Question

(Microbiology) What advantages do the API test have over the chromogenic UTI plates in identifying a urinary infection?

Answer 1

API stands for analytical index profile. It is a commercially available test system which has a miniaturized and standardized version of 20 commonly performed lab techniques for microbiological identification. It is a fast and efficient way of identifying known bacteria. API system can be purchased specific for Gram negative or gram positive bacteria.

On the other hand, identification of bacteria using chromogenic UTI plates involves the presence of a colourless soluble chromagen which is cleaved by the target organisms enzyme to produce a colored precipitate. The entire culture is carried out in agar medium. The colors are distinctive and species specific. Hence it can be easily used to identify UTI pathogens.

Advantages of API over chromogenic agar plates:

• Chromogenic agar mediums are more expensive than standardized API kits. Hence API testing is more economical.
• API testing gives faster result and a broad overview of the kind of micro organisms present in an infected sample. Compared to that, chromogenic plates requires 24 hr of incubation.
• It requires lesser level of expertise to carry out a pre made standardized test than to prepare culture medium and maintain bacterial colonies in it. Hence API testing can be easily performed by relatively less skilled person.
• Identification in a chromogenic plate requires previous knowledge of what kind of chromogen is used, it's target organism enzyme, and the color of cleaved chromophore. In contrast to that, API test kits have standard guidelines for identification of organisms.
• API test kits are pre standardized while chromogenic agar plates have to prepared and standardized in the laboratory itself.

Inspite of this, both techniques are fast, easy and reliable of studying an infected urine sample. Since, we are dealing with known pathogens, we can rely on either test to give us a satisfactory result.