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P C Fuchs

Publications and source records attributed to P C Fuchs.

At least 109 records · Page 6Linked to original sources
PubMed1993

Haemophilus test medium versus Mueller-Hinton broth with lysed horse blood for antimicrobial susceptibility testing of four bacterial species.

Studies were undertaken to determine whether broth microdilution susceptibility tests could be standardized by using a single medium for testing fastidious respiratory pathogens. Mueller-Hinton broth with lysed horse blood and the broth version of Haemophilus Test Medium (HTM) were directly compared. Ten orally administered agents were found to give essentially identical results in both media but minor differences were noted. Because the test are easier to read when HTM broth is used, that medium is to be preferred for routine testing of Haemophilus influenzae, Streptococcus pneumoniae, Streptococcus pyogenes and Moraxella catarrhalis isolates by the microdilution procedure.

Anti-Bacterial Agents↗
PubMed1993

Evaluation of disk susceptibility testing of fosfomycin tromethamine.

Fosfomycin tromethamine is an orally administered fosfomycin that may be used for single-dose therapy of uncomplicated urinary tract infections. At breakpoint concentrations [< or = 128 micrograms/ml plus 25 micrograms/ml glucose-6-phosphate (G-6-P)], fosfomycin tromethamine inhibited > 90% of the 350 bacterial isolates tested. When testing Escherichia coli, Klebsiella spp., and Enterobacter spp., we note that the performance of fosfomycin disks improved when G-6-P was added to the disks. The interpretive error rates were minimized when 200-micrograms fosfomycin disks were supplemented with either 50 or 100 micrograms G-6-P. Using < or = 128 and > or = 256 micrograms/ml as the susceptible and resistant MIC breakpoints, respectively, the regression-analysis-derived disk diffusion zone diameter breakpoints for the 200-micrograms fosfomycin disk supplemented with 50 micrograms of G-6-P are as follows: susceptible, > or = 16 mm; intermediate, 13-15 mm; and resistant, < or = 12 mm.

Bacteria↗
PubMed1993

RO 23-9424, a new cephalosporin 3'-quinolone: in-vitro antimicrobial activity and tentative disc diffusion interpretive criteria.

The susceptibility of 410 clinical bacterial isolates to RO 23-9424, a novel cephalosporin 3'-quinolone, was determined. Overall, 97% of Enterobacteriaceae and 100% of staphylococci were inhibited by < or = 8.0 mg/L of RO 23-9424. Only 60% of Pseudomonas aeruginosa and 80-90% of Pseudomonas spp. and Xanthomonas maltophilia were inhibited by this concentration. Enterococci and Listeria monocytogenes were resistant to RO 23-9424. Clinical isolates of Moraxella catarrhalis, Streptococcus spp., and Corynebacterium jekeium were all susceptible to < or = 8.0 mg/L of RO 23-9424. This drug's antimicrobial activity was superior to that of its two components fleroxacin and desacetylcefotaxime against the organisms tested. Using < or = 8.0 mg/L and > or = 32 mg/L respectively as the susceptible and resistant MIC breakpoints for RO 23-9424, the regression analysis-derived disc diffusion zone diameter breakpoints for the 30 micrograms disc are: susceptible > or = 19 mm, intermediate 16-18 mm, and resistant < or = 15 mm.

Anti-Infective Agents↗
PubMed1993

Methods for testing the susceptibility of anaerobic bacteria to two fluoroquinolone compounds, PD 131628 and clinafloxacin.

The susceptibility of anaerobic bacteria to two new fluoroquinolones, PD 131628 (the bioactive form of PD 131112 or CI-990) and clinafloxacin (CI-960 or PD 127391), was determined with the agar dilution procedures and two media, and one broth microdilution procedure. Sparfloxacin and ciprofloxacin were also tested by the broth microdilution method. One hundred anaerobic isolates and four control strains were tested by the three methods which gave minimum inhibitory concentrations (MICs) that were essentially comparable, but not identical. With the broth microdilution method, the relative potency of the four fluoroquinolones was: clinafloxacin > PD 131628 > sparfloxacin > ciprofloxacin. For the latter three drugs but not clinafloxacin, the MIC values were often near the proposed interpretive breakpoint concentrations, and thus minor methodological differences frequently influenced the interpretive categories. Replicate agar dilution tests in five laboratories established MIC control limits for each of four control strains: those MIC limits could also be used to define the expected performance of the two alternative methods.

