ESTIMATION OF THE STATE OF THE BACTERIAL-CELL WALL BY FLUORESCENT IN-SITU HYBRIDIZATION

Fluorescent in situ hybridization (FISH) is now a widely used method f or identification of bacteria at the single-cell level. With gram-posi tive bacteria, the thick peptidoglycan layer of a cell wall presents a barrier for entry of horseradish peroxidase (HRP)-labeled probes. The refore, such probes do not give any signal in FISH unless cells are fi rst treated with enzymes which hydrolyze the peptidoglycan. We explore d this feature of FISH to detect cells which have undergone permeabili zation due to expression of autolytic enzymes. Our results indicate th at FISH performed with HRP-labeled probes provides a sensitive method to estimate the states of cell walls of individual gram-positive bacte ria.