Figure 4: Power to detect minor populations.

(a) Simulation 2: power to detect minor resistant alleles in 27,000 in silico mixtures created by taking 1,000 pairs of S. aureus samples and mixing each pair in 27 different ratios. As above, we do not estimate false-negative rates for drugs where we have <10 resistant samples, as confidence intervals would be unreasonably large. Power is greatest for the drugs where resistance genes reside on multi-copy plasmids, namely erythromycin and tetracycline. Tet, tetracycline; Ery, erythromycin; Meth, methicillin; Pen, penicillin; Fuc, fusidic acid; Cip, ciprofloxacin. (b) Power to detect low-frequency coagulase-negative species (red, simulation 1, N=540, described above) is consistently higher than power to detect mecA (blue, simulation 2, N=27,000, frequencies down to 1% only due to large sample numbers; dotted lines extrapolate linearly from points at 1 and 2%), which causes methicillin resistance in S. aureus. Thus, the risk of detecting mecA but not detecting the coagulase-negative species it comes from is limited.