Note: Descriptions are shown in the official language in which they were submitted.
BACKGROIJND OF THE INVENTION
_. Field of the Invention
This invention relates generally to the filtration
art and more particularlyt to a new filtration apparatus.
2. Description of the Prior Art
In the field of microbiology, it is necessary to
conduct various tests on products such as foods, drugs and
cosmetics to quantitatively and/or qualitatively assess the
contamination absent or present in such products. Membrane
filtration has numerous advantages as a procedure for
microbiological evaluation, but cannot be used, since such
products deposit particula~e matter on the surface of the
membrane filter duriny filtration. The particulate matter
interferes with the enumeration of bacterial colonies on the
membrane filter, since these colonies can be to~ally hidden
by khe particles. An automated enumeration system has been
d~v~loped wh:ich uses a hydrophobic grid membrane filter as
~hown in U.S. patent 3,9~9,583 granted to Sharpe et al. For
this automated system to be applied to the analysis of foods,
drugs and cosmetics, it has become necessary to design a
5uitable filtration apparatus which would not only eliminate
the particulate matter from a suspension of such products
without altering the bacterial content of the suspension, but
which would also allow for the subsequent filtration of the
clariied product through a membrane filter in order to
impregnate the filter for the isolation and/or enumeration
of microorganisms.
Various filtration devices have been designed which
have in the past, been used in ihe microbiological field.
One such example is shown in U.S. patent number 4,148,732
I
1 granted to Burrow t al April 10, 1979. This unit is used as
a bacterial filter unit in anesthesia and respira-tory procedures
but does not provide an apparatus for producing an impregnated
filter suitable for an enumeration process.
Other devices, such as those shown in U.S. patent
3,888,765 (Bolk) 2,127,397 (Freedlander) 3~954,625 (Michalski),
3,919,089 (Gonzalez~ and 3,~36,464 (Brookins et al.), all
relate to filtration devices which contain a filter between two
housinys. ~one of these devices would enable a preliminary filt-
10 ration of a suspension with subsequent impregnation of a secondfilter medium for use in an enumeration procedure.
~ RY OF THE INVENTION
Accordingly, it is an object of -the present invention
to provide a novel filtration apparatus suitable for clarifying
a su.spension thus rendering the suspension filterable and which
allows for subse~uent impregnation of a second filter medium for
~3ubs~uen-t processing.
Xt is a fuxther object of the present invention to
.rov:Ld~ a novel filtrcltion apparatus whiLch u.ses a membrane
~ iltex as a second filter medium.
Itis ~ still further object o the present invention to
provide a novel filtration apparatus which incorporates a dual
filtration therein and produces an impregnated hydrophobic grid
membrane filter.
To this end, in one of its aspects, the invention
provid~s a novel filtration apparatus which comprises a first
housing portion and a second housiny portion, a first filter
medium retained in said first housing portion, means adapted to
receive and releasably retain a second filter medium between said
first and second housing portions.
,
53
1 In another of its aspects, the invention provides a
filtration apparatus which comprises a first housing portion, and
a second housiny portion which is pivotally connected to said first
housing portion, said first housing portion being divided along its
length by an annular shoulder into an upper chamber and a lower
chamber, the diameter of said lower chamber being greater than
the diameter of the upper chamber, a small opening e~tending
through the wall of said lower chamber immediately below said
annular shoulder, said second housing portion having a rectangular
1~ upper section and a base extending therefrom, a first filter medium
retained between said upper cham~er and said lower chamber of said
first housing portion, and a second filter medium retained between
said first housing portion and said second housing portion.
BRIEF DESCRIPTION OF TEIE DRAWINGS
.... _ .. ... .. .. .
FIGURE 1 is a perspective view of the novel ~iltration
app~xatus of the present invention.
~ 'CGU~E 2 is a top view thereof.
FIGVRE 3 is a section vi.~w along line 3-3 oE E:iyure 1.
~ :tGU~E 4 is a perspective view of the holdings means of
figure 1.
FIGU~E 5 is a perspective view o the second housing
portion of figure 1.
FIGURE 6 is a perspective view of a press fit ring and
the irst filter medium.
