(a) Experimental design of the forward genetic screen. A highly saturated EC958 transposon mutant library was incubated in the presence of 4 mg/L cefotaxime for 16 h and then cells were harvested, genomic DNA (gDNA) was extracted and analysed by TraDIS. (b) Genes identified by TraDIS to be associated with susceptibility of EC958 to cefotaxime. Shown in red are the significant genes required for survival in the presence of cefotaxime. (c–e) Examples of the difference in Tn5 insertion for the (c) bla_CMY-23, (d) ftsN and (e) tatB and tatC genes. A significant decrease in the Tn5 insertion frequency (expressed as number of reads) was observed following growth in LB containing 4 mg/L cefotaxime (bottom) compared with LB (top). This figure appears in colour in the online version of JAC and in black and white in the print version of JAC.