Comparison of three procedures for biochemical testing of anaerobic bacteria

The Analytab Products, Inc. (API), anaerobic multitest microsystem (MICRO) was compared with the Center for Disease Control conventional (CONV) thioglycolate (supplemented with hemin and vitamin K1) system and with pre-reduced anaerobically sterilized (PRAS) media as recommended by the Virginia Polytechnic Institute. Growth from a solid medium was suspended to produce standard inocula. Substrates included 16 carbohydrates, indole, urea, gelatin, and esculin. API strips were inoculated in air and incubated in GasPak (BBL) jars. MICRO tests were read at 1 and 2 days. CONV tests at 1, 2, and 7 days, and PRAS tests at 3 weeks. One hundred thirty well-characterized strains of anaerobes (76 gram-negative rods, 16 cocci, 26 gram-positive nonsporeforming rods, and 12 clostridia), including 48 reference strains, were studied. Of 2,600 tests performed, 2,085 (80.2%) showed agreement with all three methods. There was 90.9% agreement between the MICRO and CONV, 84.9% between the MICRO and PRAS, and 84.6% between the CONV and PRAS tests. All MICRO tests were reliable except for indole, which was not sensitive enough, and gelatin, which was very insensitive. The MICRO system permits performance of biochemical tests at the workbench in the average clinical laboratory without the need for expensive equipment and time-consuming procedures.