RAPID ORGANISM IDENTIFICATION FROM BACTEC NR BLOOD CULTURE MEDIA IN ADIAGNOSTIC MICROBIOLOGY LABORATORY

Aims-To evaluate rapid organism identification on positive blood cultu re Bactec NR media (phial types 26, 27, 42 and 17), and to assess the usefulness of these procedures in a diagnostic microbiology laboratory . Methods-Two hundred and sixty, first positive, blood culture bottles from individual patients were tested by rapid identification methods selected on the basis of Gram film organism morphology. Tube coagulase and latex agglutination were applied to presumptive staphylococci; la tex agglutination antigen detection methods to suspected pneumococci, Neisseria and Haemophilus sp; and latex agglutination grouping tests f or cultures thought to be non-pneumococcal streptococci. Results-Media type did not influence test performance (p > 0.05 for all comparisons ). Misapplication of methods occurred on eight occasions and there wer e 14 false positive results, nine involving the latex reagents for gro up C streptococci and pneumococci. The positive predictive values for tube coagulase tests and latex reactions for H influenzae type b, and N meningitidis groups B and C were 100%. The pneumococcal and staphylo coccal latex tests gave positive predictive values of 94.1% and 62.5%, respectively, and the corresponding figure for streptococcal grouping reactions was 75.9%. With the exception of staphylococcal latex testi ng (80%) all investigation negative predictive values were > 90%. Conc lusions-The performance of the staphylococcal latex agglutination meth od was unsatisfactory and it is not appropriate for use with the media studied. In view of the cross-reactions observed with the tests used to identify group C streptococci and pneumococci, positive findings mu st be interpreted with caution. In all other regards the protocol eval uated produced rapid, reliable, clinically useful information and, sub ject to local experience, is recommended to users of Bactec NR media.