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Agar-entrapped bacteria as an in vitro model of biofilms and their susceptibility to antibiotics

Thierry Jouenne, Odile Tresse, Guy-Alain Junter
DOI: http://dx.doi.org/10.1111/j.1574-6968.1994.tb06894.x 237-242 First published online: 1 June 1994


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 1011 cfu/g gel in the outer regions of the agar structure whereas the inner gel areas were less colonized (109 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 μg/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.

Key words
  • Biofilm
  • Cell immobilization
  • Latamoxef
  • Susceptibility testing

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