Comparative bactericidal activity of imipenem and other antibiotics against Pseudomonas aeruginosa

The bactericidal activity of imipenem (IM), ticarcillin (TIC), ceftazidime (CEZ), amikacin (AMK) or tobramycin (TOB), ciprofloxacin (CIP), was compared on 6 P. aeruginosa: 1 ticarcillin, susceptible strain (TICs), 5 constitutive beta-lactamases producing strains (PSE, TEM, OXA1, OXA2, cephalosporinase (CEP). The time-kill-curves method was performed. Bacteria were incubated with antibiotics at M.I.C. X2 and at concentrations obtained in vivo with usual therapeutic doses: IM 4-8 mg/l, TIC 64-128, CEZ 4-32, TOB 2-8, AMK 4-16, CIP 1-4. The bactericidal activity of IM was independent of the concentration. A 5 Log10 reduction in viability was observed at 3 h for strains TICs, TEM and PSE, 3 Log10 for strains OXA and CEP. This bactericidal activity was also observed in a non growing system. The bactericidal activity of TIC (strain TICs) and CEZ was slower and weaker: 1-2 Log10 at 6 h, 2-3 Log10 at 24 h. It is not observed in a non growing system. On the other hand, the bactericidal activity of aminoglycosides and ciprofloxacin was rapid: 3-4 Log10 at 3 h, 5 Log10 at 6 h for all strains in growing and non growing systems. IM is the only beta-lactam antibiotic bactericidal on growing and non growing cells of P. aeruginosa like aminoglycosides and new quinolones.     

In vitro activity of fosfomycin combined with ceftazidime, imipenem, amikacin, and ciprofloxacin againstPseudomonas aeruginosa

The in vitro activity of fosfomycin in combination with ceftazidime, imipenem, amikacin, or ciprofloxacin was studied by an agar plate checkerboard method against 40 clinical isolates ofPseudomonas aeruginosa with various antibiotic resistance profiles. Fosfomycin/ciprofloxacin appeared to be the most effective combination (synergy 15%, addition 80%, indifference 5%), followed by fosfomycin/amikacin (synergy 7.5%, addition 52.5%, indifference 40%), fosfomycin/imipenem (addition 37%, indifference 63%), and fosfomycin/ceftazidime (addition 20%, indifference 80%). The effects of the combinations were not significantly infl enced by the antibiotic susceptibility patterns of the strains.     

Postantibiotic effect of some antibiotics on the metabolism of Pseudomonas aeruginosa

The influence of the postantibiotic effects (PAEs) of ciprofloxacin, pefloxacin, imipenem, meropenem and amikacin in the suprainhibitory concentrations (2 × and 4 × MIC) on the metabolic processes of P. aeruginosa was studied. The synthesis of macromolecules was expressed by influencing of the incorporation rate of [¹⁴C] adenine and [¹⁴C] leucine. Remarkable affecting of both biosynthetic processes evoked the suprainhibitory concentration 4 × MIC of meropenem by inhibition of the nucleic acids synthesis to 76.1% and proteins synthesis to 61.1% against the control. The suprainhibitory concentration 4 × MIC of both pefloxacin and ciprofloxacin affected the highest suppression of the endogenous respiration to 16.5% and to 20.3%, respectively. The respiration was influenced the least after the effect of meropenem in the both suprainhibitory concentrations tested. According to our knowledge, this is first report about the evaluation of the endogenous respiration after PAE. In this study we demonstrated the inhibitory effects of 4 × MIC concentration of antibiotics studied on the metabolic processes of P. aeruginosa. The results suggest a multiple mechanism for the PAE.     

Immunotherapeutic potential of monoclonal antibodies againstPseudomonas aeruginosa protein F

European Journal of Clinical Microbiology & Infectious Diseases - To unambiguously demonstrate the immunotherapeutic potential of outer membrane porin protein F fromPseudomonas aeruginosa, a...     

In vitro and in vivo synergy between ceftriaxone and aminoglycosides againstPseudomonas aeruginosa

The antibacterial interaction between ceftriaxone and the aminoglycosides tobramycin, gentamicin and amikacin againstPseudomonas aeruginosa was investigated in vitro and in experimental systemic infections of the mouse. In vitro synergy was observed in 70% of the strains with tobramycin, 67.5% with gentamicin, and 77.5% with amikacin. Synergistic bactericidal activity was demonstrated with all three aminoglycosides in combination with ceftriaxone. In line with these in vitro results, synergism against most isolates also occurred in mice. In leukopenic mice, the addition of ceftriaxone resulted in a more than 2.5-fold reduction of the aminoglycoside dose necessary for antiinfective protection, although ceftriaxone alone was only marginally active against the pathogen used in immunocompromised animals.     

