Methods for improved detection of oxacillin resistance in coagulase-negative staphylococci: results of a multicenter study

A multilaboratory study was undertaken to determine the accuracy of the current National Committee for Clinical Laboratory Standards (NCCLS) oxacillin breakpoints for broth microdilution and disk diffusion testing of coagulase-negative staphylococci (CoNS) by using a PCR assay for mecA as the reference method. Fifty well-characterized strains of CoNS were tested for oxacillin susceptibility by the NCCLS broth microdilution and disk diffusion procedures in 11 laboratories. In addition, organisms were inoculated onto a pair of commercially prepared oxacillin agar screen plates containing 6 microg of oxacillin per ml and 4% NaCl. The results of this study and of several other published reports suggest that, in order to reliably detect the presence of resistance mediated by mecA, the oxacillin MIC breakpoint for defining resistance in CoNS should be lowered from >/=4 to >/=0.5 microg/ml and the breakpoint for susceptibility should be lowered from /=18 mm for susceptibility is suggested. Due to the poor sensitivity of the oxacillin agar screen plate for predicting resistance in this study, this test can no longer be recommended for use with CoNS. The proposed interpretive criteria for testing CoNS have been adopted by the NCCLS.     

Activity of Gatifloxacin against Haemophilus influenzae and Moraxella catarrhalis, Including Susceptibility Test Development, E-Test Comparisons, and Quality Control Guidelines for H. influenzae

In vitro antimicrobial activity and susceptibility testing interpretation criteria and quality control were studied for gatifloxacin, a new 8-methoxy fluoroquinolone, tested against Haemophilus influenzae. Moraxella catarrhalis (600 strains) and H. influenzae (1,400 strains) from the SENTRY Antimicrobial Surveillance Program in North America (Canada and the United States) were also tested against gatifloxacin and 12 other antimicrobial agents. Gatifloxacin (MIC at which 90% of the isolates are inhibited [MIC90], /=18 mm) was also suggested for H. influenzae testing. No interpretive errors were observed. Quality control guidelines for H. influenzae ATCC 49247 were determined by using the NCCLS M23-T3 (1998) study design. The results from the nine-laboratory protocol suggested the following control ranges: for broth microdilution tests, 0.004 to 0.03 microg/ml; for disk diffusion testing, 33 to 41 mm. Gatifloxacin appears to be a potent anti-Haemophilus fluoroquinolone compound with in vitro testing interpretive criteria that will produce accurate results (disk diffusion, broth microdilution, and E-test).     

Comparison of Agar Dilution, Microdilution, E-Test, and Disk Diffusion Methods for Testing Activity of Cefditoren against Streptococcus pneumoniae

This study evaluated the susceptibility of pneumococci to cefditoren by agar dilution and microdilution methods (both in air) and by E-test (AB Biodisk, Solna, Sweden) and disk diffusion methods (both in CO(2)). By the three MIC tests, the MICs at which 50 and 90% of isolates were inhibited (MIC(50)s and MIC(90)s) were, respectively, as follows (in micrograms per milliliter): for the 65 penicillin-susceptible strains tested, 0.016 and 0.03 (by agar dilution), 0.016 and 0.03 (by microdilution), and 0.016 and 0.03 (by E test); for the 68 penicillin-intermediate strains tested, 0.125 and 0.5 (by agar dilution), 0.125 and 0.5 (by microdilution), and 0. 25 and 0.5 (by E test); and for the 67 penicillin-resistant strains tested, 1.0 and 1.0 (by agar dilution), 0.5 and 1.0 (by microdilution), and 1.0 and 1.0 (by E test). With tentative cefditoren breakpoints (in micrograms per milliliter) of /=8.0 (resistant), all strains were susceptible to cefditoren by agar, microdilution, and E-test results; with breakpoints of /=4.0 microg/ml, 97% of strains were cefditoren susceptible by agar dilution results, 98% were susceptible by microdilution results, and 99% were susceptible by E-test results. When microdilution and E-test results were compared to those from the reference agar dilution method, 191 (95.5%) and 183 (91.5%) of strains gave essential agreement (+/-1 log(2) dilution); 8 (2.7%) minor discrepancies were found for both methods with a breakpoint of /=20 (susceptible), 17 to 19 (intermediate), and /=16 mm (susceptible). All three methods for testing the MIC of cefditoren showed excellent correlation.     

