scholarly journals Comparative Evaluation of the VITEK 2, Disk Diffusion, Etest, Broth Microdilution, and Agar Dilution Susceptibility Testing Methods for Colistin in Clinical Isolates, Including Heteroresistant Enterobacter cloacae and Acinetobacter baumannii Strains

2007 ◽  
Vol 51 (10) ◽  
pp. 3726-3730 ◽  
Author(s):  
Jerome R. Lo-Ten-Foe ◽  
Anne Marie G. A. de Smet ◽  
Bram M. W. Diederen ◽  
Jan A. J. W. Kluytmans ◽  
Peter H. J. van Keulen
Keyword(s):  
Acinetobacter Baumannii ◽  
Susceptibility Testing ◽  
Enterobacter Cloacae ◽  
Clinical Isolates ◽  
Disk Diffusion ◽  
Broth Microdilution ◽  
Diffusion Test ◽  
Disk Diffusion Test ◽  
Agar Dilution ◽  
Vitek 2

ABSTRACT Increasing antibiotic resistance in gram-negative bacteria has recently renewed interest in colistin as a therapeutic option. The increasing use of colistin necessitates the availability of rapid and reliable methods for colistin susceptibility testing. We compared seven methods of colistin susceptibility testing (disk diffusion, agar dilution on Mueller-Hinton [MH] and Isosensitest agar, Etest on MH and Isosensitest agar, broth microdilution, and VITEK 2) on 102 clinical isolates collected from patient materials during a selective digestive decontamination or selective oral decontamination trial in an intensive-care unit. Disk diffusion is an unreliable method to measure susceptibility to colistin. High error rates and low levels of reproducibility were observed in the disk diffusion test. The colistin Etest, agar dilution, and the VITEK 2 showed a high level of agreement with the broth microdilution reference method. Heteroresistance for colistin was observed in six Enterobacter cloacae isolates and in one Acinetobacter baumannii isolate. This is the first report of heteroresistance to colistin in E. cloacae isolates. Resistance to colistin in these isolates seemed to be induced upon exposure to colistin rather than being caused by stable mutations. Heteroresistant isolates could be detected in the broth microdilution, agar dilution, Etest, or disk diffusion test. The VITEK 2 displayed low sensitivity in the detection of heteroresistant subpopulations of E. cloacae. The VITEK 2 colistin susceptibility test can therefore be considered to be a reliable tool to determine susceptibility to colistin in isolates of genera that are known not to exhibit resistant subpopulations. In isolates of genera known to (occasionally) exhibit heteroresistance, an alternative susceptibility testing method capable of detecting heteroresistance should be used.

scholarly journals Pseudo-Outbreak of Imipenem-Resistant Acinetobacter baumannii Resulting from False Susceptibility Testing by a Rapid Automated System

2000 ◽  
Vol 38 (9) ◽  
pp. 3505-3507 ◽  
Author(s):  
Athanassios Tsakris ◽  
Anastassia Pantazi ◽  
Spyros Pournaras ◽  
Antonios Maniatis ◽  
Aleka Polyzou ◽  
...  
Keyword(s):  
Acinetobacter Baumannii ◽  
General Hospital ◽  
Susceptibility Testing ◽  
Homogeneous Group ◽  
Susceptibility Test ◽  
Automated System ◽  
Disk Diffusion ◽  
Broth Microdilution ◽  
High Prevalence ◽  
Agar Dilution

Introduction of the Vitek GNS-506 susceptibility testing cards in the Hippokration General Hospital, Thessaloniki, Greece, resulted in an apparently high prevalence of imipenem-resistant Acinetobacter baumannii. When 35 of these isolates were further tested by disk diffusion, broth microdilution, and agar dilution assays, 32 were imipenem sensitive by all tests and three were sensitive or intermediate, depending on the method. The pseudoresistant acinetobacters did not form a genetically homogeneous group. It is suggested that the detection of imipenem-resistant A. baumannii isolates by this system should be confirmed by an additional susceptibility test.

scholarly journals Comparison of Different Phenotypic Approaches To Screen and Detect mecC-Harboring Methicillin-Resistant Staphylococcus aureus

