Scanning electron microscopy detects bacteria within infection stones.

The viability and location of bacteria within infection stones were investigated. Many stones were infected with urea-splitting bacteria, such as Proteus mirabilis and Pseudomonas aeruginosa. Large numbers of bacterial impressions and bodies were found in the interstices surrounded by crystals of apatite and struvite from the nuclei to the peripheral layers. The presence of bacterial colonies even in the nuclear portion of the stones suggests that bacteria participate in the initial stone formation as well as in growth of infection stones. Streptococcus faecalis, a nonurea -splitting bacteria, also was found in some infection stones and probably represents a superimposed infection as a result of changes in bacterial flora owing to treatment with antibiotics.