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F Crokaert

Publications and source records attributed to F Crokaert.

At least 37 records · Page 2Linked to original sources
PubMed1991

Evaluation of the E test for quantitative antimicrobial susceptibility testing of Helicobacter pylori.

The Progressive Diagnostics Manufacturers epsilometer test (E test; AB Biodisk, Solna, Sweden), a quantitative variant of the disk diffusion technique, was evaluated comparatively to an agar dilution method for the antimicrobial susceptibility testing of Helicobacter pylori. A collection of 79 H. pylori clinical strains, including isolates with known resistance to various antimicrobial agents, was tested against 12 different antimicrobial agents. All strains were tested on Columbia agar supplemented with 10% horse blood. Plates were incubated at 37 degrees C in microaerobic atmosphere (5% O2, 10% CO2), and readings were done after 3 days of incubation. In general, E test MICs were easy to interpret and the correlation between MICs by the agar dilution method and the E test was good, with 86 and 99.5% of results being within, respectively, 1 and 2 log2 dilution steps in a total of 936 tests. All strains of H. pylori with documented resistance to the tested agents were detected by the E test. Thus, the E test appears to be an easy and reliable method for determination of MICs of antibiotics for H. pylori, and it may offer an interesting alternative to MIC determination by the agar dilution technique.

Drug Resistance, Microbial↗
PubMed1991

Antibacterial effects of meropenem and imipenem against Haemophilus influenzae.

Phase contrast microscopy, killing curves and turbidimetric growth curves were used in a comparative study of the antibacterial effects of imipenem and meropenem on Haemophilus influenzae. The minimal inhibitory concentrations (MICs) and their ranges of meropenem and imipenem using five beta-lactamase-producing strains of H. influenzae were 0.03 (0.015-0.06) and 0.6 (0.5-1) micrograms/ml, respectively. Imipenem and meropenem induced spheroplast formation in cultures. Killing curves showed a bacteriostatic activity for meropenem and imipenem for MIC values, and a lag of 2 h in killing for MIC x 2 to MIC x 64. For these concentrations the killing rates of the two antibiotics were similar. Turbidimetric growth curves showed a higher early increase in optical density for meropenem. As far as the MIC value of meropenem was 10 times lower than the MIC value of imipenem, we may conclude that meropenem was more active than imipenem on beta-lactamase-producing strains of H. influenzae.

Colony Count, Microbial↗
PubMed1990

Antibacterial effect of meropenem and imipenem on Proteus mirabilis.

Phase-contrast microscopy, killing-curves and turbidimetric growth-curves were used in a comparative study of the antibacterial effects of a new carbapenem, meropenem (SM 7338) and imipenem on five strains of Proteus mirabilis. Despite the low MIC (0.2 mg/l) of imipenem for the five strains included in our study, the MBC remained relatively high (4.4 mg/l). During the first few hours of incubation, imipenem induced large lemon-shaped cells while the turbidity increased without substantial changes in culture viability. Later, most of the cell-wall deficient bacteria generated small spheroplasts until the antibiotic concentration exceeded 32 times the MIC. The MIC of meropenem was lower (0.03 mg/l) with an MBC (0.08 mg/l) very close to the MIC. Meropenem also induced large bodies but these cell-wall deficient bacteria did not generate small round bodies as observed with imipenem. In conclusion, imipenem produced in strains of Pr. mirabilis an amdinocillin-like change in cell morphology, responsible for the discrepancies observed between MIC and MBC. This effect was not observed with meropenem.

Imipenem↗
PubMed1990

Inoculum effect on growth-delay time of oxacillin-resistant strains of Staphylococcus aureus and Staphylococcus epidermidis exposed to cefamandole, cefazolin, and cefuroxime.

