Comparison of Eight Methods To Detect Vancomycin Resistance in Enterococci

A collection of genetically unrelated vancomycin-resistant enterococci (VRE) including 50 vanA, 15 vanB, 50 vanC1, and 30 vanC2 VRE were used to evaluate the accuracy of eight currently available susceptibility test methods (agar dilution, disk diffusion, E-test, agar screen plate, Vitek GPS-TA and GPS-101, and MicroScan overnight and rapid panels). vanA VRE were detected by all methods. vanB VRE were often not detected by Vitek GPS-TA and MicroScan rapid (sensitivities, 47 and 53%, respectively), though the new Vitek GPS-101 was found to be a significant improvement. E-test and the agar screen were the only two methods detecting all VRE, including the vanC1/C2 VRE.     

ROLE OF AZITHROMYCIN AGAINST CLINICAL ISOLATES OF FAMILY ENTEROBACTERIACEAE: A COMPARISON OF ITS MINIMUM INHIBITORY CONCENTRATION BY THREE DIFFERENT METHODS

Purpose: To determine the effect of azithromycin, a new azalide antibiotic, on clinical isolates of the family Enterobacteriaceae and to determine and compare its minimum inhibitory concentration (MIC) by disk diffusion, agar dilution and E-test methods. Materials and Methods: One hundred fifty-nine bacterial strains belonging to the family Enterobacteriaceae, isolated from different clinical samples, were tested for their susceptibility to azithromycin by disk diffusion, agar dilution and E-test methods. The MIC values were analysed and the percentages of agreement between the different methods were mentioned. Results: Of the 159 isolates of the family Enterobacteriaceae, 60.37% were E. coli followed by Klebsiella species 28.3%, Salmonella and Shigella species 3.77% and Enterobacter and Citrobacter species 1.88% each. Maximum isolates were obtained from urine 117/159 (73.58%). Azithromycin was found to be more active against Salmonella and Shigella species, showing 100% sensitivity the by E-test and 83.33% by the disk diffusion methods. In the agar dilution method, 83.33% of Salmonella and 66.66% of Shigella species were sensitive to azithromycin. The overall agreement between disk diffusion and agar dilution method was 96.8%, between agar dilution and E-test was 88% and between disk diffusion and E-test was 91.2%. Conclusion: Azithromycin may become an important addition to our antimicrobial strategies, especially for the treatment of bacterial diarrhoea and infections caused by Salmonella typhi.     

Comparison of the new MicroScan Pos MIC Type 6 panel and AMS-Vitek Gram Positive Susceptibility Card (GPS-TA) for detection of high-level aminoglycoside resistance in Enterococcus species.

We compared the MicroScan Pos MIC Type 6 panel and AMS-Vitek Gram Positive Susceptibility Card (GPS-TA) to agar dilution screen plates for the detection of high-level aminoglycoside resistance in 182 enterococcal isolates. The specificity of the two commercial systems was 100%, with the exception of one susceptible isolate found to be streptomycin resistant by the Vitek system. The MicroScan and Vitek systems had comparable sensitivities for the detection of gentamicin resistance (90 and 95% respectively) and streptomycin resistance (85 and 78%, respectively). These results suggest that screening tests such as agar dilution screen plates, broth dilution, or disk diffusion should continue to be used to detect high-level gentamicin and streptomycin resistance.     

Evaluation of three techniques for detection of low-level methicillin-resistant Staphylococcus aureus (MRSA): a disk diffusion method with cefoxitin and moxalactam,the Vitek 2 system,and the MRSA-screen latex agglutination test

