Use of a sodium polyanetholesulfonate disk for the identification of Gardnerella vaginalis

Several methods have been previously suggested for the presumptive identification of Gardnerella vaginalis in clinical laboratories, but none is entirely satisfactory. We previously found that sodium polyanetholesulfonate (SPS) inhibits G. vaginalis in blood culture media. We compared susceptibility to an SPS-containing paper disk with beta-hemolysis on human blood agar, hippurate hydrolysis, and inhibition by alpha-hemolytic streptococci for identification of 62 previously confirmed G. vaginalis strains. All strains were positive by SPS disk and alpha-hemolytic streptococcus inhibition, 78% were positive by beta-hemolysis, and 81% were positive by hippurate hydrolysis. Although positive reactions occurred with SPS disk and alpha-hemolytic streptococcus tests for 5 and 9 of 84 other bacteria tested, respectively, none of these bacteria were positive for both tests. We conclude that a combination of SPS disk susceptibility and alpha-hemolytic streptococcus inhibition provides excellent identification of G. vaginalis when performed by the methods suggested.