Cephalosporins have been recommended as prophylactic antibiotics in patients undergoing cardiovascular surgery. The major function of these antibiotics is to protect patients against Staphylococcus aureus and Staphylococcus epidermidis infections. The lowest inoculum amount responsible for infection during surgery is unknown but is probably low. To determine the comparative activities of cefazolin, cefuroxime, and cefamandole against S. aureus and S. epidermidis for prophylactic purposes, we selected five strains of S. aureus and S. epidermidis that presented homogeneous resistances to oxacillin. A continuously monitored turbidimetric method was used to evaluate cultures with variable inoculum sizes ranging from 10(6) to 1 CFU/ml and exposed to cefazolin, cefuroxime, and cefamandole at concentrations of 0.5, 1, 2, 4, 8, 16, and 32 micrograms/ml. Growth was defined as an increase of 0.1 optical density unit. The relationship between the time required for growth, the antibiotic concentration, and the initial bacterial density showed that cefamandole was more active than cefazolin, which, in turn, was revealed to be more active than cefuroxime against S. aureus and S. epidermidis.

Cefamandole↗
PubMed1990

One shot of high-dose amikacin: a working hypothesis.

Recent information suggests that single, large daily dosages of amikacin are less nephrotoxic. The killing rate of amikacin for Escherichia coli and Pseudomonas aeruginosa also suggests to put emphasis on a high peak value. A decrease of 3 log10 CFU/ml was observed for E. coli and P. aeruginosa at 64 and 128 micrograms/ml in 20 min. In comparison, the killing rate of piperacillin was dose-independent and about 6 h were required for a reduction of 10(3) CFU/ml of P. aeruginosa. In theory, the way to proceed in the future would possibly be the one-shot administration of amikacin, followed by a long course of a beta-lactam antibiotic.

Amikacin↗
PubMed1990

Turbidimetric and microscopic analysis of Bacteroides fragilis exposed to tazobactam and piperacillin alone and in combination.

Tazobactam, a non-amino penicillanic acid sulfone, is a new beta-lactamase inhibitor and acts synergistically with piperacillin against clinical isolates of beta-lactamase-producing Bacteroides fragilis. The effectiveness of this inhibitor has been demonstrated by reduction of piperacillin MIC values and growth curves in two combinations (ratio 8:1 and 4:1). Tazobactam has an intrinsic activity against B. fragilis (MIC = 4-8 micrograms/ml). Phase contrast microscopy of treated cells showed cell-wall-deficient bacteria, predominantly filaments for piperacillin and spheric bodies for tazobactam. The combination of these two drugs induced large bulging filaments. This would suggest that with this organism, tazobactam binds to PBP2 while piperacillin binds to PBP3. The growth curves obtained with the MS-2 system showed: (1) a significant deviation (lower OD value) from the control curve with piperacillin at 1/4 MIC and numerous irregularities as compared to the control, due to the presence of filament clusters; (2) a deviation from the control curves without irregularities, quite different than these observed with piperacillin while using tazobactam at 1/8 MIC, and (3) a deviation from the control curve for lower piperacillin values in piperacillin-tazobactam combinations (8:1-4:1). In conclusion, the synergistic efficiencies of piperacillin/tazobactam against B. fragilis act in two ways, inhibition of beta-lactamase and a probable competition of PBPs.

Bacteroides fragilis↗
PubMed1989

Bactericidal activity of meropenem against Pseudomonas aeruginosa.

Ten strains of Pseudomonas aeruginosa that were susceptible to imipenem (MICs 2 mg/l) were exposed to a new parenteral carbapenem, meropenem (MIC 0.25 mg/l). Kinetic turbidometry showed that, as with other beta-lactam antibiotics, there was a prelytic increase in the culture OD following exposure to meropenem. The maximal value of the prelytic increase in the OD was higher for meropenem than for imipenem at concentrations 0.5, 1, 2, 4 and 8 x MIC. This corresponded to the formation of short filaments during exposure to low concentrations of meropenem. These filaments remained viable for 1-2 h, according to the drug concentration. For this reason, the killing began later with meropenem than with imipenem. After this delay, the killing rate for meropenem was the same as with imipenem, but occurred with lower concentrations of meropenem.

Carbapenems↗
PubMed1989

Correlation between the growth and killing curves of Escherichia coli in the presence of cefotetan or piperacillin.

Escherichia coli strains that were susceptible to multiple antibiotics were exposed to cefotetan and piperacillin. As with the majority of beta-lactam antibiotics, the growth curves showed an increase in optical density (OD) due to an increasing volume of cell-wall-deficient bacteria during the first hours before lysis. This increase in OD depended on the concentration of cefotetan and was less dependent on the concentration of piperacillin. A good correlation was found between the prelytic increase in OD and the killing curve. During the prelytic increase in OD, the number of CFU/ml remained more or less constant. The decrease in the number of CFU/ml depended on the concentration of cefotetan and was less dependent on the concentration of piperacillin.

