In the colony method of the bile solubility test, what characterizes a positive result?

In the bile solubility test, a positive result is characterized by the dissolution of the colony. This test is primarily used to identify specific types of streptococci, particularly Streptococcus pneumoniae. The bile salts present in the test media lead to the lysis of the bacterial cells in susceptible strains. When colonies dissolve, it indicates that the bacteria are bile-soluble, confirming the presence of Streptococcus pneumoniae.

The other options represent different phenomena that are not associated with the bile solubility test. The formation of gas bubbles would typically be indicative of fermentation, blackened colonies might suggest the presence of sulfur-reducing bacteria, and a zone of inhibition is commonly seen in antibiotic susceptibility tests rather than in evaluating bile solubility. Thus, the dissolution of the colony directly reflects the unique biochemical properties that characterize a positive outcome in this specific test.