The Membrane Filter technique offers the advantage of isolating discrete colonies of bacteria, whereas the MPN procedure only indicates the presence or absence of an approximate number of organisms. The concentration of larger samples on a membrane filter is a key benefit of the technique over the MPN procedure as well as over Pour Plate and Spread Plate Techniques.
Many Industries and U.S. EPA test procedures require samples of 100 mL or more to be analyzed for the presence of bacteria. The Membrane Filter technique allows for a sample size of 100 mL. The Pour Plate technique is limited to a sample volume of 2 mL and the Spread Plate technique has a limit of .5 mL.
How does the Membrane Filter technique work?
Using the Membrane Filter technique, a 100 mL sample is passed through a 47 mm membrane using a filter funnel and a vacuum system. Any organisms in the sample are concentrated on the surface of the membrane. The filter is then placed in a petri dish with nutrient medium. The passage of nutrients through the filter facilitates the growth of organisms on the upper surface of the membrane. THe discreet colonies that form on the surface of the membrane can be easily transferred to confirmation media.
What are some common applications for membrane filters?
Municipal water treatment plants monitor drinking, waste and surface water for the presence of coliform bacteria using the Membrane Filter technique. The key organism monitored in water treatment facilities if E. coli. The U.S. EPA considers this organism the leading indicator of fecal contamination.
In addition to its use by government labs for monitoring drinking water, the Membrane Filter technique is also used for microbial monitoring in the pharmaceutical, cosmetics, electronics and food and beverage industries. The Membrane Filter technique is used in these industrial labs to monitor the presence of microorganisms in process waters and final products.
The pharmaceutical and cosmetics industries typically focus on monitoring their process water for Pseudomonas species. The electronics industry monitors for any and all microorganisms because they must keep their process water free from even the smallest organisms. Microbial monitoring in the food and beverage industry typically employs several types of techniques because of the variety of samples that are encountered. Beverage samples can typically be monitored for microorganisms through the Membrane Filter technique, but when solid samples cannot be liquified, alternative methods must be used.
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PTFE membrane filters are used in a variety of applications in industries such as pharmaceutical, biosciences, laboratory testing, food and beverages, chemical engineering and air filtration. PTFE membranes have an extensive compatibility to numerous chemicals and can be exposed to higher temperatures. They are most commonly used for the filtration of organic, alkali, and strong acidic solvents. We offer PTFE Membranes in both the natural state (Hydrophobic) and the treated state (Hydrophilic) to work in an array of different applications.
PVDF (polyvinylidene fluoride) is a hydrophobic, solvent resistant membrane that is known for it's high temperature resistance and high particulate removal efficiencies. PVDF is commonly used in the offshore oil and plumbing industries, and is suitable for Gas, Vapor, High-Temperature, Food, and Medicine Filtration. PVDF is good to use with alcohols, proteins, weak acids, peptides, and other biomolecules while it must be avoided with strong acids, bases, ethers and ketones. We offer PVDF Membranes in both the natural state (Hydrophobic) and the treated state (Hydrophilic) to work in an array of different applications.
Nylon is commonly used for general laboratory filtration, and filtration of HPLC samples prior to injection. Nylon binds protein, and should not be used when maximum protein recovery is important. Nylon Membrane Filters are commonly used in the industrial waste water and beverage industries. These highly durable and tear resistant membranes are hydrophilic and constructed to wet evenly eliminating the need for wetting agents.
Cellulose Acetate (CA) is a great hydrophilic material for filtering aqueous and alcoholic media, especially at high temperatures. Cellulose Acetate is completely uneffected by temperatures up to 135°C (275°F). Cellulose Acetate membrane filters are the lowest protein binding filters currently available, they provide extremely high throughputs and require less filter changes when filtering high protein solutions. They are great for protein and enzyme filtration, biological fluid filtration, tissue culture media filtration and diagnostic cgytology.
Cellulose Nitrate (CN) is a very durable and flexible membrane material for applications involving sample preperation, biomedical tissue culture, and pharmaceutical filtration. This membrane material exhibits very high thermal stability and is very easy to handle compared to other membranes when loading into filter holders or other instruments. They also show low shrinkage rates during autoclave cycles due to their high temperature resistance.
Polypropylene (PP) Membrane filters are naturally hydrophobic and are best suited for industrial applications such as gas and chemical filtration. They are also widely used in the automotive industries. Polypropylene has extremely low extractable levels ensuring accurate and consistent results for sensitive chromotography applications. They also exhibit very little protein binding which is necessary for sample recovery in small protein samples.
PES membranes are hydrophilic, low protein and drug binding, and are ideal for use in life science applications. Due to the remarkable asymmetrical pore structure of the PES Membrane, they have a high dirt loading capacity and a remarkable flow rate as compared to symmetrical membranes. They are also commonly used in applications such as water filtration, chemical reagent filtration and high-temperature liquid filtration.
Our Track-Etched Polycarbonate Membranes are produced from a high quality polycarbonate film providing a smooth flat surface with sharply defined pore sizes. These membranes exhibit high flow rates, low levels of extactables, and chemical and thermal resistance. Polycarbonate Membranes are designed for the detection of particulates in highly corrosive fluids. These membranes are utilized in epifluorescence microscopy, environmental analysis, cell biology, fuel testing, water microbiology and air analysis applications.
MCE (Mixed Cellulose Ester) Membranes are produced of cellulose acetate and cellulose nitrate. These membranes are biologically inert and commonly used for analytical applications. They provide a more uniform surface than pure nitrocelluose filters. Mixed Cellulose Ester Membranes are commonly used in the microdialyisis of proteins as well as DNA, air particulate monitoring, and microbiology analysis applications. They are provided as plain white membranes, or in several gridded options. The color distinction on the gridded versions facilitates particle detection and reduces common eye fatigue.
These instruments are ideal for loading and hands-free dispensing of sterile membrane filter rolls. The automatic process allows for quick and easy usage and more accurate results.