Staphylococcal wound infection in the pig: Part II. Inoculation, quantification of bacteria, and reproducibility

Bacteria from full-thickness excision wounds with staphylococcal infection in the pig were cultured quantitatively. The bacterial concentration increased with the size of the inoculum, and after 2 days it had already reached a stable, maximal level of approximately log 8 CFU/g in the tissue. The correlation coefficient was 0.753 in comparing concentrations from superficial and deep biopsy halves and 0.145 from "surface wash" and superficial biopsies. The "within wound" sample distribution was logarithmic. The gain in precision when assessing the mean bacterial concentration from three instead of one biopsy was 45%. The coefficient of variation of between wound and within wound determinations was in the same range (i.e., 7.1-12.5%). Paired observations from a sample population with 7 sites (wounds) were needed to determine a 10% change in the bacterial concentration at a significance level of p less than 0.05, and a similar change could be determined from unpaired observations based on two populations with eleven sites.