Sessile microorganisms

This type of program relies as much on the detergent and surfactant properties of the biofilm control agent as it does on its biocidal properties. With the use of BCAs, rather than sole reliance of heavy-duty biocides, the sessile microorganisms are swept into the main body of the cooling system. More traditional biocides may still be required periodically. 

One immediate result of such classification of bacterial states according to availability of nutrients is that, as in almost all experiments that are being carried out under laboratory conditions, the bacteria have all the required nutrients around them, and they may be inclined to prefer planktonic growth over sessile conditions, whereas a great majority of MIC problems come from sessile bacteria, not planktonic ones. This can call into question the reliability of such experiments, especially if one bears in mind the direct relationship between corrosion rate changes and sessile microorganism growth. ... 

It is now widely recognized that sessile microorganisms cause the most damage in industrial water systems, and the development of biocides is directed towards biofilm. In order to measure the effectiveness of a biofilm control program, it is essential to accurately monitor the development of biofilms in a system and record their response to control measures. 

Haack, T. K., Lashen, E. S. and Greenley, D. E., 1988. The evaluation of biocide eflicacy against sessile microorganisms. Developments in Industrial Microbiology., 29, 247-253. 

Theis and Leder (1993) demonstrated in aerobic biofilm experiments with an oil field isolate of aerobic bacteria, containing predominantly Pseudomonas species, that OPA is more effective than formaldehyde (FA, 2.1a.) or glutaraldehyde (GA, 2.5.) in killing or inhibiting the growth of sessile microorganisms (see Table 16). OPA is effective without activation and is able to inactivate GA-restistant strains of Mycobacterium chelonae. On the other hand OPA unlike GA acts not sporicidal at its in-use concentration of 0.5% (w/v) and normal pH (6.5.). 

Sessile microorganisms do not attach directly to the actual surface, but rather to a thin layer of organic matter adsorbed on the surface (Fig. 10.9, Stages 1 and 2). As microbes attach to and multiply. 

BloFIms. Microbiologists recognize two different populations of microorganisms. Free-floating (planktonic) populations are found in the bulk water. Attached (sessile) populations colonize surfaces. The same kinds of microorganisms can be found in either population, but the sessile population is responsible for biofouling. 

In animals, we can observe the analogous situation in that many insects and other invertebrates (especially those which are sessile and unprotected by armor), but also some vertebrates, store secondary metabolites for their defense which are often similar in structure to plant allelochemicals 1,4,12,16,17,28-30,494-496,503). In many instances, the animals have obtained the toxins from their host plants 4,12,15,17,27-33). Hardly any zoologist or ecologist doubts that the principal function of these secondary metabolites (which are often termed toxins in this context) in animals is that of defense against predators or microorganisms 1,17,28,494-496). 

After colonization of the surface, the microorganisms utilize the available nutrients to grow, multiply, and synthesize both intracellular products and extracellular polymeric substances that constitute the substance of the biofilm. Significant amounts of biofilm can be produced under ideal conditions, and even if planktonic cells are no longer present in the flowing water, the sessile cells already on the surface can provide the basis for biofilm development. 

Microorganisms may either be freely suspended within the bulk solution (planktonic existence) or attached to a surface (sessile existence). When a material is first immersed in an aqueous solution, a thin layer of organic matter (referred to as the conditioning film) is adsorbed onto... 

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