Chapter 12 Flashcards
Bacterial growth curve
Lag phase: slower growth, not necessarily dividing yet but preparing to, adapting to environment (not having total access to nutrients yet)
Log phase: division is increasing as fast as it can (exponential) because the organism is adapted to its environment and nutrients
Stationary phase: plateau, cell division starts to slow down because there are no food for them. Limited resources and high amounts of waste from log phase leads to cell death during this phase. This causes the cells to stop dying
Death phase: no more nutrients, space, and too much waste and toxins, causing cells to die at exponential rate. Some bacteria might produce spores which will live and germinate while being metabollicaly inactive
What are colony forming units (CFU)
when a single living bacterium is placed on an agar plate and divides clonally to form a colony, so we count the colonies to determine the number of cells
Why are they an underestimation?
not every cell will survive on the plate, two organisms too close to eachother may look like a colony when they are really many colonies
Which two ways can you obtain CFU? What are the differences between those two ways?
treaking for isolation (useful to obtain single colonies), dilution (useful to determine how many organisms are in a specific amount of sample - CFUs/mL)
Compare a hemocytometer versus counting CFU
Hemocytometer - counts cells, both dead and alive, per measure of sample by staining the cells in the sample on a slide and examined with a microscope. Counting CFUs does not take into account the dead cells
Selective media
encourages the growth of some organisms but suppresses the growth of others (MAC - selective for gram negative and kills gram positives, MSA - selective for gram positives and kills gram negatives)
Differential media
has chemical that creates an observable change in the medium when a reaction occurs (MSA turning yellow with mannitol fermenters)
Enrichment media
has chemical that allows microbe to grow and show you something - medium contains special nutrients (like blood agar or chocolate agar)
Factors that influence growth
Carbon, nitrogen, sulfur, phosphorus, trace elements, vitamins (agar includes these nutrients for growth) physical - pH, temp, moisture, oxygen concentration, hydrostatic pressure, osmotic pressure, radiation
Be able to explain the effect of temperature on growth
37 celsius is optimal temperature for humans - temperature that is best for enzymes to function. Too high optimal temperature causes enzymes to denature
Know the names to classify organisms based on the temperature they can grow at
Psychrophile (-10C-20C optimum at 15c) , mesophile (humans: 15-45 optimum 37), thermophile (45-70 optimum 62), extreme thermophile (68-88 optimum 87)
Be able to explain the effect of pH on growth
Know the names to classify organisms based on the pH they can grow at
Optimum pH at which they grow best
Acidophile pH 0.1 to 5.4
Neutrophiles pH 5.4 to 8.0
Alkaphiles pH 8.0 to 11