Quality control guidelines for testing gram-negative control strains with polymyxin B and colistin (polymyxin E) by standardized methods

An eight-laboratory study addressed the urgent need for quality control (QC) ranges for susceptibility determination when testing colistin (polymyxin E) and polymyxin B, two polycationic peptide antimicrobial agents, against multidrug-resistant gram-negative bacilli. For Escherichia coli ATCC 25922l, the QC ranges were as follows: for colistin, 0.25 to 1 microg/ml (11 to 17 mm), and for polymyxin B, 0.25 to 2 microg/ml (13 to 19 mm). For Pseudomonas aeruginosa ATCC 27853, the QC ranges were as follows: for colistin, 0.25 to 2 microg/ml (11 to 17 mm), and for polymyxin B, 0.25 to 2 mug/ml (14 to 18 mm). More than 97% of all reported QC results were within these proposed ranges.     

Quality control guidelines for disk diffusion and broth microdilution antimicrobial susceptibility tests with seven drugs for veterinary applications

This multicenter study proposes antimicrobial susceptibility (MIC and disk diffusion methods) quality control (QC) parameters for seven compounds utilized in veterinary health. Alexomycin, apramycin, tiamulin, tilmicosin, and tylosin were tested by broth microdilution against various National Committee for Clinical Laboratory Standards (NCCLS)-recommended QC organisms (Staphylococcus aureus ATCC 29213, Enterococcus faecalis ATCC 29212, Streptococcus pneumoniae ATCC 49619, Escherichia coli ATCC 25922, and Pseudomonas aeruginosa ATCC 27853). In addition, disk diffusion zone diameter QC limits were determined for apramycin, enrofloxacin, and premafloxacin by using E. coli ATCC 25922, P. aeruginosa ATCC 27853, and S. aureus ATCC 25923. The results from five or six participating laboratories produced >/=99.0% of MICs and >/=95.0% of the zone diameters within suggested guidelines. The NCCLS Subcommittee for Veterinary Antimicrobial Susceptibility Testing has recently approved these ranges for publication in the next M31 document.     

In Vitro Studies with Cefotaxime: Disk Diffusion Susceptibility Tests

Until recently two sets of conflicting interpretive criteria existed for use with the standardized 30-mug cefotaxime diffusion disk [National Committee for Clinical Laboratory Standards (NCCLS) M2-A2S, supplement 1; product information package insert for Claforan (cefotaxime sodium), edition 10/81.] The latter criteria recently were superseded by a third set which differs radically from the first two in both minimal inhibitory concentration (MIC) and zone size breakpoints. The first two sets of criteria differed mainly in the zone of inhibition diameters used to predict resistant and intermediate organisms. The accuracies of these two sets of criteria were evaluated by paired agar dilution (World Health Organization-International Collaborative Study) and disk diffusion tests (Food and Drug Administration) with 347 clinical isolates of aerobic bacteria. A total of 274 isolates (79%) were clinically susceptible by agar dilution as defined by NCCLS (MIC /=64 mug/ml). The original product information package insert criteria proved to be most unreliable in identification of the intermediate organisms (zone of inhibition diameters of 18 to 22 mm); only 5 were correctly predicted as being intermediate, whereas 54 were predicted as being resistant, and 2 were predicted as being susceptible. In contrast, the NCCLS criteria (zone of inhibition diameter of 15 to 22 mm) predicted 41 as being intermediate and 18 as being resistant; again, 2 were susceptible. The 12 isolates resistant to cefotaxime by agar dilution were correctly predicted to be resistant by either set of breakpoints (zone of inhibition diameter of 相似文献   

