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the organism. In case of reservoirs with standing water, the WHO suggests the
applicationofadditionalmeasurestopreventthemultiplicationof
Legionella
,asfor
example, byshorteningthepipingtofacilitate the inspection, aswell as theabsence
of dead points or stagnation zones. In a more recent study, it was observed that
strains of
Legionella pneumophila
in suspensionwere able to resist concentrations
of free chlorine inferior to 0.5 mg∙L
-1
, which is the highest concentration of free
chlorine allowed by theWorldHealthOrganization (Cooper andHanlon, 2010).
These authors concluded that concentrations of free chlorine equal to 0.2 mg∙L
-1
,
0.3mg∙L
-1
and 0.4mg∙L
-1
were not able to destroy
Legionella pneumophila
over 28
days.
A fact that must be pointed out concerns the condition in which the
microorganism is in the system. For example, the use of hypochlorous acid
(HOCl), at the concentrationof 0.4mg∙L
-1
can inactivate
Legionella
in15minutes,
when its cells are in suspension. However, when the cells of this microorganism
are adhered to the surfaces of the pipes, concentrations higher than 3 mg∙L
-1
are
needed to destroy them(Lin
et al
., 1998). On the other hand,Muraca
et al
. (1987)
state that it is necessary to elevate the concentration of free chlorine to values
between 2 and 6 mg∙L
-1
.
To exemplify the influence of the age of the colony over the resistance to
treatments that aim its removal, the workmade by Cooper andHanlon (2010) is
mentioned,whoverifiedthat itwasnotpossibletorecover
Legionellapneumophila
present in biofilms aged 3 days and exposed to a concentration of free chlorine of
50mg∙L
-1
byonehour.However,aftersomedaysfromthetreatment, itwaspossible
to recover
Legionella pneumophila
in this biofilm. This work demonstrated also
that biofilms with one and two months of age ensured the survival of
Legionella
pneumophila
to the treatment with free chlorine at the concentration of 50mg∙L
-1
for one hour and the cells continued to multiply.
