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Biomedical subjects

C Thornsberry

Publications and source records attributed to C Thornsberry.

At least 163 records · Page 9Linked to original sources
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

Influence of growth medium on the in vitro activities of second- and third-generation cephalosporins against Streptococcus faecalis.

The influence of culture medium of the MICs of eight cephalosporins for 45 strains of Streptococcus faecalis was investigated. The MICs of cephalothin, cefamandole, and cefoperazone were not substantially influenced by the type of culture medium used. In contrast, MICs of cefuroxime, ceftizoxime, cefotaxime, cefmenoxime, and ceftriaxone varied markedly with both the commercial brand and the blood content of the broth used. The use of Mueller-Hinton broths (from Oxoid Ltd., GIBCO Diagnostics, and Difco Laboratories) supplemented with 5% lysed sheep blood frequently resulted in MICs that were greater than or equal to 16 times lower than the MICs obtained with these same broths without blood. Similar, but less marked, patterns were observed when supplemented and unsupplemented brain heart infusion and Sceptor broths were used. The influence of the broth on MICs suggests a complex interaction between some cephalosporins, medium components, and organisms. The cephalosporins that were affected by media share an identical moiety at the 7-acyl position (cefuroxime is slightly different), but this structure is not shared by those cephalosporins that were not affected. This commonality in structure at the 7-acyl position may be partially responsible for the observed results.

Animals↗
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↗
PubMed1984

Effect of media and blood on the antimicrobial activity of cephalosporins on serogroup D streptococci: a review.

The influence of culture medium on in vitro of selected cephalosporins on on group D streptococci was investigated by agar diffusion and broth dilution methods. The activity of cephalothin, cefamandole, and cefoperazone were not substantially influenced by the type of culture medium used, but cefuroxime, ceftizoxime, cefotaxime (CTX), cefmenoxime, and ceftriaxone varied markedly with both the commercial brand and the blood content of the broth used. The differences were more likely to occur in some Mueller-Hinton media, particularly when supplemented with 5% lysed sheep blood, and resulted in susceptible results instead of the resistant results that were obtained with these same media without blood. Some strains of Streptococcus faecalis showed these discrepancies, but S. bovis did not. The influence of the media on in vitro activity suggests a complex interaction between some cephalosporins, media components, and organisms. The cephalosporins that were affected by media share an identical moiety at the 7-acyl position (cefuroxime is slightly different); this structure is not shared by those cephalosporins that were not affected, however. It is possible that this structure may play a part in the phenomenon.

Animals↗
PubMed1983

Ceftriaxone: a summary of in vitro antibacterial qualities including recommendations for susceptibility tests with 30-micrograms disks.

The new aminothiazoyl-cephalosporin, ceftriaxone (Ro 13-9904), was found to have excellent inhibitory activity against the Enterobacteriaceae (minimum inhibitory concentration needed to inhibit 50% of isolates (MIC50) less than or equal to 0.004-0.5 microgram/ml, Haemophilus influenzae (MIC50 less than or equal to 0.004 micrograms/ml), Neisseria species (MIC50 less than or equal to 0.001 microgram/ml), pneumococci (MIC50 0.25 micrograms/ml), Staphylococcus aureus (MIC50 2.0 micrograms/ml), and Streptococcus pyogenes (MIC50 0.015 micrograms/ml). Ceftriaxone was less effective against Acinetobacter species, Pseudomonas aeruginosa, and other Pseudomonas species (MIC50 8.0-16 micrograms/ml). Methicillin-resistant S. aureus and enterococci were not significantly inhibited by ceftriaxone. Ceftriaxone was very resistant to beta-lactamase hydrolysis, although the type IV cephalosporinase minimally destroyed the compound at 16.4-19.9% of the rates for cephaloridine. Type I cephalosporinases were inhibited by ceftriaxone and related enzyme-stable cephalosporins. Based on analysis of disk-MIC regression statistics, tentative recommendations for the disk test of the National Committee for Clinical Laboratory Standards are 21 mm or more = susceptible, 14-20 mm = moderately susceptible, and 13 mm or less = resistant. These criteria produce interpretive accuracy of more than 92%, with very rare major errors. Ceftriaxone was comparable to cefotaxime in spectrum and activity, thus allowing the use of the "spectrum-class" concept (for example, cefotaxime tests in vitro to predict ceftriaxone susceptibility, and vice versa).

