BIOLOGY. Bacteria Growth Lab. Bacterial Growth. Slide 2 / 61. Slide 1 / 61. Slide 4 / 61. Slide 3 / 61. Slide 5 / 61. Slide 6 / 61

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1 Slide 1 / 61 Slide 2 / 61 New Jersey Center for Teaching and Learning Progressive Science Initiative This material is made freely available at and is intended for the non-commercial use of students and teachers. These materials may not be used for any commercial purpose without the written permission of the owners. NJCTL maintains its website for the convenience of teachers who wish to make their work available to other teachers, participate in a virtual professional learning community, and/or provide access to course materials to parents, students and others. BIOLOGY Bacteria Growth Lab Prokaryotes & Viruses Click to go to website: Slide 3 / 61 Slide 4 / 61 Prokaryotes Unit Topics Click on the topic to go to that section Bacterial Growth Antibacterial Agents Analysis & Conclusion Bacterial Growth Return to Table of Contents Slide 5 / 61 Bacterial Growth Slide 6 / 61 Bacterial Growth Bacteria reproduce by binary fission. This proliferation by cell division results in rapid bacterial population growth. As previously mentioned, bacteria can live almost anywhere and do live almost everywhere! In the lab, bacteria are grown in a medium that contains the nutrients necessary for growth and survival. Bacterial Growth Animation

2 Slide 7 / 61 Agar Bacteria can also be grown on a gelatinous, polysaccharide substance called agar that is spread out on the surface of a petri dish. Bacteria are then "plated" on the agar. Water: solvent Slide 8 / 61 Agar contains: Sugar: provides a source of carbon Salts: provide essential elements like magnesium, phosphorous, nitrogen, and sulfur needed for making proteins and nucleic acids. Slide 9 / 61 Bacterial Colonies Slide 10 / 61 Plating Bacteria Bacterial populations typically form colonies - groups of millions or billions of bacteria that live in a tightly packed area. Different types of bacteria can be distinguished by their distinct morphologies (shapes, structures, colors, or patterns). An individual bacterium can only be seen with a microscope, but a bacterial colony growing on a petri dish is visible to the naked eye. Streak Plating Demonstration Plating bacteria on agar allows one to visualize the different types of bacteria that may be present in a solution and to isolate a particular strain of bacteria for further use. Bacterial colonies growing on a plate of nutrient agar. Hans Knoll Institute. Jena, Germany Slide 11 / 61 Cultures A culture is a solution that is optimal for the growth of a specific type of bacteria. Bacterial cultures are used primarily to grow isolated strains of bacteria in the lab. Slide 12 / 61 Bacterial Growth When bacteria are placed in an environment that provides all of their metabolic needs, bacterial populations grow rapidly until they have depleted all of the nutrients in their environment.

3 Slide 13 / 61 Bacterial Growth Phases Slide 14 / 61 Lag Phase There are four phases to the bacterial growth cycle: *lag phase *log phase *stationary phase and *death phase. During the lag phase, the bacterial cell grows and prepares for cell division Slide 15 / 61 Log Phase Slide 16 / 61 During the log phase the bacterial population grows rapidly - doubling in size with each generation. watch the number of cells here Slide 17 / 61 Slide 18 / 61

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6 Slide 31 / 61 Slide 32 / 61 watch the cell number take off! Slide 33 / 61 Slide 34 / 61 Slide 35 / 61 Slide 36 / 61 Stationary Phase The stationary phase is reached when the bacteria start to run out of nutrients and the number of bacteria dying is equal to the number of bacteria reproducing.

7 Slide 37 / 61 Death Phase Slide 38 / 61 Calculating Bacterial Growth After nutrients have been used up and waste builds up, bacteria begin to die in large numbers and only very few reproduce. It is possible to estimate the number of bacteria present in a culture after a period of time using the following formula: (2 n )(initial number of bacteria) = total number of bacteria n = the number of generations. This can be determined by using the following formula: total time generation time (time it takes the bacteria to divide) Slide 39 / 61 Calculating Bacterial Growth At a fourth of July picnic, a bowl of potato salad was left out in the hot sun for 2 hours. If the salad originally contained 250 Salmonella enteritidis bacterial cells and Salmonella divides every 10 minutes, how many bacteria would be present at the end of 2 hours? Slide 40 / 61 1 Bacillus cereus divides every 30 minutes. You inoculate a culture with exactly 100 bacterial cells. After 3 hours, how many bacteria are present? Givens: Initial number of bacteria = 250 total time = 2hrs generation time = 10 minutes n = total time = 120 min. = 12 generation time 10 min. (2 n )( initial number of bacteria) = final number of bacteria 2 12 x 250 = 1,024,000 bacteria Slide 41 / 61 Slide 42 / 61 2 Staph. aureus, a disease causing bacteria, divides every 15 minutes at body temperature. A student gets a cut on her hand, is infected with 10 Staph. aureus bacterial cells, and does not clean the wound. After 1 hour, how many bacteria are present? Antibacterial Agents Return to Table of Contents

