Which of the following diphtheroids is considered normal flora in the throat?

Corynebacterium pseudodiphtheriticum is recognized as part of the normal flora of the throat. This organism is a non-pathogenic diphtheroid that typically resides in the mucosal surfaces of the upper respiratory tract. It plays a role in maintaining the balance of the microbial community and usually does not cause disease in healthy individuals.

In contrast, Corynebacterium diphtheriae is the pathogenic species responsible for diphtheria and is not part of the normal throat flora. Propionibacterium acnes, primarily associated with skin, is not typically found in the throat. Bacillus subtilis is a saprophytic bacterium commonly found in soil and not part of the normal throat flora either. Thus, Corynebacterium pseudodiphtheriticum is the correct choice as it reflects the typical microbial inhabitants of the throat without associated pathogenicity.