Supplementary rapid biochemical test panel for the API 20E bacterial identification system

Abstract

The API 20E Analytical Profile Index typically suggests 3 or 4 conventional biochemical tests to complete the identification of strains either identified to genus only or that have multiple genera consistent with the profile number. We compiled a simple panel of 8 rapid (4-h) tests that can substitute for the supplementary biochemical tests recommended by Analytab Products (Plainview, N.Y.). The rapid test panel (RTP) consisted of adonitol, cellobiose, lactose, raffinose, rhamnose, and xylose utilization, lysine decarboxylase activity, and motility. A total of 114 consecutive isolates that required additional tests to complete the identifications were each tested with the complete RTP, as well as with the recommended conventional biochemicals. All discordant identifications were resolved by using an expanded series of conventional biochemical tests. Overall, 110 (96%) strains were identified to the correct genus, and 109 (95%) strains were identified to the correct species by using the RTP, as compared with 105 (92%) identified to the correct genus and 90 (79%) identified to the correct species with the recommended tests. The identifications based on the two supplementary test systems did not agree for 7 (6.1%) strains. Four discrepancies were resolved in favor of the RTP, and 3 were resolved in favor of the recommended tests. We were unable to identify 5 (4.4%) strains with the recommended tests and only 1 (0.9%) with the RTP. A majority (86%) of the test strains were identified to the species level with the RTP after only 4 h of incubation.