A reliable test for differentiation and presumptive identification of certain clinically significant anaerobes

A modification of the slide catalase test was evaluated to determine its reliability for the presumptive identification of certain anaerobic gram-negative and gram-positive organisms isolated from clinical specimens. A total of 650 fresh isolates was evaluated. Growth from a trypticase blood agar plate or Schaedler's agar with laked blood was transferred to a slide and a drop of 15% H2O2 with Tween 80 added. Veillonella alcalescens, Proprionibacterium species, Peptococcus species, and Bacteroides fragilis, B. thetaiotaomicron, B. distasonis, B. ovatus, and B. vulgatus were positive by this method. Comparative slide and tube catalase tests were performed with the above-mentioned bacteroides species by growing each isolate on trypticase soy agar, Brucella agar, brain-heart infusion agar, each with and without added hemin, and on Schaedler's agar. Four solutions of H2O2 were used, 3 and 15%, and 3 and 15% with Tween 80. The addition of Tween 80 to H2O2 increased the sensitivity of the reaction with both slide and tube methods. The 15% H2O2 with Tween 80 consistently gave the most rapid and persistent positive reaction. A slide catalase test in combination with a Gram stain should be performed on each anaerobic isolate; this would significantly decrease the time required for presumptive identification of many anaerobic organisms.