Very-low-level methicillin-resistant Staphylococcus aureus (MRSA), or class 1 MRSA, is often misdiagnosed as methicillin-susceptible S. aureus (MSSA). We evaluated the performances of three methods for detection of low-level methicillin resistance: the disk diffusion method using the cephamycin antibiotics cefoxitin and moxalactam, the Vitek 2 system (bioMérieux), and the MRSA-screen test (Denka). Detection of the mecA gene by PCR was considered to be the "gold standard." We also determined the sensitivity of the oxacillin disk diffusion method with 5- and 1-microg disks and that of the Oxascreen agar assay with 6 mg of oxacillin liter(-1) for detection of MRSA. We compared the distributions of MICs of oxacillin and cefoxitin by the E-test (AB Biodisk), and those of moxalactam by dilutions in agar, for MRSA and MSSA isolates. The 152 clinical isolates of S. aureus studied were divided into 69 MSSA (mecA-negative) and 83 MRSA (mecA-positive) isolates, including 63 heterogeneous isolates and 26 class 1 isolates (low-level resistance). The cefoxitin and moxalactam disk diffusion tests detected 100% of all the MRSA classes: cefoxitin inhibition zone diameters were <27 mm, and moxalactam inhibition zone diameters were <24 mm. The Vitek 2 system and the MRSA-screen test detected 94 and 97.6% of all MRSA isolates, respectively. The sensitivities of the 5- and 1-microg oxacillin disks were 95.2 and 96.4%, respectively, whereas that of the Oxascreen agar screen assay was 94%. All of the tests except the 1-microg oxacillin disk test were 100% specific. For the class 1 MRSA isolates, the sensitivity of the Vitek 2 test was 92.3%, whereas those of the MRSA-screen test and the disk diffusion method with cefoxitin and moxalactam were 100%. Therefore, the cefoxitin and moxalactam disk diffusion methods were the best-performing tests for routine detection of all classes of MRSA.     

Interest of the disk diffusion method for screening Clostridium difficile isolates with decreased susceptibility to antibiotics

AimIn vitro determination of Clostridium difficile susceptibility to antibiotics is not routinely performed. The aim of this study was to evaluate the performance of antibiotic susceptibility determination with the disk diffusion method for screening C. difficile isolates with decreased susceptibility to antibiotics.MethodsThirty-six C. difficile isolates (toxigenic or not) isolated in 2005 and 2006 from three hospitals Assistance publique–Hôpitaux de Paris (Jean-Verdier, René-Muret, Beaujon) were studied by disk diffusion method with 14 antibiotics. Mueller-Hinton agar supplemented with sheep blood (Bio-Rad*) were swabbed with a C. difficile suspension at 1 McFarland. To check the results obtained with the disk diffusion method, Minimal Inhibitory Concentration (MIC) were performed respectively with E-test for glycopeptides and metronidazole and with the agar dilution reference method and E-test for new molecules with a potential activity against anaerobes: imipenem, ertapenem, linezolid and moxifloxacin.ResultsThe decreased susceptibility (resistant and intermediate) observed was 40% for amoxicillin–clavulanate, 60% for piperacillin–tazobactam, 100% for ceftriaxone, 81% for imipenem, 61% for ertapenem, 2% for chloramphenicol, 34% for erythromycin, 90% for lincomycin, 2% for linezolid, 98% for levofloxacin, 17% for moxifloxacin and 0% for vancomycin, teicoplanin and metronidazole. The results obtained with the disk diffusion method were compared to MICs obtained with E-test and reference method.ConclusionThe disk diffusion method seems to be a good method to detect isolates suspected to have a decreased susceptibility and consequently to reduce MIC determinations.     

Assessment of metronidazole susceptibility in Helicobacter pylori: statistical validation and error rate analysis of breakpoints determined by the disk diffusion test

Metronidazole susceptibility of 100 Helicobacter pylori strains was assessed by determining the inhibition zone diameters by disk diffusion test and the MICs by agar dilution and PDM Epsilometer test (E test). Linear regression analysis was performed, allowing the definition of significant linear relations, and revealed correlations of disk diffusion results with both E-test and agar dilution results (r2 = 0.88 and 0.81, respectively). No significant differences (P = 0.84) were found between MICs defined by E test and those defined by agar dilution, taken as a standard. Reproducibility comparison between E-test and disk diffusion tests showed that they are equivalent and with good precision. Two interpretative susceptibility schemes (with or without an intermediate class) were compared by an interpretative error rate analysis method. The susceptibility classification scheme that included the intermediate category was retained, and breakpoints were assessed for diffusion assay with 5-microg metronidazole disks. Strains with inhibition zone diameters less than 16 mm were defined as resistant (MIC > 8 microg/ml), those with zone diameters equal to or greater than 16 mm but less than 21 mm were considered intermediate (4 microg/ml < MIC 相似文献   

Evaluation of new Vitek 2 card and disk diffusion method for determining susceptibility of Staphylococcus aureus to oxacillin

