Evaluation of blood clot cultures for isolation of Salmonella typhi, Salmonella paratyphi-A, and Brucella melitensis.

Two types of clot culture, one with taurocholate-streptokinase and the other with bile as a culture medium, and two conventional cultures of whole blood were evaluated in parallel in an area where typhoid fever and brucellosis are endemic. Each of the four systems contained 5 ml of blood or the clot derived from 5 ml of blood and sufficient broth to yield a 1:11 dilution of the specimen. Of 542 patients studied, Salmonella paratyphi-A was isolated from 61, S. typhi from 46, and Brucella melitensis from 30. The two clot cultures yielded the salmonellae equally well; both were superior to whole blood cultured in Trypticase soy broth (P less than 0.02) but not to whole blood cultured in bile (P greater than 0.05). Only two systems were successful for isolation of B. melitensis. Blood-Trypticase soy broth identified 28 (93%), and clot-streptokinase cultures identified 21 (70%) (P greater than 0.05). The data indicate that use of clots per se offers no advantage in sensitivity over procedures which use whole blood. Nonetheless, they are excellent for isolation of enteric fever salmonellae and can be performed with clots left over after serum is removed for serological, biochemical, or other tests.