scholarly journals Performance of Ceftolozane-Tazobactam Etest, MIC Test Strips, and Disk Diffusion Compared to Reference Broth Microdilution for β-Lactam-Resistant Pseudomonas aeruginosa Isolates

2017 ◽  
Vol 56 (3) ◽  
Author(s):  
Romney M. Humphries ◽  
Janet A. Hindler ◽  
Paul Magnano ◽  
Annie Wong-Beringer ◽  
Robert Tibbetts ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Los Angeles ◽  
Performance Characteristics ◽  
Disk Diffusion ◽  
Broth Microdilution ◽  
Beta Lactam ◽  
Content Type ◽  
Test Strips ◽  
Santa Ana

ABSTRACT The performance characteristics of the ceftolozane-tazobactam (C-T) Etest (bioMérieux, Marcy l'Etoile, France), MIC test strips (MTS; Liofilchem, Italy), and disk diffusion (Hardy, Santa Ana, CA) were evaluated for a collection of 308 beta-lactam-resistant isolates of Pseudomonas aeruginosa recovered from three institutions in Los Angeles, CA. Reference testing was performed by the reference broth microdilution (rBMD) method. MIC and disk results were interpreted using Clinical and Laboratory Standards Institute breakpoints. Overall, 72.5% of the isolates were susceptible to C-T by rBMD. Etest and disk diffusion demonstrated acceptable performance, whereas MTS yielded a greater than acceptable percentage of minor errors. Categorical agreement was 96.8% for Etest, 87.0% for MTS, and 92.9% for disk diffusion. No very major errors were observed by any test, and no major errors (ME) were observed by Etest or disk diffusion. Two ME (0.9% of susceptible isolates) were observed by MTS. The incidence of minor errors was 3.2%, 12.3%, and 7.1% for Etest, MTS, and disk diffusion, respectively. Essential agreement (EA) for Etest was excellent, at 97.7%, whereas the MICs obtained by MTS tended to be 1 to 2 dilutions higher than those obtained by rBMD, with an EA of 87.0%.

scholarly journals In VitroActivity of Fosfomycin against a Collection of Clinical Pseudomonas aeruginosa Isolates from 16 Spanish Hospitals: Establishing the Validity of Standard Broth Microdilution as Susceptibility Testing Method

2013 ◽  
Vol 57 (11) ◽  
pp. 5701-5703 ◽  
Author(s):  
María Díez-Aguilar ◽  
María-Isabel Morosini ◽  
Rosa del Campo ◽  
María García-Castillo ◽  
Javier Zamora ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Susceptibility Testing ◽  
Disk Diffusion ◽  
Dilution Method ◽  
Agar Dilution Method ◽  
Broth Microdilution ◽  
Content Type ◽  
Testing Method ◽  
Broth Microdilution Method ◽  
Agar Dilution

ABSTRACTThe broth microdilution method for fosfomycin andPseudomonas aeruginosawas assessed and compared with the approved agar dilution method in 206 genetically unrelatedP. aeruginosaclinical isolates. Essential agreement between the two methods was 84%, and categorical agreement was 89.3%. Additionally, Etest and disk diffusion assays were performed. Results validate broth microdilution as a reliable susceptibility testing method for fosfomycin againstP. aeruginosa. Conversely, unacceptable concordance was established between Etest and disk diffusion results with agar dilution results.

scholarly journals Activity of Ceftolozane-Tazobactam and Ceftazidime-Avibactam against Beta-Lactam-Resistant Pseudomonas aeruginosa Isolates

2017 ◽  
Vol 61 (12) ◽  
Author(s):  
Romney M. Humphries ◽  
Janet A. Hindler ◽  
Annie Wong-Beringer ◽  
Shelley A. Miller
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Los Angeles ◽  
Beta Lactam ◽  
Content Type

ABSTRACT Ceftolozane-tazobactam (C/T) and ceftazidime-avibactam (CZA) MICs were evaluated for a collection of 309 beta-lactam-resistant isolates of Pseudomonas aeruginosa recovered from three institutions in the area of Los Angeles, CA. Overall, 12.0% of isolates were susceptible to imipenem, 15.9% were susceptible to meropenem, 20.7% were susceptible to piperacillin-tazobactam, 24.6% were susceptible to ceftazidime, 25.9% were susceptible to cefepime, 72.5% were susceptible to C/T, and 61.8% were susceptible to CZA. Among C/T-resistant isolates, 9.1% were CZA susceptible, whereas 36.4% of CZA-resistant isolates were susceptible to C/T.

