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Biomedical subjects

A L Barry

Publications and source records attributed to A L Barry.

At least 325 records · Page 18Linked to original sources
PubMed1983

Disk agar diffusion susceptibility testing with 30-micrograms ceftazidime disks: confirmation of interpretive breakpoints and quality control guidelines.

Ceftazidime is a wide-spectrum, beta-lactamase-stable cephalosporin with remarkable potency against Pseudomonas spp., Enterobacteriaceae, and some gram-positive species. The reevaluation of the 30-micrograms ceftazidime disk diffusion tests with commercially prepared disks confirms the proposed susceptibility breakpoint zone of greater than or equal to 17 mm (minimal inhibitory concentration correlate, less than or equal to 8.0 micrograms/ml) and the resistance breakpoint zone of less than or equal to 13 mm (minimal inhibitory concentration correlate, greater than or equal to 32 micrograms/ml). Major and minor interpretive errors were only 4.4%, and these errors could be further reduced to 1.1% by not testing gram-positive organisms, particularly enterococci and Staphylococcus spp. On the basis of the results from a multilaboratory quality control study, the following zone diameter quality control guidelines are suggested: Escherichia coli ATCC 25922, 27 to 31 mm; Staphylococcus aureus, ATCC 25923, 16 to 20 mm; Pseudomonas aeruginosa ATCC 27853, 24 to 28 mm.

Agar↗
PubMed1983

Proposed zone standards for interpretation of fortimicin A disk diffusion tests.

Fortimicin A microdilution tests and disk diffusion tests (10-, 30-, and 50-micrograms disks) were performed with 454 selected bacterial strains. Tests with 30-micrograms disks were preferred, with zone standards of less than or equal to 14 mm of resistant strains (minimal inhibitory concentration, greater than 16 micrograms/ml) and greater than or equal to 17 mm for susceptible strains (minimal inhibitory concentration, less than 16 micrograms/ml).

Aminoglycosides↗
PubMed1983

Influence of inoculum growth phase on microdilution susceptibility tests.

Two types of commercially available microdilution trays were inoculated with log-phase cultures, stationary-phase cultures, and direct suspensions of 18- to 24-h colonies, with essentially comparable results. Direct pick-up of colonies was also tested with two Prompt inoculation systems (3M Co.); they were found to be convenient and reliable methods for standardizing inocula without preincubation in broth and without turbidity adjustment.

Ampicillin↗
PubMed1983

Quality control parameters for susceptibility tests with 30-micrograms netilmicin disks.

A nine-laboratory cooperative study was performed to evaluate quality control parameters for susceptibility tests with 30-micrograms netilmicin disks. The applicability of currently recommended zone-size limits was confirmed. However, alternative statistical methods suggested that tighter control limits might be more appropriate but would require better standardization of reagents, especially Mueller-Hinton agars.

Agar↗
PubMed1982

Direct comparison of two mechanized systems for identification of gram-negative bacilli. Autobac ID system versus the auto microbic system (with EBC plus).

The Auto Microbic System (AMS) is an almost completely automated system, capable of identifying Enterobacteriaceae after 8 hours, and some glucose nonfermenters after 13 hours of incubation. The Autobac ID system is a mechanized, computer-assisted system capable of identifying Enterobacteriaceae and many nonfermentative gram-negative bacilli within 3-6 hours. The present report combines the results of two independent studies, both of which evaluated the AMS and the Autobac ID system compared with standard reference tests. Among the 1,510 isolates that were tested, both systems reported equivocal identifications (low confidence values) with 5-6% of the strains. AMS produced fewer erroneous identifications (3.8% vs. 4.9%) but more equivocal test results (5.7% vs. 4.9%). Reproducibility of the two systems was compared by triplicate testing of 88 selected strains in both laboratories. AMS was somewhat more reproducible than the Autobac ID system. The AMS was capable of identifying more species with greater accuracy and reproducibility, but the Autobac ID system was more rapid. Both systems demonstrated excellent accuracy and reproducibility and both could be used efficiently in the clinical laboratory.

Bacterial Infections↗
PubMed1982

Cefotetan, a new cephamycin: comparison of in vitro antimicrobial activity with other cephems, beta-lactamase stability, and preliminary recommendations for disk diffusion testing.

