I came across the term "cryptic bacteria" a few times in the context of biochemistry (Google search), but I couldn't find a definition. What does "cryptic" mean in that context?
There appears to be a reasonable definition of cryptic bacteria here:
Cryptic Bacteria in our Tissues
The role of bacteria in numerous diseases, including cancers, has been proposed since the early isolation of bacteria from human tissues. Many of these bacteria are difficult to culture and have variable forms viewed by microscope. Because these bacteria are difficult for microbiologists to handle with conventional approaches, their existence and significance has always been questioned. Use of antibiotics to treat chronic, inflammatory conditions has seemed inconsistent with the unproven existence of a bacterial cause. Thus, there is surprise when the inappropriate use of antibiotics leads to a cure.