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Biomedical subjects

C Thornsberry

Publications and source records attributed to C Thornsberry.

At least 91 records · Page 5Linked to original sources
PubMed1988

Relationship between in vitro susceptibility test results for chloramphenicol and production of chloramphenicol acetyltransferase by Haemophilus influenzae, Streptococcus pneumoniae, and Aerococcus species.

Haemophilus influenzae, Streptococcus pneumoniae, and Aerococcus species were tested for susceptibility to chloramphenicol by standard broth microdilution and disk-diffusion methods. MICs and zone diameter breakpoints were correlated with production of chloramphenicol acetyltransferase (CAT). A comparison of MICs and zone diameters indicated that the interpretative criteria for H. influenzae and S. pneumoniae should be an MIC of less than or equal to 4 micrograms/ml or a zone diameter greater than or equal to 25 mm for susceptible strains and an MIC of greater than or equal to 8 micrograms/ml or a zone diameter of less than or equal to 20 mm for resistant strains; for Aerococcus species, interpretative criteria should be an MIC of less than or equal to 8 micrograms/ml or a zone diameter of greater than or equal to 20 mm for susceptible strains and an MIC of greater than or equal to 32 micrograms/ml or a zone diameter of less than or equal to 12 mm for resistant strains. All but four strains of H. influenzae and one strain of S. pneumoniae that were resistant to chloramphenicol by these criteria produced CAT. For Aerococcus species, however, chloramphenicol-resistant strains were negative for CAT as determined by a commercially available disk test. When comparing susceptibility results with CAT production, thiamphenicol was a better indicator of the presence of the enzyme than chloramphenicol and may be useful in assaying resistance to chloramphenicol.

Chloramphenicol↗
PubMed1988

Variability of clarithromycin and erythromycin susceptibility tests with Haemophilus influenzae in four different broth media and correlation with the standard disk diffusion test.

Four separate laboratories performed antimicrobial susceptibility tests with 40 Haemophilus influenzae isolates, each tested in triplicate. Erythromycin and a new macrolide, clarithromycin (A-56268; TE-031), were tested by the disk diffusion method, by the agar dilution procedure in two different media, and by broth microdilution tests in four different media. Erythromycin MICs for 90% of the strains were 16 micrograms/ml in Mueller-Hinton broth with 3% lysed horse blood and NAD, 4.0 micrograms/ml in hemophilus test medium, and 2.0 micrograms/ml in supplemented Schaedler broth or in the fastidious broth medium from Beckman Instruments, Inc. Clarithromycin MICs were generally 1 doubling dilution greater than erythromycin MICs in each of the media. Erythromycin disk tests corresponded best with MICs determined in the fastidious broth medium. In that same medium, clarithromycin MICs were about 1 doubling dilution greater than what would be expected from the results of disk tests. Because there were fewer growth failures, hemophilus test medium is recommended for microdilution tests with H. influenzae. Incubation of all tests for a full 24 h without an increased CO2 atmosphere was needed to achieve maximal precision of the tests. Interlaboratory and intralaboratory reproducibility of all tests was satisfactory.

Clarithromycin↗
PubMed1987

Netilmicin disk susceptibility tests: effect of cations on the MIC correlates.

When testing Pseudomonas aeruginosa against netilmicin, MICs were markedly affected by the concentration of cations added to the test medium. A susceptible disk test result (zone greater than or equal to 15 mm) corresponded to MIC less than or equal to 4.0 micrograms/ml in unsupplemented broth, less than or equal to 12 micrograms/ml in broth with half the usual amount of cations and less than or equal to 32 micrograms/ml in broth with the recommended concentration of cations. Tests with 30 micrograms netilmicin disks best predicted susceptibility as determined by MICs in broth without added cations. When the MICs were determined in cation supplemented broth, the number of interpretive discrepancies increased to an unacceptably high level.

Cations↗
PubMed1987

Disk diffusion and disk elution tests with A-56268 and erythromycin.

Zones of inhibition around 15 micrograms A-56268 disks were essentially the same size as those around 15 micrograms erythromycin disks. If the same MIC breakpoints are to be used for defining susceptible categories for both macrolides, interpretive zone size standards for erythromycin disk tests may also be used for A-56268 disk tests. Against anaerobic bacteria, the two macrolides were only marginally effective when broth dilution tests were incubated in anaerobic jars. The aerobically incubated thioglycolate broth disk elution test indicated that both macrolides were much more effective against anaerobes. Three 15 micrograms disks eluted in 5 ml thioglycolate provided satisfactory results.