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   

Tiamulin activity against fastidious and nonfastidious veterinary and human bacterial isolates: initial development of in vitro susceptibility test methods

Tiamulin is a pleuromutilin derivative used in veterinary practice for the control and specific therapy of infections in swine. This report summarizes studies to establish standardized susceptibility testing methods, interpretive criteria, and reagent details for use in veterinary methods recently developed by the National Committee for Clinical Laboratory Standards (NCCLS) (standards M31-A and M37-A, NCCLS, Wayne, Pa., 1999). A total of 636 fastidious and nonfastidious animal and human pathogens were processed by using media and procedures described by the NCCLS. Tiamulin disk diffusion tests used a 30-microg disk concentration, and the proposed MIC breakpoints corresponding to levels achievable in animal target tissues (lung) were < or =4 microg/ml for susceptibility and > or =32 microg/ml for resistance. Correlate zone diameters for specific nonfastidious species were as follows: for Pasteurella multocida and staphylococci tested on Mueller-Hinton agar, susceptibility at > or =19 mm and resistance at < or =11 mm, and for Actinobacillus suis, Erysipelothrix rhusiopathiae, and Streptococcus suis tested on enriched chocolate Mueller-Hinton agar, susceptibility at > or =16 mm and resistance at < or =8 mm. When Actinobacillus pleuropneumoniae was tested, a susceptibility breakpoint of < or =16 microg/ml (> or =9 mm) was suggested for veterinary fastidious medium broth and enriched chocolate Mueller-Hinton agar. Absolute categorical agreement between NCCLS dilution and disk diffusion test results with these criteria ranged from 90.5 to 96.2%. Tiamulin susceptibility testing methods appear to be accurate in their categorical classification for indicated species, and their availability will allow immediate testing of animal isolates to guide therapy via appropriate levels of dosing and to monitor the development of resistance for agents in this unique class.     

Evaluation of the NCCLS extended-spectrum beta-lactamase confirmation methods for Escherichia coli with isolates collected during Project ICARE

To determine whether confirmatory tests for extended-spectrum beta-lactamase (ESBL) production in Escherichia coli are necessary, we selected 131 E. coli isolates that met the National Committee for Clinical Laboratory Standards (NCCLS) screening criteria for potential ESBL production from the Project ICARE (Intensive Care Antimicrobial Resistance Epidemiology) strain collection. For all 131 isolates, the broth microdilution (BMD) MIC of at least one extended-spectrum cephalosporin was >/=2 micro g/ml. For 21 of 131 (16%) isolates, the ESBL confirmatory test was positive; i.e., the BMD MICs of ceftazidime or cefotaxime decreased by >/=3 doubling dilutions in the presence of clavulanic acid (CA) or the disk diffusion zone diameters increased by >/=5 mm around ceftazidime or cefotaxime disks in the presence of CA. All 21 isolates were shown by PCR to contain at least one of the genes bla(TEM), bla(SHV), and bla(OXA), and in isoelectric focusing (IEF) tests, all isolates demonstrated at least one beta-lactamase band consistent with a TEM, SHV, or OXA enzyme. Of the 21 isolates, 3 showed a CA effect for cefotaxime by BMD but not by disk diffusion testing. A total of 59 (45%) of the 131 isolates demonstrated decreased susceptibility to cefpodoxime alone (MIC = 2 to 4 micro g/ml), and none had a positive ESBL confirmatory test result. These were classified as false positives according to ESBL screen test results. For the remaining 51 (39%) isolates, the cefpodoxime MICs ranged from 16 to >128 micro g/ml and the MICs for the other extended-spectrum cephalosporins were highly variable. All 51 isolates gave negative ESBL confirmatory test results. Most showed IEF profiles consistent with production of both a TEM and an AmpC beta-lactamase, and representative isolates of several phenotypic groups showed changes in porin profiles; these 51 isolates were considered true negatives. In all, only 16% of 131 E. coli isolates identified as potential ESBL producers by the current NCCLS screening criteria were confirmed as ESBL producers. Thus, changing the interpretation of extended-spectrum cephalosporins and aztreonam results from the susceptible to the resistant category without confirming the presence of an ESBL phenotype would lead to a large percentage of false resistance results and is not recommended. However, by increasing the cefpodoxime MIC screening breakpoint to >/=8 micro g/ml, 45% of the false-positive results could be eliminated. NCCLS has incorporated this change in the cefpodoxime screening breakpoint in its recent documents.     

