Microbiology 2
Lecture 22
Lana Hammad
Synthetic membrane filters (derived
from cellulose esters or other polymeric
materials)  they are thin, with defin ed
pore size  the major mechanism is
sieving (the matrix isn’t thick enough for
adsorption)  we call them membrane
filters or sieving filters
## adsorption and trapping happen but
they’re not the major mechanism ##
## higher flow rate than other filters
because of the defined pores ##
Fibrous pads, sintered glass and sintered
ceramic products can be regarded as
Depth filters relying principally on
mechanisms of adsorption and
entrapment.
## sintered : a powder of the material
(glass or ceramic) is pressured at a
temperature just below the melting
point , so the powder doesn’t melt ,
instead we have one block of
compressed powder with higher
diffusion ##
## depth filters don’t have a defined
pore size, that’s why the major
mechanisms are trapping and
adsorption ##
 Filtration sterilization -liquids
-Sterilization of heat-sensitive injections
and ophthalmic solutions and
biological products
( dry & moisture heat sterilization are
not suitable )
## radiation is not suitable for sterilizing
solutions, because the presence of
water increases the probability of having
free radicals which causes the active
drug to undergo degradation ##
- Treatment of air and other gases for
supply to aseptic areas
 The major mechanisms of filtration
are sieving, adsorption and trapping
within the matrix of the filter
material.
 Only sieving can be regarded as
absolute since it ensures the
exclusion of all particles above a
defined size. (the pore size is smaller
than the particulate size that we
want to exclude)
 Adsorption depends on the physical
interaction between the microbe and
the filter material itself
 Trapping depends on the tortuosity
of the filter matrix (channels within
the filter – especially if it is thickdesigned to have tortuosity )
## the higher the tortuosity the
higher the probability that a certain
microbe will be trapped after losing
its kinetic energy within the filter##
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Microbiology 2
Lecture 22
“dirt – handling capacity “ :
the ability of the filter to capture dirt in
addition to other microbes.
Lana Hammad
##in microbial removal, even though we
said that membrane filters have
absolute filtration capacity , we can use
depth filters if they were made
according to certain standards and they
would be effective ##
-in membrane filters, dirt closes the
pores, and causes obstruction, therefore
we use something called “prefilter”
to increase the estimated time for this
filter to keep working
- in depth filters, the spaces between
fibers are relatively much larger than
membrane filters so they dirt doesn’t
cause obstruction as fast as the
membrane filter
- even though it is less of a problem to
depth filters, we also use prefilters with
them to increase their life span.
“ grow –through of microorganisms”:
seen mainly in depth filters since their
majon mechanisms of action are
trapping and adsorption, there is a
possibility that –if the conditions are
suitable- microbes trapped within the
filter might grow in it. (membrane filters
mainly stop the microbes from passing,
so this effect is seen less when using
them)
“shedding of filter components” :
seen more in depth filters because they
are made out of fibers, while membrane
filters are made out of a continuous
piece of synthetic polymer(chance of
shedding of this continuous material is
less)
If we exclude stability; membrane filters
characteristics are more appealing,
that’s why in liquid sterilization we
prefer to use them not depth filters.
When we want a more stable filter, with
corrosive or organic liquids we use
depth filters.
Fluid retention & solute adsorption:
happens more in depth filters, fluid is
also absorbed in the filter instead of
adsorbing the particulate material alone.
(seen less in membrane filters)
Membrane filters usually have a pore
size within this range: 0.2 – 0.22 mm
but because this size is very small, the
flow rate is slow, and the pores are
easily clogged , so we use prefilters.
Prefilters can be membrane filters but of
larger pore size or depth filters to get rid
of larger particles and increase the flow
rate & life span of the 0.2 filter
in terms of stability:
depth filters are more stable (because
most of them are made of glass or
ceramic which are highly stable)
on the other hand, membrane filters are
very thin and made of cellulose
derivatives and so are less stable
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Microbiology 2
Lecture 22
Membrane filters are often used in
combination with a coarse-grade
fiberglass depth pre-filter to improve
their dirt-handling
Capacity
Lana Hammad
The filter must be sterilizable, ideally by
steam sterilization(autoclavable)
- Membrane filters may be sterilized
once for one use
Except industrial filters which can be resterilized few times
- Sintered filters can be re-sterilized
many times
We don’t consider pore size as the only
criteria to describe membrane filters
Two filters of 0.2 mm pore diameter
from different manufacturers will not
behave similarly, because, in addition to
the sieving effect, trapping, adsorption
and charge effects all contribute
significantly towards the removal of
particles.
To get more efficient filtration,
sometimes we apply pressure:
- Pressure-operated filter holders for
syringe mounting and in-line use
(positive pressure) (syringe-like
mechanism or a pump)
or
- Vacuum filtration tower devices
(negative pressure) (we use Büchner
funnel)
We choose one of them depending on
the set up of our device
-- for pharmaceutical solutions we
usually use negative pressure
Consequently, the depth of the
membrane, its charge and the tortuosity
of the channels are all factors which can
make the performance of one filter
superior to that of another.
