phases of bacterial growth, lag, log or exponential, stationary, and death phase. скачать в хорошем качестве

phases of bacterial growth, lag, log or exponential, stationary, and death phase.

Bacterial growth always follows a predictable pattern with four phases: Lag phase: very little to no bacterial growth. Log phase: the number of bacterial cells doubles at a constant, exponential rate. Stationary phase: population growth levels off as the rate of cell death equals the rate of cell division. Learn happily with Scientist Cindy at www.scientistcindy.com. Graphing Bacterial Growth I mentioned that bacterial growth is not infinite and constant. In fact, bacterial growth is quite complex, influenced by any number of variables, including the species, temperature, pH, available nutrients, toxin concentrations, and competition between organisms. In order to illustrate what is happening during the life of your average bacteria, let's examine another infamous bacteria: Staphylococcus aureus. This common skin bacteria is often implicated in deadly bacterial infections. The reason I've chosen Staph. aureus is that under ideal conditions, it has a generation time of 30 minutes, a nice round time for performing calculations. A generation time is simply the time it takes for one cell to become two. So, if we start with one Staph. aureus cell, in 30 minutes there will be two. In another 30 minutes, there should be four, and so on to 8, 16, 32, 64, indefinitely. If we graphed this relationship, it would look like this, a perfect exponential graph. Bacterial Growth Generation Time Bacterial Graphing Growth In reality, the graph of Staph. aureus growth will look like this. You can see a small portion that resembles the exponential graph, but before and after it looks a bit strange. Fortunately, we can break this graph into four sections, called phases. discrete colony reproduction nutrients: chemical and energy requirements Autotrophs Heterotrophs Chemotrophs Phototrophs Obligate Aerobes Obligate Anaerobes Singlet Oxygen Carotenoids Superoxide free radicals Peroxide Anion Hydroxyl radical Hydroxyl radical Hydroxyl radical Aerobes Anaerobes Facultative Anaerobes Aerotolerant Anaerobes Microaerophiles Trace Elements Growth Factors Temperature, pH, Osmotic Pressure psychrophiles mesophiles thermophiles hyperthermophiles why organisms are sensitive to changes in acidity Neutrophiles Acidophiles alkalinophiles why microbes require water endospores and cysts hypotonic solutions hypertonic solutions Crenation obligate halophiles facultative halophiles Barophiles Biofilms Quorum Sensing Inoculum Medium Environmental, Clinical, Stored Culture Pure Cultures colony forming unit Aseptic technique Streak Plates Pour Plates reducing media chemically Defined Media Complex Media Selective Media Differential Media enrichment culture budding refrigeration deep-freezing Lyophilization Binary Fission Generation time Growth Curve Lag phase Log Phase Stationary phase Death Phase Viable Plate Counts Filtration pH of bacteria pH of molds and yeasts plasmolysis chemoheterotroph chemoautotroph phosphorus sulfur nitrogen carbon sterile agar capnophiles biosafety level 1 biosafety level 2 biosafety level 3 biosafety level 4 colony serial dilutions spread plate method turbidity