Cefotetan is a new, potent, 7 alpha-methoxy cephalosporin (cephamycin). The in vitro activity of cefotetan tested in a multiphasic, collaborative study against 12,260 consecutive clinical isolates and 448 selected isolates showed 93% of Enterobacteriaceae, 90% of methicillin-susceptible Staphylococcus aureus (broth dilution), 83% of Bacteroides fragilis, and 72% of non-enterococcal streptococci to be inhibited by less than or equal to 8 micrograms/ml. Beta-Lactamase-producing and -nonproducing Haemophilus influenzae strains were inhibited by less than or equal to 1.0 micrograms/ml. Cefotetan's inhibitory spectrum paralleled those of the newest generation of cephems and exceeded those of cefoxitin and cefamandole. No useful activity was present against Streptococcus faecalis or Pseudomonas aeruginosa. Cefotetan was bactericidal without significant inoculum effect and was highly resistant to hydrolysis by Richmond-Sykes types I, III, and IV beta-lactamases. Hydrolysis of the chromogenic cephalosporin PADAC (pyridine-2-azo-p-dimethylaniline cephalosporin) by type I beta-lactamases was markedly inhibited by concentrations of cefotetan similar to those of the potent inhibitor dicloxacillin. Analysis of agar disk diffusion for several disk potencies and broth dilution susceptibility tests by regression and error rate-bounding methods produced preliminary tentative zone standards (30-micrograms disk, using minimal inhibitory concentration breakpoints of less than or equal to 8 micrograms/ml susceptible and greater than 32 micrograms/ml resistant, or 75-micrograms disk, using minimal inhibitory concentration breakpoints of less than or equal to 16 micrograms/ml susceptible and greater than or equal to 64 micrograms/ml resistant) of greater than or equal to 18 mm susceptible, less than or equal to 14 mm resistant, and 15 to 17 mm indeterminate. Staphylococcus aureus testing with the 30-micrograms disk is not recommended.

Anti-Bacterial Agents↗
PubMed1982

Identification of Enterobacteriaceae by the automicrobic system: Enterobacteriaceae biochemical cards versus Enterobacteriaceae-plus biochemical cards.

Enterobacteriaceae Biochemical Cards (EBC) may be used in the AutoMicrobic system for identification of enteric bacilli. Recently, the card has been modified to permit identification of enteric and certain nonenteric bacilli. Also, minor modifications have been in the computer program used for interpretation of tests with the new cards (EBC+). The two types of cards (EBC and EBC+) were tested in parallel and found to be in agreement with 97% of 650 Enterobacteriaceae. Most of the discrepancies were resolved when selected strains were retested on 3 separate days. A lack of absolute reproducibility with either system was demonstrated and explained most of the initial discrepancies. Approximately 97% of the AutoMicrobic system identifications agreed with those obtained from standard reference methods, after equivocal AutoMicrobic system results (P less than 0.80) were excluded. Equivocal responses occurred with 4% of our EBC tests and 7% of our EBC+ tests; additional tests are needed before such strains can be identified with confidence.

Bacteriological Techniques↗
PubMed1982

Sensitivity, specificity, and reproducibility of the automicrobic system (with the Enterobacteriaceae-plus biochemical card) for identifying clinical isolates of Gram- negative bacilli.

Two independent laboratories tested 1,743 clinical isolates by using the Enterobacteriaceae-plus Biochemical Card in the AutoMicrobic system (AMS) and identical standard reference methods. Included were 55 isolates representing 11 species that cannot be identified by the enterobacteriaceae-plus Biochemical Card computer program; 3 or these isolates were incorrectly identified as Pseudomonas cepacia. With the other 1,688 isolates, 5% of the AMS identifications were considered to be equivocal (probability value, less than 0.80), and the remaining test were 97% accurate (sensitive), Difficulty was observed in the ability of the AMS to identify some H2S-negative Citrobacter freundii species. An AMS response of P. cepacia was also considered nonspecific, because several other organisms were misidentified at P. cepacia. Reproducibility of the system was documented by testing 125 strains on 3-separate days; only 6 strains produced significantly variable results. The AMS (with the Enterobacteriaceae-plus Biochemical Card) was a very satisfactory, automated system for accurately identifying most gram-negative bacilli within 8 to 13 h.

