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Biomedical subjects

C Thornsberry

Publications and source records attributed to C Thornsberry.

At least 217 records · Page 12Linked to original sources
PubMed1980

Tentative interpretive criteria for the diffusion susceptibility test using 30-microgram netilmicin disks.

The disk diffusion inhibitory zone diameters for 10-microgram and 30-microgram netilmicin disks were correlated with minimum inhibitory concentrations against 471 clinical strains tested in cation-supplemented Mueller-Hinton broth. Regression line and error-rate bounded analysis favored the use of 30-microgram netilmicin disks utilizing zone size breakpoints of greater than or equal to 17 mm to indicate susceptibility (less than or equal to 8 microgram/ml) and less than or equal to 13 mm to indicate resistance (greater than 32 microgram/ml). Significant minor interpretive errors may be expected when testing populations of Pseudomonas that have netilmicin minimum inhibitory concentrations near the intermediate range (16 microgram/ml).

Anti-Bacterial Agents↗
PubMed1980

Interpretive standards for disk susceptibility tests with Sch 21420 and amikacin.

Disk susceptibility tests with two structurally related aminoglycosides (amikacin and Sch 21420) were evaluated. Tests with 10- and 30-micrograms amikacin disks confirmed previous recommendations for interpretive zone standards; 30-micrograms disks are preferred. Tests with 10-, 20-, and 30-micrograms Sch 21420 disks led to similar conclusions. The 30-micrograms Sch 21420 disks are recommended, with zone standards of less than or equal to 14 mm for the resistant category (minimal inhibitory concentration, greater than or equal to 32 micrograms/ml) and greater than or equal to 17 mm for the susceptible category (minimal inhibitory concentration, less than or equal to 16 micrograms/ml). If a minimal inhibitory concentration breakpoint of less than or equal to 8 micrograms/ml is preferred for defining the susceptible category, somewhat different zone standards may be used (less than or equal to 15 mm and greater than or equal to 19mm). Further evaluation documented the fact that tests with 30-micrograms amikacin disks predicted resistance or susceptibility to Sch 21420 almost as well as did a 30-micrograms Sch 21420 disk. Thus, the class concept of disk testing was judged to applicable, and routine testing with Sch 21420 may not be required.

Amikacin↗
PubMed1980

Tentative interpretive standards for disk susceptibility tests with moxalactam (LY127935).

Moxalactam (LY127935; 6059-S) is a new beta-lactam antibiotic. We propose tentative zone standards for agar diffusion susceptibility tests with 30-microgram disks. The final selection of minimal inhibitory concentration breakpoints for definition of resistant and susceptible categories must await clinical experience with this drug. Some of the clinical questions to be answered are defined. A moderately susceptible (intermediate) category is proposed for those strains with minimal inhibitory concentrations of 16 or 32 microgram/ml (zones 15 to 22 mm in diameter). Strains with minimal inhibitory concentrations of greater than or equal to 64 microgram/ml are considered resistant, and those with minimal inhibitory concentrations of less than or equal to 8 microgram/ml are considered susceptible. Tests with 30-microgram disks did not satisfactorily separate strains with minimal inhibitory concentrations of 8 microgram/ml from strains requiring < 2 microgram/ml for inhibition, because the regression line became parabolic at concentrations of 2 microgram/ml and below. However, the disk tests were satisfactory for categorizing isolates into the above-described susceptible, moderately susceptible (intermediate), and resistant categories.

Cephalosporins↗
PubMed1980

Compound A49759, the 3-O-demethyl derivative of fortimicin A: in vitro comparison with six other aminoglycoside antibiotics.

O-Demethylfortimicin A (compound A49759) was tested against 445 bacteria, and the results were compared with those obtained with fortimicin A, amikacin, gentamicin, netilmicin, sisomicin, and tobramycin. A49759 was found to be active and bactericidal against the Enterobacteriaceae, nonfermentative gram-negative bacilli, and Staphylococcus aureus. A49759 was two- to fourfold more active than fortimicin A against most species tested, but generally fourfold less active than amikacin against this population of Pseudomonas aeruginosa (85% inhibited at less than or equal to 16 microgram of amikacin per ml and 85% inhibited at less than or equal to 64 microgram of A49759 per ml). Only amikacin and A49759 were resistant to most aminoglucoside-inactivating enzymes and also had significant antipseudomonal activity. Amikacin was inactivated by aminoglycoside 6'-acetyltransferase, and A49759 was inactivated by aminoglycoside 3-acetyltransferase. The minimal inhibitory concentrations of all tested aminoglycosides were increased by augmenting the inoculum size.

Aminoglycosides↗
PubMed1980

Clinical laboratory evaluation of the Abbott MS-2 automated antimicrobial susceptibility testing system: report of a collaborative study.