Mechanism of imipenem resistance acquired by threePseudomonas aeruginosa strains during imipenem therapy

Imipenem sensitive pretherapy isolates (MICs 1–2 mg/l) and the corresponding resistant posttherapy isolates (MICs 16 mg/l) ofPseudomonas aeruginosa from three patients undergoing imipenem treatment were analyzed to establish the resistance mechanism. The identity of pyocin types, serotypes, DNA restriction endonuclease profiles and plasmid profiles strongly suggested isogenicity of pre- and posttherapy isolates. The imipenem resistant posttherapy isolates showed cross-resistance only to another carbapenem, meropenem. There were neither qualitative nor quantitative differences between pre- and posttherapy isolates in -lactamase production. Affinity of the penicillin-binding proteins 1A, 1B, 2, 3, 4, 4 and 5 for [¹⁴C]imipenem was the same in pre- and posttherapy isolates. One-dimensional and two-dimensional gel electrophoresis of outer membrane protein preparations showed diminished expression of an outer membrane protein of about 46.5 and 47.5 kilodaltons, respectively, in the posttherapy isolates. This protein had an apparent isoelectric point of about pH 5.2 in two-dimensional gel electrophoresis. Growth in proteose peptone no. 2 broth did not reduce expression of this outer membrane protein, which spoke against its identity with the outer membrane protein D1. The permeability of the outer membrane for imipenem was reduced in the posttherapy isolates, since addition of 0.5 or 0.25 of the MIC of the permeabilizing agent ethylenediaminetetraacetate reduced the MICs of imipenem for all isolates from each patient to the same (susceptible) level. The diminished expression of one of the outer membrane proteins might be the reason for this reduced permeability.     

Serum bactericidal effect on Pseudomonas aeruginosa isolates from cystic fibrosis patients.

The bactericidal activity against Pseudomonas aeruginosa strains isolated from cystic fibrosis patients was determined in a 10% concentration of normal serum or autologous cystic fibrosis serum. Of the 167 strains tested, 77 (46%) were sensitive (greater than 95% killed) in normal serum. Mucoid strains were more frequently sensitive than nonmucoid strains. Twenty-three sensitive strains tested in ethyleneglycoltetraacetic acid-chelated serum were resistant (less than 10% killed), suggesting only classical pathway activation. Absorption of cystic fibrosis serum with the autologous P. aeruginosa strain resulted in decreased killing by that serum. All sera, including the chelated and absorbed sera, had comparable total hemolytic complement levels. Patients in poor clinical condition (5 out of 12), in contrast to patients in good or moderate condition(1 out of 30), were more likely to have P. aeruginosa strains that were serum resistant in autologous serum but sensitive in normal serum. Sera from these five patients in poor clinical condition were capable of killing heterologous P. aeruginosa strains. These results suggest the presence of a protective or "blocking" activity in serum from some patients in poor clinical conditions. This association of a blocking activity with clinical condition may signal a transition point in the progression of cystic fibrosis lung disease and thus may be another contributory factor in the failure of the cystic fibrosis host to control infection.     

Bactericidal effect of pefloxacin and fosfomycin againstPseudomonas aeruginosa in a rabbit endocarditis model with pharmacokinetics of pefloxacin in humans simulated in vivo

The bactericidal activity of pefloxacin and fosfomycin alone and in combination againstPseudomonas aeruginosa was evaluated in an experimental rabbit endocarditis model after 24 h of treatment. Two strains with intermediate susceptibility to pefloxacin and good susceptibility to fosfomycin were tested. The serum kinetics obtained during administration of 400 mg every 12 h in humans were simulated in the animals using computer-controlled variable-flow infusion. Fosfomycin was administered as a continuous infusion at a constant flow, allowing a steady-state concentration of 47.4±11.9 mg/ml to be reached in serum. In valvular vegetations, pefloxacin was less bactericidal than fosfomycin, and in combination treatment, it reduced (but did not abolish) the bactericidal effect of fosfomycin. The duration of the pretreatment interval (12–48 h) had a negative effect on the bactericidal activity of both drugs, especially that of fosfomycin.     

Identification of a lytic Pseudomonas aeruginosa phage depolymerase and its anti-biofilm effect and bactericidal contribution to serum

Virus Genes - Pseudomonas aeruginosa (P. aeruginosa) infection has imposed a great threat to patients with cystic fibrosis. With the emergence of multidrug-resistant P. aeruginosa, developing an...     

Influence of zinc on Pseudomonas aeruginosa susceptibilities to imipenem.

