scholarly journals Comparative evaluation of broth microdilution with E-test, Vitek 2, and disk diffusion for susceptibility testing of colistin on Gram-negative bacteria

2021 ◽  
Vol 73 ◽  
pp. 93-98
Author(s):  
Parul Gupta ◽  
Rajni Sharma ◽  
Aruna Vyas ◽  
Amit Tak
Keyword(s):  
Gold Standard ◽  
Susceptibility Testing ◽  
Multidrug Resistant ◽  
Disk Diffusion ◽  
Broth Microdilution ◽  
Testing Methods ◽  
Geometric Means ◽  
Gram Negative ◽  
Vitek 2 ◽  
Good Concordance

Objectives: With the increasing threat of multidrug-resistant organisms, colistin has become popular in clinical practice. A better understanding of antimicrobial susceptibility testing methods for colistin is needed for optimal patient management. The aim of the study was to determine the accuracy of E-test, Vitek 2 system for the detection of colistin minimum inhibitory concentrations (MIC) against broth microdilution (BMD). Material and Methods: A total of 100 isolates of Gram-negative bacilli were subjected to susceptibility testing for colistin using the following methods: BMD, E-test, Vitek 2, and disk diffusion. Using BMD as the gold standard, comparative analysis between different methods was carried out. Results: Comparison of MIC values of E-test (GM = 0.488 mg/ml) against BMD (GM = 0.611 mg/ml using unpaired t-test (t = 2.015, P = 0.045) showed that geometric means of MIC values of E-strip were significantly lower than BMD. Similarly, comparison of MIC values of Vitek 2 system (GM = 0.615 mg/ml) against BMD (GM = 0.611 mg/ml) using unpaired t-test (t = −0.050, P = 0.960) showed no statistical significant differences in geometric means of MIC values. Taking reference as BMD method – the EA for E-strip is 57%, CA is 97%, VME is 2%, and no ME. Similarly, for the Vitek method EA is 64%, CA is 98%, VME is 1%, and ME is 1%. Conclusion: Different susceptibility testing methods for colistin show great variation in their results and BMD is the best candidate as gold standard. The Vitek 2 method showed good concordance with BMD.

scholarly journals Comparing Quantitative and Qualitative Methods for Detecting the In Vitro Activity of Colistin against Different Gram-Negative Bacilli

2021 ◽  
Vol 8 (5) ◽  
Author(s):  
Shams N ◽  
◽  
AlHiraky H ◽  
Moulana N ◽  
Riahi M ◽  
...  
Keyword(s):  
Bacterial Infections ◽  
Susceptibility Testing ◽  
High Sensitivity ◽  
Multidrug Resistant ◽  
Disk Diffusion ◽  
Broth Microdilution ◽  
Testing Methods ◽  
Gram Negative ◽  
Phenotypic Profile

The surge in the prevalence of Multidrug-Resistant (MDR) Gram-negative bacterial infections with limited treatment led to colistin reusing to treat MDR infections. This study aimed to determine economical, simple, and reliable colistin susceptibility testing methods as an alternative to the microdilution technique. We compared seven colistin susceptibility testing methods, including quantitative and qualitative, namely: Disk diffusion, E-test, ComASPTM SensiTest Colistin, Colistin broth disk elution, and colistin agar test CHROMagarTM COL-APSE, and BD Phoenix ID/AST automated identification and susceptibility testing system to the gold standard Broth Microdilution (BMD). Whole-genome sequencing was performed on all isolates to determine if the genetic resistant factors affect the phenotypic profile of the colistin resistance. Our results revealed that disk diffusion is still an ineffective method for measuring colistin susceptibility in Gram-negative Bacilli with the highest major error (31.75%), the lowest Kappa 0 (0%), and categorical agreement (68.25%) values. Phoenix, and CompASPTM SensiTest colistin methods have remained superior in reproducibility, sturdiness, and simplicity of use, similar to the currently recommended broth microdilution procedure; with high sensitivity of 95.56%, and 97.73%, specificity of 95.24, and 100%, and Kappa values of 0.89 and 0.95, respectively. This study revealed that Phoenix, and ComASPTM SensiTest colistin methods are recommended for routine microbiology laboratories with a large workload.