Detection of fluconazole-resistant Candida strains by a disc diffusion screening test

A commercial disc diffusion test has been evaluated as a screening method for the detection of Candida species with decreased susceptibility to fluconazole. A total of 1,407 Candida strains of different species were tested, and the results were compared with the MIC results. The recently published National Committee for Clinical Laboratory Standards breakpoint criteria have been used. Isolates were classified as susceptible if the MIC for the isolates was /=64 microg/ml. All 77 resistant strains and 121 of 122 S-DD strains had fluconazole zone diameters of 相似文献   

Antipneumococcal activity of telithromycin by agar dilution, microdilution, E test, and disk diffusion methodologies

Agar dilution and microdilution (both in air) and E test and disk diffusion (both in air and CO(2)) were used to test the activity of telithromycin against 110 erythromycin-susceptible and 106 erythromycin-resistant pneumococci. The MICs at which 50 and 90% of strains are inhibited (MIC(50)s and MIC(90)s, respectively) for erythromycin-susceptible strains varied between 0.008 and 0.016 microg/ml and 0.016 and 0.03 microg/ml when the samples were incubated in air. By comparison, telithromycin MIC(50)s and MIC(90)s for erythromycin-resistant strains were in air 0.03 to 0.125 and 0. 125 to 0.5 microg/ml, respectively. When agar dilution was used as the reference method, essential agreement was found for 112 of 216 strains (51.9%) for microdilution, 168 of 216 (77.8%) for E test in air, and 132 of 216 (61.1%) for E test in CO(2). With the exception of four strains tested by E test in CO(2), all organisms were susceptible to a proposed telithromycin susceptibility breakpoint of < or =1 microg/ml. By disk diffusion with 15-microg telithromycin disks, all strains but one had zones of inhibition > or =19 mm in diameter when incubated in CO(2), while all strains had zone diameters of > or = 22 mm when incubated in air. Zone diameters in air were generally 4 to 5 mm larger than in CO(2). By all methods, MICs and zones of all erythromycin-resistant strains occurred in clusters separated from those seen with erythromycin-susceptible strains. The results for macrolide-resistant strains with erm and mef resistance determinants were similar. The results show that (i) telithromycin is very active against erythromycin-susceptible and -resistant strains irrespective of macrolide resistance mechanism; (ii) susceptibility to telithromycin can be reliably tested by the agar, microdilution, E test, and disk diffusion methods; and (iii) incubation in CO(2) led to smaller zones by disk diffusion and higher MICs by E test, but at a susceptible MIC breakpoint of < or =1 microg/ml and a susceptible zone diameter cutoff of > or =19 mm in CO(2), 215 of 216 strains were found to be susceptible to telithromycin.     

Multicenter studies of tigecycline disk diffusion susceptibility results for Acinetobacter spp

Acinetobacter sp. isolates having multidrug resistance (MDR) patterns have become common in many medical centers worldwide, limiting therapeutic options. A five-center study tested 103 contemporary clinical Acinetobacter spp., including MDR strains, by reference broth microdilution and disk diffusion (15-mug disk content) methods against tigecycline. Applying U.S. Food and Drug Administration tigecycline breakpoint criteria for Enterobacteriaceae (susceptibility at < or =2 microg/ml [< or =1 microg/ml by the European Committee on Antimicrobial Susceptibility Testing]; disk diffusion breakpoints at > or =19 mm and < or =14 mm) to Acinetobacter spp. led to an unacceptable error rate (23.3%). However, an adjustment of tigecycline disk diffusion breakpoints (susceptible/resistant) to > or =16/ < or =12 mm reduced intermethod errors to an acceptable level (only 9.7%, all minor).     