DESCRIPTION OF THE PREFERRED EMBODIMENT
. .
Reference is first made to figure 1 which shows a per-
spective view of the filtration apparatus of the preferred
embodiment of the present invention. The apparatus comprises a
first housing portion 10 and a second housing portion 12, which
are pivotall~ connected by pivotting means 14. Holding means 16
is pro~ided to secure the first housing portion 10 to the second
housing portion 12.
-- 3 --
53
1 Figure 2 is a top view of the novel Eiltration apparatus.
As seen from fiyures 1 and 2, the first housing portion 10 has a
central, circular opening 18 therein, and is generally cylindrical
in shape, with an annular shoulder 20 at about one-half its length,
the purpose of which will be explained hereinafter~ The diameter
of the lower part of the first housing portion is marginally
greater than the upper part and it Pxtends into a rectangular
shape as it extends downward. A small opening 26 which leads to
a conduit (not shown) is provided in the side wall of the first
10 housing portion 10.
The top of the second housing portion 12 is rectangular
in profile and has a funnel shaped base portion 22 which ter~in-
ates in a conduit 24 which allows removal of the li~uid during the
eiltration process. The particular shape of the base portion 22
is nok critical to the invention and may be varied within the
scope and spirik of the present invention. It may, if desirad,
bcl om:itt~d completely and the top of the second housing portion 12
would constitute the entire second houl3ing poxtion 12. ln this
case, the filtrate would be removed directly from the second
housing portion 12.
~ he structure of the upper housing portion 10 will now
be more particularly described with ref~rence to figure 3 which
is a sectional view along line 3-3 of figure 1. First
housing portion 10 has a circular opening 18 on the top surface
thereo~ and forms a first chamber 28 and a second cha~ber 30.
A first filter medium 32 is interposed between the first chamber
28 and the second chamber 30 and is secured to the walls 34 of
the first housing portion 10. An opening 26 leads to a conduit
36 which communicates with a depression 38 in the interior side
wall of the lower chamber 30 immediately below the filtex medium 32.
5~
1Figure 4 shows the holdiny means 16 which in this
e~odiment, is sh~wn as an enlarged la~ch 40 which extends
beyond the lower surface of the first housi.ng portion 10~ As
seen from figure 1 and 4, the latch 40 is biased upwardly and
lip 42 projects inwardly of the exterior surface of second housing
portion 12 to hold the housing portions together.
The first filter medium 32 is secured across the open-
ing between the first chamber 28 and the second chamber 30. Pre-
fexably, the filter medium 32 is inserted and retained on a press
10fit ring 52 as shown in figure 6. The press fit ring 52 is
adapted to fit and be retained in the uppermost part of the
second chamber 30. In one embodiment, the ring 52 includes
marginally exl:ending annular protrusion 54 about its upper sur-
~ace, whi.ch pro-trusion fits into and is retained in an ann~lar
groo~e 56 which is cut in the inner surface of the shoulder 20.
'l'h.is structure allows the ring 52 and the filter medium 32 to
b~ h~ld in place.
Othe.r ~mbod:irnents Oe the ring 52 rnay be designed to
r~in the first filter medium 32 in place. For example, a
groove could be cut in the ring 52 itself and the ~ilter medium
32 could sit and be retained in the ring 52.
Other means may be provided for retaining the ring 52
and the filter medium 32 in place. For example, an annular in-
wardly extending protrusion may be included on the inner side
wall oE either the upper chamber 28 on the lower chamber 30 upon
which the ring 52 may rest.
The ring 52 is generally press fit into place and held
by tension. The inherent resiliency in the material will allow
its insertion and subsequent retent;on.
-- 5 --
O~3
1 It is of course preferred that in constructing the means
to hold the first filter medium in place, all walls be made to
slope downwardly. This structure prevents any of the filtra~
from ~ecoming trapped on any ledges which will affect the results
of the su~sequent filtration on the second filter medium.
