Evaluation of the sodium polyanethol sulfonate disk test for the identification of Peptostreptococcus anaerobius.

The previously reported sodium polyanethol sulfonate disk test for the identification of Peptostreptococcus anaerobius (Graves et al., 1974) was evaluated, with modifications. Three bands of brucella agar, three inoculum sizes, and two inoculum sources were compared. Nine stock cultures of P. anaerobius (eight normal flora isolates and ATCC 27337) and 16 fresh clinical isolates were used. All cultures of P. anaerobius showed inhibition zones of 12 to 30 mm in diameter, regardless of test conditions. Out of 103 clinical isolates of other species of anaerobic gram-positive cocci tested, only two had an inhibition zone size in this range (one P. micros of 11 studied had a zone of 12 mm and one P. prevotii of 14 studied had a zone of 16). The test had an overall accuracy of 98% in the identification of P. anaerobius from clinical specimens. Since P. anaerobius accounts for one-fifth to one-third of all anaerobic gram-positive cocci encountered in clinical specimens, this simple and rapid technique can be very useful for presumptive identification.