Deciphering Polymyxin B Minimum Inhibitory Concentration from Colistin Minimum Inhibitory Concentration and Vice Versa: An Analysis on 156 Carbapenem-Resistant Enterobacteriaceae Isolates

The susceptibility determination to polymyxins (colistin and polymyxin B) remains a challenge for clinical microbiology laboratories. We evaluated the minimum inhibitory concentration (MIC) of both antimicrobials by the broth microdilution method in a selected subset of 156 carbapenem-resistant Enterobacteriaceae (CRE) isolates. Good concordance between polymyxin B and colistin MIC values was obtained, and there was 98% categorical agreement in CRE isolates. Future large-scale multicentre study is needed to draw conclusion if the MIC of colistin can be used to extrapolate the MIC of polymyxin B and vice versa.     

Use of an oxacillin disk screening test for detection of penicillin- and ceftriaxone-resistant pneumococci

In a context of worldwide emergence of resistance among Streptococcus pneumoniae strains, early detection of strains with decreased susceptibility to beta-lactam antibiotics is important for clinicians. If the 1-microgram oxacillin disk diffusion test is used as described by the National Committee for Clinical Laboratory Standards, no interpretation is available for strains showing zone sizes of /=2.0 microgram/ml) to penicillin. For ceftriaxone, among 98 strains with no zone of inhibition in response to oxacillin, 68 had intermediate resistance (MIC, 1.0 microgram/ml), and 22 were resistant (MIC, >/=2.0 microgram/ml). To optimize the use of the disk diffusion method, we propose that the absence of a zone of inhibition around the 1-microgram oxacillin disk be regarded as an indicator of nonsusceptibility to penicillin and ceftriaxone and recommend that such strains be reported as nonsusceptible to these antimicrobial agents, pending the results of a MIC quantitation method.     

Disk diffusion test interpretive criteria and quality control recommendations for testing linezolid (U-100766) and eperezolid (U-100592) with commercially prepared reagents.

Two new oxazolidinones were tested to determine interpretive susceptibility testing criteria for MIC and disk diffusion methods. Commercial lots of linezolid (formerly U-100766) and eperezolid (formerly U-100592) disks containing 30 microg of drug were tested against 728 isolates of bacteria with defined mechanisms of resistance. Results from linezolid were highlighted because of its choice for clinical development. By using preliminary pharmacokinetic data, a tentative susceptibility breakpoint of < or = 4 microg/ml was selected. Corresponding breakpoint zone diameters for linezolid were > or = 21 mm (< or = 4 microg/ml) for susceptibility and < or = 17 mm (> or = 16 microg/ml) for resistance. Regression statistics demonstrated a high correlation coefficient (r > or = 0.98), and absolute categorical agreement between methods was obtained, when staphylococci and enterococci were tested with the cited criteria. When Streptococcus spp. (including S. pneumoniae) were tested, only the susceptibility breakpoint was suggested. Quality control (QC) guidelines for linezolid disk diffusion tests were established by a multilaboratory trial as follows: 27 to 31 mm for Staphylococcus aureus ATCC 25923 and 28 to 34 mm for S. pneumoniae ATCC 49619. More than 95% of all QC results were within these proposed ranges. Although not advanced to clinical trials, eperezolid demonstrated potency comparable to that of linezolid and had identical interpretive testing criteria. These preliminary interpretive criteria and QC limits (accepted by the National Committee for Clinical Laboratory Standards) should be applied to linezolid tests during the clinical-trial phases of oxazolidinone drug development in order to ensure test accuracy and reproducibility.     

