Rapid immunodiagnosis of streptococci and enterococci in blood cultures

We evaluated a procedure for rapid identification of blood culture isolates of pneumococci, enterococci and beta-haemolytic streptococci groups A, B, C, and G. Immunological tests were applied directly to blood culture medium and included a quellung reaction for pneumococci, and latex agglutination tests (LAT) for pneumococcal antigen and Lancefield antigens A, B, C, D and G. During a one-year trial period with approximately 12,000 blood culture sets (BacT/Alert (R), Organon-Teknika), 208 sets showed pure growth of Gram -positive cocci in pairs or chains by direct microscopy. Overall, a correct diagnosis was noted for 103 (63.2%, 95% CI: 55.370.6%) of 163 sets yieldin g pneumococci, betahaemolytic streptococci, or enterococci. A procedure exc luding Lancefield antigens only A, BI and D was implemented during a one-ye ar follow-up period. With this simplified procedure positive and negative p redictive values, respectively, were 1.00 and 0.87 for pneumococci, 1.00 an d 0.94 for betahaemolytic streptococci group A, 0.60 and 1.00 for beta-haem olytic streptococci group B, and 0.91 and 0.88 for enterococci. We conclude that rapid identification of Gram-positive cocci is feasible and may impro ve the information given to clinicians at the first notification of positiv e blood cultures.