Microbiology Guide: Membrane Filtration (MF) Method

Document ID

Document ID TE8836

Version

Version 4.0

Status

Status Published

Published Date

Published Date 08/20/2019
Question
Microbiology Guide: Membrane Filtration (MF) Method
Summary
Microbiology Guide: Media and Equipment Selection; Membrane Filtration (MF) Method
Answer
From: Microbiology Guide: Media and Equipment Selection


Dilution and Interpretation
  • Optimal colony number: 20-80 colonies per agar plate
 
  • Procedure
    • Wash hands or wear gloves if necessary.
    • Open a bottle of sterile Buffered Dilution Water.
    • Invert the sample container in a waist-to-ear motion, approximately 25 times (for 30 seconds).
    • Use a sterile pipet to add 11 mL of sample into the dilution water bottle.
    • Put the cap on the dilution water bottle. Invert the bottle in a waist-to-ear motion, approximately 25 times (for 30 seconds). This is a 10-fold or 10x dilution (sample is diluted by a factor of 10).
    • Add 11 mL of the 10x dilution to another dilution bottle and mix well (100x dilution).
    • Add 11 mL of the 100x dilution to a third bottle and mix well (1000x dilution).
    • Continue to make dilutions until the necessary dilution level has been reached
  • Dilution Series Steps
    • 10-mL sample: Transfer 11 mL of sample into 99 mL of sterile Buffered Dilution Water.
    • 1-mL sample: Transfer 11 mL of the 10-mL dilution from the previous step into 99 mL of sterile Buffered Dilution Water.
    • 0.1-mL sample: Transfer 11 mL of the 1-mL dilution from the previous step into 99 mL of sterile Buffered Dilution Water.
    • 0.01-mL sample: Transfer 11 mL of the 0.1-mL dilution from the previous step into 99 mL of sterile Buffered Dilution Water.
    • 0.001-mL sample: Transfer 11 mL of the 0.01-mL dilution from the previous step into 99 mL of sterile Buffered Dilution Water.
    • 0.0001-mL sample: Transfer 11 mL of the 0.001-mL dilution from the previous step into 99 mL of sterile Buffered Dilution Water.
 
  • Calculation
    • Calculation (single filter test): Use the following equation to calculate the result from a single membrane filter. Note that “mL sample” in the equation refers to the actual sample volume and not the diluted volume.

*If growth covers the entire filtration area of the membrane, or a portion of it, and Colonies are not discrete, report results as “Confluent Growth With or Without Coliforms.”

Filtration Step
  • Disposable Field Filtration Assemblies
    • Filter Unit, Type A  (Product # 2656600)
 
  • Filtration flask / Filter holder Options
    • Filter holder Options
      • Filter Holder, Magnetic (Product # 1352900)
      • Filter Holder, 47 mm, with Receiver (Product # 2254400)
      • Filter Holder, Glass, for Vacuum Filtration (Product # 234000)
    • Filter flask options
      • Flask, Filtering, 500 mL (Product # 54649)
        • Stopper, Neoprene, One Hole, Size 7, pk/6 (Product # 1480407)
      • Flask, Filtering, 1000 mL (Product # 54653)
        • Stopper, Neoprene, One Hole, Size 8, pk/1 (Product # 1480477)
    • Hand pumps
      • Pump, Vacuum, Hand-Operated with Vacuum Gauge (Product # 2094100)
      • Pump, Vacuum, Hand-Operated (Product # Code 1428300)
 
  • Filtration Manifold
    • Single
      • Field Vacuum Manifold (Product # 2831600)
        • Complete filter assemblies
          • Filter Funnel Assy, Microfunnel, pk/50 (Product # 2831500)
          • Filter Funnel, Microfunnel, pk/50 (Product # 2619000)
      • Millipore Filter Assembly, portable complete (Catalog Number/Order Code 2586200) - This product is currently obsolete, though the consumables are still sold.
        • Complete filter assemblies
          • Microfil funnel & filter (Catalog Number/Order Code 2586300)
          • Microfil V filtration device (Catalog Number/Order Code 2508900)
    • Multiple Place
      • Pall Filter Manifolds
        • Manifold, Filter Funnel, Aluminum (Product # 2486100)
        • Manifold, Filter Funnel, Plastic (Product # 2486150)
        • Complete filter assemblies
          • Filter Funnel Assy, Microfunnel, pk/50 (Product # 2831500)
          • Filter Funnel, Microfunnel, pk/50 (Product # 2619000)
      • Sartorius Bombisart System
        • Sartorius Combisart® 6-Place System (Product # 2519702)
        • Sartorius Combisart® 3-Place System (Product # 2519701)
        • Complete filter assemblies
          • Sartorius Biosart® 100 Monitor (Product # 2521100) - Bulk Sterile Packed
          • Sartorius Biosart® 100 Monitor (Product # 2521101) - Sterile Individually Packed
          • Sartorius Biosart® 100 Monitor (Product # 2521102) - Sterile Packed
 
  • Filter Options
    • PALL GN-6 47 mm Diameter, 0.45 µm Pore Size, individually packaged, gridded, sterile
      • Filter, Membrane, pk/200 Without Pad (Product # 1353001)
      • Filter, Membrane, pk/1000, Without Pad  (Product # 1353002)
    • Millipore® S-Pak type HA membrane filters, 47mm, 0.45um, individually packaged, sterile
      • Millipore®, Gridded, pk/600 (Product # 2936500)
    • Millipore® EZ Pak System filters
      • Filter Membrane, EZ-Pak, 0.45 micron, 47 mm, White, Gridded, pk/600 (Millipore®) (Product # 2916800) - the Dispenser these filters are used with, (Product # 2916700), is obsolete)
Petri Dish Step
  • Petri dish
    • Dish, Petri, 15 x 100 mm, pk/600 (Product # 2178900)
    • Dish, Petri, 15 x 100 mm, pk/20  (Product # 2178901)
    • Dish, Petri, 9 x 50 mm, pk/100  (Product # 1485299)
    • Dish, Petri, 9 x 50 mm, pk/500  (Product # 1485200)
 
  • Petri dish with Pad
    • Petri Dish With Pad, 9 x 50 mm, pk/100 (Pall) (Product # 1471799) *recommended
    • Dish W/Pad (Millipore®) (Product # 2936300)

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