Quantification of bacteria in operation wounds--an experimental investigation with swab sampling in pigs

Quantitative recovery by swab cultures of Staphylococcus aureus or Escherichia coli from experimental wounds in pigs was studied for assessment of wound contamination in elective surgery. The recovery rate declined rapidly over the first hour. Ten minutes after seeding the wounds with known numbers of bacteria, the recovery was respectively 0.7% and 4.1% for S. aureus and E. coli. Recovery was not affected by the size of the wound. Streaking the swab onto the culture plate, or rinsing the swab in saline and plating out the rinsing fluid immediately after sampling resulted in a three to four times higher yield than by using Stuart's transport medium for later plating. The results provide an indication of the discrepancy between the number of micro-organisms recovered from wounds in elective surgery and the number of micro-organisms required to produce suppurative infection in experiments on animals and in man.