Figure 5.
Frequency of resistance for Gram-negative isolates
Numbers included in the analysis and mean growth per mL were: amikacin n=117, 3·75 × 10−4; amoxicillin–clavulanate n=24, 2·50 × 10−3; ampicillin n=6, 6·67 × 10−7; ceftazidime n=52, 1·92 × 10−4; colistin n=96, 4·17 × 10−4; fosfomycin n=114, 3·59 × 10−4; gentamicin n=117, 4·45 × 10−3; meropenem n=117, 0·00; and piperacillin–tazobactam n=102, 1·97 × 10−4. The numbers of isolates differed across antibiotics because of susceptibility patterns, with only sensitive bacteria suitable for frequency of resistance determination. Data are presented per mL and the frequency of resistance calculated from growth at a lower dilution on control plates free from antibiotics. Results have been log-transformed with a standard of 1 × 10−10 added to enable incorporation of zero values. This standard was chosen as the lowest rate of frequency of resistance found was 1 × 10−9.