Anti-Infective Agents↗
PubMed1993

Dirithromycin disc susceptibility tests: interpretative criteria and quality control parameters.

Dirithromycin and its bioactive metabolite (erythromycylamine) were compared in vitro to erythromycin against 450 bacterial isolates. Dirithromycin and erythromycylamine did not differ in their in-vitro activity and the two compounds were additive when combined in equal proportions. Both compounds were active against erythromycin-susceptible bacteria but erythromycin was two to four times more potent on a weight-to-weight basis. Interpretive criteria for dirithromycin were not based on achievable blood concentrations since tissue concentrations may be 20-30 times greater than peak serum levels. Dirithromycin-susceptible strains were those with zones > or = 19 mm in diameter (15 micrograms dirithromycin disc) or MIC < or = 2.0 mg/L and resistance was defined as a zone < or = 15 mm or MIC > or = 8.0 mg/L. Interpretive criteria for testing Haemophilus influenzae on Haemophilus Test Medium (HTM) agar were not defined because of the drug's poor activity in the test system used. Two multi-laboratory studies were also undertaken, one to define quality control limits for disc diffusion tests and the other to define broth microdilution MIC control limits for tests with dirithromycin.

Anti-Bacterial Agents↗
PubMed1993

Susceptibilities of beta-lactamase-producing and -nonproducing ampicillin-resistant strains of Haemophilus influenzae to ceftibuten, cefaclor, cefuroxime, cefixime, cefotaxime, and amoxicillin-clavulanic acid.

In in vitro studies we evaluated the susceptibilities of beta-lactamase-producing and -nonproducing, ampicillin-resistant strains of Haemophilus influenzae and compared them with those of ampicillin-susceptible strains. Ampicillin, amoxicillin-clavulanic acid, ceftibuten, cefaclor, cefuroxime, cefixime, and cefotaxime were evaluated by broth microdilution tests and disk diffusion tests. The disk diffusion tests accurately categorized beta-lactamase-producing strains and ampicillin-susceptible strains as being susceptible to the study drugs other than ampicillin. Ampicillin-resistant, beta-lactamase-nonproducing strains were relatively resistant to all seven study drugs, but the disk diffusion test did not always predict that resistance. The clinical relevance of the decreased susceptibility to various agents remains unclear, but to be conservative, all ampicillin-resistant, beta-lactamase-nonproducing strains might be assumed to be resistant to other beta-lactams. After excluding that small group of isolates, reliable susceptibility test results were obtained with lots of Haemophilus Test Medium that met quality assurance criteria.

Amoxicillin↗
PubMed1993

Antimicrobial activity and disk diffusion susceptibility testing of Ro 40-6890, the active metabolite of the new cephalosporin ester, Ro 41-3399.

Ro 40-6890, the active metabolite of Ro 41-3399, was tested against 391 gram-negative and gram-positive clinical isolates. Ro 40-6890 was active against members of the family Enterobacteriaceae, Moraxella catarrhalis, pneumococci, other Streptococcus spp., and methicillin-susceptible staphylococci. Preliminary disk diffusion interpretive zone criteria were calculated for 5-, 10-, and 30-micrograms Ro 40-6890 disks and several possible MIC susceptibility breakpoints. We recommend the use of the 5-micrograms disk and suggest that the following zone diameters be used as breakpoints in clinical trials: susceptible, > or = 21 mm (MIC, < or = 1 microgram/ml); intermediate, 18 to 20 mm (MIC, 2 micrograms/ml); and resistant, < or = 17 mm (MIC, > or = 4 micrograms/ml).

Anti-Bacterial Agents↗
PubMed1993

Susceptibility of Haemophilus influenzae to piperacillin-tazobactam combinations: interpretive criteria and quality control limits for standardized tests.

