ABSTRACT
Bacteria of species Streptococcus pyogenes are a human pathogen, causing serious invasive infections. The culture method remains the standard way for its isolation and identification. Due to the accessible facilities, medical laboratories employ different methods in this way. In present study the most common methods have been statistically interpreted. A total of 159 beta-hemolytic streptococci isolated from different samples were tested for hemolysis potency, sensitivity to bacitracin [BC] or sulfametoxazole/trimethoprim [SXT] and Voges-proskauer [V.P]. Based on L-pyrrolidonyl-beta-naphthylamide [PYR] test, the positive predicted value [ppv], negative predicted value [npv] and sensitivity [sen] of each test were calculated. The ppv, npv and sen. of beta-hemolysis on sheep blood agar [SBA] for identification of S. pyogenes were 75, 89 and 89% respectively. It was 76, 89 and 53% for banked human blood [BHB]. For BC test the above mentioned criteria were 52, 70 and 89% and also for VP test 57, 89, and 94%. Finally SXT test with 49, 47 and 63% demonstrated the least practical identification value. The PYR test is considered the most reliable biochemical test for identification of S. pyogenes among other beta hemolytic streptococci. If it is not available, combining of hemolysis >/= 3mm with BC >/= 10mm has presumptive identification value of 89%. It was realized that the hemolytic activity of this bacterial species on BHB is documented and equal to a potent hemolysis on SBA. The VP test with 89% value is a suitable test to rule out its presence; but the accuracy of SXT test result is limited