Aeromonas↗
PubMed1982

Tentative interpretive standards for agar disk diffusion antimicrobial susceptibility testing of cefoperazone.

Cefoperazone is a new cephalosporin with a very wide spectrum of activity, including activity against Pseudomonas aeruginosa. It has less activity on enterococci and Acinetobacter. Of the 459 selected bacterial strains tested in this study, only 1.5% (7 strains and 6 genera) had minimum inhibitory concentrations of greater than or equal to 128 micrograms/ml. For a minimum inhibitory concentration breakpoint of less than or equal to 32 micrograms/ml (susceptible), we recommend that the disk diffusion test be done with a 75-micrograms disk and breakpoints of greater than or equal to 18 mm for susceptible, 15 to 17 mm for intermediate, and less than or equal to 14 mm for resistant. Diffusion tests using these criteria yielded only 1.1% very major or major errors.

Acinetobacter↗
PubMed1982

Cefoperazone disk diffusion susceptibility test: confirmation of the tentative interpretive criteria, Pseudomonas aeruginosa cross-resistance, and determination of quality control performance limits.

Cefoperazone disk diffusion test and minimum inhibitory concentration comparison studies were performed on 421 recent bacterial isolates, using 30- and 75-micrograms commercially prepared disks. Acceptable correlation coefficients (-0.82 to -0.86) and very major (false-susceptible) interpretive error rates (less than 1%) were obtained with both disk concentrations. The interpretive criteria for both disks were identical. Using the preferred 75-micrograms disk, the Thornsberry et al. criteria (J. Clin. Microbiol. 15:769-776, 1982) of greater than or equal to 18 mm = susceptible (less than or equal to 32 micrograms/ml) and less than or equal to 14 mm = resistant (greater than 64 micrograms/ml) resulted in only 5.5% of strains having indeterminate-range zone diameters; the 30-micrograms disk had 6.9% of strains with indeterminate zone diameters. The 75-micrograms disk, excluding the testing of enterococci, minimized the very major and other interpretive errors to less than 5%. Larger zone diameters will contribute few technical problems with either disk concentration. Data from 1,320 zone diameters submitted for each quality control strain indicated no significant (P greater than 0.05) difference between disks made by the three major manufacturers, and consistent results were obtained within each laboratory with numerous lots of Mueller-Hinton agar (except for one manufacturer). Individual daily test and accuracy quality control ranges were calculated from clinical investigator laboratory data at 16 hospitals based on mean zone sizes and from an additional 8 laboratories with both mean and median calculations. The quality control data were nearly identical, and ranges calculated by the two methods were very similar. Susceptibility tests of Pseudomonas aeruginosa indicate that the cefoperazone disk or minimum inhibitory concentration test would accurately predict P. aeruginosa susceptibility test results for other pseudomonas-active cephalosporins (cefsulodin and ceftazidime), thus producing no very major interpretive errors.

Cefoperazone↗
PubMed1982

In vitro evaluation of CENTA, a new beta-lactamase-susceptible chromogenic cephalosporin reagent.

CENTA is a newly synthesized, beta-lactamase-labile, chromogenic cephalosporin reagent which changes color from light yellow (lambda maximum ca. 340 nm) to chrome yellow (lambda maximum ca. 405 nm) concomitant with hydrolysis of the beta-lactam ring. This compound offers promise as a diagnostic reagent comparable to other chromogens (PADAC and nitrocefin) for the early detection of beta-lactamase-producing clinical isolates, while retaining some antimicrobial effect against Escherichia coli, Klebsiella spp., Proteus mirabilis, Staphylococcus aureus, and non-enterococcal Streptococcus spp. CENTA is relatively unaffected by commonly used microbiological media and human serum.

Bacteriological Techniques↗
PubMed1982

Accuracy and precision of the autobac system for rapid identification of Gram-negative bacilli: a collaborative evaluation.

