Resistance of artificial biofilms of Pseudomonas aeruginosa to imipenem and tobramycin

Viable cells of Pseudomonas aeruginosa were entrapped in alginate gel layers and incubated in a minimal glucose (15 g/L)-yeast extract (2 g/L)-salt medium to form artificial biofilm-like structures. After cultivation for 2 days, the biomass distribution inside the polymer was highly heterogeneous. T...

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Bibliographic Details
Published in:Journal of antimicrobial chemotherapy 1998-12, Vol.42 (6), p.755-760
Main Authors: COQUET, L, JUNTER, G.-A, JOUENNE, T
Format: Article
Language:English
Subjects:
Anti-Bacterial Agents - pharmacology
Antibacterial agents
Antibiotics. Antiinfectious agents. Antiparasitic agents
beta-Lactamases - metabolism
Biofilms - drug effects
Biological and medical sciences
Cells, Immobilized
Drug Resistance, Microbial
Imipenem - pharmacology
Life Sciences
Medical sciences
Microbial Sensitivity Tests
Pharmacology. Drug treatments
Pseudomonas aeruginosa - drug effects
Pseudomonas aeruginosa - growth & development
Space life sciences
Thienamycins - pharmacology
Tobramycin - pharmacology
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Summary:Viable cells of Pseudomonas aeruginosa were entrapped in alginate gel layers and incubated in a minimal glucose (15 g/L)-yeast extract (2 g/L)-salt medium to form artificial biofilm-like structures. After cultivation for 2 days, the biomass distribution inside the polymer was highly heterogeneous. The cell number reached approximately 1011 cells/g gel in the outer regions of the gel structures whereas the inner areas were less colonized (c. 10(8) cells g/gel). Killing of immobilized organisms by imipenem and tobramycin were compared with free-cell experiments (inoculum c. 10(9) cells/mL). Sessile-like bacteria displayed a higher resistance to the two antibiotics used alone or in combination than did suspended cells. Exposure for 10 h to 20 x MIC imipenem and 15 x MIC tobramycin reduced the number of viable immobilized bacteria to 0.3% and 3%, respectively, of the initial cell population, whereas these antibiotic concentrations were much more efficient (bactericidal) against free-cell cultures (5 log kill in 6 h). A synergic effect of tobramycin and imipenem was detected on bacterial suspensions but not on biofilm-like structures. Effective diffusivity measurements showed that the diffusion of imipenem in the alginate layer was not hindered. A slight but significant enhancement of beta-lactamase induction in immobilized cells as compared with their suspended counterparts was insufficient to explain the high resistance of sessile-like bacteria.
ISSN:0305-7453
1460-2091
DOI:10.1093/jac/42.6.755