2017 ◽  
Vol 56 (1) ◽  
Author(s):  
André Kriegeskorte ◽  
Evgeny A. Idelevich ◽  
Andreas Schlattmann ◽  
Franziska Layer ◽  
Birgit Strommenger ◽  
...  
Keyword(s):  
Staphylococcus Aureus ◽  
Susceptibility Testing ◽  
Disk Diffusion ◽  
Broth Microdilution ◽  
Disk Diffusion Test ◽  
Methicillin Resistant ◽  
Content Type ◽  
Vitek 2 ◽  
Cefoxitin Disk ◽  
Cefoxitin Disk Diffusion

ABSTRACT Similar to mecA, mecC confers resistance against beta-lactams, leading to the phenotype of methicillin-resistant Staphylococcus aureus (MRSA). However, mecC-harboring MRSA strains pose special difficulties in their detection. The aim of this study was to assess and compare different phenotypic systems for screening, identification, and susceptibility testing of mecC-positive MRSA isolates. A well-characterized collection of mecC-positive S. aureus isolates (n = 111) was used for evaluation. Routinely used approaches were studied to determine their suitability to correctly identify mecC-harboring MRSA, including three (semi)automated antimicrobial susceptibility testing (AST) systems and five selective chromogenic agar plates. Additionally, a cefoxitin disk diffusion test and an oxacillin broth microdilution assay were examined. All mecC-harboring MRSA isolates were able to grow on all chromogenic MRSA screening plates tested. Detection of these isolates in AST systems based on cefoxitin and/or oxacillin testing yielded overall positive agreements with the mecC genotype of 97.3% (MicroScan WalkAway; Siemens), 91.9% (Vitek 2; bioMérieux), and 64.9% (Phoenix, BD). The phenotypic resistance pattern most frequently observed by AST devices was “cefoxitin resistance/oxacillin susceptibility,” ranging from 54.1% (Phoenix) and 83.8% (Vitek 2) to 92.8% (WalkAway). The cefoxitin disk diffusion and oxacillin broth microdilution assays categorized 100% and 61.3% of isolates to be MRSA, respectively. The chromogenic media tested confirmed their suitability to reliably screen for mecC-harboring MRSA. The AST systems showed false-negative results with varying numbers, misidentifying mecC-harboring MRSA as methicillin-susceptible S. aureus. This study underlines cefoxitin's status as the superior surrogate mecC-positive MRSA marker.

scholarly journals Variation in erythromycin and clindamycin susceptibilities of Streptococcus pneumoniae by four test methods.

1997 ◽  
Vol 41 (1) ◽  
pp. 129-134 ◽  
Author(s):  
E L Fasola ◽  
S Bajaksouzian ◽  
P C Appelbaum ◽  
M R Jacobs
Keyword(s):  
Streptococcus Pneumoniae ◽  
Susceptibility Testing ◽  
Ambient Air ◽  
Test Methods ◽  
Disk Diffusion ◽  
Broth Microdilution ◽  
Microdilution Method ◽  
Broth Microdilution Method ◽  
Agar Dilution ◽  
Resistant Strains

Susceptibilities of 124 strains of Streptococcus pneumoniae to erythromycin and clindamycin were determined by the National Committee for the Clinical Laboratory Standards (NCCLS) broth microdilution method, with incubation for 20 to 24 h in ambient air and with modifications of this method by incubation for up to 48 h in air and CO2. Strains were also tested by agar dilution, E-test, and disk diffusion; good correlation was obtained with these methods, with clear separation into bimodal populations of susceptible and resistant stains. The broth microdilution method, however, using incubation in air for 24 h (NCCLS method), misclassified 4 of 92 erythromycin-resistant strains (1 as susceptible and 3 as intermediate) and 25 of 58 clindamycin-resistant strains (all as susceptible). With the exception of one strain with clindamycin, susceptible and resistant strains were correctly classified by the microdilution method with incubation in CO2 for 24 h or in ambient air for 48 h. Disk diffusion, agar dilution, and E-test methods with incubation in 5% CO2 are therefore reliable methods for susceptibility testing of pneumococci against these agents. However, the NCCLS microdilution method, which specifies incubation for 20 to 24 h in ambient air, produced significant very major errors (43%) clindamycin. Modification of the microdilution method by incubation in 5% CO2 or by extension of incubation time in ambient air to 48 h corrected these errors. Disk diffusion, however, was shown to be a simple, convenient, and reliable method for susceptibility testing of pneumococci to erythromycin and clindamycin and is suggested as the method of choice for these agents.

scholarly journals Ceftazidime-avibactam and Meropenem Double Disk Diffusion Test for Identifying Carbapanem-Resistant Enterobacteriaceae and Distinguishing Between Serine and Metallo-β-Lactamase Producing Organisms

