IDENTIFICATION OF CORYNEFORM AND OTHER GRAM-POSITIVE RODS WITH SEVERAL METHODS

The identification of 202 isolates of aerobically growing Gram-positiv e rods from clinical material was attempted by using a combination of ''traditional'' morphological and biochemical tests (Hollis & Weaver ( 20)) plus patterns of cellular and metabolic fatty acids. This system served as the ''gold standard'' for three others, i.e. API Coryne (Rap id Coryne), MIDI TSBA and MIDI CLIN Aerobic. In addition, several grow th, biochemical and susceptibility tests (growth on cystine-tellurite blood agar, DNase, hippurate and starch hydrolysis, methanethiol forma tion, API ZYM, CAMP reaction, susceptibility to 0/129 and to six antim icrobials) were done in order to check their usefulness for the identi fication of this group of bacteria. Our system, with the help of chemo taxonomic tests (m-DAP and mycolic acids), was able to identify 154/20 2 (76%) of the isolates by species and an additional 41/202 (21%) by g enus only; 7 (3%) could not be identified. The API Coryne system ident ified to species or genus level 140/195 isolates (72%). Corresponding figures for the MIDI TSBA and CLIN systems were 63/195 (32%) and 88/19 5 (45%); further details of species and genus identification are prese nted in the text. The main drawback of the commercial systems is the e xtent and probably the numerical depth of the data base. We recommend the use of our multisystem approach for the identification of Gram-pos itive rods until commercial systems are based on a broader and numeric ally more extensive data base. The additional tests did not prove spec ies- or genus-specific.