Growth curves for WHO X³⁵ parent strain and the in vitro selected high-level gentamicin-resistant WHO X₁₀₀ mutant and competition experiment using coculture in an HFIM for gonorrhoea.^36,43 (a) shows the cfu/mL of WHO X compared with WHO X₁₀₀ during growth for 7 days and (b) displays the CI^36,43 during coculture for 7 days, which illustrates how WHO X is outcompeting WHO X₁₀₀ (especially during the first 4 days). A negative value indicates that the in vitro selected high-level gentamicin-resistant WHO X₁₀₀ mutant has a lower biofitness compared with the gentamicin-susceptible WHO X³⁵ parent strain. This figure appears in colour in the online version of JAC and in black and white in the print version of JAC.