Detection of methicillin resistance in Staphylococcus aureus is a challenge, especially low-level resistance, which is often misdiagnosed. The aim of this study was to compare the diagnostic accuracies of the automated Vitek 2 system and disk diffusion tests, using cefoxitin and moxalactam, for the detection of methicillin resistance in S. aureus strains. Four sets of genotypically diverse isolates were selected from a national reference collection, including mecA-negative S. aureus isolates (n = 56), hospital-acquired (n = 88) and community-acquired (n = 40) S. aureus isolates, and heterogeneous methicillin-resistant S. aureus isolates (n = 29). Oxacillin susceptibility was tested by the Vitek 2 system with the AST P549 card and by disk diffusion methods using 10, 30, and 60 microg cefoxitin and 30 microg moxalactam. Oxacillin resistance was confirmed by PCR for the mecA gene. The overall sensitivities for oxacillin resistance detection were 97.5% for the Vitek 2 automated system, 98.7% for 60-microg cefoxitin and moxalactam disk diffusion, and 99.6% for 10- and 30-microg cefoxitin disks, respectively. Methicillin-susceptible S. aureus isolates were correctly reported as susceptible by all methods. The median times for methicillin testing were 7 h for the Vitek 2 system versus 24 h for disk diffusion methods. In conclusion, the cefoxitin and moxalactam disk diffusion methods and the Vitek 2 automated system are highly accurate methods for methicillin resistance detection, including a range of representative Belgian methicillin-resistant S. aureus strains and unusual strains exhibiting cryptic or low-level oxacillin resistance.     

Evaluation of the Automated Vitek 2 System for Detection of Various Mechanisms of Macrolide and Lincosamide Resistance in Staphylococcus aureus

We evaluated the performance of the automated Vitek 2 system against disk diffusion for susceptibility testing of Staphylococcus aureus strains showing various resistance mechanisms to macrolides and lincosamides (ML). The Vitek 2 system showed 100% concordance with the D-zone test in detection of the most common resistance mechanisms to ML, including methylase and efflux systems.     

Comparison of susceptibility test methods to detect penicillin susceptibility in Streptococcus pneumoniae isolates

The increasing prevalence of penicillin-resistant Streptococuus pneumoniae urges for fast and accurate susceptibility testing methods. This study evaluated the comparability of three commonly used techniques; disk diffusion, E-test and agar dilution, to detect penicillin susceptibility in clinical isolates of S. pneumoniae. Fifty pneumococcal isolates, obtained from patients at the University of Malaya Medical Centre, were selected to include both penicillin-susceptible strains and those that had decreased susceptibility (resistant and intermediate) to penicillin. The minimum inhibitory concentration (MIC) values of penicillin to serve as the reference was determined by the agar dilution method in which, based on the MIC breakpoints recommended by the National Committee for Clinical Laboratory Standards (NCCLS), 27 strains had decreased susceptibility to penicillin with 17 strains resistant and 10 intermediate. Comparing to the agar dilution method, oxacillin disk diffusion test detected all strains with decreased penicillin susceptibility as such while E-test showed a close agreement of susceptibility (92%) of the isolates to penicillin. This confirmed that oxacillin is a good screening test for S. pneumoniae isolates with decreased susceptibility to penicillin while E-test is very reliable for rapid and accurate detection of penicillin susceptibility.     

Comparison of Agar Dilution, Disk Diffusion, MicroScan, and Vitek Antimicrobial Susceptibility Testing Methods to Broth Microdilution for Detection of Fluoroquinolone-Resistant Isolates of the Family Enterobacteriaceae

Fluoroquinolone resistance appears to be increasing in many species of bacteria, particularly in those causing nosocomial infections. However, the accuracy of some antimicrobial susceptibility testing methods for detecting fluoroquinolone resistance remains uncertain. Therefore, we compared the accuracy of the results of agar dilution, disk diffusion, MicroScan Walk Away Neg Combo 15 conventional panels, and Vitek GNS-F7 cards to the accuracy of the results of the broth microdilution reference method for detection of ciprofloxacin and ofloxacin resistance in 195 clinical isolates of the family Enterobacteriaceae collected from six U.S. hospitals for a national surveillance project (Project ICARE [Intensive Care Antimicrobial Resistance Epidemiology]). For ciprofloxacin, very major error rates were 0% (disk diffusion and MicroScan), 0.9% (agar dilution), and 2.7% (Vitek), while major error rates ranged from 0% (agar dilution) to 3.7% (MicroScan and Vitek). Minor error rates ranged from 12.3% (agar dilution) to 20.5% (MicroScan). For ofloxacin, no very major errors were observed, and major errors were noted only with MicroScan (3.7% major error rate). Minor error rates ranged from 8.2% (agar dilution) to 18.5% (Vitek). Minor errors for all methods were substantially reduced when results with MICs within ±1 dilution of the broth microdilution reference MIC were excluded from analysis. However, the high number of minor errors by all test systems remains a concern.     

