Ofloxacin tolerance in aging biofilms is SOS-response-dependent.

<p>(A) The influence of the SOS response on the ofloxacin tolerance of aging biofilms was evaluated and compared between biofilms of wild-type TG1 (WT), Δ<i>recA</i>, and <i>lexAind3</i>. (B) A close-up of the data obtained in panel A for the 24- and 48-h biofilms. Briefly, all biofilms were grown for 24, 48, 72 and 96 h in M63B1_Gluc with medium renewal every 24 h and treated for 24 h with ofloxacin (5 µg ml⁻¹, 80× MIC) in M63B1_Gluc (no starvation). Survivors were quantified by viable cell counts. Percent survival represents the tolerant population after 24 h of treatment compared to untreated biofilm prior to addition of antibiotics. All compared biofilms had similar numbers of CFUs prior to antibiotic treatment (data not shown). Data represented are mean ± SEM of at least three replicates. Asterisks indicate values significantly different than WT (panel A). Statistics were performed by the two-tailed unpaired t-test: * <i>P</i>≤0.05, ** <i>P</i>≤0.01, *** <i>P</i>≤0.0001, and n.s. (not significant). The genotypes of the different strains used are detailed in <a href="http://www.plosgenetics.org/article/info:doi/10.1371/journal.pgen.1003144#pgen.1003144.s007" target="_blank">Table S1</a> or as follows: WT (TG1), Δ<i>recA</i> (TG1Δ<i>recA</i>::KmFRT ), and <i>lexAind3</i> (TG1<i>lexAind3</i>).