Intracellular persistence of Escherichia coli in urinary bladders from mecillinam-treated mice.

It has been suggested recently that intracellular bacteria surviving antibiotic treatment might serve as a reservoir for recurrent infection. The purpose of this study was to directly examine the location of Escherichia coli bacteria in the mouse bladder after treatment with mecillinam. The bladders were studied by use of colony counts, in situ hybridization and electron microscopy. The bacterial counts in the bladder remained approximately 10(3-4) cfu/bladder even after mecillinam treatment had finished, and re-growth in the urine was observed. In the bladder epithelium from treated mice, bacteria cells were occasionally seen, presumably representing intracellularly located bacteria. This is the first in vivo study indicating that during mecillinam treatment E. coli cells can penetrate the mouse bladder epithelium and persist.