BETA-GALACTOSIDASE AND LACTOSE FERMENTATION IN THE IDENTIFICATION OF ENTEROBACTERIA INCLUDING SALMONELLAE

Area of Science:

• Microbiology
• Bacteriology
• Clinical Diagnostics

Background:

• Traditional lactose fermentation tests can be slow and sometimes ambiguous for bacterial identification.
• Accurate and rapid differentiation of bacterial species is crucial for clinical diagnostics and epidemiological studies.

Purpose of the Study:

• To evaluate the efficacy of the ortho-nitro-phenyl-beta-D-galactopyranoside (O.N.P.G.) test against standard lactose fermentation tests.
• To determine the utility of the O.N.P.G. test in differentiating bacterial genera, especially Salmonella, and aiding in routine pathogen isolation.

Main Methods:

• Comparison of 114 non-lactose fermenting and 127 lactose fermenting bacterial strains.
• Utilized 5% and 1% lactose fermentation tests and the O.N.P.G. test for beta-galactosidase production.
• Tested wild and stock strains of Salmonella, Proteus, Providencia, Pseudomonas aeruginosa, Arizona, Shigella, and Pasteurella.

Main Results:

• The O.N.P.G. test demonstrated superiority in positive results and rapidity over lactose fermentation tests.
• Most Salmonella strains were O.N.P.G. negative, supporting their classification as such in Great Britain.
• Arizona strains showed variable O.N.P.G. test results, with most being positive but a minority negative.

Conclusions:

• The O.N.P.G. test is recommended for routine bacterial identification and differentiation of Salmonella from other enterobacteria.
• Parallel use of the 5% lactose fermentation test is advised for isolating routine pathogens, as some O.N.P.G. positive organisms (e.g., Shigella) require further differentiation.