Activity of six contemporary antibacterial agents against 96 isolates from purulent meningitis: the contribution of desacetylcefotaxime to antimicrobial potency.
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Bacteria↗
Biomedical subjects
A L Barry
Publications and source records attributed to A L Barry.
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↗
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↗
Antimicrobial activity and spectrum of LY146032, a lipopeptide antibiotic, including susceptibility testing recommendations.
LY146032, a new lipopeptide, was found to have a spectrum of gram-positive antimicrobial activity that includes activity against staphylococci (methicillin susceptible and resistant), beta-hemolytic Streptococcus spp., pneumococci, viridans group Streptococcus spp., anaerobic gram-positive cocci, Clostridium spp., and enterococci. The new lipopeptide was generally bactericidal and showed more rapid killing of Listeria spp. (MIC, 1 to 2 micrograms/ml) and staphylococci than either vancomycin or teicoplanin. The 30-micrograms disk was preferred to the 15-micrograms disk on the basis of the preliminary interpretive criteria for susceptibility which indicated zone diameters of greater than or equal to 16 mm for susceptible strains (MIC, less than or equal to 2.0 micrograms/ml) and greater than or equal to 12 mm for resistant strains (MIC, greater than or equal to 8.0 micrograms/ml). These criteria are valid pending the testing of additional gram-positive strains which have LY146032 MICs of greater than or equal to 8 micrograms/ml.
Anti-Bacterial Agents↗
Antimicrobial activity of ceftriaxone, cefotaxime, desacetylcefotaxime, and cefotaxime-desacetylcefotaxime in the presence of human serum.
Eighty-seven organisms were tested against ceftriaxone, cefotaxime, desacetylcefotaxime, and the combination of cefotaxime and desacetylcefotaxime (1:1 ratio) in broth containing 0, 25, or 50% human serum. In the presence of human serum, ceftriaxone MICs were four- to eightfold higher than those obtained in broth, changing 98% of Staphylococcus aureus strains from the susceptible to the moderately susceptible category and 53% of selected gram-negative strains to a more resistant category. The MICs of cefotaxime, desacetylcefotaxime, and cefotaxime plus desacetylcefotaxime were not adversely affected by human serum; in fact, the bactericidal activity was slightly improved.
Bacteria↗
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↗
Reliability of high-content disks and modified broth dilution tests for detecting staphylococcal resistance to the penicillinase-resistant penicillins.
In vitro susceptibility tests were performed with 271 isolates of Staphylococcus species (204 Staphylococcus aureus), including 110 strains resistant to the penicillinase-resistant penicillins. Disks containing 5 or 10 micrograms of methicillin, 1 or 4 micrograms of oxacillin, and 1 or 4 micrograms of nafcillin were evaluated. After a full 24 h of incubation at 35 degrees C, tests with 1-microgram oxacillin disks provided optimal results. Use of the more potent oxacillin, nafcillin, or methicillin disks only increased the number of false-susceptible test results. For broth microdilution tests, 2% NaCl should be added to cation-supplemented Mueller-Hinton broth, and MICs should be recorded after a full 24 h at 35 degrees C. Microdilution tests with oxacillin in broth with 2% NaCl were more reliable than similar tests with methicillin.
Culture Media↗
Optimal dilution susceptibility testing conditions, recommendations for MIC interpretation, and quality control guidelines for the ampicillin-sulbactam combination.
The ampicillin-sulbactam combination was evaluated in vitro to determine the optimal susceptibility testing conditions among five combination ratios and four fixed concentrations of sulbactam. The organisms tested were markedly resistant to aminopenicillins and most other beta-lactams. The ratio of 2:1 is recommended to assure recognition of the ampicillin-sulbactam spectrum and minimize false-susceptible results among strains known to be resistant to this combination. Proposed MIC breakpoint concentrations were compatible with levels in serum achieved with recommended clinical doses. Cross-resistance analyses comparing ampicillin-sulbactam and amoxicillin-clavulanate showed comparable activity and spectra. However, the major interpretive disagreement was sufficient to require separate testing of these aminopenicillin-inhibitor combinations. The recommended ampicillin-sulbactam MIC susceptibility breakpoints are as follows: (i) less than or equal to 8.0/4.0 micrograms/ml for tests against members of the family Enterobacteriaceae, anaerobes, nonenteric gram-negative bacilli, staphylococci, Haemophilus influenzae, and Branhamella catarrhalis; (ii) the ampicillin MICs alone interpreted by National Committee for Clinical Laboratory Standards criteria should predict ampicillin-sulbactam susceptibility for the enterococci, streptococci, and Listeria monocytogenes. MIC quality control ranges were determined by multiple laboratory broth microdilution trials for the ampicillin-sulbactam 1:1 and 2:1 ratio tests.
Amoxicillin↗
Disk diffusion susceptibility testing and broth microdilution quality control guidelines for BMY-28100, a new orally administered cephalosporin.