The MS-2 system (Abbott Diagnostics, Division of Abbott Laboratories, Dallas, Tex.) was evaluated for its efficacy in determining the susceptibilities of both clinical and selected challenge (nonfastidious, facultative, and aerobic) isolates. The MS-2 results were compared with standard Kirby-Bauer disk diffusion and microdilution results by using fresh clinical isolates. For gram-positive isolates other than enterococci, overall agreement between MS-2 and reference results was 93 to 98%. With enterococci, MS-2 agreement with disk diffusion was 68% but with microdilution was 86% (agreement between disk diffusion and microdilution was 73%). The main discrepancies with enterococci were with cephalothin, penicillin, gentamicin, and kanamycin. With clinical gram-negative isolates, the overall agreement was 91 to 93%, with most discrepancies occurring with Enterobacter spp. and beta-lactam antibiotics (MS-2 versus disk diffusion, 84%; MS-2 versus microdilution, 84%; disk diffusion versus microdilution, 87%) and with Serratia spp. and colistin (false-susceptible results). The agreement of MS-2 results with established reference antibiograms of a special collection of challenge strains was 91 to 97% for the gram-positive cocci and 86 to 98% for the gram-negative strains. (With Enterobacter spp., agreement was 86%, but was greater than 90% for all other organism groups.) Of the 98 finite MS-2 minimum inhibitory concentrations (MICs) that could be directly compared with microdilution MICs, 77 (79%) were within +/- 1 well of the geometric mean microdilution MIC. MS-2 analysis time ranged from 2.8 to 6.5 h (mean, 4.2 h). On the basis of these results, we conclude that the MS-2 can be expected to yield rapid and accurate results with most nonfastidious, facultative, and aerobic pathogens.

Anti-Bacterial Agents↗
PubMed1979

In-vitro activities of cefamandole and cephalothin against 1,881 clinical isolates. A multi-center study.

By use of an agardilution technic, 1,881 clinical isolates were tested against cefamandole and cephalothin. The isolates represented 18 genera, recovered in five geographically separate centers within the United States. The majority of strains were susceptible (MICs less than or equal to 8 micrograms/ml) to both drugs. Cefamandole showed greater activity against most of the bacterial pathogens. Enterococci, Serratia spp., and Acinetobacter spp. were resistant to both drugs. Cephalothin was more active against Staphylococcus aureus, and both cephalosporins were relatively inactive against methicillin-resistant strains of S. aureus. Enterobacter spp. and indole-positive Proteus spp. were susceptible to cefamandole but resistant to cephalothin.

Bacteria↗
PubMed1979

In vitro activity of rosamicin, josamycin, erythromycin, and clindamycin against beta-lactamase-nagative and beta-lactamase-positive strains of Neisseria gonorrhoeae.

Randomly selected strains of beta-lactamase-negative and beta-lactamase-positive Neisseria gonorrhoeae were tested by an agar dilution method for susceptibility to rosamicin, josamycin, erythromycin, clindamycin, and penicillin G. Rosamicin was more active than erythromycin, which was more active than josamycin or clindamycin; the latter two were similar in their activity. The susceptibility to the macrolide antibiotics and clindamycin was independent of beta-lactamase production, but the penicillin minimal inhibitory concentrations were higher in the beta-lactamase-positive group because of the enzyme.

Anti-Bacterial Agents↗
PubMed1979

Interpretation of the disk diffusion susceptibility test for amikacin: report of a collaborative study.

Because excessively high rates of false resistance have been encountered with the 10-mug amikacin disk in diffusion susceptibility tests, a study was performed to examine existing zone diameter interpretative criteria and to compare the accuracy of 10- and 30-mug amikacin disks by the error rate-bounded classification scheme. Although current zone diameter interpretative criteria eliminate false susceptibles, there is an unacceptably high rate of false resistants. This problem can be resolved in most instances by revising the zone diameter interpretative criteria for the 10-mug disk (resistant, </=9 mm; indeterminate, 10 to 11 mm; susceptible, >/=12 mm) or, preferably, by replacing the 10-mug disk with a 30-mug disk and adopting new interpretative criteria (resistant, </=14 mm; indeterminate, 15 to 16 mm; susceptible, >/=17 mm). Because of significant differences in performance among media, it is necessary to include Pseudomonas aeruginosa ATCC 27853 among controls routinely tested and to exclude from use lots of Mueller-Hinton agar yielding results outside the 75% tolerance (90% confidence) limits for amikacin.

Amikacin↗
PubMed1979

Resistance mechanisms of multiply resistant pneumococci: antibiotic degradation studies.

