Biomedical subjects

T L Gavan

Publications and source records attributed to T L Gavan.

At least 37 records · Page 2Linked to original sources

PubMed1985

Interpretive standards and quality control guidelines for cefpiramide disk susceptibility tests.

Disk susceptibility tests with 30- and 75-micrograms cefpiramide disks were evaluated with 614 bacterial isolates. Quality control parameters were also evaluated, and control limits for disk tests are recommended. Tests with 75-micrograms disks are recommended, with zone size standards of greater than or equal to 19 mm for susceptible (MIC, less than or equal to 32 micrograms/ml) and less than or equal to 15 mm for resistant (MIC, greater than or equal to 128 micrograms/ml).

Cephalosporins↗

PubMed1984

3-0-demethyl fortimicin A: in vitro activity and interpretive zone standards for disk diffusion susceptibility tests.

The in vitro activity of 3-0-demethyl fortimicin A was compared to that of amikacin and tobramycin against 5,230 clinical isolates in four institutions. Amikacin and tobramycin were more active than 3-0-demethyl fortimicin A against Pseudomonas aeruginosa and Acinetobacter spp., but all three drugs had similar activity against the Enterobacteriaceae and Staphylococcus aureus. Additional tests with 335 representative gram-negative bacilli compared five different aminoglycosides, demonstrating differences with some isolates. Standardized disk diffusion tests were also performed with 30 micrograms 3-0-demethyl fortimicin A disks, according to the National Committee for Clinical Laboratory Standards. The following interpretive breakpoints are proposed: less than or equal to 11 mm for resistant (MIC greater than or equal to 32 micrograms/ml) and greater than or equal to 15 mm for susceptible (MIC less than or equal to 16 micrograms/ml).

Acinetobacter↗

PubMed1984

In vitro activity of ticarcillin plus clavulanic acid against bacteria isolated in three centers.

Over 10,000 bacterial isolates were tested against ticarcillin alone or combined with clavulanic acid (2.0 micrograms/ml). Of 5,295 Enterobacteriaceae, 72% were susceptible to ticarcillin alone, whereas 91% were susceptible to the combination. Bacteroides fragilis and Bacteroides melaninogenicus isolates were more susceptible to the combination. The activity of ticarcillin against other microorganisms was not profoundly influenced.

Anti-Bacterial Agents↗

PubMed1984

In vitro activity of apalcillin compared with those of piperacillin and carbenicillin against 6,797 bacterial isolates from four separate medical centers.

Quantitative susceptibility tests were performed in four separate medical centers, in which apalcillin was compared with piperacillin and carbenicillin. Data from tests of 6,797 isolates confirmed that apalcillin and piperacillin had nearly identical spectra of activity but that apalcillin was significantly more active against Pseudomonas aeruginosa (MIC required to inhibit 90% of strains, 2.0 versus 64 micrograms/ml) and Acinetobacter calcoaceticus subsp. anitratus (MIC required to inhibit 90% of strains, 2.0 versus 16 micrograms/ml). Against 166 anaerobic bacterial isolates, apalcillin demonstrated in vitro activity.

Ampicillin↗

PubMed1984

Interpretive criteria and tentative quality control limits for apalcillin disk susceptibility tests.

In vitro studies with 661 bacterial isolates were performed to establish interpretive criteria. In addition, a nine-laboratory study was performed to establish quality control limits for tests with 100-micrograms apalcillin disks and to confirm testing criteria for tests with 100-micrograms piperacillin disks. The two drugs were very similar, and nearly identical criteria were recommended for interpretation and for control of the two types of disks. Neither disk is recommended for testing Staphylococcus spp. or Haemophilus spp.; with other microorganisms, zone size limits of less than or equal to 13 mm (resistant) and greater than or equal to 18 mm (susceptible) are proposed for tests with 100-micrograms apalcillin disks.

Ampicillin↗

PubMed1984

Disk diffusion testing, quality control guidelines, and antimicrobial spectrum of HR810, a fourth-generation cephalosporin, in clinical microbiology laboratories.

HR810 is a new, very broad-spectrum cephalosporin with significant activity against members of the family Enterobacteriaceae, pseudomonads, gram-positive cocci, and anaerobes that is generally greater than the third-generation cephalosporins (99.6% of 4,128 clinical facultative enteric isolates were inhibited by less than or equal to 8.0 micrograms of HR810 per ml). Tests and statistical methods to establish in vitro antimicrobial susceptibility test criteria favor tentative breakpoints of greater than or equal to 18 mm (less than or equal to 8.0 micrograms/ml) as susceptible and less than or equal to 14 mm (greater than or equal to 32 micrograms/ml) as resistant. This provides a 93.7 to 98.3% absolute interpretive accuracy. Several preliminary ranges for zone sizes obtained with quality control organisms are proposed for the 30-micrograms HR810 disk diffusion test used during the clinical trials.

