<< Chapter < Page Chapter >> Page >

Membrane filters

Filtration can also be used to remove microbes from liquid samples using membrane filtration . Membrane filters for liquids function similarly to HEPA filters for air. Typically, membrane filters that are used to remove bacteria have an effective pore size of 0.2 µm, smaller than the average size of a bacterium (1 µm), but filters with smaller pore sizes are available for more specific needs. Membrane filtration is useful for removing bacteria from various types of heat-sensitive solutions used in the laboratory, such as antibiotic solutions and vitamin solutions. Large volumes of culture media may also be filter sterilized rather than autoclaved to protect heat-sensitive components. Often when filtering small volumes, syringe filter s are used, but vacuum filter s are typically used for filtering larger volumes ( [link] ).

a) Photo of 2 chambers separated by a filter; a tube runs from below the filter to a device. B) A photo of a syringe with a filter on the end.
Membrane filters come in a variety of sizes, depending on the volume of solution being filtered. (a) Larger volumes are filtered in units like these. The solution is drawn through the filter by connecting the unit to a vacuum. (b) Smaller volumes are often filtered using syringe filters, which are units that fit on the end of a syringe. In this case, the solution is pushed through by depressing the syringe’s plunger. (credit a, b: modification of work by Brian Forster)
  • Would membrane filtration with a 0.2-µm filter likely remove viruses from a solution? Explain.
  • Name at least two common uses of HEPA filtration in clinical or laboratory settings.

[link] and [link] summarize the physical methods of control discussed in this section.

A table titled physical methods of control; 4 columns – method, conditions, mode of action, and examples of use. Groupings are: heat, cold, pressure, desiccation, radiation, sonication, and filtration. Heat. Boiling, 100 °C at sea level, Denatures proteins and alters membranes; usese Cooking, personal use, preparing certain laboratory media. Dry-heat oven, 170 °C for 2 hours, Denatures proteins and alters membranes, dehydration, desiccation; uses Sterilization of heat-stable medical and laboratory equipment and glassware. Incineration, Exposure to flame,Destroy by burning, Flaming loop, microincinerator. Autoclave, Typical settings: 121 °C for 15–40 minutes at 15 psi, Denatures proteins and alters membranes, Sterilization of microbiological media, heat-stable medical and laboratory equipment, and other heat-stable items. Pasteurization, 72 °C for 15 seconds (HTST) or 138 °C for ≥ 2 seconds (UHT), Denatures proteins and alters membranes, Prevents spoilage of milk, apple juice, honey, and other ingestible liquids. Cold. Refrigeration, 0 °C to 7 °C, Inhibits metabolism (slows or arrests cell division), Preservation of food or laboratory materials (solutions, cultures). Freezing, Below −2 °C, Stops metabolism, may kill microbes, Long-term storage of food, laboratory cultures, or medical specimens. Pressure. High-pressure processing, Exposure to pressures of 100–800 MPa, Denatures proteins and can cause cell lysis Preservation of food, Hyberbaric oxygen therapy. Inhalation of pure oxygen at a pressure of 1–3 atm, Inhibits metabolism and growth of anaerobic microbes, Treatment of certain infections (e.g., gas gangrene). Dessication. Simple desiccation, Drying, Inhibits metabolism, Dried fruits, jerky. Reduce water activity, Addition of salt or water Inhibits metabolism and can cause lysis, Salted meats and fish, honey, jams and jellies. Lyophilization, Rapid freezing under vacuum, Inhibits metabolism Preservation of food, laboratory cultures, or reagents. Radiation. Ionizing radiation, Exposure to X-rays or gamma rays, Alters molecular structures, introduces double-strand breaks into DNA, Sterilization of spices and heat-sensitive laboratory and medical items; used for food sterilization in Europe but not widely accepted in US. Nonionizing radiation, Exposure to ultraviolet light, Introduces thymine dimers, leading to mutations, Surface sterilization of laboratory materials, water purification. Sonication, Exposure to ultrasonic waves, Cavitation (formation of empty space) disrupts cells, lysing them, Laboratory research to lyse cells; cleaning jewelry, lenses, and equipment. Filtration. HEPA filtration, Use of HEPA filter with 0.3-µm pore size Physically removes microbes from air, Laboratory biological safety cabinets, operating rooms, isolation units, heating and air conditioning systems, vacuum cleaners. Membrane filtration Use of membrane filter with 0.2-µm or smaller pore size, Physically removes microbes from liquid solutions, Removal of bacteria from heat-sensitive solutions like vitamins, antibiotics, and media with heat-sensitive components.
See alt text for previous figure. This figure is a continuation of a 2 part figure, the contents of which are described in full in the alt text for the previous figure.