8 Slide 43 / 61 Antibacterial Agents Antibacterial agents are chemical substances that either kill bacteria or inhibit growth. There are 3 main types: antiseptics disinfectants antibiotics Slide 44 / 61 Antibacterial Agents antiseptics: chemicals used to kill or inhibit growth on living tissues (examples - hydrogen peroxide, soap, mouthwash) disinfectants: used to kill or inhibit growth on nonliving objects (examples - bleach and boiling water) antibiotics: chemicals produced by living organisms (fungi or bacteria) that inhibit growth of bacteria (examples - penicillin and tetracycline) NOTE: some antiseptics are also disinfectants and vice versa Slide 45 / 61 An experiment was done to test the effectiveness of various disinfectants and antibiotics. The experiment had 5 steps. Slide 46 / 61 Step 1 A sterile cotton swab was inserted into a culture of E. Coli bacteria. Slide 47 / 61 Step 2 The tip of the cotton swab was then placed on the agar plate, streaking the sample of bacterial culture across the plate as show below to inoculate the plate with bacteria. 3 filter paper disks were dipped in 3 different types of disinfectants and placed in the middle of each quadrant of the first petri dish. Distilled water was placed in the 4 th quadrant as a control Slide 48 / 61 Step 3 Disinfectant 1: bleach Disinfectant 2: hydrogen peroxide Disinfectant 3: window cleaner

9 3 disks coated in 3 different antibiotics were placed in the middle of each quadrant of the second petri dish. Distilled water was placed in the 4 th quadrant as a control. Antibiotic 1: ampicillin Antibiotic 2: penicillin Antibiotic 3: tetracycline Slide 49 / 61 Step 4 Both petri dishes were then taped shut, flipped upside down to prevent condensation from dripping onto the bacteria, and placed inside a 37 degree incubator for 48 hours. Slide 50 / 61 Step 5 Slide 51 / 61 Predictions and Results Make your prediction about whether bacteria is killed... Slide 52 / 61 Predictions and Results Results Dish 1 Results Dish The clearer areas surrounding the disks are called zones of inhibition and indicate that bacterial growth was inhibited Slide 53 / 61 Predictions and Results CHECK if a zone of inhibition is present on the plate Slide 54 / 61 Fighting Bacteria with Viruses Another mechanism of inhibiting bacterial growth is to infect the bacteria with a virus. A drop of solution containing bacteriophage viruses was added to the bacterial culture below resulting in several clear zones. These clear zones are called plaques. Viral plaques indicate that bacteriophages have infected and killed bacterial cells. Plaques may be counted and used to determine the number of viruses present in a bacterial culture.

10 Slide 55 / 61 Slide 56 / 61 Analysis and Conclusions 1). Which disinfectant most effectively inhibited the growth of E. coli? Analysis & Conclusions Return to Table of Contents Slide 57 / 61 Slide 58 / 61 2). Which antibiotic was most effective in preventing the growth of E. coli? 3). How do you know that any inhibition you have observed is due to the disinfectants and antibiotics on the disk? Slide 59 / 61 Slide 60 / 61 4). If the same experiment was repeated using a different strain of bacteria and a zone of inhibition was observed around the disk soaked in window cleaner, what could account for the different results? 5). You wake up one morning with a severe sore throat and notice white dots lining your tonsils. You quickly visit the doctor, who diagnoses you with a Streptococcus infection (strep throat) and prescribes a 10-day antibiotic treatment. After 3 days, you begin to feel better. Why should you continue taking the antibiotic for the full 10 days?

11 Slide 61 / What causes a zone of inhibition?