Search PubMed⌕ Search

Biomedical subjects

E Yourassowsky

Publications and source records attributed to E Yourassowsky.

At least 37 records · Page 2Linked to original sources
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

Enoxacin in acute exacerbations of chronic bronchitis: a comparison with amoxycillin.

A total of 43 hospitalized adult patients with acute exacerbations of chronic bronchitis or bronchiectasis due to Gram-negative bacteria were randomized to receive either enoxacin (400 mg bd) or amoxycillin (1,000 mg tid) for 7-12 days. Micro-organisms isolated included 24 Haemophilus influenzae (three beta-lactamases positive), 11 Branhamella catarrhalis (six beta-lactamase positive), two Pseudomonas aeruginosa and two Neisseria meningitidis in 37 evaluable patients. In the enoxacin group (23 patients) 82.6% of the patients were clinically cured or improved against 93% of patients in the amoxycillin group (14 patients). In the enoxacin group 76% of the pathogens were eradicated with two failures (P. aeruginosa), one relapse (H. influenzae) and three superinfections (Streptococcus pneumoniae). In the amoxycillin group, 71% of the pathogens were eradicated with 29% relapses. The differences between the two groups were not statistically significant. An increase in theophylline concentration occurred in 15 of 16 patients receiving simultaneous administration of theophylline, without clinical evidence of toxicity when theophylline dosage was reduced and enoxacin continued. Enoxacin appears to be as effective as amoxycillin in the treatment of acute exacerbations of chronic bronchitis due to susceptible Gram-negative bacteria.

Acute Disease↗
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

In vitro susceptibility of Alcaligenes denitrificans subsp. xylosoxidans to 24 antimicrobial agents.

The in vitro susceptibilities of 37 clinical isolates of Alcaligenes denitrificans subsp. xylosoxidans to 24 antimicrobial agents were determined. Imipenem was the only drug with consistent activity (MIC for 90% of isolates, 2 micrograms/ml). Piperacillin, ticarcillin-clavulanic acid, ceftazidime, and co-trimoxazole were active against most strains. All the isolates were resistant to ampicillin, cefazolin, cefuroxime, cefamandole, cefotetan, ceftriaxone, cefotaxime, aztreonam, amdinocillin, and temocillin. Most isolates were resistant to the aminoglycosides tested, including amikacin. Lack of activity was also observed for all new 4-quinolone antimicrobial agents.

Alcaligenes↗
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↗
PubMed1988

Bactericidal effect and regrowth of Streptococcus faecalis exposed to amoxicillin following beta-lactamase.

Streptococcus faecalis usually requires high concentrations of penicillin or ampicillin to achieve killing (i.e. a high MBC/MIC ratio). However, most strains show the Eagle or paradoxical effect. We subjected 12 strains of S. faecalis to 0.1, 1, 10 and 100 micrograms/ml of amoxicillin. Turbidometry studies have shown that 3 h after the inactivation of amoxicillin by penicillinase, there was a longer effect for 1 micrograms/ml following beta-lactamase (12 h 31 min +/- 2 h 09 min) than for 10 micrograms/ml (7 h 0 min +/- 1 h 12 min) or 100 micrograms/ml (5 h 22 min +/- 0 h 52 min). After 3 h, the reduction of CFU/ml (inoculum 10(6) CFU/ml) was -1.8 +/- 0.6 for 1 micrograms/ml, -0.56 +/- 0.56 for 10 micrograms/ml and -0.21 +/- 0.20 for 100 micrograms/ml. The more rapid killing at 3 h was not the only reason for the longer effect following beta-lactamase observed with 1 micrograms/ml. Indeed, the growth curve obtained with an inoculum of 10(3) CFU/ml was 2 h delayed from the control curve (10(6) CFU/ml). In conclusion, a paradoxical effect (killing curves and effect following beta-lactamase) was observed for all S. faecalis strains included in this series.

Amoxicillin↗
PubMed1988

Penetration of aminoglycosides in uninfected pleural exudates and in pleural empyemas.

The concentrations of gentamicin, netilmicin, and amikacin were determined after one single intravenous injection in uninfected pleural fluid after thoracotomy and in purulent pleural empyemas. The mean peak concentrations in the pleural fluid after the injection of gentamicin (1.5 mg/kg), netilmicin (2.0 mg/kg), and amikacin (7.5 mg/kg) were 2.9 +/- 0.3 mg/L, 3.7 +/- 0.8 mg/L, and 11.0 +/- 3.1 mg/L, respectively. The pleural penetration of the drugs was very high (from 80.0 to 99.1 percent). By contrast, gentamicin and netilmicin were not detectable in empyema pus; in this exudate the mean peak level of amikacin was 5.7 +/- 2.2 mg/L, with the penetration of this drug being 31.0 percent. The concentrations of parenterally administered aminoglycosides are substantially lower in empyema pus than in sterile pleural fluid. The possibility of poor pleural penetration of some aminoglycosides, as well as the presence of local conditions in pleural empyema unfavorable to the bioactivity of these drugs, must be kept in mind when treating pleural infections.

Amikacin↗
PubMed1988

[Prospective considerations on the dose-effect relationship in antibiotic therapy].

Even though antibiotic in vivo and in vitro modes of action are not superposable, laboratory studies allow a logical approach to the treatment of infections. The answer to the question "What dose and for how long?" frequently asked during the treatment of a severe infection is not necessarily "The maximum dose for a long duration". The following points among many others, should be taken into consideration. The rate of bacterial action of beta-lactams on Gram negative bacilli is concentration dependent for ampicillin and amoxicillin for instance. This rate is hardly concentration dependent for ureidopenicillins (azlocillin, mezlocillin and piperacillin) and azthreonam which bind principally on PBP3. With third generation cephalosporins, in relation to concentrations, two steps in bactericidal rate may be observed. The post-antibiotic effect is often short (1 hour). The rate of bactericidal action of beta-lactams on Staphylococcus aureus is hardly concentration dependent. The post-antibiotic effect may be long (4 to 6 hours). A paradoxical effect may be observed namely with Streptococcus faecalis. The killing rate of beta-lactams is inoculum dependent. The aminoglycosides have a very high bactericidal activity rate on Gram positive and Gram negative bacteria. The post-antibiotic effect is long (4 to 6 hours). The antibacterial effect is little inoculum dependent. These conclusions are driven from experiences performed on cultures in growth phase. One of the controversial point related to the in vitro in vivo relationship is the ignorance of the multiplication rate of the bacteria in the infected site.(ABSTRACT TRUNCATED AT 250 WORDS)

Aminoglycosides↗
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↗