In vitro studies evaluated methods for testing the susceptibility of Haemophilus influenzae to piperacillin-tazobactam combinations. Ampicillin-resistant beta-lactamase-nonproducing strains of H. influenzae may be presumed to be relatively resistant to combinations of piperacillin-tazobactam, even though they frequently appear to be susceptible by disk diffusion methods. Other ampicillin-resistant or -susceptible strains were predictably susceptible; i.e., 130 such strains gave zones of inhibition > or = 26 mm in diameter, and MICs for these strains were < or = 0.125/4.0 micrograms/ml (< or = 1.0/0.12 micrograms/ml when an 8:1 ratio was tested). A resistant category has yet to be defined. For quality control purposes, H. influenzae ATCC 49247 should give zones of inhibition 32 to 38 mm in diameter, and broth microdilution MICs should be 0.12/4.0 to 0.5/4.0 micrograms/ml.

Ampicillin Resistance↗
PubMed1993

Levofloxacin disk potency and tentative interpretive criteria for susceptibility tests.

Levofloxacin disk susceptibility test criteria were evaluated by testing 350 bacterial isolates. Either 5- or 10-micrograms disks could be used satisfactorily. A 5-micrograms levofloxacin disk with zone size breakpoints of < or = 12 mm for resistance (MIC, > or = 8.0 micrograms/ml) and > or = 16 mm for susceptibility (MIC, < or = 2.0 micrograms/ml) is recommended.

Evaluation Studies as Topic↗
PubMed1993

Ramoplanin susceptibility testing criteria.

Ramoplanin and mupirocin are two antimicrobial agents that may be applied topically. They had similar potencies against susceptible gram-positive cocci, but they differed in their spectra of activity. In plastic microdilution trays, the in vitro activity of ramoplanin was slightly diminished but that activity was restored by the addition of bovine serum albumin (0.02%). Susceptible strains were defined as those for which MICs of ramoplanin were < or = 2.0 micrograms/ml (without bovine serum albumin) and which had > or = 11-mm zones around 60-micrograms ramoplanin disks. Criteria for a resistant category cannot be defined at this time.

Anti-Bacterial Agents↗
PubMed1993

Tentative interpretive criteria for disk diffusion susceptibility testing of sparfloxacin.

Susceptibility to sparfloxacin was tested simultaneously by the agar dilution and disk diffusion methods. For tests with 5-micrograms sparfloxacin disks, we propose that the breakpoints for the susceptibility and resistance categories should be > or = 19 and < or = 15 mm, respectively. Most minor discrepancies involved tests with pseudomonads.

Anti-Infective Agents↗
PubMed1993

Tentative criteria for confirming the in vitro susceptibilities of Haemophilus influenzae and Neisseria gonorrhoeae to two fluoroquinolones (sparfloxacin and levofloxacin), including quality control parameters.

Sparfloxacin and levofloxacin were evaluated against 150 Haemophilus influenzae isolates and 149 Neisseria gonorrhoeae isolates in order to define susceptibility testing parameters. Sparfloxacin-susceptible H. influenzae strains were defined as those for which the MICs were < or = 0.25 microgram/ml and the zones were > or = 30 mm, and N. gonorrhoeae susceptible strains were those for which the MICs were < or = 0.03 microgram/ml and the zones were > or = 39 mm (5-micrograms disks). Levofloxacin-susceptible strains of H. influenzae included those for which the MICs were < or = 0.12 microgram/ml and the zones were > or = 32 mm and N. gonorrhoeae susceptible strains were those for which the MICs were < or = 0.12 microgram/ml and the zones were > or = 37 mm (5-micrograms disks). Criteria for a resistant category cannot yet be defined for either quinolone. In multilaboratory studies with different lots of Haemophilus Test Medium, replicate tests with the standard control strain of H. influenzae (ATCC 49247) were evaluated. For sparfloxacin disk tests, the proposed zone size limits were 33 to 42 mm and broth microdilution MIC limits were 0.004 to 0.016 microgram/ml, whereas for levofloxacin tests, zone size limits were 32 to 41 mm and broth microdilution MIC limits were 0.008 to 0.03 microgram/ml. Other multilaboratory studies evaluated tests with supplemented GC agar and N. gonorrhoeae ATCC 49226; for both drugs, zone size limits were 44 to 52 mm and agar dilution MIC limits were 0.004 to 0.016 microgram/ml.

Anti-Infective Agents↗
PubMed1992

Error rates in cefoperazone and cefoperazone-sulbactam disk tests with Enterobacteriaceae and Pseudomonas aeruginosa.

