(20, 21) and Malka et al. (25). (A) Li et al. derived an equation that includes an experimentally determined bacterial killing constant and the bacterial growth rate (20, 21). It predicts the CNC is constant at all B values. Their experiments show, however, that the bacterial growth rate and killing constant decrease, and the CNC increases (curved dashed line), at B values greater than 10⁷ CFU/ml in stirred suspension and greater than 10⁶ CFU/ml in fibrin gel (not shown). Most importantly, this equation predicts B will decrease or increase at all N values below or above the CNC, respectively, and remain constant at the CNC. (B) In contrast, as reported here by Malka et al., the bacterial population is bistable at N at or very near the CNC, creating favorable conditions for uncontrolled bacterial growth (25). N₁ and N₂ and the dashed line indicate the N and B values that define the zone of bistability in the bacterial population. For N below the CNC (solid yellow line), the bacterial population grows exponentially. Note also that in fibrin gels and rabbit dermis, the CNC at all N values is at least 2-fold larger than in stirred suspensions, a reflection of the effect of the former environment on the bacterial killing constant.