The API 20E System is a miniatuized version of conventional tsts that is used for the identification of members of the family Enterobacteriaceae and other gram-negative bacteria. This system utilizes a plastic strip with 20 separated compartments. Each compartments consists of a depression, or cupule, and a small tube that contains a specific dehydrated medum. After you inoculated each compartment with an unknown bacteria, a reaction will occur within 24 hours. The results of each reaction are tabulated and then given a number based on the results. The unknown bacteria is identified by searching through a book, Analytical Profile Index (may be in other book), and searching for the number corresponding to your unknown.
The test consists of the following:
ONPG: galactosidase
ADH: Arginine DiHydolase
LDC: LysineDeCarboxylase
ODC: Ornithinine DeCarboxylase
CIT: Citrate utilization
H2S: Hydogen sulfide production
URE: Ureaase
TDA: Tryptophane DeAminase
IND: Indole Production
VP: acetoin production (Voges Proskauer)
GEL: Gelatinase
GLU: fermentaion / oxidation (Glucose)
MAN: fermentaion / oxidation (Mannitol)
INO: fermentaion / oxidation (Inositol)
SOR: fermentaion / oxidation (Sorbitol)
RHA: fermentaion / oxidation (Rhamnose)
SAC: fermentaion / oxidation (Saccharose)
MEL: fermentaion / oxidation (Melibiose)
AMY: fermentaion / oxidation (Amygdalin)
ARA: fermentaion / oxidation (Arabinose)
Supplemental Test also may be done with the API test
OXI:
NO2:
N2 GAS:
MOT:
MAC:
OF-O:
OF-F:
The reactions of each compartment are given a (+) or (-). Each compartment has a corresponding points. If a reaction for a certain compartment, like GLU, is possible then the points are counted.
Every 3 compartment (or test) is given a number. The points of every 3 set is 1, 2, and 4 (in order)... Do not get mixed up with points and number. Each test has a corresponding points and Every 3 tests is given a number based on the results...
For example:
ONPG (1), ADH (2), and LDC (4)
If ONPG and LDC are positive and ADH reaction is negative, then the number given to this set is 5 (1pt from ONPG and 4pt from LDC; No point is given to ADH because the result is negative)
THERE SHOULD BE 9 NUMBERS
[27 tests/compartments divided into 3 groups each is 9]
A test result for a specific bacteria of Eshcerichia coli (E. coli) is
+ - + + - - - - + - - + + - + + - + - + - + - + + + +
5 1 4 4 5 5 2 5 7
The number is 514455257
An important thing to remember is that they have a lot of bacteria. Some bacterias have different strains, so there may be more than 1 number that identifies to be E. coli. It's just they are different strains of E. coli
Information taken from Benson's MICROBIOLOGY APPLICATIONS Tenth edition by Alfred E. Brown
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