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Biomedical subjects

E Yourassowsky

Publications and source records attributed to E Yourassowsky.

At least 19 recordsLinked to original sources
PubMed1992

[Is there in Belgium an increase in resistance to the combination amoxicillin/clavulanic acid of Escherichia coli as reference bacteria?].

The difficulties encountered in measuring the susceptibility of the association amoxicillin/clavulanate can be a cause for disagreements between laboratories. With an inoculum standardized at 10(4) CFU/spot, the resistance level of E. coli approaches 10%. If the variety of current methods is taken into account, the evaluation of a resistance increase can only be an internal one, specific for each laboratory, provided that methods do not change in the course of time.

Amoxicillin↗
PubMed1992

Comparative kill and growth rates determined with cefdinir and cefaclor and with Streptococcus pneumoniae and beta-lactamase-producing Haemophilus influenzae.

The relationship between the growth rate and the kill rate was used to evaluate and to compare the in vitro bactericidal activities of cefdinir, a new oral cephalosporin, and cefaclor against Streptococcus pneumoniae and beta-lactamase-producing strains of Haemophilus influenzae. These frequently encountered pathogens of community-acquired respiratory tract infections are usually susceptible to both drugs. The MIC ranges for cefdinir and cefaclor were, respectively, 0.03 to 0.06 and 0.25 to 0.5 micrograms/ml for S. pneumoniae and 0.25 and 4 to 8 micrograms/ml for H. influenzae. The colony counts (CFU per milliliter) measured after 6 h of exposure to a range of antibiotic concentrations in broth were plotted against the colony count of the control culture over the same period of time. Higher kill rates versus bacterial growth rates were noted for S. pneumoniae for both drugs (positive balance). Conversely, lower kill rates versus growth rates were noted for H. influenzae for both drugs (negative balance). In conclusion, the bactericidal activities of both drugs against S. pneumoniae and H. influenzae were similar when expressed by the relationship between the growth rate and the kill rate at 6 h, but cefdinir was more active at lower concentrations.

Cefaclor↗
PubMed1992

Killing rate and growth rate comparison for newer beta-lactamase-stable oral beta-lactams against Streptococcus pneumoniae, Haemophilus influenzae and Moraxella catarrhalis.

A new method of data presentation that takes into account the relationship between growth and killing rate was used to evaluate the comparative in vitro bactericidal activity of cefpodoxime, cefuroxime, cefixime and an amoxicillin/clavulanic acid combination against Streptococcus pneumoniae and beta-lactamase-producing strains of Haemophilus influenzae and Moraxella catarrhalis. For each strain, the viable count decrease (log CFU/ml) after 6 h of exposure to different antibiotic concentrations was plotted against the viable count increase in the control culture, over the same time. Higher killing rates than those predicted by growth rates were defined as a positive balance; lower rates than those predicted by growth rates were defined as a negative balance. The activity of the 4 drugs against S. pneumoniae and M. catarrhalis was characterized by a positive balance. Conversely, the 3 cephalosporins showed a negative balance for H. influenzae.

Anti-Bacterial Agents↗
PubMed1992

Susceptibility of anaerobic microorganisms to hypothiocyanite produced by lactoperoxidase.

The susceptibility of Capnocytophaga ochracea, Eikenella corrodens, Eubacterium yurii, Fusobacterium nucleatum, Peptostreptococcus micros, Prevotella intermedia, Selenomonas sputigena, Wolinella recta to hypothiocyanite (OSCN-) produced by the lactoperoxidase system was tested. Results showed a decrease of bacterial survival rate after OSCN- exposure, with an intra- and inter-species variability from 0 to 95% for C. ochracea, 34-100% for E. corrodens, 0-83% for E. yurii, 1-15% for F. nucleatum, 8-61% for P. micros, 0-100% for P. intermedia, 0-44% for S. sputigena and 0-8% for W. recta. The survival rate did not correlate with the NADH/OSCN- oxidoreductase activity present in the lysed bacteria (r = -0.3248; N = 15; NS).

Anti-Bacterial Agents↗
PubMed1991

Gas-liquid chromatographic analysis of cellular fatty acid methyl esters in Aeromonas species.

The cellular fatty acids of 39 strains belonging to the genus Aeromonas (Aeromonas hydrophila, Aeromonas caviae, Aeromonas sobria, Aeromonas media, Aeromonas schubertii, Aeromonas veronii) were determined by high resolution gas-liquid chromatography. The fatty acid profiles were characterized by major amounts (60% or more) of one saturated (hexadecanoic acid = 16:0) and two unsaturated (hexadecenoic acid = 16:1 and octadecenoic acid = 18:1) acids. While the majority of the strains of the six species exhibited, qualitatively, very similar fatty acid compositions, only minor and inconsistent differences could be observed which would be useful for a distinction of the different taxons. The following fatty acids were qualitatively identified: 12:0, i-13:0, 14:0, 3-OH 13:0, i-15:0, 15:0, 2-OH 14:0, 3-OH 14:0, i-16:0, 16:1, 16:0, i-17:1, i-17:0, a-17:0, 17:0 cyclopropane, 17:1, 17:0, 18:1 (3 isomers), 18:0 and i-20:0. Excellent congruence was found in reproducibility studies. Fatty acid analyses show a great homogeneity within the group and the technique does not appear to be the ideal method in distinguishing between Aeromonas species.

Aeromonas↗
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↗
PubMed1991

Cellular fatty acid composition of Acinetobacter strains.

The cellular fatty acids of the different biotypes of Acinetobacter calcoaceticus were determined by high resolution gas-liquid chromatography. While all strains exhibited, qualitatively, similar fatty acid compositions, quantitative differences were observed in strains belonging to defined phenotypic subgroups which can be used for differentiation.

Acinetobacter↗
PubMed1990

Capsular types and antibiotic sensitivity of pneumococci isolated from patients with serious infections in Belgium 1980 to 1988.

A total of 2,765 strains of Streptococcus pneumoniae isolated in more than 60 Belgian laboratories from blood or normally sterile body fluids between 1 November 1980 and 31 December 1988 were serotyped. From January 1983 onwards susceptibility of the strains to antimicrobial agents was also tested. The 2,765 isolates belonged to 57 of the 84 currently identified serotypes. Overall, 94% of the strains were represented in the current 23-valent vaccine. The remaining 6% of strains were distributed among 18 serotypes. More than 84% of the middle ear fluid isolates came from children under ten years. Meningitis was commonest in children under five years and in adults over sixty years. Two-thirds of pneumococcal bacteremia isolates came from patients over 50 years. Of 1,933 isolates tested for susceptibility to antibiotics, 335 (17%) were resistant to one or more of the agents tested (tetracycline, erythromycin, chloramphenicol, penicillin). Only 19 strains were relatively resistant to penicillin, while six were fully resistant. Resistance to erythromycin increased significantly from 5.2% in 1986 to 11.5% in 1988. The resistance of Streptococcus pneumoniae to other antimicrobial agents did not change significantly during the study period. There was no relationship between age group and resistance to any of the agents tested.

Adolescent↗
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↗