Sonication provides maximal recovery of staphylococcus epidermidis from slime-coated vascular prosthetics

Staphylococcus epidermidis (S. epidermidis) prosthetic vascular graft infections are often difficult to detect. A reliable culture method is needed so that appropriate therapeutic decisions can be initiated in a timely fashion. Sonication of graft material has been proposed as a method of enhancing bacterial recovery. Theoretically, however, this could cause cell lysis and false-negative culture results. Several methods of obtaining bacterial cultures were compared to determine the best method of quantitative bacterial recovery from infected graft material. Polytetrafluoroetehylene (PTFE) and knitted Dacron graft segments (n = 192) were exposed to a slime-producing strain of S. epidermidis or Escherichia coli (E. coli) at four different bacterial concentrations. Recovery of bacteria from the segments was then compared using three different methods to obtain organisms. One-third of the segments were pressed directly onto the agar to transfer bacteria while the other two-thirds were placed in broth and then either sonicated or vortexed prior to plating onto agar. The direct technique was significantly less effective (P less than 0.01) at recovering bacteria than either sonicating or vortexing for both graft materials at bacterial concentrations of 10, 10(2), and 10(4) CFU/ml of S. epidermidis. Sonication was significantly better at recovery from either material at 10(2) and 10(4) CFU/ml of S. epidermidis than vortexing (P less than 0.05). E. coli graft adherence was poor, and significant recovery occurred only at 10(8) CFU/ml. Sonication is necessary to maximally recover S. epidermidis from infected prosthetic grafts.