What condition is indicated by a positive indole test?

A positive indole test is indicative of the organism's ability to produce indole from the amino acid tryptophan, which is a characteristic feature of certain bacteria, notably Escherichia coli, a common pathogen associated with urinary tract infections (UTIs). When a urine sample tests positive for indole, it suggests the presence of E. coli, which is one of the primary causes of UTIs due to its ability to colonize the urinary tract and persist in that environment.

In contrast, the other conditions listed are generally associated with different pathogens or do not specifically involve the production of indole. For example, gastroenteritis can be caused by a variety of organisms that may or may not produce indole, while typhoid fever is primarily attributed to Salmonella enterica serotype Typhi, which does not produce indole. Diarrhea caused by Vibrio species typically involves organisms like Vibrio cholerae, which also do not exhibit indole production. Thus, a positive indole test is specifically reflective of E. coli’s involvement, making urinary tract infection the best choice.