Final answer:
The appropriate sequence for bacterial isolation in a lab starts with Nutrient agar, a general all-purpose medium, followed by MacConkey agar, a selective medium for differentiating gram-negative bacteria. Answer choice A) Nutrient agar, MacConkey agar is thus the correct option.
Step-by-step explanation:
When isolating bacteria in a lab setting, the type of media chosen is crucial in identifying and supporting growth of the organisms of interest. Initially, one would use an all-purpose medium like Nutrient agar, which supports a wide variety of bacterial growth. As the first option, Nutrient agar is a non-selective, general growth medium. Following the initial isolation, a selective medium such as MacConkey agar should be used as the second type of media to differentiate and select for specific types of bacteria.
MacConkey agar is a selective and differential medium designed to isolate and differentiate enteric gram-negative bacteria. It contains bile salts and crystal violet to inhibit the growth of gram-positive bacteria while allowing gram-negative bacteria to grow, and lactose to differentiate between lactose fermenters and non-fermenters. Therefore, the best sequence when isolating bacteria should be Nutrient agar first, to grow a broad spectrum of bacteria, followed by MacConkey agar, to select for and differentiate between specific groups of gram-negative bacteria. Answer choice A) Nutrient agar, MacConkey agar is correct