In a collaborative study involving five medical centers, 6% of 2,440 consecutive isolates of Enterobacteriaceae were resistant to cefoperazone; resistance to cefoperazone was reduced to < 1% by the addition of sulbactam. Susceptibility to cefoperazone and cefoperazone-sulbactam was accurately predicted by disk diffusion tests. Resistance to cefoperazone, however, was not as reliably detected by disk tests and results of dilution tests were not always consistent. The prevalence of resistance to cefoperazone and/or the ability to detect resistance had a significant influence on very major error rates for individual laboratories.

Agar↗
PubMed1992

Comparison of fixed concentration and fixed ratio options for testing susceptibility of gram-negative bacilli to piperacillin and piperacillin/tazobactam.

Piperacillin combined with tazobactam was tested at both a fixed ratio (8:1) and fixed tazobactam concentration (4 micrograms/ml) against 2,685 consecutively isolated gram-negative bacilli and 56 highly piperacillin-resistant isolates. Tazobactam significantly enhanced the spectrum of piperacillin activity. Overall, at a concentration of 16 micrograms/ml piperacillin alone inhibited 78.8% of the Enterobacteriaceae isolates compared to inhibition of 92.7% and 95.5% by the 8:1 ratio and fixed (4 micrograms/ml) tazobactam combinations, respectively. In MIC tests the two combination options performed comparably against both routine and highly piperacillin-resistant isolates. Synergistic inhibition was observed for comparable numbers of isolates with the two combination options, the most marked effect being seen in the more highly piperacillin-resistant isolates. Both testing options are supported by the available human pharmacokinetic data; however the 8:1 ratio of piperacillin to tazobactam may be preferable given that the clinical formulation contains the two compounds in an 8:1 ratio and this ratio is maintained in vivo.

Drug Synergism↗
PubMed1992

Spontaneously occurring staphylococcal mutants resistant to clinically achievable concentrations of ciprofloxacin and temafloxacin.

The frequency of spontaneously occurring mutants resistant to 0.5, 1, 2, 4 and 8 micrograms of temafloxacin or ciprofloxacin per milliliter was documented with four Staphylococcus aureus and four Staphylococcus epidermidis strains. Resistant mutants were recovered at two- to four-fold the MIC of either drug, and they displayed cross-resistance to other fluoroquinolones. Resistance to temafloxacin occurred at frequencies lower than those observed with equal concentrations of ciprofloxacin. Resistance to greater than four-fold the MIC of either drug was not detected (frequencies less than 10(-10).

Anti-Infective Agents↗
PubMed1992

Ticarcillin and ticarcillin-clavulanic acid susceptibility tests: error rates for disk tests with consecutively isolated members of the family Enterobacteriaceae.

A five-laboratory coordinated study was undertaken to determine whether ticarcillin and ticarcillin-clavulanic acid disk susceptibility tests could accurately detect resistance among enteric bacilli. Each facility performed disk tests and broth microdilution susceptibility tests with reagents distributed from a common source, and appropriate controls were included in order to ensure methodologic uniformity. Each institution tested 500 consecutively isolated enteric bacilli against ticarcillin and ticarcillin-clavulanic acid. The prevalence of discrepancies between disk tests and dilution tests with 2,435 unselected enteric bacilli provided a valid estimate of the true error rate for tests with the two disks. The current interpretive criteria for susceptibility tests with ticarcillin and ticarcillin-clavulanic acid disks were found to be reliable; i.e., there were major or very major discrepancies between MIC categories and disk test results for less than 1% of all strains and minor discrepancies for only 5 to 10%. Even lower error rates would occur if the zone size-interpretive criteria were modified, but at this time it is difficult to determine whether the practical problems created by making such changes can be justified by the magnitude of the problem that is being resolved.

Clavulanic Acids↗
PubMed1992

Interpretive criteria and quality control parameters for testing susceptibility of Haemophilus influenzae to enoxacin, ofloxacin, and temafloxacin.

Haemophilus influenzae isolates were uniformly susceptible to enoxacin, ofloxacin, and temafloxacin. Zone diameter and MIC interpretive criteria were proposed to define susceptible populations so that mutants with diminished susceptibility might be detected when and if they appear in clinical specimens. Additional collaborative quality control studies defined MIC and zone size limits for tests with H. influenzae ATCC 49247.

Anti-Infective Agents↗