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.

scholarly journals Comparative performances of Vitek-2, Disk Diffusion, and Broth Microdilution for antimicrobial susceptibility testing of canine Staphylococcus pseudintermedius

2021 ◽  
Author(s):  
Elisa Rampacci ◽  
Michele Trotta ◽  
Caterina Fani ◽  
Serenella Silvestri ◽  
Valentina Stefanetti ◽  
...  
Keyword(s):  
Antimicrobial Susceptibility ◽  
Susceptibility Testing ◽  
Antimicrobial Susceptibility Testing ◽  
Disk Diffusion ◽  
Health Concern ◽  
Broth Microdilution ◽  
Major Error ◽  
Staphylococcus Pseudintermedius ◽  
Cutaneous Infections ◽  
Vitek 2

Staphylococcus pseudintermedius is the primary cause of canine cutaneous infections and sporadically isolated as pathogen from humans. Rapidly emerging antibiotic-resistant strains are creating serious health concern so that accurate and timely antimicrobial susceptibility testing (AST) is crucial for patient care. Here, the performances of AST methods Vitek-2, Disk Diffusion (DD) and Broth Microdilution (BMD) were compared for the determination of susceptibility of 79 S. pseudintermedius isolates from canine cutaneous infections and one from human pyoderma to oxacillin (OXA), amoxicillin/clavulanate (AMC), cephalothin (CEF), gentamicin (GEN), enrofloxacin (ENR), doxycycline (DOX), clindamycin (CLI), inducible clindamycin resistance (ICR), mupirocin (MUP) and trimethoprim-sulfamethoxazole (SXT). Overall, the agreement of DD and Vitek-2 using veterinary AST-GP80 card with reference BMD was ≥ 90%, suggesting reliable AST performances. While DD generated mainly minor errors and one major error for OXA, Vitek-2 produced one very major error for GEN and it failed in identifying one ICR-positive isolate. Moreover, five bacteria were diagnosed as ICR-positive by Vitek-2 but they showed a non-induction resistance phenotype by manual methods. All S. pseudintermedius were interpreted as susceptible or intermediately susceptible to DOX using CLSI breakpoints for human staphylococci that match the DOX concentration range included in AST-GP80. However, this could lead to inappropriate antimicrobial prescription for S. pseudintermedius infections in companion animals. Considering the clinical and epidemiological importance of S. pseudintermedius , we encourage updating action by the system manufacturer to address AST for this bacterium.

scholarly journals Aerococcus urinae and Aerococcus sanguinicola: Susceptibility Testing of 120 Isolates to Six Antimicrobial Agents Using Disk Diffusion (EUCAST), Etest, and Broth Microdilution Techniques

2017 ◽  
Vol 11 (1) ◽  
pp. 160-166 ◽  
Author(s):  
Derya Carkaci ◽  
Xiaohui C. Nielsen ◽  
Kurt Fuursted ◽  
Robert Skov ◽  
Ole Skovgaard ◽  
...  
Keyword(s):  
Antimicrobial Agents ◽  
Susceptibility Testing ◽  
Treatment Options ◽  
Disk Diffusion ◽  
Broth Microdilution ◽  
Testing Methods ◽  
European Committee ◽  
Aerococcus Urinae ◽  
Background Data ◽  
Tract Infections

Background: Aerococcus urinae and Aerococcus sanguinicola are relatively newcomers and emerging organisms in clinical and microbiological practice. Both species have worldwide been associated with urinary tract infections. More rarely cases of bacteremia/septicemia and infective endocarditis have been reported. Treatment options are therefore important. Just recently, European recommendations on susceptibility testing and interpretive criteria have been released. Objective: In this investigation 120 A. urinae and A. sanguinicola isolates were tested for susceptibility to six antimicrobial agents: Penicillin, cefotaxime, meropenem, vancomycin, linezolid, and rifampicin. Methods: Three susceptibility testing methods were used; disk diffusion according to The European Committee on Antimicrobial Susceptibility Testing (EUCAST) standardized disk diffusion methodology and MIC determination with Etest and broth microdilution (BMD). All testing was performed with EUCAST media for fastidious organisms. Results: Data obtained in this study were part of the background data for establishing EUCAST breakpoints. MIC values obtained by Etest and BMD were well correlated with disk diffusion results. Conclusion: All isolates were found susceptible to all six antimicrobial agents: penicillin, cefotaxime, meropenem, vancomycin, linezolid, and rifampicin.

scholarly journals Evaluation of cefiderocol activity for Gram-negative bacteria and performance of cefiderocol disk diffusion testing using multiple brands of Mueller Hinton Agar

