Lecture 6 Flashcards
Microbial growth can be estimated by measuring two things:
-Cell concentration (the number of viable cells per unit volume of culture)
-Biomass concentration (dry weight of cells per unit volume of culture)
What is a viable cell count?
It is typically considered the measure of cell concentration
Original culture or suspension undergoes serial dilution producing plating aliquots on an agar media then undergoes counting calculations which produces the number of colony-forming units (CFU) /mL
How does turbidity work?
the growth turbidity of a bacterial culture can be measured by spectrophotometer
-It is based on the fact that microbial cells scatter light striking them. The amount of scattering is directly proportional to the biomass of cells.
-It is a more rapid and sensitive technique
-Cells may lose viability without resulting in a loss in turbidity of the culture
How can biomass density be measured?
It can be measured directly by determining the dry weight of a microbial culture after it has been washed with distilled water
The concentration of biomass can be estimated indirectly by measuring an important cellular component such as protein, DNA, or pigment
The growth of bacteria can be plotted as the logarithm of the number of viable cells vs the incubation time, this is known as:
The growth curve
What are the 4 distinct phases of the growth curve?
- Lag phase
- Log (exponential growth) phase
- Stationary phase
- Decline (death) phase
In this phase:
The cells adapt to their new medium (environment)
-Synthesize new components, enzymes, and proteins to a limit that permits growth to resume
-Cell division does not take place in this phase
The lag phase
In this phase:
-Microorganisms are growing and dividing at the maximal rate
-This continues until either nutrients in the medium become exhausted or toxic metabolic products accumulate and inhibit growth
-The population is most uniform in terms of chemical and physiological properties
The log (exponential) phase
In this phase:
-The exhaustion of nutrients and the accumulation of toxic products.
-There is a slow loss of cells through death, which is balanced by the formation of new cells through growth.
The stationary phase
In this phase:
-Cell viability begins to decrease at a defined rate due to nutrient deprivation and build-up of toxic waste
-The death rate increases until it reaches a steady level
-After the majority of cells have died, a small number of survivors may persist for months or even years
The Decline (death) phase
What is the VBNC phenomenon?
-Viable but not culturable
After the death phase, some bacteria form spores as a survival mechanism, while others can become dormant without changes in morphology and show a VBNC phenomenon
VBNC bacteria could pose a public health threat, as many assays that test food and drinking water are culture based
What is the long-term stationary phase and how long can it last?
After the death phase, it is a period of time where the population size remains more or less constant.
It can last months to years
Bacterial biofilms:
- are complex, slime-encased communities of microbes
-are ubiquitous in nature
-A single bacterium nucleating on a surface followed by cell division and ultimately to the formation of an intimate community of bacteria
The biofilm surrounds itself with an _____ for environmental protection, and to keep the biofilm community intact
ECM or glycocalyx
Biofilms are associated with health problems such as:
-Streptococcus viridian’s on heart valves
-Pseudomonas aeruginosa in lung infections
-S. aureus on catheters
-Legionella pneumophila colonization of hospital water systems
Bacterial cultivation is the process of propagating organisms by providing the proper environmental conditions including:
-Nutrients that provide the main elements of CHNOPS
-Organisms require metabolic energy to synthesize macromolecules (fermentation, respiration, and photosynthesis)
-Factors that must be controlled during growth include pH, temperature, aeration, and salt concentration
