Final answer:
The types of bacteria that cannot utilize citric acid are citrate-negative bacteria. They lack the enzymes needed to transport and metabolize citric acid, which is why they cannot grow on a medium that contains citric acid as the sole carbon source.
Step-by-step explanation:
The types of bacteria that cannot utilize citric acid are citrate-negative bacteria. Citrate utilization test is a method used to determine whether bacteria can utilize citric acid as their carbon source.
Bacteria that have the necessary enzymes, citrate permease for transport and citrase for catabolism, can utilize citric acid; these are citrate-positive bacteria. On the other hand, citrate-negative bacteria lack these enzymes and thus cannot grow on a medium such as Simmons' citrate agar, which solely contains citric acid.
When these bacteria are cultured on such a medium, they will not be able to grow and will not cause the pH indicator to change color, resulting in a negative test result. Hence, the correct answer is D) Citrate-negative bacteria.