Antipneumococcal Activities of Levofloxacin and Clarithromycin as Determined by Agar Dilution, Microdilution, E-Test, and Disk Diffusion Methodologies

The activities of levofloxacin and clarithromycin against 199 penicillin- and macrolide-susceptible and -resistant pneumococci were tested by agar and microdilution methods in air and by disk diffusion and E-test methods in air and CO₂. For levofloxacin, ≥99.0% of strains were susceptible at ≤2.0 μg/ml with zone diameters of ≥17 mm, regardless of incubation in air or CO₂. Although zone sizes were smaller and E-test MICs were higher for clarithromycin in CO₂ than those in air, category differences were minor, and susceptibility rates for clarithromycin were similar to those obtained by agar and microdilution in air (range, 76.9 to 80.9% by all methods). For clarithromycin, adjustment of breakpoints based upon distribution of results resulted in susceptibility rates which were similar by all methods (75.8 to 76.9% susceptible, 0 to 1.5% intermediate, 22.6 to 23.1% resistant). Minor discrepancies were obtained with levofloxacin for one strain (0.5%) by microdilution and two strains (1.0%) by disk diffusion in CO₂. For clarithromycin, minor discrepancies were found in three strains (1.5%) by microdilution, seven strains (3.5%) by agar dilution, four strains (2.0%) by E-test in air, six strains (3.0%) by disk diffusion in air, and five strains (2.5%) by disk diffusion in CO₂. Major discrepancies occurred with levofloxacin in one strain (0.5%) by microdilution but were not found with clarithromycin. Very major discrepancies were not seen with levofloxacin, but occurred with clarithromycin in five strains (2.5%) by microdilution, three strains (1.5%) by agar dilution, two strains (1.0%) by E-test in air, eight strains (4.0%) by disk diffusion in air, and one strain (0.5%) by disk diffusion in CO₂.     

Comparison of the AMS gram-negative susceptibility flex panel GNS-V and agar disk diffusion for testing of Pseudomonas aeruginosa.

Sixty Pseudomonas aeruginosa isolates were tested by the agar disk diffusion, AMS Vitek GNS-V flex panel (Vitek Systems, Inc., Hazelwood, Mo.), and agar dilution methods. Although the results of aminoglycoside tests were satisfactory, those of piperacillin and cefoperazone by Vitek GNS-V (T2.05 program) were not acceptable.     

Detection of Methicillin-Resistant Coagulase-Negative Staphylococci by the Vitek 2 System

The accurate performance of the Vitek 2 GP67 card for detecting methicillin-resistant coagulase-negative staphylococci (CoNS) is not known. We prospectively determined the ability of the Vitek 2 GP67 card to accurately detect methicillin-resistant CoNS, with mecA PCR results used as the gold standard for a 4-month period in 2012. Included in the study were 240 consecutively collected nonduplicate CoNS isolates. Cefoxitin susceptibility by disk diffusion testing was determined for all isolates. We found that the three tested systems, Vitek 2 oxacillin and cefoxitin testing and cefoxitin disk susceptibility testing, lacked specificity and, in some cases, sensitivity for detecting methicillin resistance. The Vitek 2 oxacillin and cefoxitin tests had very major error rates of 4% and 8%, respectively, and major error rates of 38% and 26%, respectively. Disk cefoxitin testing gave the best performance, with very major and major error rates of 2% and 24%, respectively. The test performances were species dependent, with the greatest errors found for Staphylococcus saprophyticus. While the 2014 CLSI guidelines recommend reporting isolates that test resistant by the oxacillin MIC or cefoxitin disk test as oxacillin resistant, following such guidelines produces erroneous results, depending on the test method and bacterial species tested. Vitek 2 cefoxitin testing is not an adequate substitute for cefoxitin disk testing. For critical-source isolates, mecA PCR, rather than Vitek 2 or cefoxitin disk testing, is required for optimal antimicrobial therapy.     

Comparison of the Vitek GPS-TB card with disk diffusion testing for predicting the susceptibility of enterococci to vancomycin.

