Agar-entrapped bacteria as an in vitro model of biofilms and their susceptibility to antibiotics.
A simple in vitro system was developed as a model structure of biofilms and to evaluate their susceptibility to antibiotics. Viable Escherichia coli cells were entrapped in agar gel layers and incubated for 2 days in a minimal salt medium supplemented with glucose. After subsequent culture for 3 weeks under metal ion depletion, the biomass distribution inside the gel layer was highly heterogeneous. The cell concentration reached 10(11) cfu/g gel in the outer regions of the agar structure whereas the inner gel areas were less colonized (10(9) cfu/g gel). Immobilized cells displayed enhanced resistance to latamoxef as compared with free microorganisms. Moreover, a 3-week-old immobilized-cell membrane was less susceptible to the antibiotic than a younger (2 days old) one. The exposure for 11 h to 64 micrograms/cm3 latamoxef killed about 90% of the bacteria entrapped in the older agar layer, whereas the number of killed cells was 100-fold higher in the younger structure. Effective diffusivity measurements showed that the diffusion of latamoxef in the biofilm-like agar structures was moderately restricted as compared to that in water, and independent of the immobilized-cell content.
Jouenne
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Laboratoire des Polymères, Biopolymères, Membranes, URA 500 du CNRS, Université de Rouen, Mont-Saint-Aignan, France.
Tresse
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O
Junter
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GA
D000362:Agar; D004058:Diffusion; D004926:Escherichia coli / Q000187:drug effects*; D008826:Microbial Sensitivity Tests / Q000379:methods*; D009070:Moxalactam / Q000494:pharmacology*
D000362:Agar; D009070:Moxalactam