Bacteria↗
PubMed1987

CI-934, a new difluoroquinolone: in vitro antibacterial activity and proposed disk diffusion test interpretive criteria.

The susceptibility of 7,763 clinical isolates at four medical centers to CI-934 and three comparative quinolones was tested. CI-934 was the most active compound against Gram-positive isolates, such as staphylococci (MIC 90 = 0.25 microgram/ml), and enterococci (MIC 90 = 0.5 microgram/ml). CI-934 was the least active of these drugs against Pseudomonas spp. (MIC 90 = greater than 8.0 micrograms/ml). Against all other organisms CI-934 was very effective, being most comparable with enoxacin. With a selected group of isolates, CI-934 demonstrated high activity against Haemophilus influenzae (MIC 90 = 0.06 microgram/ml), Neisseria meningitidis and N. gonorrhoeae (MIC 90 = 0.13 microgram/ml), Listeria monocytogenes (MIC 90 = 1.0 microgram/ml), methicillin-resistant staphylococci (MIC 90 = 0.13 microgram/ml), and modest activity against anaerobes. Disk diffusion susceptibility testing of CI-934 was evaluated using 3-, 5-, and 10-micrograms disks. Because of its lower interpretive error rate, the 3-micrograms disk is tentatively recommended. With less than or equal to 2 micrograms/ml and greater than 4 micrograms/ml as the susceptible and resistant MIC breakpoints, the corresponding 3-micrograms disk zone diameters breakpoints are greater than or equal to 15 mm and less than or equal to 11 mm. Because most isolates of Pseudomonas spp. are not susceptible to CI-934 and the zone size interpretive error rate is particularly high (33%) with Pseudomonas spp., we suggest that isolates of this genus not be tested for clinical purposes.

Anti-Bacterial Agents↗
PubMed1987

RO 23-6240 (AM-833), a new fluoroquinolone: in vitro antimicrobial activity and tentative disk diffusion interpretive criteria.

The susceptibility of over 7000 recent clinical bacterial isolates to RO 23-6240, a new trifluorinated quinolone, was determined at four medical centers. Over 99% of Enterobacteriaceae and 97% of staphylococci were inhibited by less than or equal to 2.0 micrograms/ml of RO 23-6240. Only 71% of Pseudomonas spp. were inhibited by this concentration. Streptococci and enterococci were resistant to RO 23-6240. Clinical isolates of Haemophilus spp., pathogenic Neisseria spp., and Branhamella catarrhalis were inhibited by less than or equal to 0.25 micrograms/ml of RO 23-6240. This drug's antibacterial activity was comparable with that of enoxacin and norfloxacin, but was less than that of ciprofloxacin against most species. Using less than or equal to 2.0 micrograms/ml and greater than or equal to 8.0 micrograms/ml as the susceptible and resistant MIC breakpoints for RO 23-6240, the regression analysis-derived disk diffusion zone diameter breakpoints for the 5 micrograms disk are: Susceptible greater than or equal to 19 mm intermediate 16-18 mm, and resistant less than or equal to 15 mm.

Anti-Bacterial Agents↗
PubMed1987

Mechanism of aminoglycoside resistance among beta-lactam-resistant Escherichia coli in the United States.

We examined aminoglycoside (AG) resistance in ampicillin-resistant Escherichia coli obtained from nine hospitals participating in the National Nosocomial Infections Study. The isolates were tested to 25 antimicrobials using broth microdilution methods. If the organism was intermediate or resistant to gentamicin, tobramycin, netilmicin, or amikacin, we determined the class of aminoglycoside-modifying enzyme (AME) using the phosphocellulose paper binding assay. Of 423 E. coli, 21 (5%) were intermediate or resistant to one or more of the AGs. All but two of these E. coli isolates had at least one AME. Twelve isolates had phosphotransferase (APH) enzymes; seven had adenyltransferase (ANT) enzymes (all ANT[2"]); and four had acetyltransferase (AAC) enzymes. The seven ANT[2"]-producing isolates were more likely to be acquired in the community than in the hospital (4/7 ANT[2"]-producing E. coli versus one of 14 of the other AG-resistant E. coli, p = 0.03, Fisher's exact test). These findings suggest that for E. coli resistant to both ampicillin and an AG, APH enzymes are the predominant AME class. Additionally, isolates with certain AMEs may be acquired both in the community and in the hospital.