Strains of Streptococcus pneumoniae resistant to penicillin have been reported from several countries around the world. Many South African isolates, in addition, exhibit resistance to tetracycline, chloramphenicol, erythromycin, clindamycin, and cotrimoxazole in varying patterns. A qualitative test of the ability of antibiotic-resistant pneumococci to inactivate penicillin, oxacillin, cephalothin, cefoxitin, chloramphenicol, tetracycline, minocycline, erythromycin, clindamycin, streptomycin, gentamicin, and cotrimoxazole revealed that only chloramphenicol was degraded. This finding was confirmed in a quantitative test in which the residual antimicrobial activity of broth containing chloramphenicol in subinhibitory concentrations was determined after incubation with antibiotic-resistant bacteria. Chloramphenicol resistance was shown to be associated with the production of inducible chloramphenicol acetyltransferase. No beta-lactamase activity was demonstrated. Plasmid deoxyribonucleic acid was not demonstrable in partially purified lysates of antibiotic-resistant strains of S. pneumoniae.

Acetyltransferases↗
PubMed1979

Piperacillin susceptibility tests by the single-disk agar diffusion technique.

Piperacillin is a new semisynthetic penicillin with a spectrum of activity broader than that of carbenicillin or ticarcillin. Studies were performed to establish standards for agar diffusion susceptibility tests with piperacillin disks. Tests with 100-, 150-, and 200-micrograms piperacillin disks and with 100-micrograms carbenicillin disks were evaluated. With both penicillins, 100-micrograms disks were satisfactory, in spite of the fact that piperacillin is a larger molecule and diffuses at a slower rate. With both carbenicillin and piperacillin disks, resistant strains of Staphylococcus aureus produced zones less than or equal to 28 mm and susceptible strains gave zones greater than or equal to 29 mm in diameter. When testing other microorganisms, zone standards of less than or equal to 13 mm for resistant (minimal inhibitory concentration, greater than or equal to 256 micrograms/ml) and greater than or equal to 17 mm for susceptible (minimal inhibitory concentration, less than or equal to 64 micrograms/ml) are recommended for tests with 100-micrograms piperacillin disks. Similar zone standards are currently recommended for carbenicillin and ticarcillin disk tests.

Bacteria↗
PubMed1979

Methods of measuring zones of inhibition with the Bauer-Kirby disk susceptibility test.

Standard Bauer-Kirby disk tests were performed with 85 selected isolates, each tested in triplicate by four different investigators. Each disk test was observed, and zone diameters were measured, under two lighting conditions (transmitted light and reflected light). The two lighting systems produced similar zone measurements (+/-2 mm) with 96% of the tests. When there were greater differences, zones appeared to be larger when observed with reflected light. Interlaboratory reproducibility was much greater when using reflected light rather than transmitted light. We concluded that zone diameters should be measured from the back of the plate while it is resting on, or held 2 to 3 inches [ca. 5.1 to 7.6 cm] above, a black, nonreflecting, flat surface, illuminated by a reflected light source.

Anti-Bacterial Agents↗
PubMed1979

Simple inoculum standardizing system for antimicrobial disk susceptibility tests.

A collaborative study was undertaken to evaluate a simple, convenient device which expedites inoculum standardization for antimicrobial disk susceptibility tests. The Inocupac system (Minnesota Mining & Manufacturing [3M] Co., St. Paul, Minn.) was used to perform disk tests in parallel with the standard Bauer-Kirby method. Five investigators tested 100 selected isolates, each in triplicate. Inter- and intralaboratory precision of both disk procedures was essentially comparable. The Inocupac system failed to consistently provide satisfactory growth with some streptococci, but when testing common gram-negative bacilli, staphylococci, and most enterococci, the Inocupac system gave zones about the same size (+/-2 mm) as the Bauer-Kirby procedure. Interpretive agreement between the two test systems varied from 90 to 99% with different antimicrobial agents, and repeated tests with the Bauer-Kirby method demonstrated the same degree of interpretive agreement. The Inocupac system is a valid alternative method for inoculating disk susceptibility tests.

Anti-Bacterial Agents↗
PubMed1979

Piperacillin (T-1220), a new semisynthetic penicillin. II. In vitro antimicrobial activity and synergy comparison with carbenicillin and gentamicin.

Piperacillin, a new semisynthetic penicillin, was found to have potent antimicrobial activity against nearly all (405) tested bacterial species. Piperacillin was consistently 4 approximately 16-fold more active than carbenicillin against the Enterobacteriaceae, 16 approximately 32-fold against Pseudomonas aeruginosa and Pseudomonas species, and 16-fold against Streptococcus faecalis. Carbenicillin and piperacillin were equally effective against Staphylococcus aureus, but inactivated by beta-lactamase. A 38% overall synergy rate for the piperacillin-gentamicin combination was identified, a finding similar to that for carbenicillin-gentamicin. Highest incidences of synergy were found for both antibiotic pairs tested on gentamicin-resistant isolates (Ps. aeruginosa and Providencia). In vitro findings suggest that piperacillin alone or in combination with aminoglycosides may be highly efficacious in the treatment of most serious bacterial infections.

Bacteria↗