T/F: A single bacterial species is able to grow in pure human saliva alone.

• A. True
• B. False
• C. Not determinable
• D. Depends on conditions

Answer: (B)

Saliva is not a simple growth medium. It contains antimicrobial components such as lysozyme, lactoferrin, and IgA, plus factors that limit nutrients like iron, making it hostile to many bacteria. It also provides only a limited set of nutrients, not the rich, balanced supply that a single bacterial species typically needs to grow robustly on its own. In the mouth, many bacteria rely on interactions with other microbes for nutrients and a suitable microenvironment; these ecological relationships help them thrive in a biofilm. Because of these factors, a single bacterial species generally cannot grow to produce a sustained pure culture in pure human saliva.