Figure 3

Expression levels of endogenous β-lactamase gene in E. coli surviving selection at different ampicillin concentrations. Transcript abundances were determined using a total of 29 Affymetrix E. coli 2.0 oligonucleotide microarrays. Expression levels are in arbitrary Affymetrix expression units. Survivors at higher ampicillin concentrations show significantly increased β-lactamase expression.