OBJECTIVE: To compare the ability of the Vitek GPS-TB card with disk diffusion testing for determining the susceptibility of enterococci to vancomycin. DESIGN: Vitek susceptibility testing was performed using the GPS-TB card and software version R05.03. Disk diffusion susceptibility testing was performed according to National Committee for Clinical Laboratory Standards guidelines. When discrepancies occurred between the interpretation of Vitek and disk diffusion, both tests were repeated and the epsilometer test (E test) and agar screen containing 6 microgram/mL vancomycin were performed. RESULTS: Of 415 isolates tested, 313 were susceptible to vancomycin and 97 were resistant to vancomycin by both test methods. Two isolates were intermediate by Vitek and resistant by disk diffusion, 2 were intermediate by Vitek and susceptible by disk diffusion, and 1 was susceptible by Vitek and intermediate by disk diffusion. All but 1 of these latter 5 isolates (intermediate by Vitek and susceptible by disk diffusion) were available for retesting. On repeat testing, the 2 isolates that were intermediate by Vitek and resistant by disk diffusion were resistant by both methods, the 1 isolate that was intermediate by Vitek and susceptible by disk diffusion was susceptible by both methods, and the isolate that was susceptible by Vitek and intermediate by disk diffusion was also susceptible by both methods. These results were confirmed by E test and agar screen. CONCLUSION: We found the results of the GPS-TB card compared well with disk diffusion. However, isolates with intermediate results by Vitek should be retested using another method, such as the E test.     

Evaluation of the E Test for Antimicrobial Susceptibility Testing of Pseudomonas aeruginosa Isolates from Patients with Long-Term Bladder Catheterization

The E test was evaluated in comparison with reference agar methods (National Committee for Clinical Laboratory Standards) for the susceptibility testing of 248 Pseudomonas aeruginosa isolates from bladder-catheterized patients against nine antibiotics. The E-test MICs correlated well with those determined by the agar dilution and disk diffusion reference methods (88 and 92.5% within 1 log₂ dilution step, respectively), confirming that the E test is a reliable method for the determination of MICs of antibiotics for catheterization-associated P. aeruginosa isolates.     

Factors influencing determination of high-level aminoglycoside resistance in Enterococcus faecalis.

The ability of seven methods to detect high-level gentamicin (58 strains) and streptomycin resistance (56 strains) among 107 Enterococcus faecalis isolates was investigated at the University of Chicago Medical Center and the University of Nebraska Medical Center. Methods included a standard agar screen plate, high-content disk diffusion, Remel (Lenexa, Kans.) EF Synergy Quad plates, standard microdilution panels prepared in house, Pasco MIC Gram-Positive panels (Difco Laboratories, Detroit, Mich.), MicroScan MIC Type 5 dry panels (Baxter Healthcare Corp., MicroScan Div., West Sacramento, Calif.), and Vitek GPS-TA cards (Vitek Systems Inc., Hazelwood, Mo.). Results indicating false resistance were not obtained by any method, and there was 100% agreement between the results of the disk diffusion and standard agar screen methods. Prolonging incubation from 24 to 48 h increased resistance detection for both agar and microdilution screens. EF Synergy Quad plates inoculated with micropipettes detected 100% of the streptomycin- and gentamicin-resistant isolates. Resistance detection for streptomycin and gentamicin, respectively, was 93 and 96% by standard microdilution, 93 and 98% by Pasco panels, 88 and 89% by MicroScan panels, and 88 and 91% by Vitek GPS-TA cards. False susceptibility occurred more frequently with streptomycin-resistant isolates than it did with gentamicin-resistant strains and appeared to be strain related in some instances. The use of an increased inoculum size enhanced resistance detection with these strains, but it complicated interpretation of results and led to the selection of streptomycin-resistant mutants. Until results of further studies delineate optimum test conditions, a delay in the final interpretation of agar and microdilution screen results until 48 h for isolates showing no or light growth at 24 h may help to minimize the occurrence of false susceptibility reporting.     

