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Protozoa
Legionella
were the first bacteria shown to infect and grow parasitically
within protist hosts commonly found in building water systems and then
also to incidentally infect people exposed to building system water. The life
cycle of
Legionella
is: 1) Amoebae graze on biofilm consuming bacteria for
food but are 2) infected by
Legionella
which, 3) grow parasitically and then
4) overwhelm the protozoan host cell, differentiate into motile cells and
5) cause lysis of the host cell releasing hundreds or thousands of infective
progeny in search of new amoeba to infect.
Today, we know that many other opportunistic waterborne pathogens
are also parasitic to protozoa and some of themare also pathogenic to people
(Table 1). Some of these pathogens are known to become more virulent to
people after growth inside their amoebic hosts.