2017 ◽  
Vol 4 (suppl_1) ◽  
pp. S375-S375
Author(s):  
Lynn-Yao Lin ◽  
Ian Critchley ◽  
David Melnick
Keyword(s):  
Enterobacter Cloacae ◽  
Disk Diffusion ◽  
Screening Methods ◽  
Diffusion Test ◽  
Disk Diffusion Test ◽  
Carbapenem Resistant ◽  
The Us ◽  
Susceptible Control ◽  
Carbapenem Resistant Enterobacteriaceae ◽  
Selection Of

Abstract Background Early detection of carbapenem-resistant Enterobacteriaceae(CRE) is crucial for selection of effective treatment. While KPC is the most prevalent carbapenemase in the US, phenotypic screening methods, such as the carbapenemase inactivation method (CIM) and CarbaNP, cannot easily distinguish between serine and metallo-β-lactamases (MBL). The aim of this study was to evaluate a simple double disk diffusion (DD) test to confirm carbapenem (meropenem) resistance (MER disk) and that resistance was due to a serine carbapenemase as indicated by susceptibility to ceftazidime-avibactam (CAZ-AVI disk). MBL-producing organisms are likely to be resistant to both MER and CAZ-AVI. Methods In total, 83 clinical isolates of Enterobacteriaceae were selected for the validation: 54 Klebsiella pneumoniae (KP), 16 Enterobacter cloacae (ECL) and 13 Escherichia coli (EC). All isolates were screened for specific β-lactamase genes (Checkpoints, Wageningen, Netherlands) and included KPC, OXA, IMP, VIM, NDM as well as strains with KPC and alterations on OmpK35 and OmpK36. Isolates were tested for susceptibility to MER and CAZ-AVI by disk diffusion and broth microdilution (BMD) per CLSI guidelines. Results were analyzed to evaluate suitability of the DD test to distinguish between serine and MBL-producing organisms. Results Overall correlation between disk and BMD was 97–100% for CAZ-AVI and 94–100% for MER. Among the 50 CRE that were susceptible to CAZ-AVI were strains positive for KPC, or OXA, or in combination with ESBLs. Among the 16 isolates that were resistant to both CAZ-AVI and MER were strains that produced MBLs such as IMP, VIM and NDM and included strains with alteration in OmpK35 and OmpK36. Among the 17 carbapenem-susceptible control strains all were susceptible to both agents and were positive for AmpC or ESBLs. Conclusion The CAZ-AVI and MER DD test was successful in confirming CRE phenotype and in distinguishing between serine carbapenemase-producing and MBL-producing organisms. The test will be useful in screening patients in future trials to evaluate the efficacy of CAZ-AVI in global CRE studies where MBL’s are more prevalent in other geographic regions. Both disks are commercially available and can be performed in most clinical laboratories. Disclosures L. Y. Lin, Allergan plc: Employee, Salary; I. Critchley, Allergan plc: Employee, Salary; D. Melnick, Allergan plc: Employee, Salary

scholarly journals In Vitro Activities of Fluconazole and Voriconazole against Clinical Isolates of Candida spp. Determined by Disk Diffusion Testing in Turin, Italy

2009 ◽  
Vol 53 (4) ◽  
pp. 1657-1659 ◽  
Author(s):  
Narcisa Mandras ◽  
Vivian Tullio ◽  
Valeria Allizond ◽  
Daniela Scalas ◽  
Giuliana Banche ◽  
...  
Keyword(s):  
Clinical Isolates ◽  
Disk Diffusion ◽  
In Vitro Activity ◽  
High Susceptibility ◽  
Diffusion Test ◽  
Candida Spp ◽  
Disk Diffusion Test ◽  
Disk Diffusion Testing ◽  
Fluconazole Resistant

ABSTRACT The in vitro activities of fluconazole and voriconazole against 1,024 clinical isolates of Candida spp. were determined by the agar disk diffusion test using the Clinical and Laboratory Standards Institute (CLSI) M44-A guidelines. The results of this investigation demonstrated the broad-spectrum in vitro activity of voriconazole, relative to that of fluconazole, against yeasts tested, in particular fluconazole-resistant isolates, such as Candida krusei that showed high susceptibility to voriconazole. The situation in Turin, Italy, is quite similar to that of the rest of Italy, reflecting the worldwide trend.

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