Neutrophils in the war against Staphylococcus aureus: predator-prey models to the rescue

To address the question of whether a minimum concentration of blood neutrophils is necessary to decrease Staphylococcus aureus concentration in mastitic milk, literature was searched for studies in which neutrophils were incubated with Staph. aureus. Different mathematical models that describe the changes in Staph. aureus population as a function of neutrophilic concentrations were applied to the collected data. The best fitted model established (1) that the rate of bacterial killing depended on the ratio of neutrophils to bacteria with neutrophilic attack rate accelerating at first before decelerating as the ratio increases, and (2) that neutrophil concentration should be within a limited range to trigger a decline in the bacterial population. Outcomes of this model are supported by what is known about neutrophilic functions and laboratory findings in bovine and human neutrophils. These results may be of assistance in setting selection goals for a better resilience to Staph. aureus mastitis in dairy cattle. Indeed, an optimal neutrophilic concentration appears to exist for successful clearance of Staph. aureus infection, which is neither the lowest nor the highest one.