Bacterial culture of perfusion blood after open-heart surgery.

The results of routine culture of 595 consecutive specimens of perfusion blood are presented. Ten per cent of the specimens yielded bacteria overall, but it was found that the isolation rate was increased to 17.7% when the prophylactic antibodies being given during the bypass were specifically neutralised. Coagulase-negative staphylococci and diphtheroids formed the majority of organisms isolated, but Gram negative bacilli or "coliform" type were also occasionally found. A comparison of the relative findings in patients receiving prophylactic flucloxacillin or cephradine showed that the isolation rates of coagulase-negative staphylococci and diphtheroids were lower in the group receiving flucloxacillin. The origin of the bacteria isolated from perfusion blood remains uncertain but speciation of coagulase-negative staphylococci from perfusion blood and similar organisms isolated subsequently from catheter tips in the same patients revealed no evidence that the two sources of organisms were linked. Although organisms are easily and commonly found in perfusion blood, the relevance of this phenomenon to post-operative endocarditis is not clear.