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Department
of Microbiology, Monash University, Melbourne, Australia. david.figdor@med.monash.edu
The ability of Enterococcus faecalis to survive starvation for long
periods in the obturated root canal is likely to be an important factor in
the pathogenesis and maintenance of a persistent infection after
endodontic treatment. The response of E. faecalis to starvation survival
in water and glucose-, phosphate- or amino acid-limited chemically defined
medium was studied, along with the capacity for growth and recovery of
starved cells of E. faecalis in pooled human serum. After an initial rapid
fall in cell numbers, a small remaining population of E. faecalis was able
to survive in water for over 4 months and in nutrient-limited media for
extended periods. A high cell density at the onset of starvation was
critical for the ability of E. faecalis to endure prolonged nutrient
limitation. Upon starvation, a static population of starved cells
developed and were apparently in a minimal metabolic state, since blocking
cell wall synthesis with penicillin G or inhibiting DNA synthesis with
norfloxacin during starvation resulted in limited change in the rate of
loss of viable cells. In 50% serum, E. faecalis grew, then stabilized at a
relatively constant population of 106 colony-forming units/ml for 4 months,
irrespective of the initial cell density. In summary, E. faecalis is
capable of withstanding prolonged periods of starvation in a minimal
metabolic state provided that there is a high cell density at the onset of
starvation. Starved cells were capable of recovery upon addition of human
serum.
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