Serial dilution susceptibility testing of imipenem against 59 clinical isolates of Pseudomonas aeruginosa, conducted simultaneously on single lots of Difco and BBL Mueller-Hinton agar (MHA), resulted in MICs for 90% of strains tested of 8 and 16 micrograms/ml, respectively. MICs for Escherichia coli, Klebsiella pneumoniae, and Pseudomonas spp. were also higher on BBL MHA. Quantification of the cation content of the two MHAs by atomic absorption spectroscopy demonstrated that the zinc concentration in BBL MHA was 15 times greater than that measured in Difco MHA (2.61 and 0.17 micrograms/ml, respectively). Concentrations of calcium, magnesium, iron, manganese, and copper in the two agars were similar. Addition of zinc to Difco MHA resulted in increases in MICs of imipenem for P. aeruginosa but not in the MICs of ceftazidime or cefpirome for P. aeruginosa (P < 0.01). A lesser zinc effect was seen on the activity of imipenem against E. coli, K. pneumoniae, and Pseudomonas spp. The activities of ceftazidime and cefpirome were similar on both MHAs when tested against all gram-negative organisms in this study. Thus, the effect of zinc in MHA was clearly demonstrated by a significant increase in the MICs of imipenem for P. aeruginosa, and, to a lesser extent, for other gram-negative bacilli.     

Instability of in vitro resistance to imipenem in Pseudomonas aeruginosa

In 3 from 19 clinical isolates of Pseudomonas aeruginosa imipenem-resistant subpopulations could be detected in vitro. In comparison to their wild strains these imipenem-resistant cells were lacking an outer-membrane-protein of 50 kD. In the subpopulation derived from Pseudomonas aeruginosa 76 resistance to imipenem was found to be instable. It could be lost within a short period of time after subcultivation in the absence of imipenem. Cells with restored sensitivity to imipenem possess the outer membrane protein of 50 kD as the wild strain does.     

Comparison of two techniques for measurement of in vitro killing kinetics of five antibiotics againstPseudomonas aeruginosa

The in vitro activity of ticarcillin, imipenem, gentamicin, amikacin and ciprofloxacin against sixPseudomonas aeruginosa isolates was evaluated by two time-killing curve methods: the conventional broth technique, and another method previously described which employs a transfer filter membrane. The patterns of the killing curves obtained over a 5 h period with the two techniques were similar. In contrast to the results obtained for beta-lactam agents, the reduction of inoculum was great and increased with the concentration for aminoglycosides and ciprofloxacin. After 5 h, regrowth of the six strains tested was observed in broth with all antibiotics, whereas a bactericidal effect was observed over 24 h with the filter membrane method. Further studies are warranted to determine the reasons for this difference.     

Comparative bactericidal activity of cefsulodin and ceftazidime on Pseudomonas aeruginosa

This research concerns the bacteriostatic and the bactericidal activity of two beta-lactams (cefsulodin and ceftazidime) on ten strains of Pseudomonas aeruginosa affected by carbenicillin. Additionally to classical approaches in the broth and agar technics, a method of culture on filter membrane is used. The results obtained after a 2 hours and 24 hours contact are reported. The resulting values of minimum inhibitory concentrations are comparable. As far as minimum bactericidal concentrations values are concerned, there is no significant difference between the two methods or between the two antibiotics. The analysis of the bactericidal effect of a 2 hours contact allows no inference relative to the comparative effect of the two antibiotics. Each strain of P. aeruginosa has its specific behaviour, and there seems to be no way to extrapolate from their minimum inhibitory concentrations the bactericidal effect of cefsulodin and ceftazidime.     

Characterization of imipenem resistance mechanisms in Pseudomonas aeruginosa isolates from Turkey

The emergence of carbapenem resistance in Pseudomonas aeruginosa threatens the efficacy of this important anti-pseudomonal antibiotic class. Between 2003 and 2006, an increase in the number of carbapenem-resistant P. aeruginosa isolates at the Zonguldak Karaelmas University Hospital was observed (Zongul-dak, Turkey). To assess the imipenem resistance mechanisms emerging in these P. aeruginosa isolates, they were characterized by amplified fragment length polymorphism typing, which revealed diversity among imipenem-resistant isolates as well as two clonally related outbreak groups. The molecular mechanism of carbapenem resistance was characterized in a representative isolate from each clonal group. Mutational disruption of oprD was the most frequently encountered resistance mechanism (23/27 isolates).     

New and sensitive assay for determining Pseudomonas aeruginosa metallo-beta-lactamase resistance to imipenem

We present an imipenem lysate metallo-beta-lactamase (MBL) functional assay. This assay eliminates false-positive results due to the bactericidal effects of EDTA, can be performed with inexpensive reagents available in most laboratories, and is as accurate as the MBL Etest. It is appropriate for both high-accuracy screens and laboratories in developing countries with limited resources.