Tyrosine degradation in presumptive identification of Peptostreptococcus anaerobius

A new tyrosine medium was developed and evaluated for the differentiation of Peptostreptococcus anaerobius from other anaerobic, gram-positive cocci. The strains included 159 originating from clinical specimens and 13 reference strains received from other workers in the field. Only one strain of each species was included in the study from multiple cultures from the same patient. This medium is simple to prepare and can be used in a small clinical laboratory. One hundred seventy-two strains of anaerobic gram-positive cocci were grown and evaluated with the new tyrosine medium; 36 strains (100%) of P. anaerobius degradated the tyrosine crystals when incubated at 37 degrees C under anaerobic conditions in a GasPak jar (Baltimore Biological Laboratory) for approximately 72 h. On the other hand, 135 of 136 other anaerobic gram-positive cocci were negative for tyrosine degradation, but grew on the tyrosine agar plate when incubated anaerobically. The single strain that degraded tyrosine was 1 of the 13 isolates of Peptostreptococcus micros studied.