Therefore, the major criterion by which
filters should be compared, is their titre
reduction values, i.e. the
ratio of the number of organisms
challenging a filter under defined
conditions to the number penetrating it.
The higher the values the better,
the lowest value possible is 1
and the highest is infinity.
The exact value is set for the filter
depending on the intended application
 Filtration sterilization –
gases:
The principal application for filtration
sterilization of gases is in the provision
of sterile air to
Aseptic manufacturing sites
Hospital isolation units
Some operating theatres
Other applications include
Sterilization of venting air in tissue
and microbiological culture
Decontamination of air in mechanical
ventilators
## filters do not kill microorganismsm
that’s why they should be sterilized &
Filtration sterilization for aseptic
products has to be carried out in as
aseptic area. (to prevent post filtration
contamination) ##
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Microbiology 2
Lecture 22
Treatment of exhausted air from
microbiological safety cabinets (air
coming in and going out in : to
protect the cabinet from contamination
out: to protect the workers )
The clarification and sterilization of
medical gases (nitrous oxide, oxygen)
Lana Hammad
The operational efficiency and
integrity of a HEPA filter is
monitored:
Pressure differential and airflow rate
measurements (if the filter is intact, the
flow rate will be within a certain range,
 if it is higher; that means that there is
tearing and leakage
 if it is lower; that means we have
clogging
Dioctylphthalate smoke particle
penetration tests.  aerosols (size just
above 0.3 ) is directed towards HEPA
filters, then UV light is used (on the
other side of the filter) and if there is a
tear the smoke will pass and the UV light
will detect it (for quick inspection)
## dioctylphthalate is liquid at room
temperature , but under certain
conditions can be transformed to
“smoke” = aerosol with droplets just
above 0.3 ##
high-efficiency particulate air (HEPA):
to consider it as a HEPA filter it should
remove up to 99.997% (99.97%
minimum) of particles greater than
0.3 mm indiameter.
(( 5 log reduction  efficient
sterilization))
## clean rooms:
they have grades  the number of
particles should not exceed the grade
number of the room per cubic meter ,
example: clean room 1000 : it means
that the number of particles &
microorganisms in this room shouldn’t
exceed 1000 particles per cubic meter.
highest sterile rooms : clean room 100
the lower the number the more clean
the room is . ##
HEPA filters consist of pleated sheets of
glass microfibres (to increase surface
area) separated and supported by
corrugated sheets of Kraft paper or
aluminium and thus are acting as depth
filters.
(the four techniques we talked about in
this chapter are the most commonly
used and are accepted by
pharmacopeias, but sometimes we use
other technologies, that’s what we’ll talk
about next)
 New Sterilization
Technologies:
• For thermolabile products & aqueous
drugs that are damaged by radiation,
aseptic manufacture is costly option
with lower SAL.
HEPA filters are depth filters, which
means they don’t have absolute
retention, therefore continuous
monitoring is needed to make sure no
clogging or tearing occurred.
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Microbiology 2
Lecture 22
• 2 examples of new technologies: high
intensity light & low temperature
plasma but still unsuitable for protein or
nucleic acid-containing biotechnology
products.
Lana Hammad
Two types: low pressure and
atmospheric pressure.
 Plasma may be generated from many
substances: (active gases) among the
established methods, chlorine and
hydrogen peroxide plasmas are
used which possess excellent
antimicrobial activity. (they only work at
low pressure )
at atmospheric pressure , noble gases
are used such as helium ,argon, which
form free radicals when they’re oxidized
and these radicals kill microorganisms
Application: on most items sterilized
by ethylene oxide, i.e. medical devices
but not drugs.
It is not used for powders, liquids &
certain fabrics
• High intensity light
(has very high energy)
It is based on the generation of
short flashes of broad wavelength light
(continuous spectrum)
from xenon lamp that has an intensity of
100,000 that of the sun, almost 25% of
the flash is UV
(intensity is much higher than
conventional UV lights , plus it has
visible light as well)
Application: sterilization of food
products, water & terminal sterilization
of injectables in UV transmitting plastic
ampoules (e.g. polyethylene,
polypropylene).
their container has to allow the
penetration of light (especially UV)
But not useful for colored solutions
or those with solutes that has
high UV absorbance, or containers that
absorb UV (polyvinylchloride,
polystyrene)
Good Luck =)
“It wouldn't be Merciful of
Allah to give us everything
we want, when we want,
while knowing that what
we are asking for is
• Low Temperature Plasma
Plasma(‫ )الحالة الرابعة للمادة‬is a gas or
vapor that has been subjected to
electrical or magnetic field which causes
a substantial proportions of the
molecules to become ionized.
actually bad for us.”


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