scholarly journals Assessment of 30/20-Microgram Disk Content versus MIC Results for Ceftazidime-Avibactam Tested against Enterobacteriaceae and Pseudomonas aeruginosa

2018 ◽  
Vol 56 (6) ◽  
Author(s):  
Helio S. Sader ◽  
Paul R. Rhomberg ◽  
Michael D. Huband ◽  
Ian A. Critchley ◽  
Gregory G. Stone ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Data Analysis ◽  
Error Rates ◽  
Disk Diffusion ◽  
Broth Microdilution ◽  
Content Type ◽  
Inhibition Zones ◽  
Challenge Group ◽  
The U.S

ABSTRACT We evaluated the correlation between MIC and disk diffusion inhibition zones when testing ceftazidime-avibactam, using the 30/20-μg disk and the disk diffusion and MIC breakpoints established by the U.S. FDA and the Clinical and Laboratory Standards Institute (CLSI). Organisms used included 2 groups of Enterobacteriaceae isolates and 2 groups of Pseudomonas aeruginosa isolates; 1 group of each consisted of randomly selected isolates and the second group consisted of a challenge group from thousands of surveillance isolates with an increased proportion of organisms displaying ceftazidime-avibactam MIC values close to the breakpoints. Broth microdilution, disk diffusion tests, and data analysis were performed according to reference standardized methods. Ceftazidime-avibactam breakpoints of ≤8/4 (susceptible) and ≥16/4 μg/ml (resistant) for MIC and ≥21/≤20 mm for disk diffusion, as established by the U.S. FDA and the CLSI, were applied for Enterobacteriaceae and P. aeruginosa . Ceftazidime-avibactam MIC and disk zone (30/20-μg disk) correlation were acceptable when testing Enterobacteriaceae (overall, very major [VM] and major [Ma] error rates of 0.4% and 0.0%, respectively) and nearly so when testing P. aeruginosa (2.3% VM and 2.9% Ma errors). In summary, disk diffusion and broth microdilution testing results demonstrated good categorical agreement for ceftazidime-avibactam against Enterobacteriaceae and P. aeruginosa , using 30/20-μg disks.

scholarly journals Multicenter Evaluation of the Etest Gradient Diffusion Method for Ceftolozane-Tazobactam Susceptibility Testing of Enterobacteriaceae and Pseudomonas aeruginosa

2018 ◽  
Vol 56 (9) ◽  
Author(s):  
Adam L. Bailey ◽  
Tom Armstrong ◽  
Hari-Prakash Dwivedi ◽  
Gerald A. Denys ◽  
Janet Hindler ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Susceptibility Testing ◽  
Clinical Isolates ◽  
Diffusion Method ◽  
Beta Lactam ◽  
Content Type ◽  
Gradient Diffusion ◽  
Tract Infections ◽  
Abdominal Infections ◽  
Inhibitor Combination

ABSTRACT Ceftolozane-tazobactam (C/T) is a novel beta-lactam–beta-lactamase inhibitor combination antibiotic approved by the U.S. Food and Drug Administration in 2014 for the treatment of complicated intra-abdominal infections (in combination with metronidazole) and complicated urinary tract infections. In this study, we evaluated the performance of the C/T Etest, a gradient diffusion method. C/T Etest was compared to broth microdilution (BMD) for 51 Enterobacteriaceae challenge isolates and 39 Pseudomonas aeruginosa challenge isolates at three clinical sites. Essential agreement (EA) between the methods ranged from 47 to 49/51 (92.2 to 96.1%) for the Enterobacteriaceae, and categorical agreement (CA) ranged from 49 to 51/51 (96.1 to 100.0%). EA and CA for P. aeruginosa were 100% at all sites. The C/T Etest was also compared to BMD for susceptibility testing on 966 clinical isolates (793 Enterobacteriaceae, including 167 Klebsiella pneumoniae and 159 Escherichia coli isolates, in addition to 173 P. aeruginosa isolates) collected at four clinical sites. EA between Etest and BMD was 96.9% for Enterobacteriaceae isolates and 98.8% for P. aeruginosa isolates. Within the Enterobacteriaceae, isolates from each species examined had >96% CA. For the clinical isolates, no very major errors were identified but two major errors were found (one for K. pneumoniae and one for Providencia rettgeri). By BMD, 47.0% of Enterobacteriaceae and 46.2% of P. aeruginosa challenge strains were nonsusceptible to C/T by CLSI breakpoint criteria; 8.2% of clinical Enterobacteriaceae isolates and 12.1% of clinical P. aeruginosa isolates were nonsusceptible to C/T by CLSI breakpoint criteria. In conclusion, Etest is accurate and reproducible for C/T susceptibility testing of Enterobacteriaceae and P. aeruginosa.

