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Biomedical subjects

A L Barry

Publications and source records attributed to A L Barry.

At least 361 records · Page 20Linked to original sources
PubMed1980

Comparison of in vitro activity of Sch 21420, a gentamicin B derivative, with those of amikacin, gentamicin, netilmicin, sisomicin, and tobramycin.

Sch 21420 is a new aminoglycoside synthesized from gentamicin B. Susceptibility tests with Sch 21420, amikacin, gentamicin, netilmicin, sisomicin, and tobramycin were performed on a variety of bacterial species including 44 with known mechanisms of resistance to aminoglycosides. Sch 21420 and amikacin had similar effects on all except Haemophilus influenzae and Neisseria species, which were more susceptible to amikacin. Except with some strains of Serratia marcescens, the drugs used were bactericidal. Sch 21420 and amikacin were more stable than the other four aminoglycosides in the presence of the inactivating enzymes produced by some strains. Strains which were very resistant to Sch 21420 and emikacin either were permeability mutants or produced AAC (6')-I inactivating enzyme. The effect of cations on the susceptibilities of these strains to Sch 21420 and amikacin was seen mostly with Pseudomonas aeruginosa and to Sch 21420 with Acinetobacter. Cations did not affect the susceptibilities of other Pseudomonas species, Enterobacteriaceae, Staphylococcus aureus, or Streptococcus faecalis to Sch 21420 or amikacin.

Amikacin↗
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↗
PubMed1979

In-vitro methods for determining minimal lethal concentrations of antimicrobial agents.

To determine the minimal lethal concentration of an antimicrobial agent, broth dilution tests may be performed and then a sample from each tube showing no visible growth may be subcultured onto a drug-free agar medium. By counting the number of viable cells recovered from each tube, the minimal concentration of drug required to kill 99.9% of the cells in the initial inoculum can be determined. Studies were undertaken to determine the circumstances under which false-negative tests could occur as a result of continued inhibition of growth by the antimicrobic carried over in the sample. Drug carryover did significantly reduce the number of viable cells recovered from broth containing relatively high concentrations of antimicrobic: the larger the sample, the greater the effect of drug carryover. The effect was minimal with samples of 10 microliter or less. Furthermore, the effect of drug carryover was reduced by spreading the sample over the surface of an agar medium. The relative precisions of four methods for performing subcultures with such small-volume samples were determined; coefficients of variation were 16-25%. Sampling errors inherent in the procedure for subculturing broth tubes should be taken into consideration when interpreting results of individual tests, and replicate subcultures will improve the reliability of the colony counts.

Enterococcus faecalis↗
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

A system for reporting quantitative antimicrobic susceptibility test results.

A reporting system for the laboratory to communicate quantitative antimicrobic susceptibility test results to the physician in a manner that will optimize proper utilization of such test results is described. Minimal inhibitory concentrations are reported on a scale of clinically achievable concentrations, thus indicating the degree of susceptibility.

Anti-Bacterial Agents↗
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

Collaborative evaluation of a proposed reference dilution method of susceptibility testing of anaerobic bacteria.

An agar dilution method for susceptibility testing of anaerobic bacteria was evaluated to determine whether results obtained would be consistent enough to recommend it as a reference method. The study was conducted in 10 laboratories where the minimum inhibitory concentrations of six antibiotics (carbenicillin, cefoxitin, chloramphenicol, clindamycin, penicillin G, and tetracycline) were determined against 10 bacterial strains on Wilkins-Chalgren agar prepared by three manufacturers. Minimum inhibitory concentrations falling on the modes varied from 57 to 80% of all determinations and on the mode or within +/-1 log(2) dilution of the mode from 87 to 100% within each laboratory. When data from all laboratories were pooled, minimum inhibitory concentrations from each laboratory agreed with the overall mode 48 to 71% of the time, with an overall agreement at +/-1 log(2) dilution of 96%. This degree of reproducibility allows for recommendation of the procedure as a reference method. Results with three of the test strains were very consistent, and these strains are recommended as control strains: Clostridium perfringens ATCC 13124, Bacteroides fragilis ATCC 25285 and Bacteroides thetaiotaomicron ATCC 29741. The minimum inhibitory concentrations for these strains were on the mode or within +/-1 log(2) dilution of the mode 98, 99, and 99% of the time, respectively. The remaining anaerobic bacteria are recommended as reference strains.

Anaerobiosis↗
PubMed1979

Fortimicin A: collaborative in vitro susceptibility. Comparison with amikacin and gentamicin against 11,840 clinical bacterial isolates.

The susceptibility of 11,840 clinical bacterial isolates to fortimicin A was determined by agar dilution or broth microdilution methods and compared with their susceptibility to amikacin and gentamicin. In general, the in vitro activity of fortimicin A was essentially the same as that of amikacin. Significant exceptions were the increased effectiveness of fortimicin A against Serratia marcescens and the greater activity of amikacin against Pseudomonas and other nonfermentative gram-negative bacilli. On a weight-for-weight basis, gentamicin showed greater activity than the other two antimicrobial drugs against most species; S. Marcescens was the major exception. However, at concentrations equivalent to achievable nontoxic serum levels, the proportion of isolates inhibited by the three drugs was quite comparable. There were several strains with unusually high resistance to one or more of the tested antibiotics. These usually occurred in one of the six participating institutions and could be traced to specific enzyme-producing or permeability mutants endemic to that particular institution.

Amikacin↗
PubMed1979

Rapid identification of Enterobacteriaceae with the micro-ID system versus API 20E and conventional media.

The Micro-ID system for rapid (4 h) identification of Enterobacteriaceae was evaluated by testing 433 enteric bacilli and 9 other gram-negative bacilli. Each isolate was identified with conventional tubed media and was also tested in the Micro-ID and API 20E systems. The overall accuracy of both systems was 97%. Micro-ID tests for the Voges-Proskauer reaction, indole and H2S production, and ornithine and lysine decarboxylase all demonstrated a 97 to 99% correlation with conventional methods. Only 86% of the Micro-ID urease tests agreed with Christenson urea agar. Two inoculum densities were tested in Micro-ID panels, with 157 stock cultures. Over 90% of the tests were unaffected by changes in inoculum density. Tests with four control strains suggested that the Micro-ID system was more reproducible when a light inoculum was used. The Micro-ID system was found to be a very convenient method for rapid, accurate, and precise identification of the Enterobacteriaceae.

Bacteriological Techniques↗