Journal of Antimicrobial Chemotherapy, Vol 42, 755-760, Copyright © 1998 by The British Society for Antimicrobial Chemotherapy
L Coquet, GA Junter and T Jouenne
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.
Resistance of artificial biofilms of Pseudomonas aeruginosa to imipenem and tobramycin [In Process Citation]
Laboratoire des Polymeres, Biopolymeres, Membranes, UMR 6522 du CNRS, Bois Guillaume, France.
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