Requirements for Growth

Transcription

1

2 Requirements for Growth Definition: Bacterial growth defined as an increase in the number of cells. Physical Requirements: temperature, ph, tonicity Temperature: On the basis of growth range of temperature microbes are classified as psychrophiles (cold-loving), psychrotrophs (cool), mesophiles (moderate-temperatureloving), and thermophiles (heat-loving). Mesophiles with a temperature range of being the most common. Our incubation temperature will be 37 0 C. Fig 6.1 ph: Most bacteria grow between ph 6.5 and 7.5. Molds and yeast will grow optimally at ph 5-6. Tonicity: In a hypertonic solution, microbes undergo shrinkage and plasmolysis; halophiles can tolerate high salt. Examples are Staph and Enterococcus. Fig 6.4

3 Figure 6.1

4 Figure 6.2

5 Figure 6.3

6 Figure Overview

7 Figure 6.4a

8 Figure 6.4b

9 Chemical Requirements for Growth All organisms require a carbon source, nitrogen, sulfur, and phosphorus. Nitrogen- Protein containing material, ammonium ions, or nitrate Sulfur- Sulfate ion, hydrogen sulfide, some amino acids Phosphorus- Phosphate ion On the basis of oxygen requirements, organisms are classified as - Table 6.1 Obligate aerobes - require oxygen to live Facultative anaerobes - can use oxygen when present, but can continue to grow by using fermentation or anaerobic respiration when oxygen is not available Obligate anaerobes - unable to use molecular oxygen for energy-yielding reaction and may even be harmed by it. Aerotolerant anaerobes - cannot use oxygen, but they tolerate it well Microaerophiles - are aerobic requiring oxygen but grow in concentration lower than air

10 Table 6.1

11 Culture Media Culture Media. Description - Material prepared for growth of bacteria in the laboratory. Common solidifying agent is agar. Can be on petri dishes, slants, or deeps. Can be chemically defined (known, Table 6.2) or complex (Table 6.4). We use complex media made up of nutrients such as yeast extracts, meat, or plants, or digests of proteins from these and other sources. Anaerobic Growth Media and Methods Reducing media is used. These media chemically remove O 2. Can use an anaerobe jar (Figure 6.5) or chamber (fig 6.6). Special Culture Techniques Some bacteria require CO 2 Fig 6.7 Have candle jars or CO 2 incubators. Jembec plates. Some organisms require living cells. Examples: M. leprae, Chlamydia, virus.

12 Table 6.2

13 Table 6.3

14 Table 6.4

15 Figure 6.5

16 Figure 6.6

17 Figure Overview

18 Figure 6.7a

19 Figure 6.7b

20 Culture Media Selective and Differential Media Fig 6.8, 6.9 Can use salts, dyes, or other chemicals to inhibit the growth of some organisms and allow others to grow. Differential media are used to distinguish among different organisms. Often use color differences based on ph change around colony. Example - Mannitol Salt Agar (MSA). It is selective and differential. Salt is selective for Staph Mannitol causes diffentiation. Enrichment Culture Staph aureus = yellow Other Staph sp. = red Media that favors the growth of some organisms to detectable levels, but not others. Example: Shigella in enrichment broth.

21 Figure 6.8

22 Figure Overview

23 Table 6.5

24 Culture Media Obtaining Pure Culture fig 6.10 A clone is a population of cells arising from a single cell. Colonies are visible clones that have grown on solid media. Called CFU- Colony Forming Units Pure cultures are obtained by the streak plate method. Preserving Bacterial Cultures Can be frozen or freeze-dried (lyophilization). In class we can leave at room temp or refrigerate.

25 Figure Overview

26 Growth of Bacterial Cultures Division - binary fission fig 6.11 Generation Time fig 6.12 & 6.13 Most have a generation time (time required for cell to divide and its population double) is from 20 minutes to 24 hours. Some longer. Example for E. coli after 20 generations 1 cell would increase to over 1 million in about 7 hours, 1 billion in 10 hours. Phases of the growth curve fig 6.14 Lag - little or no change in #, but metabolic activity is high Log - multiply at the fastest rate possible Stationary - equilibrium between new cells and deaths Death - number of death exceeds new cells.

27 Figure Overview

28 Figure Overview

29 Figure 6.12a

30 Figure 6.12b

31 Figure 6.13

32 Figure 6.14

33 How the Compound Growth Curve Can Help You in Your Career/Retirement Old Versus New Money: The Magic of Compound Growth

34 Growth of Bacterial Cultures Measurement of Microbial Growth A variety of methods are described in the text Examples: plate count, serial dilution, pour plate, filtration, MPN, direct microscopic observation, plating, etc. For this course we will concern ourselves with two methods: plate count and turbidity. Plate count (Urine culture) Use standardized loop (1 ul) dipped in urine Next day count cells on plate and multiply by 1000 >100,000/ml is indicative of infection Turbidity (Indirect method) Use spectrophotometer to determine turbidity Measure the amount of light that passes through a suspension Correlate readings with serial dilution and plating Used to standardize amounts for use in antibiotic testing

35 Figure 6.15

36 Figure Overview

37