scholarly journals Correlation between Broth Microdilution and Disk Diffusion Results when Testing Ceftazidime-Avibactam against a Challenge Collection of Enterobacterales Isolates: Results from a Multilaboratory Study

2020 ◽  
Vol 58 (4) ◽  
Author(s):  
Helio S. Sader ◽  
Paul R. Rhomberg ◽  
Sukantha Chandrasekaran ◽  
Marisol Trejo ◽  
Kelley A. Fedler ◽  
...  
Keyword(s):  
Error Rates ◽  
Disk Diffusion ◽  
Broth Microdilution ◽  
Content Type ◽  
Inhibition Zones

ABSTRACT We assessed the ceftazidime-avibactam disk diffusion breakpoints that provide the lowest discrepancy error rates by testing an Enterobacterales isolate collection with ceftazidime-avibactam MIC values near the breakpoints. Isolates (n = 112) were susceptibility tested by broth microdilution and disk diffusion methods in 3 laboratories. Current disk diffusion breakpoints (≥21/≤20 mm for susceptible/resistant) provided the lowest error rates, but confirmatory MIC testing is indicated for isolates with inhibition zones of 20 to 22 mm.

scholarly journals Is a New Standard Needed for Diffusion Methods forIn VitroSusceptibility Testing of Fosfomycin against Pseudomonas aeruginosa?

2015 ◽  
Vol 60 (2) ◽  
pp. 1158-1161 ◽  
Author(s):  
María Díez-Aguilar ◽  
Laura Martínez-García ◽  
Rafael Cantón ◽  
María Isabel Morosini
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Reference Method ◽  
Inhibition Zone ◽  
Clinical Isolates ◽  
Disk Diffusion ◽  
Content Type ◽  
Agar Dilution

ABSTRACTWe analyzed fosfomycin susceptibility results inPseudomonas aeruginosaclinical isolates obtained by MIC gradient strips and disk diffusion methods using two different inocula, 108and 106CFU/ml, and compared them to the agar dilution reference method. Essential and categorical agreements were 93.6% and 95%, respectively, for the 106CFU/ml alternative inoculum, and they were 67.6% and 78.2%, respectively, for the standard inoculum (108CFU/ml). The use of the 106CFU/ml inoculum improves the agreement values and inhibition zone readings.

scholarly journals Regional Resistance Surveillance Program Results for 12 Asia-Pacific Nations (2011)

2013 ◽  
Vol 57 (11) ◽  
pp. 5721-5726 ◽  
Author(s):  
Rodrigo E. Mendes ◽  
Myrna Mendoza ◽  
Kirnpal K. Banga Singh ◽  
Mariana Castanheira ◽  
Jan M. Bell ◽  
...  
Keyword(s):  
Escherichia Coli ◽  
Staphylococcus Aureus ◽  
Pseudomonas Aeruginosa ◽  
Streptococcus Pneumoniae ◽  
South Korea ◽  
Geographic Region ◽  
Asia Pacific ◽  
Surveillance Program ◽  
Broth Microdilution ◽  
Content Type

ABSTRACTThe Regional Resistance Surveillance program monitored susceptibility rates and developing resistance by geographic region, including 12 Asia-Pacific (APAC) countries. Reference broth microdilution methods for susceptibility/interpretations were applied, processing 5,053 strains. AmongStaphylococcus aureusisolates (37% methicillin-resistantS. aureus[MRSA], highest in South Korea [73%]), linezolid (LZD), tigecycline (TIG), and vancomycin were 100% active, but 33 and 34% of strains were levofloxacin (LEV) or macrolide resistant, respectively.Streptococcus pneumoniaewas most resistant to β-lactams and macrolides (45%) but was LZD, LEV, and TIG susceptible (>98%). Extended-spectrum β-lactamase (ESBL) phenotype rates inEscherichia coliandKlebsiellaspp. were 48 and 47%, respectively, and were highest in Taiwan, at 75 to 91%. The best anti-ESBL-phenotype agents were amikacin (81 to 96% susceptible), colistin (COL; >98%), TIG (>98%), and carbapenems (81 to 97%).Pseudomonas aeruginosashowed ≥20% resistance to all drugs except COL (99% susceptible). In conclusion, endemic evolving antimicrobial resistances in APAC nations show compromised roles for many commonly used antimicrobials.