2021 ◽  
Vol 156 (Supplement_1) ◽  
pp. S5-S5
Author(s):  
Robert Potter ◽  
Meghan Wallace ◽  
Carey-Ann Burnham
Keyword(s):  
Susceptibility Testing ◽  
Disk Diffusion ◽  
Resistant Bacteria ◽  
Clinical Microbiology Laboratory ◽  
Gram Negative Bacteria ◽  
Broth Microdilution ◽  
Gram Negative ◽  
Mueller Hinton ◽  
Significant Difference ◽  
Mueller Hinton Agar

Abstract Cefidericol is a cephalosporin-siderophore antibiotic for the treatment of multidrug resistant Gram-negative bacteria. Similar to other cephalosporin antibiotics, the lethal mechanism of action is due to inhibition of penicillin binding proteins leading to lysis of the bacteria. However, unlike previously developed antibiotics, the siderophore portion of cefidericol is able to bind iron and then be actively transported into the periplasmic space. To ascertain the feasibility of cefidericol antibiotic susceptibility testing in the Barnes-Jewish Clinical Microbiology Laboratory, we collected a cohort of multidrug Enterobacteriacae (5 Enterobacter cloace, 8 Escherichia coli, 12 Klebsiella pneumoniae), Pseudomonas aeruginosa (n=23), Stenotrophomonas maltophila (n=24), and Acinetobacter baumannii (n=25). We evaluated activity of cefidericol on these strains, and the performance of disk diffusion using three different brands of Mueller-Hinton Agar (BD, Hardy, and Remel). The reference method for comparison was an FDA-cleared broth microdilution panel containing cefidericol (ThermoFisher Scientific). Using CLSI breakpoints, we found that disk diffusion with BD agar had 96% categorical agreement for Enterobacterales, 100% for P. aeruginosa, 92% for A. baumannii, 96% for S. maltophila. We found that Hardy had 96% categorical agreement for Enterobacterales, 92% for P. aeruginosa, 92% for A. baumannii, 96% for S. maltophila. Finally, we found that Hardy had 96% categorical agreement for Enterobacterales, 92% for P. aeruginosa, 92% for A. baumannii, 96% for S. maltophila. Minor errors on any media never exceed 4% and there were no very major errors. Resistance to cefidericol within our cohort of selected antibiotic resistant bacteria was rare, one E. coli isolate and two P. aeruginosa isolates had minimal inhibitory concentrations (MICs) > 32 μg/mL. The highest MICs for one isolate of A. baumannii and one isolate S. maltophila was 8 μg/mL and 4 μg/mL, respectively, both of which were intermediate. There was no difference in the distribution of zone disk diffusion diameter for A. baumannii or Enterobacterales. However, there was a significant difference in the distribution of zone disk diffusion diameters for P. aeruginosa and S. maltophila on BD vs Hardy agar. The median for P. aeruginosa on BD is 25 mm while it is 29 mm on Hardy. The trend for S. maltophila is the opposite as the median for BD was 31.5 mm and 28.5 mm for Hardy. Use of FDA vs CLSI vs EUCAST breakpoints significantly changes outcome of susceptibility testing for broth microdilution and disk diffusion. As one example for broth microdilution of A. baumannii, we had one isolate intermediate using CLSI breakpoints, 4 resistant using EUCAST breakpoints, and 4 resistant and 3 intermediate isolates using FDA breakpoints. Our work demonstrates that cefedericol testing can be performed in a routine format, with certain organismal differences on Mueller-Hinton agar, and that different interpretative criteria significantly change outcomes.

scholarly journals Colistin and Polymyxin B Susceptibility Testing for Carbapenem-Resistant and mcr -Positive Enterobacteriaceae: Comparison of Sensititre, MicroScan, Vitek 2, and Etest with Broth Microdilution

2017 ◽  
Vol 55 (9) ◽  
pp. 2609-2616 ◽  
Author(s):  
Ka Lip Chew ◽  
My-Van La ◽  
Raymond T. P. Lin ◽  
Jeanette W. P. Teo
Keyword(s):  
Susceptibility Testing ◽  
Polymyxin B ◽  
Error Rates ◽  
Test Results ◽  
Broth Microdilution ◽  
Major Error ◽  
Testing Methods ◽  
Content Type ◽  
Carbapenem Resistant ◽  
Vitek 2

