Fig. 10.

$\mathrm{\beta }$-LEAF assays with second generation probe to determine $\mathrm{\beta }$-lactamase production and cefazolin susceptibility in S. aureus ATCC strains with known production of $\mathrm{\beta }$-lactamase. $\mathrm{\beta }$-LEAF assays were performed with the two ATCC S. aureus control strains [known $\mathrm{\beta }$-lactamase producer #1 – B-lac(+) and nonproducer #2 – B-lac(-)], with cefazolin as a test antibiotic. The bacteria were incubated with probe alone and probe+cefazolin, respectively, and fluorescence monitored over 60 min. (a) The data from 60 min are graphically presented. (b) Data from only the first 20 min are graphically shown. For both panels (a) and (b), the $y$-axis represents the cleavage rate of $\mathrm{\beta }$-LEAF (measured as RFU change rate—RFU/min) normalized by bacterial OD (optical density) at 600 nm. The white patterned bars depict the fluorescence change in probe alone reaction to show $\mathrm{\beta }$-lactamase production. The black bars depict the fluorescence change when both the probe and cefazolin are included in the reactions. Where the two bars are significantly different, the antibiotic is predicted to be less active. Results are presented as the average of three independent experiments (each experiment contained samples in triplicates), and error bars represent the standard error.