Fluconazole and voriconazole multidisk testing of Candida species for disk test calibration and MIC estimation

Fluconazole and voriconazole MICs were determined for 114 clinical Candida isolates, including isolates of Candida albicans, Candida glabrata, Candida krusei, Candida lusitaniae, Candida parapsilosis, and Candida tropicalis. All strains were susceptible to voriconazole, and most strains were also susceptible to fluconazole, with the exception of C. glabrata and C. krusei, the latter being fully fluconazole resistant. Single-strain regression analysis (SRA) was applied to 54 strains, including American Type Culture Collection reference strains. The regression lines obtained were markedly different for the different Candida species. Using an MIC limit of susceptibility to fluconazole of < or =8 microg/ml, according to NCCLS standards, the zone breakpoint for susceptibility for the 25-microg fluconazole disk was calculated to be > or =18 mm for C. albicans and > or =22 mm for C. glabrata and C. krusei. SRA results for voriconazole were used to estimate an optimal disk content according to rational criteria. A 5-microg disk content of voriconazole gave measurable zones for a tentative resistance limit of 4 microg/ml, whereas a 2.5-microg disk gave zones at the same MIC level for only three of the species. A novel SRA modification, multidisk testing, was also applied to the two major species, C. albicans and C. glabrata, and the MIC estimates were compared with the true MICs for the isolates. There was a significant correlation between the two measurements. Our results show that disk diffusion methods might be useful for azole testing of Candida isolates. The method can be calibrated using SRA. Multidisk testing gives direct estimations of the MICs for the isolates.     

Standardization of disk diffusion and agar dilution susceptibility tests for Neisseria gonorrhoeae: interpretive criteria and quality control guidelines for ceftriaxone, penicillin, spectinomycin, and tetracycline.

A six-laboratory study developed a standardized method for determining the susceptibilities of Neisseria gonorrhoeae strains to penicillin, tetracycline, spectinomycin, and ceftriaxone. Three quality control organisms were also selected, and quality assurance guidelines were initially generated for the disk diffusion and agar dilution methods. The medium recommended for gonococcal susceptibility testing was GC agar with a defined "XV-like" supplement. The supplement should be free of cysteine, a component implicated in the inactivation of some newer beta-lactam compounds. Penicillin, tetracycline, spectinomycin, and ceftriaxone were stable in agar plates stored at 3 to 5 degrees C for at least 2 weeks. Numerous GC agar and drug disk lots were used during the trials without significant variation in test results. Several other gonococcal strains were recommended for additional medium quality assurance. The disk quality control zone limits were established for N. gonorrhoeae ATCC 49226 (formerly CDC F-18) and Staphylococcus aureus ATCC 25923. MIC quality control ranges were also developed for N. gonorrhoeae ATCC 49226 and S. aureus ATCC 29213. The interpretive criteria for penicillin were as follows: susceptibility, greater than or equal to 47 mm (diameter of inhibition zone) (less than or equal to 0.06 micrograms/ml [MIC]); resistance, less than or equal to 26 mm (greater than or equal to 2 micrograms/ml). For tetracycline they were as follows: susceptibility, greater than or equal to 38 mm (less than or equal to 0.25 microgram/ml); resistance, less than or equal to 30 mm (greater than or equal to 2 micrograms/ml). For spectinomycin they were as follows: susceptibility, >/= 18 mm (/= 128 micrograms/ml). For ceftriaxone susceptibility, the criterion was >/= 35 mm (相似文献   

Preliminary evaluation of a semisolid agar antifungal susceptibility test for yeasts and molds