Bacteria↗

PubMed1984

Quality control of susceptibility tests with 5-micrograms trimethoprim disks.

In 1981 and again in 1984, we performed multi-laboratory studies to develop quality control limits for susceptibility tests with 5-micrograms trimethoprim disks. Zone size limits of 21 to 28 mm are recommended for tests with Escherichia coli ATCC 25922, and limits of 19 to 26 mm are recommended for tests with Staphylococcus aureus ATCC 25923. For screening Mueller-Hinton agar, tests with Streptococcus faecalis ATCC 33186 or ATCC 29212 are recommended: zones should be fairly clear and greater than or equal to 22 mm (trimethoprim disks) or greater than or equal to 24 mm (trimethoprim-sulfamethoxazole disks).

Drug Combinations↗

PubMed1984

Interpretive standards and quality control guidelines for imipenem susceptibility tests with 10-micrograms disks.

Tests with 10-micrograms imipenem disks accurately categorized 98.5% of 551 bacterial isolates when interpretive breakpoints of less than or equal to 13 mm for resistant and greater than or equal to 16 mm for susceptible were used. Because a sufficient number of resistant or moderately susceptible strains were not available for testing, these interpretive standards must be considered tentative. Quality control limits for tests with Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853 are 26 to 32 and 20 to 28 mm, respectively. Zones obtained with Staphylococcus aureus ATCC 25923 were too large and variable to be useful for quality control purposes.

Anti-Bacterial Agents↗

PubMed1983

Vancomycin.

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Adolescent↗

PubMed1983

In vitro evaluation of Augmentin by broth microdilution and disk diffusion susceptibility testing: regression analysis, tentative interpretive criteria, and quality control limits.

Augmentin (Beecham Laboratories, Bristol, Tenn.), a combination drug consisting of two parts amoxicillin to one part clavulanic acid and a potent beta-lactamase inhibitor, was evaluated in vitro in comparison with ampicillin or amoxicillin or both for its inhibitory and bactericidal activities against selected clinical isolates. Regression analysis was performed and tentative disk diffusion susceptibility breakpoints were determined. A multicenter performance study of the disk diffusion test was conducted with three quality control organisms to determine tentative quality control limits. All methicillin-susceptible staphylococci and Haemophilus influenzae isolates were susceptible to Augmentin, although the minimal inhibitory concentrations for beta-lactamase-producing strains of both groups were, on the average, fourfold higher than those for enzyme-negative strains. Among the Enterobacteriaceae, Augmentin exhibited significantly greater activity than did ampicillin against Klebsiella pneumoniae, Citrobacter diversus, Proteus vulgaris, and about one-third of the Escherichia coli strains tested. Bactericidal activity usually occurred at the minimal inhibitory concentration. There was a slight inoculum concentration effect on the Augmentin minimal inhibitory concentrations. On the basis of regression and error rate-bounded analyses, the suggested interpretive disk diffusion susceptibility breakpoints for Augmentin are: susceptible, greater than or equal to 18 mm; resistant, less than or equal to 13 mm (gram-negative bacilli); and susceptible, greater than or equal to 20 mm (staphylococci and H. influenzae). The use of a beta-lactamase-producing organism, such as E. coli Beecham 1532, is recommended for quality assurance of Augmentin susceptibility testing.

Amoxicillin↗

PubMed1983

Quality control of moxalactam susceptibility disks.

In vitro evaluation of two types of moxalactam disks revealed significant performance differences when Staphylococcus aureus was being tested. The differences were traced to the amount of decarboxylated moxalactam present in the disks. The decarboxylated analog was much more active than the parent compound against S. aureus, not active against Pseudomonas aeruginosa, and approximately as active as the parent compound against Escherichia coli. A nine-laboratory coordinated study was performed to establish quality control parameters for 30-micrograms moxalactam disks. Problems with the establishment of interpretive standards for moxalactam disk tests were evaluated in the light of differences between disks utilized in earlier studies and those that are now commercially available. The type of disk greatly influences standards for tests with S. aureus but has insignificant influence on testing gram-negative bacilli.

Bacteria↗

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

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

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

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↗