Acinetobacter↗
PubMed1983

Cefuroxime, cefamandole, cefoxitin, and cephalothin in vitro susceptibility tests: reassessment of the "class representative" concept, confirmation of disk interpretive criteria, and proposed quality control guidelines.

The relationship of cefuroxime in vitro susceptibility tests to similar cephalosporins (cefamandole, cefoxitin, and cephalothin) was evaluated using 396 recent clinical isolates. The previously published interpretive criteria of greater than or equal to 18 mm (less than or equal to 8.0 micrograms/mL) = susceptible and less than or equal to 14 mm (greater than or equal to 32 micrograms/mL) = resistant for each drug were considered appropriate. The results of all study methods demonstrated cefuroxime to be slightly less active than cefamandole against most species, yet both drugs possessed nearly identical antimicrobial spectra. Cephalothin and cefoxitin were confirmed to have spectra significantly different from cefamandole and from each other, thus requiring separate testing. The application of the "class representative" concept to cefuroxime and cefamandole seems justified. Use of a 30-micrograms cefuroxime disk yielded the best predictive results and minimized the number of false-susceptible (very major) interpretive errors. Quality control guidelines are presented in a tentative form for cefuroxime, and modifications in the cephalothin and cefamandole zone limits are suggested.

Bacteria↗
PubMed1983

Susceptibility of Propionibacterium acnes clinical isolates to 22 antimicrobial agents.

Susceptibilities of 104 Propionibacterium acnes isolates to each of 22 antimicrobial agents was evaluated by broth microdilution. These isolates were susceptible to all of the test agents except metronidazole. N-Formimidoyl thienamycin, a penem coded Sch 29482, and penicillin ranked first, second, and third, respectively, in activity and were significantly more active than other penicillins, cephalosporins, tetracyclines, clindamycin, or chloramphenicol.

Anti-Bacterial Agents↗
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

In vitro evaluation of three new macrolide antimicrobial agents, RU28965, RU29065, and RU29702, and comparisons with other orally administered drugs.

Three new macrolide drugs (RU28965, RU29065, and RU29702) were compared in vitro with erythromycin and five other orally administered antimicrobial agents by using 733 recent clinical isolates. All of the investigational macrolides had a spectrum very similar to that of erythromycin, but with slightly higher (two- to fourfold) minimum inhibitory concentrations against Haemophilus influenzae, staphylococci, and streptococci including Streptococcus faecalis. RU29065 and RU29702 were more active than erythromycin against Neisseria gonorrhoeae and Neisseria meningitidis. The drugs appeared to be predominantly bacteriostatic and were ineffective against gram-negative bacilli, and their minimum inhibitory concentrations were greatly increased by high inoculum concentrations. Cross-resistance between the macrolides was nearly complete, favoring the use of a single agent for in vitro susceptibility test if in vivo therapeutic differences are not observed.

Administration, Oral↗
PubMed1983

Agar disk elution method for susceptibility testing of Mycobacterium marinum and Mycobacterium fortuitum complex to sulfonamides and antibiotics.

An agar disk elution method using round well plates, supplemented Mueller-Hinton agar, and commercial drug disks is described for susceptibility testing of Mycobacterium marinum and the rapidly growing mycobacteria to antibiotics and sulfonamides. By this method, 14 of 14 strains of M. marinum were susceptible to rifampin, doxycycline, minocycline, and trimethoprim-sulfamethoxazole. Identical results were obtained with Middlebrook 7H10 agar and drugs prepared from standard powders. With 58 isolates of Mycobacterium fortuitum and Mycobacterium chelonei, this method had a 92% correlation with broth minimal inhibitory concentration determinations for cefoxitin and greater than 98% for doxycycline, kanamycin, amikacin, and the sulfonamides. Sixty-nine percent of isolates of M. chelonei susceptible to amikacin on supplemented Mueller-Hinton agar were resistant on 7H10 agar, and 15 of 16 M. chelonei isolates susceptible to erythromycin in broth were resistant by disk elution when an endpoint of no growth was used with either agar. The agar disk elution method offers a practical method for testing of most antibacterial agents against these mycobacterial species.

Agar↗
PubMed1983

Evaluation of the cefonicid disk test criteria, including disk quality control guidelines.