The first hous~ng portion and the second housing
portion are pivotally connected by any well known means. One
embodiment of a suitable pivoting means is shown in figures 1 and
2. The second housing portion 12 has a pair of arms 50 ex-
tending outwardly wi$h a cylindrical pin 48 extending therebe-
tween and marginally ~eyond the plane of each arm 50. The
first housing portion 10 has a pair of curved flanges 51 in which
is journalled the respective ends o~ the pin 48 which extends
outwardly ~eyond the arm 50. A curved cover 53 extends out-
wardl~ from the first hous~ng portion lO and is adapted to fit
over the area of the pin 48 between the flanges 51.
Thus, when latch 40 is relea,sed, the first housiny
portlon 10 may be pivotted open as pin 48 rotakes in the
~langes 51 and the cover 53. S~nce the cover 53 does not extend
29 as far downwardly as flanges 51, t~ere is a space provided there-
~etween which allows the pin 48 to he removed thus ~eparating ,
the first and the second housing portions. This particular
structure enables the first ~ousing portion ~o be pivotted upon
or if desired, separated from the second housing portion.
The first filter medium 32 is provided to provide a
preliminary filtration for the material to be filtered. It may
be made of a variety of materials and generally has a micron
porosity which comprises an absolute particle retention size
of from about 4 microns to about 15 microns, preferably about
8 microns. Most microorganisms have a particle size in the area
-- 6 --
i53
o~ about 0~5 microns to about 1.5 ~lcr~ns and accordin~ly, a
filter medium with an absolute ~article retention size of about
8 microns is suitable.
As stated before, filter medium 32 may be made of
a variety of materials, this material not being critical to
the present invention.
The filter medium 32 must be autoclavable as is necessary
for the entire apparatus and, to effectively allow m~croor~anisms
to pass through the filter, .it must be of sufficient porosity
and structure to pass throuyh large microorganismsO The pores
or passageways in the filter should not twist; otherwise,
bacteria may be trapped even though the pore size is sufficiently
large. A pore size of at least about 4 microns is preferred.
One example of a suitable material is a stainless steel
twilled-weave dutch filter cloth which is available from man~
ou.rces. This material is a dense, strong material o~ warp wires
w1th r~ular passageways therethrough.
The vacuum which is introduce3d throu~h hole 2fi and
corlduit 36 must be sufficient to aid in the primary filtrat~on
of the liquid passing through the first filter medium 32. The
exact parameters of the vacuu~, .including the amount, time and
size oE the vacuum are determined by experimentation. The li~uid
passin~ through the filter medium 32 will not be pulled into
conduit 36 as the entrance of the conduit is recessed in
depression 38.
When the ring as shown in figure 6 is put in place,
it is seen that the ring forms a small vertical channel with the
depression 38. The vacuum is drawn from the chamber 30 upwardly
through the funnel channel and out through the conauit 36 and the
opening 26. This effectively prevents any of the filtrate from
bein~ removed from the chamber 30 due to the action of the vacuum.
53
If desired, the conduit 36 ;ma~ communicate w,ith a
corresponding conduit in the ring 52 which then communicates
with the second chamber 30. Thi,s structure is more dif~icult to
assemble since it would be necessary to accurately aliyn the
conduit in the ring 52 with the conduit 36.
The second filter medium ~s placed on the top o~ the
second housing portion 12 and receives the clarified filtrate
which has been filtered through the ~irst filter medium 32. The
clarified filtrate i5 then filtered through'the second filter
medium with the aid of a vacuum drawn throu~h conduit 24.
While the second filter medium may be of any type o
fi,lter depending upon the use of the apparatus, within the scope
of the present invention, the apparatus is particularly suitable
for use with a membrane filter which retains microorganisms on
:lt~ ~urface for ~ubsequent,processing. A membrane filter
~enerally comprises a porous, non-fibrous plastic film material
in whlch the abso:lute size and the uniEormity of size'of the
po~ ctr~ careEIllLy controllcd.
'rhc mernbrarle ~ilter should have c~ pore size'o$ ~bout
0.l~ to 1.0~ and preferably from about 0.2~ to about 0~7~ The
most preferred pore size is abou-t, 0.45,u. The membrane must be
h~drophilic to allow waker and various nu-trients to pass there-
through and it must be capable o~ being sterilized without
structural or functional damage. It must also be non-~toxic to
bacteria. The thickness of the ~ilter is not critical but,
preferably, should not exceed 0.5 mm. The apparatus is also suited
for usin~ a hydrophobic grid membrane filter (HGMF) as the
second filter medium.