Gram-negative bacilli were identified within 3 to 6 h by determining susceptibility to 18 different antibacterial agents in the Autobac I system and by applying a two-stage quadratic discriminant analysis to the susceptibility patterns. The Autobac system was compared with standard reference methods for identifying glucose nonfermenters and glucose fermenters. Intralaboratory and interlaboratory precision of the Autobac system was comparable to that of the reference methods. Sensitivity (accuracy) and specificity of the two systems were also comparable, although there were some differences with certain species. Autobac responses were considered to be equivocal (needing additional tests) if the relative probability of an accurate identification was less than 0.70. Only 5% of 2,889 strains produced such equivocal results; a similar number of strains gave low probability levels with the reference methods. When the two systems disagreed, an independent reference laboratory arbitrated, confirming 49% of the Autobac responses and 36% of the reference identifications. With equivocal responses excluded, the overall accuracy of the Autobac system was 95.3% compared with 95.9% for the reference method. The respective accuracy estimates would be 93.8% and 93.1% if all first-choice identifications were evaluated.

Anti-Bacterial Agents↗
PubMed1982

Azlocillin, a ureido penicillin active against Pseudomonas aeruginosa: interpretive zone standards and quality control parameters for tests with 75-mu g disks.

A nine-laboratory coordinated study was performed to establish tentative control limits for 75-mu g azlocillin disks tested against the standard control strain of Pseudomonas aeruginosa (ATCC 27853). Control limits for individual tests were 24 to 30 mm (25 to 29 mm for means of five separate tests). To establish interpretive zone standards for 75-mu g azlocillin disks, three separate laboratories each tested 93 strains of P. aeruginosa or related species. Geometric mean minimal inhibitory concentrations (MICs) were plotted against arithmetic mean zone diameters. Regression analyses were performed with zone diameter as the independent variable and also with MIC as the independent variable. The following interpretive categories were recommended: resistant, less than or equal to 14 mm (MIC, greater than 128 mu g/ml); intermediate, 15 to 17 mm (MIC, 128 mu g/ml); and susceptible, greater than or equal to 18 mm (MIC, less than or equal to 64 mu g/ml).

Azlocillin↗
PubMed1982

Evaluation of the MICUR system for quantitative antimicrobial susceptibility testing: a multiphasic comparison with reference methods.

Four laboratories participated in a three-phase study to evaluate the MICUR antimicrobial broth microdilution system (Boehringer Mannheim Diagnostics, Inc., Houston, Tex.). The dried-antimicrobial agent MICUR system was compared with a reference broth microdilution method (National Committee for Clinical Laboratory Standards) by using 304 recently isolated clinical strains and two collections of stock or challenge organisms. Of 7,092 minimum inhibitory concentration (MIC) datum pairs derived from the clinical isolates, 96.6% were within an acceptable (+/- 1 log2 dilution) range. MICUR MICs agreed with the reference broth microdilution method MICs in 95.3% of 6,840 MIC pair determinations performed on stock or challenge cultures. The MICUR intralaboratory reproducibility within +/- 1 log2 dilution step for the clinical isolates was 98.4%. The MICUR intralaboratory and interlaboratory reproducibilities for 26 stock cultures were 98.4 and 95.1%, respectively. For 180 challenge cultures (4,199 MIC pairs) which were included in the MICUR testing to provide a wide variety of antimicrobial susceptibility and resistance patterns, the results for 92.5% were in close agreement with the reference broth microdilution results. No specific resistance mechanism went unrecognized by this new commercial system. The MICUR system gives comparable MIC results when evaluated against the reference broth microdilution method, and it would be acceptable for use in clinical microbiology laboratories.

Anti-Bacterial Agents↗
PubMed1982

Collaborative evaluation of the micro-media systems anaerobe susceptibility panel: comparisons with reference methods and test reproducibility.

The Micro-Media Systems (MMS) anaerobe susceptibility testing panel results from four laboratories were compared for interlaboratory and intralaboratory variations and for the results with the reference agar dilution and a broth microdilution method. The interlaboratory agreement was 98.0% and intralaboratory agreement was 97.3% (+/- 1 log2 dilution). When interpretive criteria for each antimicrobial agent (susceptible, intermediate, and resistant) were assigned, the MMS anaerobic minimum inhibitory concentration data showed an interpretive accuracy of 91.0 and 95.5% for comparisons to the reference agar dilution and the broth methods, respectively. Most significant interpretive errors were considered minor, and nearly half of all errors involved tetracycline, a drug rarely used for serious anaerobic infections. The MMS anaerobe panels appear to be acceptable for selected use in clinical microbiology laboratories.

Anaerobiosis↗