Role of the culture medium in porin expression and piperacillin-tazobactam susceptibility in Escherichia coli

Elizabeth Pinet (1) , Christine Franceschi (2) , Anne Davin-Regli (1) , Gilles Zambardi (2) , Jean-Marie Pagès (1)

1 TMCD2 - Transporteurs membranaires, chimioresistance et drug-design
2 Bio-Mérieux [Marcy l'Etoile]

The continuing emergence of the multidrug resistance phenotype in Gram-negative bacteria makes the development of rapid susceptibility tests mandatory. To achieve this goal, proprietary specific media for bacterial growth can be used but may have some adverse effects. In this study, we dissected the role of media on porin, efflux pump and b-lactamase expression. Depending on the medium used, we observed a change in piperacillin-tazobactam susceptibility for some isolates, such as increases in MIC values. No significant alteration in efflux activity or in b-lactamase production was detected after changing the incubation medium. The ratio of piperacillinase:nitrocefinase showed no specific alteration, indicating that the various media did not affect significantly the relative enzymic affinity for the substrates. In contrast, osmotic variation was able to modulate both porin expression and OmpC : OmpF balance, thus modulating the antibiotic uptake. This study suggests that porin expression may be impacted by a susceptibility testing medium, which may modify the antibiotic diffusion into the bacteria, thus affecting MIC results.

Domaines: Bactériologie; Biochimie, Biologie Moléculaire

Elizabeth Pinet, Christine Franceschi, Anne Davin-Regli, Gilles Zambardi, Jean-Marie Pagès. Role of the culture medium in porin expression and piperacillin-tazobactam susceptibility in Escherichia coli. Journal of Medical Microbiology, 2015, 64 (11), pp.1305-1314. ⟨10.1099/jmm.0.000152⟩. ⟨hal-01463290⟩