Aminoglycosides↗
PubMed1987

Quality control limits for microdilution susceptibility tests with aztreonam, imipenem, ceftriaxone, ceftazidime, ceftizoxime, cefuroxime, and cefonicid.

A six-laboratory collaborative study was performed in order to define quality control limits for microdilution tests with seven new beta-lactams (aztreonam, imipenem, ceftriaxone, ceftazidime, ceftizoxime, cefuroxime, and cefonicid). Four standard control strains were tested and the expected MIC limits for each of the appropriate drug-microorganism combinations were defined.

Anti-Bacterial Agents↗
PubMed1987

Antimicrobial activity of LY164846, a new oral cephalosporin, and recommendations for disk diffusion tests.

LY164846 is a new oral cephalosporin with a limited spectrum of antimicrobial activity that includes staphylococci (other than methicillin-resistant), streptococci (other than enterococci), Haemophilus influenzae (beta-lactamase-negative and beta-lactamase-positive), Branhamella catarrhalis (beta-lactamase-negative and beta-lactamase-positive), and Neisseria species (beta-lactamase negative and beta-lactamase-positive). The tentative recommendations for susceptibility breakpoints are less than or equal to 4 micrograms/ml and greater than or equal to 19 mm for susceptible, 8 micrograms/ml and 15-18 mm for intermediate, and greater than or equal to 16 micrograms/ml and less than or equal to 14 mm for resistant.

Cephalosporins↗
PubMed1987

Influence of cation supplements on activity of netilmicin against Pseudomonas aeruginosa in vitro and in vivo.

In vitro studies were performed with 74 Pseudomonas aeruginosa isolates which were collected during a multicenter trial. The isolates were obtained from 70 patients who had been treated with netilmicin as the only antipseudomonal antibiotic. Clinically, 83% of the patients were cured or improved, and 64% of the Pseudomonas isolates were eliminated by chemotherapy. The 74 clinical isolates and 38 additional isolates with known mechanisms of aminoglycoside resistance were tested in three separate laboratories by disk diffusion methods and by microdilution tests with three broth media (Mueller-Hinton broth with full, half, and no cation supplements). Isolates that responded to netilmicin therapy and those that failed to respond were all susceptible by the disk test, and most were susceptible by microdilution tests with unsupplemented broth. However, over half of the clinical isolates appeared to be resistant when cations were added to the broth medium. Strains capable of producing enzymes that inactivate netilmicin were resistant by all methods tested. Broth dilution and agar dilution results were most comparable when half of the recommended cation supplements was added to Mueller-Hinton broth. Further consideration should be given to reducing the concentration of cations that are added to Mueller-Hinton broth when netilmicin susceptibility tests are being performed. However, additional studies with other aminoglycosides are needed before appropriate testing conditions can be standardized.

Adult↗
PubMed1987

In vitro activity of a new macrolide, A-56268, compared with that of roxithromycin, erythromycin, and clindamycin.

A new macrolide (A-56268) was found to be approximately twice as active as erythromycin and four to eight times more active than roxithromycin. All three macrolides were similar in their potency against anaerobes. Human plasma enhanced the antistaphylococcal activity of A-56268 and erythromycin but reduced the activities of roxithromycin and clindamycin.

Anti-Bacterial Agents↗
PubMed1987

Quality control limits for microdilution susceptibility tests with norfloxacin.

A multilaboratory study was designed to define quality control limits for microdilution susceptibility tests with norfloxacin. The following limits were proposed: for Escherichia coli ATCC 25922, 0.03 to 0.125 micrograms/ml; for Pseudomonas aeruginosa ATCC 27853, 1.0 to 4.0 micrograms/ml; for Staphylococcus aureus ATCC 29213, 0.5 to 2.0 micrograms/ml; and for Streptococcus faecalis ATCC 29212, 2.0 to 8.0 micrograms/ml. The latter represents a change in the previously recommended control limits.

Enterococcus faecalis↗
PubMed1987

In vitro antimicrobial spectrum, occurrence of synergy, and recommendations for dilution susceptibility testing concentrations of the cefoperazone-sulbactam combination.

