Rapid, modified oxidase test for oxidase-variable bacterial isolates

Area of Science:

• Microbiology
• Bacteriology

Background:

• The oxidase test is crucial for identifying Gram-negative bacteria.
• Detecting weakly oxidase-positive bacteria can be challenging with standard reagents.

Purpose of the Study:

• To evaluate a modified oxidase reagent for improved detection of weakly oxidase-positive Gram-negative bacteria.
• To compare the efficacy of a novel reagent against the standard reagent.

Main Methods:

• A modified oxidase reagent (1% tetramethyl-p-phenylenediamine in dimethyl sulfoxide) was prepared.
• Bacterial inoculum was collected using a cotton-tipped swab.
• The modified reagent was tested against the standard aqueous tetramethyl-p-phenylenediamine dihydrochloride for detecting oxidase-positive bacteria after 24-hour growth on agar.

Main Results:

• The modified reagent detected 40 of 40 (100%) weakly oxidase-positive Gram-negative bacteria.
• The standard reagent detected only 22 of 40 (55%) weakly oxidase-positive Gram-negative bacteria.
• The reaction with the modified reagent was rapid, requiring less than 15 seconds.

Conclusions:

• The modified oxidase reagent in dimethyl sulfoxide is superior for detecting weakly oxidase-positive Gram-negative bacteria.
• Using a cotton-tipped swab for inoculum collection improves detection sensitivity.
• This enhanced method offers a more reliable approach for bacterial identification.