The BMY-28100 30-micrograms-disk test was evaluated by using 615 clinical isolates. Regression analyses and error rates were determined, leading to the recommendation of greater than or equal to 18-mm zone diameters (MIC correlate, greater than or equal to 8.0 micrograms/ml) for susceptibility and less than or equal to 14-mm zone diameters (MIC correlate, greater than or equal to 32 micrograms/ml) for resistance. Nearly all false-susceptible disk test results were among the Providencia spp. and the beta-lactamase-positive Haemophilus influenzae strains. Susceptibility disk test results for these species should be interpreted with caution. The following broth microdilution MIC quality control guidelines were determined from results of a multilaboratory trial: Escherichia coli ATCC 25922, 1.0 to 4.0 micrograms/ml; Enterococcus faecalis ATCC 29212, 4.0 to 16 micrograms/ml; Staphylococcus aureus ATCC 29213, 0.25 to 1.0 microgram/ml; and Pseudomonas aeruginosa ATCC 27853, greater than 32 micrograms/ml.
Cephalosporins↗
Susceptibility testing of carumonam: interpretive criteria for 30-microgram disk tests and quality control guidelines for disk diffusion and broth microdilution methods.
Carumonam 30-microgram disk diffusion tests with 342 gram-negative organisms suggested modifying earlier interpretive zone criteria, i.e., a susceptibility zone diameter of greater than or equal to 23 mm (less than or equal to 8.0 micrograms/ml MIC correlate) and a resistance zone diameter of less than or equal to 17 mm (greater than or equal to 32 micrograms/ml MIC correlate). Quality assurance guidelines were determined by multilaboratory investigations. Recommended limits were calculated for the gram-negative quality control organisms only. For Escherichia coli ATCC 25922, the recommended limits are 30 to 36 mm and 0.03 to 0.25 micrograms/ml, and for Pseudomonas aeruginosa ATCC 27853, they are 24 to 32 mm and 1.0 to 4.0 micrograms/ml.
Anti-Bacterial Agents↗
Collaborative clinical laboratory study of a broth-disk test for determination of bacterial susceptibility to beta-lactams in combination with amdinocillin.
Methodology for the performance of synergistic antibiotic susceptibility studies has not been standardized. We addressed this problem collaboratively with combinations of amdinocillin and select other beta-lactam antibiotics by using a simple broth-disk test compared with a microdilution approach. Each method used the same drugs singly and in combination. The broth-disk test evaluated each agent and the combinations at concentrations that reflected the breakpoints for each drug; the same ratios of beta-lactam to amdinocillin were used in doubling dilutions with the microdilution method. Initially, each participant studied the same 50 members of the family Enterobacteriaceae; each bacterium was studied on three occasions. Thereafter, 500 representatives of Enterobacteriaceae isolated recently from clinical specimens were studied. Designated strains served as controls. Reproducibility between the two approaches studied in phase 1 of the investigation indicated good agreement between the methods, ranging from 87 to 100%. Agreement between the microdilution and broth-disk tests for the 2,551 clinical isolates ranged from 86 to 95%, with slightly better correlations between combination results than with the single agents. The findings indicate that antibiotic disks used routinely in the clinical laboratory can be used in a simple elution test to determine susceptibility of organisms to beta-lactam antibiotics alone and in combination with amdinocillin.
Amdinocillin↗
Cross susceptibility and absence of cross resistance to cefotetan and cefoxitin.
Tests with 2,713 bacterial isolates (members of the family Enterobacteriaceae and gram-positive cocci) from 14 laboratories compared cefoxitin MICs with cefotetan MICs. Strains that were susceptible to cefoxitin could be assumed to be susceptible to cefotetan. Over half of the cefoxitin-resistant isolates of the Enterobacteriaceae were susceptible to cefotetan.
Cefotetan↗
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↗
Preliminary antimicrobial susceptibility interpretive criteria for cefetamet (Ro 15-8074) and cefteram (Ro 19-5247) disk tests.
Preliminary interpretive zone criteria were calculated for cefetamet (Ro 15-8074) and cefteram (Ro 19-5247) by using 10- and 30-micrograms disks and three possible MIC susceptibility breakpoints. Absolute interpretive agreement between MICs and zone size criteria ranged from 91.8 to 97.2%. Very major errors (false susceptibility) were less than or equal to 1.2% for both cephalosporin disk tests. Morganella morganii strains appeared to produce the highest rates of very major interpretive errors with cefetamet disks.
Bacteria↗
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↗
Bacterial antibiotic resistance before and after clinical application in the United States.
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Anti-Bacterial Agents↗
Cefixime: spectrum of antibacterial activity against 16,016 clinical isolates.
The spectrum of antibacterial activity of cefixime was defined by reviewing data from two multicenter studies and three independent studies that we performed within the past 3 years. Microdilution tests were performed with 16,016 bacterial isolates. An isolate was considered susceptible to cefixime if the minimal inhibitory concentration was less than or equal to 1.0 microgram/ml and resistant if the minimal inhibitory concentration was greater than or equal to 4.0 micrograms/ml. Cefixime was effective against the Enterobacteriaceae (87.7% susceptible to 1.0 microgram/ml) as well as against pathogenic Neisseria spp. (including penicillin-resistant gonococci), Haemophilus influenzae (including ampicillin-resistant strains), penicillin-susceptible Streptococcus pneumoniae and other Streptococcus species (minimal concentration inhibiting 90% of organisms less than or equal to 0.25 micrograms/ml). Species resistant to cefixime included penicillin-resistant pneumococci, Staphylococcus spp., Enterococcus spp., Listeria spp., Acinetobacter spp. and Pseudomonas spp.
Bacteria↗
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↗