Pseudomonas aeruginosa, Escherichia coli and
Staphylococcus aureus were used to hydrolyse
colorless flourescein diacetate (FDA) to fluorescein,
a yellowish green compound. P. aeruginosa
completely hydrolyzed FDA to fluorescein,
producing a yellowish green colour. There were no
significant colour and absorbance changes using E.
coli and Stap. aureus which suggested that they
might not be able to hydrolyse fluorescein diacetate
(FDA) to fluorescein. Therefore, P. aeruginosa was
selected for the assay. Six antibiotics were tested for
their effectiveness against P. aeruginosa by the disc
diffusion assay.15 It was found that streptomycin is
significantly active against P. aeruginosa.
Chloramphenicol and tetracycline were moderately
active. Ampicilin, penicillin and erythromycin were
inactive. Streptomycin was used as standard drug for
the FDA assay.