Evaluation of Screening and Commercial Methods for Detection of Methicillin Resistance in Coagulase-Negative Staphylococci

The National Committee for Clinical Laboratory Standards recommends 48 h of incubation by the oxacillin salt agar screen (OSAS) method for the detection of methicillin-resistant coagulase-negative staphylococci (CoNS). An earlier identification of methicillin resistance is desirable. The time to detection of the mecA gene by PCR was compared with the times to detection by OSAS, by the oxacillin disk diffusion (ODD) method, and with MicroScan Gram Positive Combo type 6 panels (MicroScan Inc. Sacramento, Calif.) and Vitek GPS-SA cards (bioMérieux Vitek Inc., Hazelwood, Mo.). The combination of the Vitek card and the ODD method detected 92 of 99 methicillin-resistant strains of CoNS at 24 h; however, 6 mecA-positive strains were phenotypically methicillin susceptible. We conclude that most methicillin-resistant CoNS can be detected and the results can be reported after overnight incubation by a combination of methods.     

Misclassification of susceptible strains of Staphylococcus aureus as methicillin-resistant S. aureus By a rapid automated susceptibility testing system

Eight Staphylococcus aureus strains initially identified by Vitek GPS-BS or GPS-SA cards as resistant to oxacillin, but susceptible to most non-beta-lactam antibiotics, were found on further testing to be susceptible to oxacillin and ceftizoxime by disk diffusion tests. For all these strains, the MICs of oxacillin were 相似文献   

Coagulase-negative staphylococci: comparison of phenotypic and genotypic oxacillin susceptibility tests and evaluation of the agar screening test by using different concentrations of oxacillin

This study evaluated the oxacillin susceptibilities of 152 coagulase-negative staphylococcal (CoNS) strains of 12 species by disk diffusion; agar dilution; E-test; the slide latex agglutination test (Slidex MRSA Detection test; bioMérieux S/A, Paris, France); the agar screening test with 1, 2, 4, or 6 microg of oxacillin per ml and incubation for 24 or 48 h; and detection of the mecA gene by PCR. The results revealed that the agar screening test with 4 micro g of oxacillin per ml and incubation for 48 h was superior to any single phenotype-based susceptibility assay, presenting a sensitivity and a specificity of 100% each. For the different methods evaluated, the sensitivities and specificities were as follows: for disk diffusion, 94.2 and 91.8%, respectively; for the agar dilution test 100 and 73.5%, respectively; for E-test, 100 and 71.4%, respectively; and for the slide latex agglutination test, 97.1 and 98%, respectively. A good correlation was observed between oxacillin susceptibility testing results and PCR results for Staphylococcus epidermidis, S. haemolyticus, S. hominis subsp. hominis, and all mecA-positive strains. However, at least 60% of the mecA-negative isolates of the species S. saprophyticus, S. cohnii subsp. urealyticum, S. lugdunensis, and S. sciuri were erroneously classified as oxacillin resistant by the agar dilution test. Conversely, the slide latex agglutination test presented a high sensitivity (97.1%) and a high specificity (98%) for all CoNS species. Our results demonstrated the accuracy of the agar screening test with 4 micro g of oxacillin per ml and incubation for 48 h and the slide latex agglutination test for the appropriate detection of the oxacillin susceptibilities of CoNS isolates. Both assays are technically simple and can be easier to perform in routine laboratories than PCR.     

Comparison of workflow and accuracy of identification and antimicrobial susceptibility testing of clinical isolates of Enterobacteriaceae, Pseudomonas aeruginosa and enterococci by Vitek 2 and routine methods

Three hundred and fifty-three consecutive urine cultures growing Enterobacteriaceae, Pseudomonas aeruginosa or enterococci were subjected to parallel identification (ID) and antimicrobial susceptibility testing (AST) by Vitek 2 and routine methods, including simple screening tests or API 20 E for ID and standardized disc diffusion for AST. Accuracy of results, technician hands-on time required by both methods and time to results were compared. Vitek 2 correctly identified 322 (94.7%) of the 340 gram-negative isolates and 17 (81%) of the 21 Enterococcus faecalis strains. AST by Vitek 2 and disc diffusion gave category agreement for 4,058 (95.5%) of 4,248 organism-antimicrobial agent combinations. With MIC determination by E-test as reference, AST by Vitek 2 and disc diffusion produced 15 and 3 very major errors, respectively. Six (40%) of the fifteen very major errors by Vitek 2 were associated with trimethoprim-sulfamethoxazole. With an average of 22 specimens processed per day, use of Vitek 2 saved 80 min per day of technician hands-on time as compared to routine methods. Regarding the cost of hands-on worktime and consumables, use of Vitek 2 for identification of Escherichia coli-screened Enterobacteriaceae saved 0.70 p per sample in comparison to API 20 E. More than 80% of Enterobacteriaceae introduced to Vitek 2 in the morning could be reported by 16:00.