Microbial death curves display the logarithmic decline of living microbes exposed to a method of microbial control. The time it takes for a protocol to yield a 1-log (90%) reduction in the microbial population is the decimal reduction time, or D-value.
What is microbial death?
Microbial Death STUDY Flashcards Learn Write Spell Test PLAY Match Gravity Created by callumscott46 Terms in this set (35) Definition of Microbial Death A permanent loss of reproductive ability under ideal environmental conditions Autolysis Death due to self-degradation via the microbes own enzymes D Value (Viable Cell Count Graph)
What is a bacterial growth curve?
This pattern can be graphically represented as the number of living cells in a population over time and is known as a bacterial growth curve. Bacterial growth cycles in a growth curve consist of four phases: lag, exponential (log), stationary, and death.
What is the death phase of bacteria?
The death phase is characterized by an exponential decrease in the number of living cells. Bacteria require certain conditions for growth, and these conditions are not the same for all bacteria. Factors such as oxygen, pH, temperature, and light influence microbial growth.
Do first-order reaction kinetics explain microbial survival curves?
Reinterpretation of microbial survival curves The heat inactivation of microbial spores and the mortality of vegetative cells exposed to heat or a hostile environment have been traditionally assumed to be governed by first-order reaction kinetics. The concept of thermal death time and the standard methods of calculating the safety of commercial …
Abstract
Occasionally, experimental survival curves of micro-organisms exposed to a lethal agent have a flat region and traditionally it has been interpreted as evidence of the existence of a “shoulder”.
1. Introduction
Traditional calculations of the efficacy of preservation and disinfectation processes are based on an assumption that microbial mortality or sporal inactivation follows known kinetics.
3. An absolute thermal death time
The semilogarithmic survival curves of the four types shown in Fig. 2 can be produced by several empirical mathematical models, and these can be used to fit experimental survival data with the corresponding shape. For example ( Peleg and Cole, 1998, Peleg and Penchina (in press), Peleg and Cole (in press), Peleg, 1999 ):
What is the death phase of a growth curve?
Death or Decline phase. In the last phase of the growth curve, the death or decline phase, the number of viable cells decreases in a predictable ( or exponential) fashion. The steepness of the slope corresponds to how fast cells are losing viability.
How is microbial growth measured?
While growth for muticelluar organisms is typically measured in terms of the increase in size of a single organism, microbial growth is measured by the increase in population, either by measuring the increase in cell number or the increase in overall mass.
What are the metabolites that are missing from the lag period?
Typically cells in the lag period are synthesizing RNA, enzymes, and essential metabolites that might be missing from their new environment (such as growth factors or macromolecules), as well as adjusting to environmental changes such as changes in temperature, pH, or oxygen availability.
What are the phases of growth in bacteria?
It has been determined that in a closed system or batch culture (no food added, no wastes removed) bacteria will grow in a predictable pattern, resulting in a growth curve composed of four distinct phases of growth: the lag phase, the exponential or log phase, the stationary phase, and the death or decline phase.
What is the exponential phase of cell division?
Exponential or Log phase. Once cells have accumulated all that they need for growth, they proceed into cell division. The exponential or log phase of growth is marked by predictable doublings of the population, where 1 cell become 2 cells, becomes 4, becomes 8 etc. Conditions that are optimal for the cells will result in very rapid growth ...
What is the lag phase of bacteria?
The lag phase is an adaptation period, where the bacteria are adjusting to their new conditions. The length of the lag phase can vary considerably, based on how different the conditions are from the conditions that the bacteria came from, as well as the condition of the bacterial cells themselves. Actively growing cells transferred from one type of media into the same type of media, with the same environmental conditions, will have the shortest lag period. Damaged cells will have a long lag period, since they must repair themselves before they can engage in reproduction.
What is the process of dividing bacteria and archaea?
Bacteria and archaea most commonly engage in a process known as binary fission, where a single cell splits into two equally sized cells.
What is the growth curve of bacteria?
Bacterial growth curve. The term growth is more commonly used to refer to growth in the size of a population. Population growth is often studied by analyzing the growth of microbes in liquid (broth) culture. When microorganisms are cultivated in broth, they usually are grown in a batch culture; that is, they are incubated in a closed culture vessel ...
