Which organism is typically positive for B-galactosidase?

Which organism is typically positive for B-galactosidase?

• A. Salmonella spp.
• B. Shigella spp.
• C. Proteus spp.
• D. E. coli

Answer: (D)

The organism that is typically positive for B-galactosidase is Escherichia coli (E. coli). This enzyme, B-galactosidase, is essential for the breakdown of lactose into glucose and galactose, which is a critical metabolic process for lactose-fermenting bacteria. E. coli is known for its ability to ferment lactose, which is commonly tested for in laboratory settings using selective media. When cultured on lactose-containing media, a positive reaction indicates that E. coli can effectively utilize lactose, resulting in acid production and a color change in the medium due to the fermentation. Other organisms listed, such as Salmonella spp., Shigella spp., and Proteus spp., typically do not produce B-galactosidase or exhibit lactose fermentation. Salmonella and Shigella are both generally lactose non-fermenters; hence, they do not show a positive reaction when lactose is the sole carbon source. Proteus spp. are also non-lactose fermenters and are characterized by their ability to produce urease rather than fermenting lactose. This differentiation helps microbiologists identify E. coli in samples, confirming its presence based on the positive B-galactosidase reaction.

The organism that is typically positive for B-galactosidase is Escherichia coli (E. coli). This enzyme, B-galactosidase, is essential for the breakdown of lactose into glucose and galactose, which is a critical metabolic process for lactose-fermenting bacteria. E. coli is known for its ability to ferment lactose, which is commonly tested for in laboratory settings using selective media. When cultured on lactose-containing media, a positive reaction indicates that E. coli can effectively utilize lactose, resulting in acid production and a color change in the medium due to the fermentation.

Other organisms listed, such as Salmonella spp., Shigella spp., and Proteus spp., typically do not produce B-galactosidase or exhibit lactose fermentation. Salmonella and Shigella are both generally lactose non-fermenters; hence, they do not show a positive reaction when lactose is the sole carbon source. Proteus spp. are also non-lactose fermenters and are characterized by their ability to produce urease rather than fermenting lactose. This differentiation helps microbiologists identify E. coli in samples, confirming its presence based on the positive B-galactosidase reaction.