Decline phase

The death rate coefficient is usually relatively small unless inhibitoiy substances accumulate, so Eq. (24-10) shows an exponential rise until S becomes depleted to reduce [L. This explains the usual growth curve (Fig. 24-21) with its lag phase, logarithmic phase, resting phase, and declining phase as the effect of takes over. 

For those infectious diseases that are transmitted to humans via insect vectors the onset and decline phases of epidemics are rarely observed other than as a reflections of the seasonal variation in the prevalence of the insect. Rather, the disease is endemic within the population group and has a steady incidence of new cases. Diseases such as these are generally controlled by public health measures and environmental control of the vector with vaccination and immunization being deployed to protect individuals (e.g. yellow fever vaccination). 

The rate of cadaver decomposition in soil can be affected by how often a particular site is subjected to cadaveric material. Microbial degradation is typically described as having three phases. The initial lag phase is defined by microbial or enzymatic enrichment. During the second phase the substrate is rapidly degraded. This is followed by a declining phase that results from a lack of readily available substrate or formation of humic substances (Ajwa and Tabatabai 1994). Forensic taphonomy holds that the burial of a number of cadavers in soil over time will result in an increased number of soil microorganisms (Janaway 1996). Experiments using controlled burial environment... 

The rate of change of px at the decline phase can also help in phenomena identification. For example, an abrupt fall in the px value is an indication of nutrient limitation. Once the limiting nutrient has reached a critical concentration, complete depletion and a decrease in growth will occur quickly. On the other hand, when a reduction of px occurs slowly, the phenomenon responsible is usually the formation of an inhibiting metabolite, which has gradually accumulated in the system. 

The same effect of bacterial contaminations was observed with an electronic nose equipped with CP sensors in an antibiotic fermentation with Micro-monospora carbonacea [34]. Infections of E. coli and Gram-positive bacteria can be discriminated in the plot. The same culture also exhibited characteristic response patterns at the different fermentation stages over a nine-day period. The character of the trajectory in the PCA mirrored the growth phase, the antibiotic synthesis phase as well as the declination phase. The starting point of the trajectory almost coincided with the end point. 

A batch experiment takes 3-5 days to grow cells to confluency, up to 5 more days to investigate antibody production during decline phase and 1-2 days for cleaning and sterilizing. Optimization of parameters in chemostat experiments requires 5-12 days per selected value. The time required depends essentially on the dilution rate. Provided that the 12-1 NLF 22 bioreactor is the final scale for production. 

Fig. 3.8 Typical bacterial growth curve in closed batch liquid culture. (A) Lag or adaptive phase (B) logarithmic or exponential phase (C) stationary phase (D) decline phase.

After intravenous administration, the mean elimination half-life was calculated to be 2.7-2.9 h (Putter, 1980 Putter et al., 1982), but there was evidence for a third more slowly declining phase (currently below the limits of accurate detection) with a terminal half-life of about 9h (Muller and Hillebrand, 1986). 

When a conventional (immediate-release) dosage form of a drug is administered orally or by other than intravenous (for example, i.m. or s.c.) injection, the half-life based on the decline phase of the plasma concentration-time curve is an apparent, rather than the true, half-life of the drug. This is because absorption continues after the time (fmax) of the observed peak plasma concentration (Cmax). The apparent half-life varies not only with the route (and site) of administration but also with the formulation of the dosage form of the drug (Baggot Brown, 1998). 

When the drug is administered by an extravascular route, correction for dose must be made in the systemic availability (F) and the apparent first-order elimination rate constant, obtained from the late decline phase of the curve, should be substituted for (3 in the area method equation. 

The time course curve, or growth curve, for a batch culture usually consists of six phases, namely the lag, accelerating, exponential growth, decelerating, stationary, and declining phases. 

Finally, growth stops in the stationary phase. In some cases the rate of cell growth is limited by the supply of oxygen to the medium. When the stationary phase cells begin to die and destroy themselves (by lysis) in the declining phase, the result is a decrease in the cell concentration. 

Roszell et al. (1990) described changes in toxin profile (by HPLC-UV) within batch cultures of P. brevis (clone unspecified but probably Wilson s). PbTx-2 was the predominant toxin with lesser amounts of PbTx-1 ( 30%) and PbTx-3 (-10%) in logarithmic phase cultures but in the stationary and decline phases there was an increase in PbTx-3 with a concurrent decline in PbTx-2. As cells entered stationary phase other analogues (PbTx-7) began to appear. It was concluded that... 

During the declining phase of a product s life, direct costs are very important to the pricing decision. Normally, competition has driven the price down close to direct costs. Only those sellers who were... 

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