J. Iriberri et al., DIFFERENTIAL ELIMINATION OF ENTERIC BACTERIA BY PROTISTS IN A FRESH-WATER SYSTEM, Journal of Applied Bacteriology, 77(5), 1994, pp. 476-483
The short-term (1 h) and long-term (3 d) elimination of low and high d
ensities of five enteric bacteria, Klebsiella pneumoniae, Aeromonas hy
drophila, Escherichia coli, Enterococcus faecalis and Staphylococcus e
pidermidis, by flagellate and ciliate protists were measured in a fres
hwater system. In addition, the two processes, ingestion and digestion
, which cause the disappearance of those enteric bacteria as time pass
es, were quantified. The results showed that the elimination of these
enteric bacteria by protists depends on their initial density, which c
onfirms that the lower the bacterial density the more difficult is the
ir elimination. On the other hand, the short-term and long-term elimin
ation rates of each enteric bacteria were different, and moreover, the
order of priority for elimination in the two cases was not the same.
Escherichia coli showed the highest elimination rate in short-term exp
eriments, while Aer. hydrophila disappeared at highest rates in long-t
erm experiments. This different order of priority in the elimination r
ates and the different digestion rates on the five enteric bacteria by
phagotrophic protists indicated that the elimination in time is very
much influenced by the digestive capacity on each enteric bacteria of
those protists. Thus, the low digestion rates of Ent. faecalis and Sta
ph. epidermidis by flagellates and ciliates as well as their low disap
pearance percentages in the long-term experiments confirm that enteric
Gram-positive bacteria are eliminated from the aquatic systems at low
er rates, because their digestion is difficult.