradient strips (21.3%). By antimicrobial, the highest rates of discrepant MICs ranged 16.7% (imipenem) to 0.7% (linezolid). No discrepant MICs were obtained with daptomycin or levofloxacin. Mayor errors (MEs) occurred with linezolid (1.1%/EUCAST) and ciprofloxacin (5.0%/CLSI), and very major errors (VMEs) with vancomycin (27.1%/EUCAST and 33.3%/CLSI) and teicoplanin (5.7%/EUCAST and 2.3%/CLSI). For linezolid, ciprofloxacin, and vancomycin, discrepant MICs were responsible for these errors, while for teicoplanin, errors were due to a misassignment of the clinical category. An unacceptable high percentage of VMEs was obtained using gradient strips (14.8%), especially with vancomycin, teicoplanin and daptomycin; (c) 86.4% of the centers identified VanA and VanB phenotypes correctly, and 95.0% the VanC phenotype. Conclusion: Most Spanish microbiology laboratories can reliably determine AS in VRE, but there is a significant percentage of inadequate interpretations (warning of false susceptibility) for teicoplanin in isolates with the VanB phenotype.(AU)

Introducción: Se evaluó la capacidad de los laboratorios de microbiología españoles para: (a) determinar la sensibilidad antimicrobiana (SA); y (b) detectar correctamente el fenotipo de resistencia a vancomicina (FRV) en Enterococcus spp. resistente a vancomicina (ERV). Métodos: Se enviaron 3 aislados de ERV (E. faecium/VanA, E. faecium/VanB y E. gallinarum/VanC) a 52 laboratorios, a los que se les solicitó: (a) método de SA; (b) CMI de ampicilina, imipenem, vancomicina, teicoplanina, linezolid, daptomicina, ciprofloxacino, levofloxacino y quinupristina-dalfopristina y resistencia de alto nivel a gentamicina y estreptomicina; y (c) fenotipo de resistencia a vancomicina. Resultados: (a) El sistema más utilizado fue MicroScan; y (b) el mayor porcentaje de CMI discrepantes se produjo con las tiras de gradiente (21,3%). Las tasas más elevadas de CMI discrepantes variaron entre el 16,7% (imipenem) y el 0,7% (linezolid). Se produjeron errores mayores con linezolid (1,1%/EUCAST) y ciprofloxacino (5,0%/CLSI) y errores máximos con vancomicina (27,1%/EUCAST y 33,3% CLSI) y teicoplanina (5,7%/EUCAST y 2,3%/CLSI). Para linezolid, ciprofloxacino y vancomicina las CMI discrepantes fueron las responsables de estos errores, mientras que para teicoplanina los errores se debieron a una asignación errónea de la categoría clínica. Se obtuvo un alto porcentaje de errores máximos utilizando tiras de gradiente (14,8%), especialmente con vancomicina, teicoplanina y daptomicina; y (c) el 86,4% de los centros identificaron correctamente los fenotipos VanA y VanB y el 95,0% el fenotipo VanC. Conclusión: La mayoría de los laboratorios de microbiología españoles determinan de forma fiable la SA en ERV, pero existe un porcentaje significativo de interpretaciones inadecuadas (falsa sensibilidad) para teicoplanina en aislados con fenotipo VanB.(AU)

Reporting antimicrobial susceptibilities and phenotypes of resistance to vancomycin in vancomycin-resistant Enterococcus spp. clinical isolates: A nationwide proficiency study.

INTRODUCTION: The ability of Spanish microbiology laboratories to (a) determine antimicrobial susceptibility (AS), and (b) correctly detect the vancomycin resistance (VR) phenotype in vancomycin-resistant Enterococcus spp. (VRE) was evaluated. METHODS: Three VRE isolates representing the VanA (E. faecium), VanB (E. faecium) and VanC (E. gallinarum) VR phenotypes were sent to 52 laboratories, which were asked for: (a) AS method used; (b) MICs of ampicillin, imipenem, vancomycin, teicoplanin, linezolid, daptomycin, ciprofloxacin, levofloxacin and quinupristin-dalfopristin, and high-level resistance to gentamicin and streptomycin; (c) VR phenotype. RESULTS: (a) The most frequently used system was MicroScan; (b) according to the system, the highest percentage of discrepant MICs was found with gradient strips (21.3%). By antimicrobial, the highest rates of discrepant MICs ranged 16.7% (imipenem) to 0.7% (linezolid). No discrepant MICs were obtained with daptomycin or levofloxacin. Mayor errors (MEs) occurred with linezolid (1.1%/EUCAST) and ciprofloxacin (5.0%/CLSI), and very major errors (VMEs) with vancomycin (27.1%/EUCAST and 33.3%/CLSI) and teicoplanin (5.7%/EUCAST and 2.3%/CLSI). For linezolid, ciprofloxacin, and vancomycin, discrepant MICs were responsible for these errors, while for teicoplanin, errors were due to a misassignment of the clinical category. An unacceptable high percentage of VMEs was obtained using gradient strips (14.8%), especially with vancomycin, teicoplanin and daptomycin; (c) 86.4% of the centers identified VanA and VanB phenotypes correctly, and 95.0% the VanC phenotype. CONCLUSION: Most Spanish microbiology laboratories can reliably determine AS in VRE, but there is a significant percentage of inadequate interpretations (warning of false susceptibility) for teicoplanin in isolates with the VanB phenotype.

Susceptibility testing and detection of ß-lactam resistance mechanisms in Enterobacteriaceae: a multicentre national proficiency study.

