Which of the following is a characteristic of alpha-hemolytic streptococci?

Alpha-hemolytic streptococci are primarily represented by Streptococcus pneumoniae and the viridans group streptococci. One of the key characteristics of these organisms is their resistance to the optochin disk, which is a diagnostic tool used to differentiate between various types of alpha-hemolytic streptococci. For example, Streptococcus pneumoniae is sensitive to optochin, whereas members of the viridans group are resistant. This characteristic helps microbiologists distinguish between these groups during laboratory diagnostics.

The other options provide different traits associated with various bacterial species. Hippurate hydrolysis, for example, is primarily associated with Group B Streptococcus (Streptococcus agalactiae), while beta-hemolysis is indicative of Group A Streptococcus (Streptococcus pyogenes) and other beta-hemolytic streptococci. Capsular swelling, on the other hand, is a characteristic feature of encapsulated bacteria, such as Streptococcus pneumoniae, but this is not a characteristic exclusive to alpha-hemolytic streptococci as a whole. Therefore, being optochin disk resistant is a defining trait that specifically highlights the distinction within the group of