ABSTRACT Colistin and polymyxin B remain part of the last line of antibiotics for multidrug-resistant Gram-negative bacteria, such as carbapenem-resistant Enterobacteriaceae . Current joint EUCAST-CLSI recommendations are for broth microdilution (BMD) to be performed for MIC testing of colistin. Commercial susceptibility testing methods were evaluated and compared against the reference BMD, using a susceptibility breakpoint of ≤2 mg/liter for both colistin and polymyxin B. Seventy-six Enterobacteriaceae were included, of which 21 were mcr-1 positive (18 Escherichia coli isolates, 2 Klebsiella pneumoniae isolates, and 1 Enterobacter aerogenes isolate). Rates of essential agreement (EA) of colistin test results between BMD and Vitek 2, Sensititre, and Etest were 93.4%, 89.5%, and 75.0%, respectively. Rates of EA of polymyxin B test results between BMD and Vitek 2, Sensititre, and Etest were 96.1%, 96.1%, and 48.7%, respectively. A positive MIC correlation with a categorical agreement of >90% was achieved for Sensititre (colistin Spearman's ρ = 0.863, and polymyxin B Spearman's ρ = 0.877) and Vitek 2 (polymyxin B [only] Spearman's ρ = 0.8917). Although a positive MIC correlation (Spearman's ρ = 0.873) with the reference method was achieved for colistin testing with Vitek 2, categorical agreement was <90%, with very major error rates of 36%. Correlation with the Etest MIC was lower, with very major error rates of 12% (colistin) and 26.1% (polymyxin B). MicroScan (colistin) categorical agreement was 88.2%, with a very major error rate of 4%. Colistin MICs for 15 of the 21 mcr-1 -positive isolates were >2 mg/liter, and polymyxin MICs for 17 of them were >2 mg/liter by broth microdilution. The use of a lower breakpoint of ≤1 mg/liter further improves detection of mcr-1 for all testing methods. However, further data on the correlation between MICs and clinical outcome are required to determine the most suitable breakpoint to guide clinical management.

scholarly journals Increased Azithromycin Susceptibility of Multidrug-Resistant Gram-Negative Bacteria on RPMI-1640 Agar Assessed by Disk Diffusion Testing

Antibiotics ◽  
2020 ◽  
Vol 9 (5) ◽  
pp. 218 ◽  
Author(s):  
Milton Meerwein ◽  
Andrea Tarnutzer ◽  
Michelle Böni ◽  
Françoise Van Bambeke ◽  
Michael Hombach ◽  
...  
Keyword(s):  
Bacterial Infections ◽  
Low Complexity ◽  
Multidrug Resistant ◽  
Disk Diffusion ◽  
Gram Negative Bacteria ◽  
Broth Microdilution ◽  
Gram Negative ◽  
Minimal Inhibitory Concentrations ◽  
Mueller Hinton

Increasing antibiotic resistances and a lack of new antibiotics render the treatment of Gram-negative bacterial infections increasingly difficult. Therefore, additional approaches are being investigated. Macrolides are not routinely used against Gram-negative bacteria due to lack of evidence of in vitro effectiveness. However, it has been shown that Pseudomonas spp. are susceptible to macrolides in liquid RPMI-1640 and clinical data suggest improvement in patients’ outcomes. So far, these findings have been hardly applicable to the clinical setting due to lack of routine low-complexity antimicrobial susceptibility testing (AST) for macrolides. We therefore optimized and compared broth microdilution and disk diffusion AST. Multidrug-resistant Gram-negative bacteria (Escherichia coli, Enterobacter cloacae, Klebsiella pneumoniae, Pseudomonas aeruginosa) were tested for azithromycin susceptibility by disk diffusion and broth microdilution in Mueller–Hinton and RPMI-1640 media. Azithromycin susceptibility of Enterobacteriaceae and a subgroup of P. aeruginosa increased significantly on RPMI-1640 agar compared to Mueller–Hinton agar. Further, a significant correlation (Kendall, τ, p) of zone diameters and minimal inhibitory concentrations (MICs) was found on RPMI-1640 agar for E. coli (−0.4279, 0.0051), E. cloacae (−0.3783, 0.0237) and P. aeruginosa (−0.6477, <0.0001). Performing routine disk diffusion AST on RPMI-1640 agar may lead to the identification of additional therapeutic possibilities for multidrug-resistant bacterial infections in the routine clinical diagnostic setting.

scholarly journals 710. In Vitro Activity and Performance of Available Susceptibility Testing Methods for Eravacycline Against Carbapenem-Resistant Enterobacteriaceae (CRE)

2019 ◽  
Vol 6 (Supplement_2) ◽  
pp. S319-S320
Author(s):  
Chelsea E Jones ◽  
Ellen G Kline ◽  
Minh-Hong Nguyen ◽  
Cornelius J Clancy ◽  
Ryan K Shields
Keyword(s):  
Susceptibility Testing ◽  
Multidrug Resistant ◽  
Vitro Activity ◽  
Clinical Isolates ◽  
Disk Diffusion ◽  
In Vitro Activity ◽  
Testing Methods ◽  
And Performance ◽  
Susceptibility Breakpoint