Key concepts and summary

  • Heat is a widely used and highly effective method for controlling microbial growth.
  • Dry-heat sterilization protocols are used commonly in aseptic techniques in the laboratory. However, moist-heat sterilization is typically the more effective protocol because it penetrates cells better than dry heat does.
  • Pasteurization is used to kill pathogens and reduce the number of microbes that cause food spoilage. High-temperature, short-time pasteurization is commonly used to pasteurize milk that will be refrigerated; ultra-high temperature pasteurization can be used to pasteurize milk for long-term storage without refrigeration.
  • Refrigeration slows microbial growth; freezing stops growth, killing some organisms. Laboratory and medical specimens may be frozen on dry ice or at ultra-low temperatures for storage and transport.
  • High-pressure processing can be used to kill microbes in food. Hyperbaric oxygen therapy to increase oxygen saturation has also been used to treat certain infections.
  • Desiccation has long been used to preserve foods and is accelerated through the addition of salt or sugar, which decrease water activity in foods.
  • Lyophilization combines cold exposure and desiccation for the long-term storage of foods and laboratory materials, but microbes remain and can be rehydrated.
  • Ionizing radiation , including gamma irradiation, is an effective way to sterilize heat-sensitive and packaged materials. Nonionizing radiation , like ultraviolet light, is unable to penetrate surfaces but is useful for surface sterilization.
  • HEPA filtration is commonly used in hospital ventilation systems and biological safety cabinets in laboratories to prevent transmission of airborne microbes. Membrane filtration is commonly used to remove bacteria from heat-sensitive solutions.

Fill in the blank

In an autoclave, the application of pressure to ________ is increased to allow the steam to achieve temperatures above the boiling point of water.


Got questions? Get instant answers now!


Ionizing radiation can penetrate surfaces, but nonionizing radiation cannot.


Got questions? Get instant answers now!

Moist-heat sterilization protocols require the use of higher temperatures for longer periods of time than do dry-heat sterilization protocols do.


Got questions? Get instant answers now!

Short answer

What is the advantage of HTST pasteurization compared with sterilization? What is an advantage of UHT treatment?

Got questions? Get instant answers now!

How does the addition of salt or sugar help preserve food?

Got questions? Get instant answers now!

Which is more effective at killing microbes: autoclaving or freezing? Explain.

Got questions? Get instant answers now!