scholarly journals Effects of KPC Variant and Porin Genotype on the In Vitro Activity of Meropenem-Vaborbactam against Carbapenem-Resistant Enterobacteriaceae

2019 ◽  
Vol 63 (3) ◽  
Author(s):  
William R. Wilson ◽  
Ellen G. Kline ◽  
Chelsea E. Jones ◽  
Kristin T. Morder ◽  
Roberta T. Mettus ◽  
...  
Keyword(s):  
Susceptibility Testing ◽  
Disk Diffusion ◽  
Broth Microdilution ◽  
Wild Type ◽  
Content Type ◽  
E Coli ◽  
Carbapenem Resistant ◽  
Strip Testing ◽  
Carbapenem Resistant Enterobacteriaceae

ABSTRACT Meropenem-vaborbactam is a new agent with the potential to treat carbapenem-resistant Enterobacteriaceae (CRE) infections. We describe the in vitro activity of meropenem-vaborbactam against representative CRE genotypes and laboratory-engineered Escherichia coli isolates harboring mutant blaKPC genes associated with ceftazidime-avibactam resistance. We also compared disk diffusion and gradient strip testing methods to standard broth microdilution methods. Against 120 CRE isolates, median ceftazidime-avibactam and meropenem-vaborbactam MICs were 1 and 0.03 µg/ml, respectively. Ninety-eight percent (117/120) of isolates were susceptible to meropenem-vaborbactam (MICs ≤ 4 µg/ml). Against Klebsiella pneumoniae isolates harboring mutant blaKPC, the addition of vaborbactam lowered the meropenem MICs in 78% of isolates (14/18); 100% were susceptible to meropenem-vaborbactam. Median meropenem-vaborbactam MICs were higher against K. pneumoniae carbapenemase (KPC)-producing K. pneumoniae isolates with mutant ompK36 porin genes (n = 26) than against those with wild-type ompK36 porin genes (n = 54) (0.25 versus 0.03 µg/ml; P < 0.0001). Against E. coli TOP10 isolates with plasmid constructs containing wild-type blaKPC or mutant blaKPC, the addition of vaborbactam at 8 µg/ml lowered the meropenem MICs 2- to 512-fold, resulting in meropenem-vaborbactam MICs of 0.03 µg/ml. The rates of categorical agreement with broth microdilution for disk diffusion or gradient strips ranged from 90 to 95%. Essential agreement rates were higher for research-use-only (RUO) gradient strips manufactured by bioMérieux (82%) than for those manufactured by Liofilchem (48%) (P < 0.0001). Taken together, our data highlight the potent in vitro activity of meropenem-vaborbactam against CRE, including isolates resistant to ceftazidime-avibactam. Vaborbactam inhibited both wild-type and variant KPC enzymes. On the other hand, KPC-producing K. pneumoniae isolates with ompK36 mutations displayed higher meropenem-vaborbactam MICs than isolates with wild-type ompK36. The results of susceptibility testing with RUO bioMérieux gradient strips most closely aligned with those of broth microdilution methods.

scholarly journals Multicenter Evaluation of Colistin Broth Disk Elution and Colistin Agar Test: a Report from the Clinical and Laboratory Standards Institute

2019 ◽  
Vol 57 (11) ◽  
Author(s):  
Romney M. Humphries ◽  
Daniel A. Green ◽  
Audrey N. Schuetz ◽  
Yehudit Bergman ◽  
Shawna Lewis ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Antimicrobial Susceptibility ◽  
Susceptibility Testing ◽  
Polymyxin B ◽  
Antimicrobial Susceptibility Testing ◽  
Broth Microdilution ◽  
Content Type ◽  
Clinical Laboratories

