Norfloxacin Promotes Generation of “Spider-like” Formations and SOS Response Induction in Escherichia coli K-12 Macrocolony Biofilms in a Regime below of Sub-inhibitory Concentrations

Quinolones are an important kind of antibiotics employed in the treatment of clinical relevant bacterial infections. It is well known that quinolones causes DNA damage inducing the SOS response system of DNA repair. Many ideas about the effect of these antibiotics on bacterial physiology have been obtained through of treatment of planktonic cultures and sessile biofilms. However, despite these studies, many aspects of how quinolones affect to bacterial metabolism and growth of colonies remains still poorly understood. Here, I report that norfloxacin quinolone antibiotic interferes with the normal development of Escherichia coli K-12 old macrocolony biofilms, altering its morphology, abolishing the formation over its surface of characteristic autoaggregative chondrule-like formations observed in macracolonies non treated with norfloxacin; but intriguingly the norfloxacin treatment induces in this kind of biofilms the formation of a new kind of superficial structures that exhibit a “spider-like” morphology, which has not previously been reported. Interestingly, these spider-like formations are also found outside the colony. Most importantly, when macrocolony biofilms carrying a recA-gfp transcriptional fusion were ordered sequentially in rows, the norfloxacin promoted the SOS induction of recA-gfp activity as well as the alteration of morphology of E. coli K-12 macrocolonies in norfloxacin concentrations lower that the sub-inhibitory concentrations, in a regime of influence that is not expected to be active. The biological implications of these findings are discussed.