Questions & Answers

similarities between prokaryotic cell and eukaryotic cell
Ednah Reply
Eukaryotic cells contain membrane-bound organelles, including a nucleus. ... Prokaryotic cells do not contain a nucleus or any other membrane-bound organelle. Prokaryotes include two groups: bacteria and another group called archaea.
what is different between plasma and serum?
difference between plasma and serum is that plasma is liquid n serum is fluid
what is microbiology
what is the diseases caused by the microorganisms
both cells have plasma membrane, which services as a barrier between the inside of the cell and outside. both prokaryotes and eukaryotes have ribosomes. they receive messages from messanger RNA molecules, telling them what proteins the cell needs.
Some bacteria infection
what are pathogens
Oluka Reply
any disease causing microorganism that can invade the body and cause harm
hepatitis b
what's da answer
any diseases that course harmful to body
hepatitis is usually implementery of the liver and is commonly course by virus infection
a type of virus that causes severe illness lasting from two to six weeks it may cause massive lived necrosis and cirrhosis
hepatitis B are transmitted when in contact with body fluid such as blood,semen,varginal secration that contain the hepatitis b virus
I understand necrosis,means death of all cell or injury of blood supply, but what is cirrhosis pls
sorry meant liver cirrhosis
good evening all
ok liver damage
I have a question
Hey welcome all of you...i think you are discussing about Micro-organisms..what does it Micro?
how about, scabies (bacteria) yeah can some one gist me abt it
sorry what doest it mean Micro organism?
microorganism are minute living organisms found almost everywhere. they can be autotrophic heterotrophic or chemotrophic
Tell me about enzyme kinetics
wowoww thanks a lot farmuyiwa Alice
have anyone colony pigmentation of different types of bacteria such as Aeromonas, Edwardsiella, vibros,
yes dear sadiqur Bacterias are live in everywhere.. .
microorganisms are arganism that cannot been seen with 👀 until by the use of microscope
microorganisms are arganism that cannot been seen with 👀 until by the use of microscope
yhea organisms are organisms they are naked eye/can't seen by our eyes
and scabies are one of the most common skin condition that can course itches and raches.
and also scabies are not infection, but an infestation
my Q is what is the contribution of van-leeuwenhoek in field of microbiology
Antony van leevenhoek is father of microbiology.
Anton Van leewun hook is discovered Microscope it's true or not? who can brief me please
micro organisms are organism that cannot be seen with an aided eyes ,but by the use of microscope
Yes.. He discover first microscope. He take 2 lence at a time and he saw the plant cells... Thus he was called father of microbiology
who examined water from a bathtub and discovered microbes
for instance any type of Stagnant water is creat there are d/t tupes of small animals.. so those animals are called Micro organism?
thank you javpal for Describing.
can you please differentiate between vacuoles and inclusion bodies
Noor Reply
vacuoles consists of watery solution called cell sap while bodies are organelles
5 difference please
Archaea is an odd type of bacteria that live in extreme environments; high salt, high temperature etc. usually called extremophiles.
Danesia Reply
you know anyone that has delt with enterobacter agglomerans.
it is a type of gram negative bacteria and its ubiquitous mostly isolated from plant stuffs and also from faecal material of animals. I heard the name pantoea . it is bacillus in structure.
What are the classification of microorganisms
Portia Reply
Basic classification are eukaryotic and prokaryotic..
micro organisms are classified into three namely: Archaea, eukaryote and prokaryotic organisms
Yay that's right
what is archaea
I've got an issue with the message view
Frank Reply
Is there any effective way to learn microbiology.
Frank Reply
I have some basic knowledge of biology. I mean i'm totally beginner in that field.
Assuming that i'm interested in neuroscience. What is the best way to master that particular subject.
Can you wait me just a minute
Iam apologies for guidance you in neuroscience.. I'm not physician.. I'm microbiologist
My pleasure to join to you
Let's begin a conversation
Frank Reply
What would be saying
do you know anything about microbiology
I have so much studying to catch up on🙄
any study tips
Yas of course
What would you like to know
well i'm studying Pharmacy second year and i just started With Microbiology
if you have any basics to tell us 🤷🏻‍♀️ would be helpful
Yas, first you must know that you will have a very easy lecture..
In second stage you will try to learn the type of microbiology
A simple definition for microbiology
In second stage you will try to learn the type of microbiology.. you must learn the bacteria..its structure.. Classification of bacteria according to shape..
It's so easy
What triggers the natural killer cells
jenipher Reply
microbiology is the study of science which deals with study of microorganism e.g .virus,bacteria
sufian Reply
microbiology is a branch of science that deals with invisible microorganisms.
microbiology is the branch of science which deals with the study of organisms too small to be seen with the naked eye
what is microbiology
Safwan Reply
history of microbiology
give all details about cell
Samim Reply
Give me another names for all hypersensitivity
Don Reply
Give me the modern father of microbiology
Antonie van Leeuwenhoek
Louis pasteur is father of modern microbiology Antonie van Leeuwenhoek is only the father of microbiology
Antonie van Leeuwenhoek was the first person to observe the mos. whereas pasteur is the one who described about the vaccine , pasteurization etc.
what is the virulence factor
mukhtar Reply
is the abilityof pathogen that cause disease

Get the best Microbiology course in your pocket!

Source:  OpenStax, Microbiology. OpenStax CNX. Nov 01, 2016 Download for free at http://cnx.org/content/col12087/1.4
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Microbiology' conversation and receive update notifications?