Evaluation of rapid identification of gram-positive cocci in positive blood cultures by use of the AutoMicrobic system Gram-Positive Identification Card

Abstract

Because rapid identification of gram-positive organisms from blood cuitures may provide valuable information for patient care and because the AutoMicrobic system Gram-Positive Identification (AMS-GPI) Card (Vitek Systems, Inc., Hazelwood, Mo.) is designed for the identification of these organisms in 4 to 13 h, we designed this study to evaluate the performance of the AMS-GPI Card in the direct identification of grampositive organisms upon detection of growth in blood culture bottles. We compared direct identification by the AMS-GPI Card with the final AMS-GPI Card identification and with our standard identification methods. We evaluated 51 gram-positive organisms from clinical blood cultures as well as 49 simulated blood cultures. The isolates included Streptococcus pneumoniae (17), Streptococcus pyogenes (13), group D enterococci (12), Streptococcus agalactiae (11), viridans streptococci (10), coagulase-negative staphylococci (21), Staphylococcus aureus (15), and Listeria monocytogenes (1). The AMS-GPI Card identified all of the group D entercocci, viridans streptococci, and coagulase-negative staphylococci and all but one each of the Streptococcus pyogenes and Streptococcus agalactiae isolates. L. monocytogenes was also correctly identified. However, the AMS-GPI Card identified only 12 of 17 Streptococcus pneumoniae and 9 of 15 Staphylococcus aureus isolates by direct inoculation. We therefore conclude that the results of direct identification of gram-positive organisms by the AMS-GPI Card may be used cautiously for rapid direct identification of gram-positive organisms from positive blood cultures.

DNA hybridization and contour-clamped homogeneous electric field electrophoresis for identification of enterococci to the species level

“…Confirmation of the identity of organisms in the event that biochemical reactions are equivocal is sometimes needed. Several systems for identification of gram-positive cocci are commercially available (2,6,11,(16)(17)(18)24), but many are unable to recognize some of the more recently described enterococcal species because of phenotypic similarities among these strains (5,13,14,23,29). Standardized automated methods provide accurate species identification of the majority of isolates but have lacked reliability for identification of some strains (23,29).…”

Evaluation of MicroScan for identification of Enterococcus species

“…Several systems for identification of gram-positive cocci are commercially available (1,2,6,7,10). MicroScan (Baxter Healthcare Corp., West Sacramento, Calif.) has developed a microdilution system which simultaneously provides identification of gram-positive cocci and antimicrobial agent susceptibility results.…”

Update on detection of bacteremia and fungemia.

“…The Vitek system (bioMérieux Vitek) has been tested with some success for identifying a variety of streptococci and staphylococci. Unfortunately, the performance in one study was not ideal for S. aureus (60% correct) and Streptococcus pneumoniae (42% correct) (64).…”