Adsorption microbial cells

Considerable work has been done to try to explain why quats are antimicrobial. The following sequence of steps is beheved to occur in the attack by the quat on the microbial cell (/) adsorption of the compound on the bacterial cell surface (2) diffusion through the cell wall (J) binding to the cytoplasmic membrane (4) dismption of the cytoplasmic membrane (5) release of cations and other cytoplasmic cell constituents (6) precipitation of cell contents and death of the cell. 

Sorption of microbial cells is selective but there is no obvious relation between Gram-staining characteristics and attachment, in Fig. 7.41, bacterial cells are shown adsorbing onto larger solid particles (a) or free in suspension (b) (c) illustrates the opposite effect -small particles are shown adsorbed onto bacterial cells. The bacterial cells are adsorbed onto flocculated particles in (d), onto solid surfaces in (e) (f)-(i) show the more complicated behaviour of bacterial forms with coats, cilia and flagella. The adsorption affects growth partly by masking the cell surface and... 

Divalent cations (e.g. Mg2+, Ca2+) present in hard water may also interact with the microbial cell surface and block disinfectant adsorption sites necessary for activity. On the other hand, cationic compounds may disrupt the outer membrane of Gram-negative bacteria and facilitate their own entry. 

W. Lee, S. Furusaki, K. Saito, T. Sugo and K. Makuuchi, Adsorption Kinetics of Microbial Cells onto a Novel Brush-Type Polymeric Material Prepared by Radiation-Induced Graft Polymerization, Biotechnol. Prog., 12 (1996) 178. 

The cases mentioned above are typical of simple liquid-liquid extraction systems, which can be found in the traditional chemical industries. However, extraction systems in the biotechnological industries are more complicated because of the presence of microbial cells and surface active compounds produced during fermentation. The adsorption to the interface of soluble and insoluble surface-active compounds present in the fermentation broth usually causes a mass transfer resistance that reduces the transfer rates (Pursell et al., 2003a, 2003b, 2003c). This is in agreement with what has been found (Pursell et al., 1999) for the case of the extraction of the antibiotic erythromycin-A from a buffer solution and from filtered fermentation broth into 1-decanol the presence of the naturally occurred soluble surface active compounds in the filtered broth led to a 45% reduction in... 

The efficacy of a preservative and the concentration level of a microbicide to be added are very much dependent on the germ content of the material to be protected. This is in particular valid for electrophilic active microbicides which in general react irreversibly with nucleophilic components of the microbial cell, that means that they are used up by being effective. But membrane active microbicides which adsorptively coat microbial cell walls are also withdrawn from action at least temporarily if large numbers of microbial cells are present. The exponential growth profile of microbes (p. 2) always has to be taken into consideration. 

Analytically important enzymes present in microbial cells may often be utilized without further purification. The cells are easily harvested and immobilized on the surface of a sensor by a simple attachment using dialysis membrane, entrapment into gel (agar, collagen, gelatin, etc.) layers, adsorption on filter paper or other supports and only rarely covalently bound. Riedel [186] gives in his review paper characteristics... 

Membrane-active molecules act via non-specific adsorption on the microbial cell membrane and disturbance of the embedded proteins by influencing the penetration of ions and organic molecules and by inhibition of the ATP-synthesis. 

Although it is still difficult to establish clear cause effect relationships, it is widely accepted that chemical pollution contributes for antibiotic resistance dissemination [10, 33, 34]. There are evidences that antibiotic resistance increase is related with environmental pollution and anthropic pressures. In this respect, antibiotics seem to be a major, although not the unique, form of pollution, mainly because it is estimated that about 75% of the antibiotics consumed by humans and animals are eliminated as active substances [35, 36]. In the environment, antibiotics can suffer adsorption, photolysis or biodegradation, reaching very low concentrations [37]. Nevertheless, at sub-inhibitory levels, as they are found in the environment, antibiotics can promote several alterations on housekeeping functions of the cells. Apparently, some of these alterations are not associated with antibiotic resistance. Even though, they contribute for the perturbation of the microbial community, leading, eventually, to an overall resistance increase [1, 34, 38]. 

---