Cefonicid (SKF 75073) is a second-generation cephalosporin which has a spectrum of antimicrobial activity similar to that of cefamandole, but cefoxitin (a cephamycin) and cephalothin have uniquely different spectra of activity. The second-generation cephalosporins tested displayed comparable susceptibility to beta-lactamases and inhibited type I beta-lactamases. Although cefonicid has a longer serum half-life (3 to 4 h) compared with the currently used drugs, the same minimal inhibitory concentration breakpoints separating susceptible and resistant categories were applied to tests with cefonicid, cefamandole, and cephalothin. Regression analysis of the disk diffusion test results confirmed the use of identical zone size breakpoints for 30-micrograms cefonicid, cefamandole, and cephalothin disks: all three produced similar parabolic regression lines. Further analysis of disk test data confirmed the fact that cefonicid and cefamandole disks might be used interchangeably. But for routine tests, cefonicid disks might be preferred in order to minimize the number of very major (false-susceptible) interpretive errors. Suggested cefonicid 30-micrograms disk interpretive criteria are: susceptible, greater than or equal to 18 mm (less than or equal to 8.0 micrograms/ml), and resistant, less than or equal to 14 mm (greater than 16 micrograms/ml). Quality control zone diameter limits were calculated from data obtained in a multilaboratory collaborative study.

Bacteria↗
PubMed1983

Inoculum standardization in antimicrobial susceptibility testing: evaluation of overnight agar cultures and the Rapid Inoculum Standardization System.

Using the Rapid Inoculum Standardization System [RISS; Minnesota Mining & Manufacturing Co. (3M Co.)], we investigated the use of overnight agar cultures in the preparation of inocula for disk diffusion and microdilution susceptibility tests and compared our results with susceptibility results obtained with the standard methods. The 3M system consists of an inoculation wand, with which a reproducible number of bacteria can be removed from an agar plate, and a diluent in which to suspend the organisms. We used 25 gram-positive cocci, 75 enteric and nonfermentive gram-negative bacilli, and 40 more fastidious bacteria (Haemophilus, Neisseria, and pneumococci) for the evaluation. The geometric mean inoculum size for all organisms tested was 9.7 X 10(7) CFU/ml by the standard method and 1.1 X 10(8) CFU/ml for the RISS. The categories of susceptibility obtained by both methods in the disk diffusion tests were comparable, as were the minimal inhibitory concentrations. We recommend that the use of overnight agar cultures and the use of the RISS to prepare inocula for susceptibility tests be acceptable alternative procedures in the standard methods for susceptibility tests.

Agar↗
PubMed1983

Chloramphenicol and penicillin resistance in pneumococci isolated from blood and cerebrospinal fluid: a prevalence study in metropolitan Denver.

From January through October 1981, we screened blood and cerebrospinal fluid pneumococcal isolates from 101 patients in the Denver, Colorado area. Isolates from seven patients (6.9%) showed relative resistance to penicillin, with minimal inhibitory concentrations ranging from 0.12 to 1.0 microgram/ml. Two isolates (2.0%) were resistant to chloramphenicol, both with a minimal inhibitory concentration of 16 micrograms/ml. One of these was multiply resistant (to penicillin, chloramphenicol, and tetracycline). All isolates were susceptible to erythromycin, sulfamethoxazole-trimethoprim, and rifampin. On the basis of penicillin susceptibilities performed by participating hospitals on the isolates from 215 patients in the Denver area (101 included in the survey, 114 not included), we estimated the rate of relative resistance to penicillin to be approximately 4.3%. Compared with resistance rates reported in a previous study in Denver, these penicillin and chloramphenicol resistance rates may represent a trend of increasing resistance to these antibiotics in the Denver area. We recommend screening all isolates from invasive pneumococcal infections for penicillin and chloramphenicol susceptibility.

Blood↗
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

Comparison of the antibacterial spectra of cephalexin and cefaclor with those of cephalothin and newer cephalosporins: reevaluation of the class representative concept of susceptibility testing.

The validity of the class representative concept for in vitro susceptibility testing of older cephalosporins was reevaluated. Two oral cephalosporins, cephalexin and cefaclor, were compared with the established cephalosporin class representative, cephalothin, by using reference microdilution minimal inhibitory concentrations of 528 isolates of a wide variety of gram-positive and gram-negative bacterial pathogens. For each comparison, there were only 15 (2.8%) random major and very major interpretive discrepancies. Additional comparisons confirmed the need to test second-generation (cefamandole) and third-generation (cefotaxime) cephalosporins separately. These results provide reasonable assurance that the use of cephalothin as an in vitro predictor of qualitative bacterial susceptibility to these two oral cephalosporins remains an acceptable alternative to testing each antibiotic individually.

Bacteria↗
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↗