A nationwide study was developed to evaluate the ability of 60 Spanish clinical microbiology laboratories to predict the underlying ß-lactam resistance mechanisms of 12 Enterobacteriaceae strains (CCS01-CCS12). Results obtained by two reference laboratories were compared with those reported by the participant laboratories that used their own routine susceptibility testing methodology. Clinical and Laboratory Standards Institute (CLSI) interpretive criteria were used in 53.3% of centres, whilst 46.7% used European Committee on Antimicrobial Susceptibility Testing (EUCAST) criteria. Overall categorical agreement (CA) was 85.5%. Rates of very major errors (VME), minor errors (MinE) and major errors (ME) were 5%, 9.7% and 5.5%, respectively. The lowest CA values were obtained for carbapenems (56.7-78.1%). ß-Lactam/ß-lactamase inhibitors were also problematic compounds: VME for amoxicillin/clavulanic acid were 8% (EUCAST criteria) and MinE for piperacillin/tazobactam were 45.7% (CLSI criteria). OXA-48 (CCS02, CCS10, CCS11), VIM-1 (CCS09) and KPC-3 (CCS05) were correctly identified by 75-87%, 65% and 71% of centres, respectively. Strains with an extended-spectrum ß-lactamase (ESBL) plus a carbapenemase (CCS03, CCS04, CCS06) were correctly detected in 32-68% of centres. Seven percent correct identifications were recorded for CCS08 (chromosomal K1 ß-lactamase hyperexpression plus IMP-8). Strains with permeability deficiencies [CCS07 (ACT-1 plus porin deficit) and CCS12 (TEM-24 plus porin deficit)] were correctly detected in 17% and 10% of centres, respectively. The TEM-1-producer (CCS01) was detected in 40% of centres. Microbiologists should be aware of new antibiotic resistance mechanisms, and these surveillance studies are particularly useful for this purpose and for the communication of such traits.

Inhibitor-resistant TEM- and OXA-1-producing Escherichia coli isolates resistant to amoxicillin-clavulanate are more clonal and possess lower virulence gene content than susceptible clinical isolates.

In a previous prospective multicenter study in Spain, we found that OXA-1 and inhibitor-resistant TEM (IRT) ß-lactamases constitute the most common plasmid-borne mechanisms of genuine amoxicillin-clavulanate (AMC) resistance in Escherichia coli. In the present study, we investigated the population structure and virulence traits of clinical AMC-resistant E. coli strains expressing OXA-1 or IRT and compared these traits to those in a control group of clinical AMC-susceptible E. coli isolates. All OXA-1-producing (n = 67) and IRT-producing (n = 45) isolates were matched by geographical and temporal origin to the AMC-susceptible control set (n = 56). We performed multilocus sequence typing and phylogenetic group characterization for each isolate and then studied the isolates for the presence of 49 virulence factors (VFs) by PCR and sequencing. The most prevalent clone detected was distinct for each group: group C isolates of sequence type (ST) 88 (C/ST88) were the most common in OXA-1 producers, B2/ST131 isolates were the most common in IRT producers, and B2/ST73 isolates were the most common in AMC-susceptible isolates. The median numbers of isolates per ST were 3.72 in OXA-1 producers, 2.04 in IRT producers, and 1.69 in AMC-susceptible isolates; the proportions of STs represented by one unique isolate in each group were 19.4%, 31.1%, and 48.2%, respectively. The sum of all VFs detected, calculated as a virulence score, was significantly higher in AMC-susceptible isolates than OXA-1 and IRT producers (means, 12.5 versus 8.3 and 8.2, respectively). Our findings suggest that IRT- and OXA-1-producing E. coli isolates resistant to AMC have a different and less diverse population structure than AMC-susceptible clinical E. coli isolates. The AMC-susceptible population also contains more VFs than AMC-resistant isolates.

Relationship between beta-lactamase production, outer membrane protein and penicillin-binding protein profiles on the activity of carbapenems against clinical isolates of Acinetobacter baumannii.

Twenty blood isolates of Acinetobacter baumannii were studied, representing eight pulsed-field gel electrophoresis patterns and all different antimicrobial susceptibility patterns observed during 1995-97 at the University Hospital Virgen Macarena, Seville, Spain. The MIC(90)s (mg/L) of imipenem and meropenem decreased from 16 to 0.5 and from 8 to 4, respectively, in the presence of BRL 42715 (BRL) but not clavulanic acid. Hydrolysing activity (nmol/min/mg) of bacterial supernatants against cefaloridine ranged from 8.8 to 552.3 for A. baumannii type I (imipenem MICs < or = 2), which expressed only a beta-lactamase of pI > or = 9, and from 12.3 to 1543.5 for A. baumannii type II (imipenem MICs > or = 4), which expressed a beta-lactamase of pI > or = 9 and two others of pI 6.3 and 7. The hydrolysing activities of A. baumannii type II against imipenem, meropenem and oxacillin were higher than those observed for A. baumannii type I. Ten outer membrane protein (OMP) profiles (A. baumannii types I and II) were visualized on 10% SDS-PAGE gels with 6 M urea, whereas only five OMP profiles (A. baumannii types I and II) were differentiated in 12% SDS-PAGE gels. Five A. baumannii with OMP profile type B, characterized by the absence of a 22.5 kDa OMP, were resistant to meropenem and/or imipenem. Twelve penicillin-binding protein (PBP) patterns were observed. PBP patterns of A. baumannii type II were characterized by the absence of a 73.2 kDa band (PBP 2). We concluded that production of beta-lactamases of pI 6.3 and 7.0 and reduced expression of PBP 2 are the most frequently observed mechanisms of resistance to carbapenems. In some isolates, loss of a 22.5 kDa OMP is also related to resistance to carbapenems.