Cefotetan↗
PubMed1989

Correlation between growth curves and killing curves of Escherichia coli in the presence of fleroxacin and ampicillin.

Fleroxacin, a new long-acting quinolone, induces rapid killing and bacterial filamentation as do other quinolones. Ten strains of Escherichia coli were exposed comparatively to fleroxacin and ampicillin in order to determine the effect of sub- and supra-inhibitory concentrations of each of these two compounds on turbidimetric growth curves and viable counts. By comparing the maximal early increase in optical density (OD, PIOD) as colony-forming units per milliliter (CFU/ml) after 2 and 6 h of exposure to antibiotics, we observed a reduced number of CFU/ml in comparison with the control after the 2-hour exposure at 1/4 the minimum inhibition concentration (MIC) and after 6 h at 1/8 MIC, but a high OD value was also seen among the fleroxacin exposed bacteria. For ampicillin, PIOD rates and killing rates were slower and dose dependent. This discrepancy was due to filament formation, which increased the PIOD value to the same extent as the control curve. After exposure to fleroxacin at 1/2 MIC the PIOD decreased significantly and after 2 and 6 h E. coli killing rates of 99 and 99.9%, respectively, were observed. With exposure to 2 and 4 x MIC, both PIOD values and CFU/ml decreased substantially. Combined analysis of continuous turbidimetric monitoring and viable counts showed that subinhibitory concentrations of fleroxacin and beta-lactam had different effects on E. coli. Fleroxacin's rapid killing rate, despite filament formation, contrasted with the result obtained with ampicillin. The minimum antibiotic concentration of fleroxacin against E. coli was around 1/8 MIC.

Ampicillin↗
PubMed1989

Growth curve patterns of Escherichia coli, Serratia marcescens, and Proteus vulgaris submitted to different tigemonam concentrations.

Five strains of Escherichia coli, Serratia marcescens, and Proteus vulgaris were exposed to a new monobactam, tigemonam, in comparison with aztreonam. The study, evaluated by kinetic turbidimetry, has shown that tigemonam exerts a prelytic increase in optical density (OD) similar to that of other beta-lactam antibiotics. The maximal value of the prelytic increase in OD was similar for the two study antibiotics at concentrations of 1, 2, 4, and 8 times the minimum inhibitory concentration, corresponding with filament formation. The OD values varied according to the bacterial species. Bactericidal activity was observed for the three species evaluated. At 6 hours, the killing rate was not dose-related. In conclusion, tigemonam and aztreonam induced first filament formation followed after a few hours by bactericidal activity.

Aztreonam↗
PubMed1988

Rate of bactericidal activity for Branhamella catarrhalis of fleroxacin compared with that of amoxycillin-clavulanic acid.

The rate of bactericidal activity of fleroxacin was compared with that of the combination of amoxycillin and clavulanic acid (in the proportion of 4 to 1) on beta-lactamase producing strains of Branhamella catarrhalis. The rate of bactericidal activity of 1 mg/l was as rapid as that of 1 mg/l of amoxycillin-clavulanic acid combination. This rate was not significantly more rapid if the concentrations of fleroxacin were increased to 10 mg/l. In conclusion, the bactericidal activity of fleroxacin is at least as good as that of the combination of amoxycillin and clavulanic acid. Fleroxacin showed a bactericidal effect for B. catarrhalis at concentrations that would be achieved in humans.

Amoxicillin↗
PubMed1988

Protective effect of amdinocillin against emergence of resistance to ceftazidime in Enterobacter cloacae.