-- 8 --
53
1 In the preferred embodiment of the apparatus designed
for use wit:h an EIGMF, the lower part of the first housing 10 and
the upper part of the second housing 12 are rectangular in
profile to allow a rectangular HGMF to be secured therebetween~
However, the shape of these sections may be varied within the
scope of ~he invention. For example, many standard membrane
~ilters are rounded so in this case, the respective sections of the
irst and second housing portions will be rounded in profile. The
exact shape of these sections will depend upon the nature of the
10 second filter medium and its shape.
The entire filtration apparatus may be manufactured of
any material. It is recornmended that such material be autoclavable
and t:hat khe entire app~ratus be steriliæed prior to use. Two
suitable examples include a polysulfone made by Union Carbide Co.
or TPX* which is a methylpentane polymer sold by Mitsui Petro
chcmlcal Industries Ltd. of Japan.
Thf~ principles o~ the process using the novel filtration
p~ara~us wlll now be described as illustrative only and not
limiting in nature. While not restricted thereto, the invention
20 will be described with a hydrophobic grid membrane filter ~HGMF)
as the second filter medium~
It is essential in many industries to be able to
determine whether or not microorganisms are present in raw
materials, finished products and intermediate products used and
made in that industry, as well as by-products and ef~luent
resulting from the industrial process, and also to be able to
classify the microoxganisms if present into their proper taxonomic
categories. Many such microorganisms are not only undesirable but
some are detrimental to the health of the consumer of the product
3~ and thus prohibited by government regulation.
.~
*Trade Mark 9 -
1 This need exists for many industries, but it is part-
icularly important for such industries as the drug industry,
the food industry and the cosmetic industry. Government regulations
in most jurisdictions strictly control the quantity of certain
microorganisms which is permitted in food, drug~ cosmetic and
similar products, and accurate tests must be performed at regular
intervals to ensure compliance with these regulations.
Several methods ~xist today for detecting, c~unting and
identifying microorganisms present in a sample. Most methods
~O entail depositiny a portion of the sample in or upon one or more
culture media which encourage the growth of the microorganisms.
Usually, a different kind of culture medium is used for each type
oP rnicroorganism of interest. Once the microorganisms have grown
on these culture media, further tests are often required to complete
their .identiEication. This usually requires the transfer of a
port:ion of the growth to other culture media, in order to
cle~.rmln~ vax.iou~ impor-tant ch~racteY:ist:.ics of the mi.crooryanisms
(Kuch a~ the ability to ferment certain sugars, or to grow in the
presence of certain chemicals)
~ ~hese methods are widely used in a number of areas
including testing of foods, water and effluent for pathogenic
bacteria, spoilage organisms, or bacteria indicative of poor
sanitary practices, testing of pharmaceutical products, and
testing of urine in the diagnosis of urinary tract infections.
Other applications include, for example, the control of starter
cultures used in fermentation processes (such as in cheese or
yoghurt manu:Eacture and in the production of beers and wines).
~ novel apparatus for enumerating mic.roorganisms has
been developed. As discussed in United States patent number
3,929,583 granted on December 30, 1975 to Canadian Patents
and Development Limiked, this apparatus comprises a membrane
fi.ltsr capable of retaining microorganisms on its surface when
-- 10 --
a53
1 a fluid sarnple is passed through it. ~ barrier material is
imprinted on the surface of the filter which restricts the ~pre~d
of colonies through its physical properties. The pattern
produced defines a plurality of ordered, microbial colony-
isolating cells wherein the cells are usually smaller in area
than in normal colony area.
The use of the hydrophobic grid membrane filter
(hereinafter referred to as HGME~) has produced a substantial
advance in the field of microbiology. The regulari-ty in size,
10 shape and optical density, and the orderly arrangement of colonies
as a result of the gridded pattern of barrier material of the
HGM~ has permitted the replacement of manual counting with opto-
~lectronic scanniny, thus saving analyst time and producing more
reliable and reproducible results.