This report presents a semisolid agar antifungal susceptibility (SAAS) method for the rapid susceptibility screening of yeasts and molds. The reproducibility and accuracy of the SAAS method were assessed by comparing the MICs of amphotericin B and fluconazole obtained for 10 candidate quality control (QC) American Type Culture Collection yeast strains in >/=15 replicates with those found by six independent laboratories using the National Committee for Clinical Laboratory Standards (NCCLS) M27-P broth macrodilution method (M. A. Pfaller et al., J. Clin. Microbiol. 33:1104-1107, 1995). Overall, 96% of MICs for both drugs fell within 1 log(2) dilution of the modal MIC for each strain. The MICs for amphotericin B showed 99% agreement with the NCCLS proposed QC ranges within 1 log(2) dilution. Likewise, the MICs for fluconazole at >/=75% growth reduction showed 99% agreement for seven strains. Three strains, Candida albicans ATCC 24333 and ATCC 76615 and Candida tropicalis ATCC 750, showed a less sharp fluconazole endpoint at >/=75% growth reduction, but at >50% growth reduction, the agreement was 98% within 1 log(2) dilution of the proposed range. The MIC agreement within the proposed range for the suggested QC strains Candida parapsilosis ATCC 22019 and Candida krusei ATCC 6258 was 100% for fluconazole and 100% within 1 log(2) dilution of the proposed range for amphotericin B. The SAAS method demonstrated the susceptibility or resistance of 25 clinical isolates of filamentous fungi such as Aspergillus fumigatus to amphotericin B, itraconazole, and fluconazole, usually within 48 h. Although the results are preliminary, this SAAS method is promising as a rapid and cost-effective screen and is worthy of concerted investigation.     

Determination of disk diffusion and MIC quality control ranges for GSK1322322, a novel peptide deformylase inhibitor

GSK1322322 is a novel peptide deformylase inhibitor in the early phase of development for treatment of complicated bacterial skin and skin structure infection and hospitalized community-acquired pneumonia. This quality control (QC) study was performed to establish broth microdilution and disk diffusion QC ranges for strains Staphylococcus aureus ATCC 29213 (MIC range, 1 to 4 μg/ml), Haemophilus influenzae ATCC 49247 (MIC and disk diffusion zone diameter ranges, 0.5 to 4 μg/ml and 20 to 28 mm, respectively), Streptococcus pneumoniae ATCC 49619 (MIC and disk diffusion zone diameter ranges, 0.12 to 0.5 μg/ml and 23 to 30 mm, respectively), and S. aureus ATCC 25923 (disk diffusion zone diameter range, 18 to 26 mm). These ranges are crucial for evaluating GSK1322322 potency as it progresses through clinical trials.     

Investigation of ampicillin-intermediate strains of Haemophilus influenzae by using the disk diffusion procedure and current National Committee for Clinical Laboratory Standards guidelines.

It was noted in our laboratory that certain strains of Haemophilus influenzae yielded zone sizes interpreted as resistant to the ampicillin (AMP) disk on chocolate-Mueller-Hinton agar (CMH) but showed no evidence of beta-lactamase (beta-Lac) activity. Although it is known that a second mechanism of AMP resistance exists, strains with this mechanism are uncommon. To investigate this apparent discrepancy, a study of 100 consecutive clinical isolates of H. influenzae collected over a 6-month period was performed. Isolates were simultaneously tested against five antibiotics (AMP, chloramphenicol, cefotaxime, ciprofloxacin, and AMP-sulbactam) on CMH and on two brands of Haemophilus test medium (HTM) by using the disk diffusion procedure and National Committee for Clinical Laboratory Standards (NCCLS) standards. By using CMH and NCCLS standard M2-A3-S2, strains of H. influenzae showing zone sizes of greater than or equal to 20 mm with AMP were considered sensitive. By using HTM and NCCLS standard M2-A4, strains showing zone sizes of greater than or equal to 25 mm to AMP on HTM were considered sensitive. Intermediate strains had zone sizes of 22 to 24 mm. The majority of isolates (68%) were sensitive to all antibiotics. Two percent of the isolates were resistant to chloramphenicol. Seventeen percent of the isolates were AMP-resistant, beta-Lac-producing strains of H. influenzae. Thirteen percent of the isolates gave at least one intermediate or resistant zone for AMP but were beta-Lac negative. MIC determinations with NCCLS standard M7-A2 were performed with resistant and intermediate strains. MICs for beta-Lac-producing strains of H. influenzae were >/= 8.0 microgram/ml. MICs for beta-Lac-negative strains were 相似文献