Broth microdilution tests and an antimicrobial interaction (synergy) studies using various combinations of cefoperazone and sulbactam were performed in an effort to determine the most appropriate in vitro dilution test system. The test results with cefoperazone and sulbactam were categorized as synergistic (complete or partial) for nearly 80% of the strains isolated from clinical trial patients. The results indicate that the cefoperazone-sulbactam fixed ratio (2:1) maximized the cefoperazone spectrum of activity and best approximated the parenteral formulation of the drug. The cefoperazone-sulbactam combination had a greater antimicrobial activity than did the other comparison beta-lactams, except for imipenem, tested against strains of the family Enterobacteriaceae. To be consistent with the National Committee for Clinical Laboratory Standards interpretive breakpoints for cefoperazone alone, the following MIC breakpoints should be applied to the combination (2:1 ratio): less than or equal to 16/8 micrograms/ml, susceptible; 32/16 micrograms/ml, moderately susceptible; and greater than or equal to 64/32 micrograms/ml, resistant.

Bacteria↗
PubMed1987

Quality control limits for teicoplanin susceptibility tests and confirmation of disk diffusion interpretive criteria.

For monitoring the performance of teicoplanin susceptibility tests, the following quality control limits are recommended: Staphylococcus aureus ATCC 29213, MIC of 0.12 to 0.5 micrograms/ml; Enterococcus faecalis ATCC 29212, MIC of 0.06 to 0.25 micrograms/ml; and S. aureus ATCC 25923, zones 15 to 19 mm in diameter (30-micrograms disks). However, some lots of Mueller-Hinton agar provided unusually large zones of inhibition with both vancomycin and teicoplanin disks, and these lots should be excluded before routine use. Teicoplanin and vancomycin differed only in their activity against oxacillin-resistant strains of Staphylococcus haemolyticus, which had decreased susceptibility to teicoplanin but were fully susceptible to vancomycin. For tests with 30-micrograms teicoplanin disks, zones less than or equal to 10 and greater than or equal to 14 mm in diameter represent resistant and susceptible breakpoints, respectively.

Anti-Bacterial Agents↗
PubMed1986

In vitro activity of the aryl-fluoroquinolones A-56619 and A-56620 and evaluation of disk susceptibility tests.

The activity of two new quinolones, A-56619 and A-56620, was compared in vitro to that of norfloxacin and ciprofloxacin against 6,699 bacterial isolates in four separate clinical laboratories. The overall percentage of strains susceptible to designated concentrations were as follows: 99.1% for norfloxacin (MIC less than or equal to 4.0 micrograms/ml), 96.1% for ciprofloxacin (MIC less than or equal to 1.0 micrograms/ml), 96.8% for A-56620 (MIC less than or equal to 2.0 micrograms/ml) and 96.1% for A-56619 (MIC less than or equal to 4.0 micrograms/ml). For disk diffusion susceptibility tests 10 micrograms A-56619 disks are tentatively recommended with interpretive standards of greater than or equal to 18 mm for susceptibility and less than or equal to 13 mm for resistance; 5 micrograms A-56620 disks may be used with tentative standards of greater than or equal to 19 mm for susceptibility and less than or equal to 14 mm for resistance.

Anti-Infective Agents↗
PubMed1986

In vitro activity of DJ-6783 (a keto carboxylic acid) compared with six other orally administered antimicrobial agents.

DJ-6783 is a new keto carboxylic acid having an expanded antimicrobial activity when compared with nalidixic acid or cinoxacin. Its usable activity includes the following: Enterobacteriaceae (MIC90, less than or equal to 0.06-4.0 micrograms/ml), Acinetobacter species (MIC90, 0.25-1.0 microgram/ml), Pseudomonas species (MIC90, 1.0-2.0 micrograms/ml), P. aeruginosa (MIC90, 16 micrograms/ml), Staphylococcus species (MIC90, 1.0-32 micrograms/ml), Haemophilus influenzae (MIC900, less than or equal to 0.06 microgram/ml), and Neisseria species (MIC90 less than or equal to 0.06 microgram/ml). The Streptococcus species were resistant to DL-6783 with MIC50 ranging from 16 to greater than 32 micrograms/ml. The drug appears to be bactericidal, minimally influenced by increasing inocula, but resistant mutants can be selected by serial subinhibitory concentration passages of strains in DJ-6783. The resulting resistant organisms also have higher MICs to related drugs such as norfloxacin, cinoxacin, and nalidixic acid. DJ-6783 was the most active organic acid not having structural characteristics of the fluorinated 4-quinolones.

Anti-Bacterial Agents↗