Abstract Background Eravacycline (ERV) is a recently-approved, fully synthetic fluorocycline agent that demonstrates broad in vitro activity against multidrug-resistant pathogens. We sought to compare the activity of ERV with minocycline (MIN) and tigecycline (TGC) against diverse CRE clinical isolates, and to evaluate the performance of commercially-available susceptibility testing methods. Methods ERV, MIN, and TGC minimum inhibitory concentrations (MICs) were determined in triplicate by broth microdilution against previously characterized CRE isolates. ERV susceptibility was also measured by disk diffusion (20 µg disk; Mast Group) and MIC test strips (MTS; Liofilchem) according to manufacturer instructions. Results 148 CRE were tested, including 92 K. pneumoniae, 32 Enterobacter spp, 11 E. coli, 5 C. freundii, 4 K. oxytoca, and 4 S. marcescens. 72% of isolates harbored blaKPC, which encoded KPC-2 (n = 33), KPC-3 (n = 48), and other KPC variants (n = 22). 77% and 19% of isolates were resistant to meropenem and ceftazidime–avibactam, respectively. By BMD, the ERV, MIN, and TGC MIC range, MIC50 and MIC90 for shown in the Table. ERV MICs were ≥2-fold lower than MIN and TGC against 99% and 43% of isolates, respectively. ERV MICs did not vary by species or KPC-subtype. ERV MICs determined by BMD and MTS were well-correlated showing 89% essential agreement (MIC within one 2-fold dilution; Figure). The rate of categorical agreement (CA) was 73%. By comparison, the CA rate between BMD and disk diffusion was 78%. By both MTS and disk diffusion methods, susceptibility results clustered on either side of the susceptibility breakpoint. 50% of disk diffusion zones clustered between 14 and 16 millimeters (mm), which is 1 mm on either side of the susceptibility breakpoint (≥15 mm). Conclusion This study confirms the in vitro activity of ERV against CRE clinical isolates, which is comparable to TGC. ERV MTS demonstrated high rates of EA, but lower rates of CA. Clinicians should be aware of the nuances of ERV susceptibility testing and recognize that the modal distribution of ERV MICs against CRE lies on either side of the susceptibility breakpoint. Disclosures All authors: No reported disclosures.

scholarly journals Performance of Four Fosfomycin Susceptibility Testing Methods against an International Collection of Clinical Pseudomonas aeruginosa Isolates

2020 ◽  
Vol 58 (10) ◽  
Author(s):  
Elizabeth C. Smith ◽  
Hunter V. Brigman ◽  
Jadyn C. Anderson ◽  
Christopher L. Emery ◽  
Tiffany E. Bias ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Susceptibility Testing ◽  
Wide Spectrum ◽  
Multidrug Resistant ◽  
Supporting Evidence ◽  
Broth Microdilution ◽  
Testing Methods ◽  
Content Type ◽  
E Coli ◽  
Agar Dilution

ABSTRACT Fosfomycin has been shown to have a wide spectrum of activity against multidrug-resistant Gram-negative bacteria; however, breakpoints have been established only for Escherichia coli or Enterobacterales per the Clinical and Laboratory Standards Institute (CLSI) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST), respectively. A lack of additional organism breakpoints limits clinical use of this agent and has prompted extrapolation of these interpretive categories to other organisms like Pseudomonas aeruginosa without supporting evidence. Further complicating the utility of fosfomycin is the specified method for MIC determination, namely, agar dilution, which is not widely available and is both labor and time intensive. We therefore sought to determine the susceptibility of a large international collection of P. aeruginosa isolates (n = 198) to fosfomycin and to compare testing agreement rates across four methods: agar dilution, broth microdilution, disk diffusion, and Etest. Results were interpreted according to CLSI E. coli breakpoints, with 49.0 to 85.8% considered susceptible, dependent upon the testing method used. Epidemiological cutoff values were calculated and determined to be 256 μg/ml and 512 μg/ml for agar dilution and broth microdilution, respectively. Agreement rates were analyzed using both agar dilution and broth microdilution with a resulting high essential agreement rate of 91.3% between the two susceptibility testing methods. These results indicate that broth microdilution may be a reliable method for fosfomycin susceptibility testing against P. aeruginosa and stress the need for P. aeruginosa-specific breakpoints.

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