▁and ▁it ▁can ▁make ▁colon ies ▁greater ▁than ▁ 5   mm ▁in ▁size . ▁ ▁Like ▁other ▁c oc ci , ▁stre pt oc oc ci ▁are ▁round ▁b acter ia . ▁ ▁The ▁species ▁name ▁is ▁derived ▁from ▁Greek ▁words ▁meaning ▁' a ▁chain ' ▁() ▁of ▁ber ries ▁( ▁[ Lat in ized ▁from ▁ ]) ▁and ▁p us ▁() - form ing ( gen es ), ▁because ▁stre pt oc oc cal ▁cells ▁tend ▁to ▁link ▁in ▁ch ains ▁of ▁round ▁cells ▁( see ▁image ) ▁and ▁a ▁number ▁of ▁in fe ctions ▁caused ▁by ▁the ▁b acter ium ▁produce ▁p us . ▁ ▁The ▁main ▁criter ion ▁for ▁different iation ▁between ▁St ap hy loc oc cus ▁s pp . ▁and ▁Stre pt oc oc cus ▁s pp . ▁is ▁the ▁catal ase ▁test . ▁ ▁St ap hy loc oc ci ▁are ▁catal ase ▁positive ▁whereas ▁stre pt oc oc ci ▁are ▁catal ase - negative . ▁ ▁S . ▁py ogen es ▁can ▁be ▁cult ured ▁on ▁fresh ▁blood ▁ag ar ▁pl ates . ▁ ▁Under ▁ideal ▁conditions , ▁it ▁has ▁an ▁inc ub ation ▁period ▁of ▁ 1 ▁to ▁ 3 ▁days . ▁ ▁An ▁estimated ▁ 7 0 0 ▁million ▁G AS ▁in fe ctions ▁occur ▁world wide ▁each ▁year . ▁While ▁the ▁overall ▁mort ality ▁rate ▁for ▁these ▁in fe ctions ▁is ▁ 0 . 1 %, ▁over ▁ 6 5 0 , 0 0 0 ▁of ▁the ▁cases ▁are ▁severe ▁and ▁invas