Search

MICs of plazomicin were determined by agar dilution and broth microdilution in 187 ESBL-producing Escherichia coli (n = 73), carbapenemase-producing Klebsiella pneumoniae (n = 55) methicillin-resistant Staphylococcus aureus (n = 59) clinical isolates. Inoculum effect was determined by broth microdilution assay using two different inocula; 1-5 × 10 5 (standard inoculum) and 1-5 × 10 8  CFU/mL. For all isolates tested >98% categorical agreement and ≥95% of essential agreement (±1elog2) was found. At high inocula, MICs of plazomicin increased ≥ eight-fold for 25% of E. coli, 24% of K. pneumoniae and 7% of S. aureus isolates tested. The results indicate that agar dilution and broth microdilution methods were equally suitable for determining plazomicin MICs. Inoculum effect was observed for plazomicin in Escherichia coli and Klebsiella pneumoniae isolates. Further studies that establish the genetic background of the isolates are required to better understand the reasons behind the inoculum effect., (Copyright © 2019 Elsevier Inc. All rights reserved.)

The activity of daptomycin was evaluated against 702 staphylococcal blood isolates (316 methicillin-susceptible Staphylococcus aureus, 187 methicillin-resistant S. aureus [MRSA], and 199 coagulase-negative staphylococci [CoNS]) collected in 41 Spanish hospitals. Glycopeptide tolerance and the incidence of heterogeneous glycopeptide-intermediate (hGISA) isolates were also examined. Vancomycin MICs determined by the Etest were compared with those obtained by the reference broth microdilution method. Daptomycin exhibited good activity, and only 2 isolates were nonsusceptible to this antibiotic. Resistance to linezolid was observed in 2 MRSA isolates and in 16 CoNS. The cfr gene was detected in 7 of these 18 isolates. Vancomycin and teicoplanin tolerance was 9.6% and 21.9%, respectively, in MRSA isolates. We detected the hGISA phenotype in 5.8% of MRSA isolates. Vancomycin MICs by the Etest were slightly higher than those obtained by broth microdilution. Daptomycin retained activity against isolates that were not susceptible to linezolid, teicoplanin, or quinupristin-dalfopristin., (Copyright © 2011 Elsevier Inc. All rights reserved.)

The presence of qnr genes in 191 extended-spectrum beta-lactamase-producing Escherichia coli from 2005, with 75% of resistance to ciprofloxacin, was evaluated. An SHV-12-producing E. coli carried qnrB19; both genes were transferred by conjugation. No qnrA- or qnrS-positive strains were detected. In addition, we identified 3 new parC mutations (S80W, E84R, and E84A)., (Copyright 2010 Elsevier Inc. All rights reserved.)

Antimicrobial resistance and the mechanisms implicated were studied in 148 clinical Enterococcus faecium isolates with a quinupristin-dalfopristin (Q/D) MIC > or =1 microg/mL. As expected, higher levels of resistance were detected for macrolide antibiotics (94% erythromycin, 100% azithromycin, 100% josamycin). High-level resistance to gentamicin and streptomycin was detected in 18.9% and 66.2% of isolates, respectively, in our series of enterococci. Resistance against tetracycline was found in only 12.8% of the isolates, and 13 isolates were resistant to vancomycin. The dalvabancin MIC(90) for these isolates was >16 microg/mL. Polymerase chain reaction screening for the previously described streptogramin resistance determinants erm(A), erm(B), mefA/E, vat(D), and vat(E) was performed to determine the prevalence of streptogramin resistance mechanisms in these clinical enterococcal isolates. The combination of erm(B) and vat(D) genes encoding resistance to streptogramins was detected in 1 Q/D-resistant E. faecium isolate. A total of 131 Q/D-nonsusceptible enterococci only contained the erm(B) gene. The erm(B) promoter sequence reveals no differences between the strains analyzed, regardless of the Q/D MIC value.

We used the broth microdilution method to determine the MICs of daptomycin and 13 comparator agents against 319 methicillin-susceptible Staphylococcus aureus isolates, 201 methicillin-resistant S. aureus (MRSA) isolates, and 183 coagulase-negative staphylococci (CoNS). Isolates were consecutively collected from bloodstream infections in 39 Spanish medical centers during a 3-month period (March through May 2008). Among MRSA, 1 isolate with intermediate susceptibility to vancomycin and 6 isolates resistant to linezolid were found. Nonsusceptibility to teicoplanin was detected in 3.9% of CoNS. Daptomycin was highly active against the staphylococcal blood isolates tested-all were inhibited at the daptomycin susceptibility breakpoint of < or = 1 microg/mL. Daptomycin retained its activity against the isolates that were resistant to teicoplanin or linezolid, or that had reduced susceptibility to vancomycin. These data suggest that daptomycin could be useful for the treatment of bloodstream infections caused by staphylococci.

The antimicrobial activity of tigecycline, a novel glycylcycline, was evaluated against 1102 bacterial isolates from 20 centers in Spain. The MIC of tigecycline at which 90% (MIC(90)) of the pneumococci tested were inhibited was the lowest (0.06 microg/mL) of all the antibiotics tested. The MICs of tigecycline against enterococci ranged from 0.03 to 0.125 microg/mL. All staphylococci were inhibited by < or =0.25 microg/mL of tigecycline, and 99.6% of Enterobacteriaceae isolates were inhibited by < or =2 microg/mL of tigecycline. Tigecycline demonstrated good activity against Bacteroides fragilis group organisms with an MIC(90) of 4 microg/mL. The results of this study confirm the excellent activity of tigecycline against multiresistant Gram-positive and Gram-negative pathogens.

The evolution of susceptibility to the newer fluoroquinolones, moxifloxacin and trovafloxacin, of Bacteroides fragilis group organisms isolated in our hospital from 1997 to 2002 was studied. A total of 927 strains were included in the study. Trovafloxacin was more active than moxifloxacin against the various species of the group. During the study period, an increase in resistance to both quinolones was observed. Rates of resistance to moxifloxacin at a breakpoint of 8 microg/mL remained stable at around 6% during the period 1997-1998 and increased to 11.4% in 2000 and to 16.5% in 2001-2002 (P<0.005). Resistance to trovafloxacin rose significantly from 0.6% in 1998 to 6.8% in 1999 (P<0.05) and did not change appreciably over the last 3 years studied. This study confirms the increasing resistance of B. fragilis group organisms to trovafloxacin and moxifloxacin and emphasizes the need to perform periodic antimicrobial susceptibility tests to guide the selection of appropriate antimicrobial therapy.