Final answer:
Selective plating can reliably detect and quantify specific bacteria in a sample, while replica plating is valuable for identifying auxotrophic bacterial mutants that require specific nutrients to grow.
Step-by-step explanation:
Selective plating is a microbiological technique that allows for the isolation of a specific type of bacteria from a mixture by inhibiting the growth of others. This technique is more reliable for detecting and estimating the presence and quantity of specific bacterial pathogens in a sample, as growth on selective media implies the ability to survive and replicate under the restrictive conditions imposed by that media. Selective media may contain substances that inhibit the growth of some bacteria while allowing others to grow; thus, you can get a reliable count of bacteria that are resistant to the inhibitory substances.
Replica plating, on the other hand, is a technique used to transfer the same pattern of microbial colonies from one plate to another, which often have different growth mediums. This method is particularly valuable for identifying bacterial mutants, called auxotrophs, that require specific nutrients missing from some of the media. Since auxotrophs will not grow on these selective media lacking the nutrients they cannot synthesize, while wild-type cells will, replica plating provides a reliable way to differentiate between these and identify mutants based on their inability to grow under specific conditions that the wild type would withstand.