Neisseria lactamica closely resembles Neisseria meningitidis but can be differentiated from it by its ability to metabolize which sugar?

• A. Maltose
• B. Lactose
• C. Glucose
• D. Sucrose

Answer: (B)

Carbohydrate use among Neisseria species is a practical way to tell closely related organisms apart. Neisseria meningitidis typically ferments glucose and maltose but not lactose, while Neisseria lactamica can also ferment lactose. That lactose-fermenting capability is what distinguishes the two in routine tests. In the lab, you’d inoculate a lactose-containing medium and look for an acid end-product (color change), indicating lactose metabolism. Since glucose and maltose fermentation occur in meningitidis as well, those sugars wouldn’t separate them, making lactose the differentiating test.