Enterobacter cloacae infections have been shown clinically to respond less reliably to monotherapy with broad-spectrum cephalosporins than was initially expected. Selection of populations producing high levels of beta-lactamase has been shown to be the most frequent reason for treatment failure, and the use of these agents with another active antibiotic is recommended. In this study, E. cloacae strains from clinical specimens susceptible to ceftazidime and amdinocillin by broth dilution and disk tests were examined. In the presence of ceftazidime at 10 micrograms/ml, in vitro selection of resistant organisms was demonstrated for 3 of 11 strains. Selection was prevented when amdinocillin was added in combination. A more rapid killing was also demonstrated with this combination. At inocula of 10(8) CFU/ml, ceftazidime-resistant populations were isolated from 6 of 11 strains in vitro, and the emergence of this resistance was prevented by amdinocillin. The enhanced killing effect noted for amdinocillin with ceftazidime may have resulted in part from complementary activity of the antibiotics on penicillin-binding proteins. The ceftazidime-amdinocillin combination offers an interesting prospect for the therapy of infections caused by E. cloacae strains which are initially susceptible to both antibiotics.

Amdinocillin↗
PubMed1988

Determination of serum bactericidal activity against Escherichia coli by an automated photometric method.

The resistance of gram-negative bacteria to complement-mediated serum activity is supposedly an important virulence factor. However, the lack of standardization in the methods used to determine serum activity and the many definitions applied make the comparisons between studies very difficult. We developed a rapid photometric method that we compared with a classical killing one. Escherichia coli in the exponential phase of growth in brain heart infusion broth (final inoculum, 10(7) CFU/ml) at 35 degrees C was added to 50% human serum in Veronal buffer. Viable counts and automatic recording of the variations in the optical densities were obtained for 40 E. coli strains isolated from the stools of healthy adults. With the viable count method, 17 (42.5%) were susceptible (at least a 1 log CFU/ml decrease), 17 (42.5%) were resistant (a 0.6 log CFU/ml increase), 4 (10%) were intermediate (poorly growing inoculum or a decrease of less than 1 log CFU/ml), and 2 could not be classified (nonreproducible results). Agreement between both methods was observed for 87.5% of the stool strains. Eight reference strains of known susceptibilities were classified identically by both methods, leading to a final concordance rate of 89.6%. A total of 129 blood isolates were tested by the photometric method: 64 (49.6%) were resistant, 50 (38.8%) were susceptible 5 (3.9%) showed early regrowth, and 10 (7.7%) were not perfectly reproducible. Of these 129 blood isolates, 5 were also tested by the killing method: 37 (49%) were resistant, 32 (43%) were susceptible, and 6 (8%) were intermediate. The concordance rate between both assays was 89% for the blood isolates; when the minor discordances were ruled out, it was 97%. This automated method could be a useful screening tool for detecting resistance to serum in clinical trials and for studying the in vitro variations of this property.

Blood Bactericidal Activity↗
PubMed1988

Rate of bactericidal activity for Branhamella catarrhalis of a new macrolide, CP-62,993, compared with that of amoxicillin-clavulanic acid.

The rate of bactericidal activity of a new macrolide, CP-62,993, was compared with that of the combination of amoxicillin and clavulanic acid (in the proportion of 4 to 1) on strains of Branhamella catarrhalis beta-lactamase producers. The antibacterial activity of CP-62,993 was bacterostatic at 0.01 micrograms/ml. After a 6-hour period of bacteriostasis a bactericidal activity (3 log10 CFU/ml) was observed for all concentrations from 0.1 to 10 micrograms/ml after 24 h. The bactericidal rate of amoxicillin-clavulanic acid combination was more rapid during the first 6 h at 1 and 10 micrograms/ml. However, the concentration required to kill 99.9% of bacteria within 24 h was 1 microgram/ml. In conclusion, CP-62,993 was a bactericidal antibiotic for B. catarrhalis at a lower concentration. This in vitro study suggests that this macrolide may be of great interest in infections due to the B. catarrhalis beta-lactamase producer.

Amoxicillin↗
PubMed1987

Selection and counting of aerobic gram-negative bacilli in saliva by the spiral system.

A four-month pilot study involving 100 volunteers, 100 hospitalised patients not on antibiotics and 100 patients on antibiotics was performed using a non labor-intensive system involving inoculator, laser colony counter and 14-cm petri dishes containing MacConkey medium to determine the number of aerobic gram-negative bacilli present in saliva. All colonies greater than or equal to 0.75 mm in diameter were found to be aerobic gram-negative bacteria. This was also valid for Pseudomonas aeruginosa, but only after incubation for 48 h. This study showed that the novel and practical technique used can be applied to a large number of saliva specimens, and antibiotics have limited impact on the buccal microflora (intensive care unit excluded).

Adolescent↗