The present invention facilitates the use of the HGMF.
rl'he ~IGMF is clasped between the first housing portion lO and the
~ cond hous:Lng port:ion 12. As shown in :Eigure 2, in the preerred
~mhod:im~nt, the .lower part o the first housing portion lO and
the upper part of the second housing portion 12 are rectangular,
20 thus allowing the HGMF to si~ on the upper surface of the second
housing portion 12, so that when the two housing portions are
clamped together the HGMF will receive the liquid which is filtered
through the fil-ter medium 32. The HGMF acts as a "seal" or
"gask~t" between the housing portions lO and 12.
A suspensiQn of the sample to be tested is prepared and
then fed into opening 18. The suspension is filtered through
the first filter medium 32 with the aid of the vacuum which
is drawn through opening 26. Particulate matter is filtared
out of the suspension and is retained on the surface of the first
30 filter medium 32, and the filtrate passes therethrough. As the
53
1 pore size of the filter medium 32 is sufficiently large to allow
microoorganisms to pass through, the filtrate will contain all of
the microorganisms present in the original sample suspension.
The filtrate then contacts the HGMF which is secured
between the first housing portion 10 and the second housing
portion 12. l'he filtrate is filtered through the HGMF with the
aid of a vacuum drawn throuyh conduit 24. The HGMF retains on
its surface all of the microorganisms which were present in the
original sample suspension.
The latch 40 is then unclasped by moving clip 42
outwardly. The first housing portion 10 is pivotted away from
the second housing portion 12 and the impregnated ~IGMF is removed
for ~ubsequent processing and evaluation.
A further embodimenk of the invention includes the use
o~ multiple first and second filter med:ia within a single housing.
In this embodiment, the first housing portion 10 comprises a
plural~ty O.e lonyitudinally extending, conti.nuous and discrete
channel~ ~hroucJhout its length. Each chal-nel i5 interrupted with
a discrete ~irst filter medium located across the channel at the
20 axis of the annular shoulder 20.
With this structure, the conduit 36 leads directly to
each of the channels below the first filter medium or altern-
atively, there may be provided a plurality of openings 26 and
corresponding conduits 36 leading separately to each channel
thus allowing a vacuum to be pulled from each channel. In the
former case, only one opening 26 is required and only one vacuum
is pulled. In the latter case, a plurality of openings correspond-
ing to the number of channels is re~uired and a vacuum must be
pulled through each opening 26.
- 12 -
3,S~3
1 Each of the channels terminates at the juncture
between the firs-t housing portion 10 and the second houslng
portion ]2, and a discrete second filter medium is secured at
the end of each channel~ Each discrete second f-ilter medium
is of a size and is aligned such that all the material passing
through the channel is filtered through the second filter medium
and will not contact any of the other filter media.
This embodiment allows for the testing of a plurality
of samples simultaneously. Each ~est suspension is fed into a
~ separate channel at opening 18. Each suspension is filtered
through the first filter media with the aid of the vacuum and the
particulate matter is filtered out of the suspension and the
filtrate passes therethrough into the corresponding lower portio~
oE ~ach channel in chamber 30. The filtrate then contacts each
respective second filter mediwm and each second filter medium
retains on its surface, all of the microorganisms which were
~rc~nt in the original sample suspension. Since the material
ing throucJh the second filter media is waste material, it is
co.llect~d in th~ common second housing portion 12.
The first housing portion 10 is then pivotted away ~rom
the second housing portion 12 and the plurality of impregnated
second filter media are removed for subsequent processing and
evaluation.
The adva~tages of this embodiment are that a plurality
of impreynated second filter media are obtained simultaneously,
each one of which is impregnated with the microorganisms of a
different suspension. This allows for the testing of a number
of sampl~s without the need for removing the second filter
media after each suspension is filtered.
i Although the disclosure describes and illuskrates a
preferred embodiment of the invention, it is to b~ understood
that the invention is not restricted to this particular embodiment.
~0
- 14 -
