Adherence of bacteria, yeast, blood cells, and latex spheres to large-porosity membrane filters

Abstract

Strong adherence of bacteria, yeast, erythrocytes, leukocytes, platelets, spores, and polystyrene spheres to membrane filter materials was noted during filtration through membranes with pore size diameters much larger than the particles themselves. Quantitative recovery on the membrane filters of these particles from low-concentration suspensions was achieved during gravity- or vacuum-assisted filtration through membranes with pore diameters as much as 30 times that of the filtered particles. Mechanical sieving was not responsible. The phenomenon was judged to be electrostatic. It could be partially blocked by pretreating the filter with a nonionic surfactant (Tween 20), and elution of adherent particles was achieved with 0.05% Tween 20. Gram-positive cocci were removed from suspension more efficiently than gram-negative rods. The commonly used cellulose membranes adsorbed more bacteria, blood cells, and other particles than did polycarbonate filters. Of lesser adsorptive capacity were vinyl acetate, nylon, acrylic, and Teflon membranes. Backwashing with saline, serum, 6% NaCl, dextran solutions, or phosphate buffers of varying molality and pH removed only a fraction of adherent particles. Tween 20 (0.05%) eluted up to 45% of adherent particles in a single back-filtration. Selected filters quantitatively removed the particles tested, which then could be washed and subjected to reagents for a variety of purposes. It is important to anticipate the removal of particles during membrane filtration, since it is not a simple mechanical event.

Selective isolation of bacteria for metagenomic analysis: Impact of membrane characteristics on bacterial filterability

“…By using teflon filters it was possible to obtain quantities of cells that were sufficient for DNA extraction. Zierdt 68 reported a similar observation that Teflon membrane adsorbed the least, with 100% recovery of cells within the filtrate. They established that filter paper with larger pores retained cells the most, because debris/particulates surrounding the bacteria entered the pores, thereby preventing their passage.…”

“…31 the filter. 68 Removal efficiency differs between filters with similar pore sizes but made of different matrices, 69 suggesting that membrane pore size alone as a determinant of filtration efficiency is limited. It is, therefore, not surprising that in water treatment, membrane filtration performance is determined by challenge testing to confirm the membrane's ability to reject a target organism or a suitable surrogate.…”

“…Adhesion of particles onto filter membranes has also been reduced by pretreating the filter with nonionic surfactants or detergents (e.g., Tween 20). 68 Generally, bacteria have high adhesion tendencies (coefficients) to all filter materials, and not limited hydrophobic filters. By pretreating a hydrophobic membrane, it is rendered relatively more hydrophilic.…”

“…Teflon retained the least of all the filters as it is naturally hydrophobic. 68 The hydrophobicity of teflon membranes makes them an attractive option to filter gases, including humidified air. 110 These differences have been attributed to the membrane surface, which is neither smooth nor uniform at the molecular level and as a result may require a longer wetting time for all the pores even if the contact angle is less than 908.…”

“…One oversized pore can lead to failure of a sterility filtration. 68 But the focus of this review is not on sterility filtration, rather on how to recover sufficient and representative cell populations in filtrates from environmental samples. Thus, in order to recover cells in the filtrate, it is necessary to decrease flow rate, by decreasing pore size, in order to reduce the flow of sample into the pores.…”