How to get a growth curve of a species of bacteria?
The bacterial growth curve of a particular species of bacteria can be obtained by the following steps; The growth curve of a population of a particular species can be obtained by growing a pure culture of the organism in a liquid medium at a constant temperature.
What happens to bacteria during the stationary phase?
During the stationary phase, the bacterial cells also produce secondary metabolites or metabolites produced after active growth, such as antibiotics.
What happens during the metabolic phase of a bacterial cell?
During this step the cells start their metabolic activity but don’t divide. In this phase the bacterial cells also synthesis RNA, enzymes, and essential metabolites, as well as adjusting to environmental changes such as changes in temperature, pH, or oxygen availability.
Why do microbes enter stationary phase?
One of the most important reasons is nutrient limitation; if an essential nutrient is severely depleted, population growth will slow and eventually stop. Aerobic organisms often are limited by O2 availability.
What causes bacteria to die?
The depletion of essential nutrients and the accumulation of toxic wastes; such as acids are the main reasons for the Death or Decline phase of growing bacterial cells. It is thought to be under specific conditions the dead cells might be revived, this condition is known as viable but nonculturable (VBNC).
What happens to the population of bacteria during the inoculum phase?
During this phase, the bacterial cells start to increase their size and physiologically they are becoming very active and are synthesizing new protoplasm.
What happens to bacteria during the death phase?
The depletion of nutrients and the subsequent accumulation of metabolic waste products and other toxic materials in the media will facilitates the bacterium to move on to the Death phase. During this, the bacterium completely loses its ability to reproduce.
Why do bacteria cells die?
The number of bacterial cells declines in death phase , as the metabolic waste products and lack of nutrients both prevents division of bacterial cells, and causes cell death... the Y axis of the graph represents number of living bacterial cells, and therefore will decline during death phase. see more.
What is the degree of turbidity in broth culture?
The degree of turbidity in the broth culture is directly related to the number of microorganism present, either viable or dead cells, and is a convenient and rapid method of measuring cell growth rate of an organism.
How long does it take for a bacteria to double in number?
The time taken by the bacteria to double in number during a specified time period is known as the generation time. The generation time tends to vary with different organisms. E.coli divides in every 20 minutes, hence its generation time is 20 minutes, and for Staphylococcus aureus it is 30 minutes. 3.
What happens in the stationary phase of a bacterial population?
As the bacterial population continues to grow, all the nutrients in the growth medium are used up by the microorganism for their rapid multiplication. This result in the accumulation of waste materials, toxic metabolites and inhibitory compounds such as antibiotics in the medium.
How to study the dynamics of bacterial growth?
The dynamics of the bacterial growth can be studied by plotting the cell growth (absorbance) versus the incubation time or log of cell number versus time. The curve thus obtained is a sigmoid curve and is known as a standard growth curve. The increase in the cell mass of the organism is measured by using the Spectrophotometer.
How do bacteria divide?
Bacteria are unicellular (single cell) organisms. When the bacteria reach a certain size, they divide by binary fission, in which the one cell divides into two, two into four and continue the process in a geometric fashion. The bacterium is then known to be in an actively growing phase.
Lag Phase
Exponential Or Log Phase
- Once cells have accumulated all that they need for growth, they proceed into cell division. The exponential or log phaseof growth is marked by predictable doublings of the population, where 1 cell become 2 cells, becomes 4, becomes 8 etc. Conditions that are optimal for the cells will result in very rapid growth (and a steeper slope on the growth curve), while less than ideal conditions …
Stationary Phase
- All good things must come to an end (otherwise bacteria would equal the mass of the Earth in 7 days!). At some point the bacterial population runs out of an essential nutrient/chemical or its growth is inhibited by its own waste products (it is a closed container, remember?) or lack of physical space, causing the cells to enter into the stationary phase. At this point the number of n…
Death Or Decline Phase
- In the last phase of the growth curve, the death or decline phase, the number of viable cells decreases in a predictable (or exponential) fashion. The steepness of the slope corresponds to how fast cells are losing viability. It is thought that the culture conditions have deteriorated to a point where the cells are irreparably harmed, since cells c...