ABSTRACT Susceptibility testing of the polymyxins (colistin and polymyxin B) is challenging for clinical laboratories. The Clinical and Laboratory Standards Institute (CLSI) Antimicrobial Susceptibility Testing Subcommittee evaluated two methods to enable accurate testing of these agents. These methods were a colistin broth disk elution (CBDE) and a colistin agar test (CAT), the latter of which was evaluated using two inoculum volumes, 1 μl (CAT-1) and 10 μl (CAT-10). The methods were evaluated using a collection of 270 isolates of Enterobacterales, 122 Pseudomonas aeruginosa isolates, and 106 Acinetobacter spp. isolates. Overall, 94.4% of CBDE results were in essential agreement and 97.9% in categorical agreement (CA) with reference broth microdilution MICs. Nine very major errors (VME; 3.2%) and 3 major errors (ME; 0.9%) were observed. With the CBDE, 98.6% CA was observed for Enterobacterales (2.5% VME, 0% ME), 99.3% CA was observed for P. aeruginosa (0% VME, 0.7% ME), and 93.1% CA was observed for Acinetobacter spp. (5.6% VME, 3.3% ME). Overall, CA was 94.9% with 6.8% VME using CAT-1 and improved to 98.3% with 3.9% VME using CAT-10. No ME were observed using either CAT-1 or CAT-10. Using the CAT-1/CAT-10, the CA observed was 99.4%/99.7% for Enterobacterales (1%/0.5% VME), 98.7%/100% for P. aeruginosa (8.3%/0% VME), and 88.5%/92.3% for Acinetobacter spp. (21.4%/14.3% VME). Based on these data, the CLSI antimicrobial susceptibility testing (AST) subcommittee endorsed the CBDE and CAT-10 methods for colistin testing of Enterobacterales and P. aeruginosa.

scholarly journals Cefiderocol Antimicrobial Susceptibility Testing against Multidrug-Resistant Gram-Negative Bacilli: a Comparison of Disk Diffusion to Broth Microdilution

2020 ◽  
Vol 59 (1) ◽  
pp. e01649-20 ◽  
Author(s):  
C. Paul Morris ◽  
Yehudit Bergman ◽  
Tsigedera Tekle ◽  
John A. Fissel ◽  
Pranita D. Tamma ◽  
...  
Keyword(s):  
Antimicrobial Susceptibility ◽  
Susceptibility Testing ◽  
Multidrug Resistant ◽  
Antimicrobial Susceptibility Testing ◽  
Disk Diffusion ◽  
Broth Microdilution ◽  
Gram Negative ◽  
Content Type ◽  
Carbapenem Resistant ◽  
Alternative Approach

ABSTRACTAntimicrobial susceptibility testing (AST) of cefiderocol poses challenges because of its unique mechanism of action (i.e., requiring an iron-depleted state) and due to differences in interpretative criteria established by the Clinical and Laboratory Standards Institute (CLSI), U.S. Food and Drug Administration (FDA), and European Committee on Antimicrobial Susceptibility Testing (EUCAST). Our objective was to compare cefiderocol disk diffusion methods (DD) to broth microdilution (BMD) for AST of Gram-negative bacilli (GNB). Cefiderocol AST was performed on consecutive carbapenem-resistant Enterobacterales (CRE; 58 isolates) and non-glucose-fermenting GNB (50 isolates) by BMD (lyophilized panels; Sensititre; Thermo Fisher) and DD (30 μg; research-use-only [RUO] MASTDISCS and FDA-cleared HardyDisks). Results were interpreted using FDA (prior to 28 September 2020 update), EUCAST, and investigational CLSI breakpoints (BPs). Categorical agreement (CA), minor errors (mE), major errors (ME), and very major errors (VME) were calculated for DD methods. The susceptibilities of all isolates by BMD were 72% (FDA), 75% (EUCAST) and 90% (CLSI). For DD methods, EUCAST BPs demonstrated lower susceptibility at 65% and 66%, compared to 74% and 72% (FDA) and 87% and 89% (CLSI) by HardyDisks and MASTDISCS, respectively. CA ranged from 75% to 90%, with 8 to 25% mE, 0 to 19% ME, and 0 to 20% VME and varied based on disk, GNB, and BPs evaluated. Both DD methods performed poorly for Acinetobacter baumannii complex. There is considerable variability when cefiderocol ASTs are interpreted using CLSI, FDA, and EUCAST breakpoints. DD offers a convenient alternative approach to BMD methods for cefiderocol AST, with the exception of A. baumannii complex isolates.

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