What should the follow-up test be for cultured bacteria from a patient with alpha-hemolytic pneumonia?

In cases of alpha-hemolytic pneumonia, particularly when Streptococcus pneumoniae is suspected, the bile solubility test is the appropriate follow-up test for the cultured bacteria. This organism exhibits sensitivity to bile salts due to the presence of a bile-soluble enzyme that will cause the lysis of the bacterial cells. When a culture of Streptococcus pneumoniae is exposed to bile salts, it results in the clearing of the culture, definitively identifying it among other alpha-hemolytic streptococci such as Streptococcus mitis or Streptococcus sanguinis, which are not lysed by bile.

The other options are useful for differentiating other bacterial species or features but do not specifically apply to confirming Streptococcus pneumoniae. For example, the pyrrolidonyl arylamidase (PYR) test is pertinent for identifying Streptococcus pyogenes and Enterococcus species, while hippurate hydrolysis is used to identify Group B Streptococcus. The CAMP test is crucial for identifying Streptococcus agalactiae (Group B), especially in pregnant women but does not assist in identifying or confirming cases involving Streptococcus pneumoniae. Therefore, utilizing the bile solubility test is the most direct