Yoslaine Albelo
Pg. 121
Generation Time
Direct Method: Requires enumeration of Viable cells in serially diluted samples of the test culture taken at 30 Min intervals.
Direct Method: Monitors bacterial growth by estimating Turbidity. This measurements is done by using a spectrophotometer where a beam of light is transmitted through a bacterial suspension to a light sensitive detector. This change of light would be the percentage of transmission and will also give you the logarithmic expression called absorbance. This method is more useful in measuring contamination of liquids by large numbers, rather than small numbers, of bacteria. This is done at a 30 min intervals as well.
Pg. 122
Review Questions
1. Does the term growth convey the same meaning when applied to bacteria and to multicellular organism?
- No, Growth when referring to bacteria, it means an increase in the number of individual organism or and increase in the size of a population. When referring to the growth in multicellular organism, its referring to an increase in the number of cells in a single individual organism.
2. Why do Variations in generation time exist?
A) Among different species of microorganisms?
- Because in any given environment, the optimal conditions will vary between species. A fast growing bacteria have generation times of 15-20 min under optimum growth conditions, in the other hand slow growing bacteria can take up to 24 hrs under optimum condition.
B) Within a single microbial species?
- Because generation time depends on several factors, temperature, PH, etc. Growth medium can influence growth within a single microbial species.
3. The generation time and growth rate of an organism grown in the laboratory can be each determined by constructing a typical growth curve.
A) Would you expect the growth rate of the infectious organisms found in an abscess that developed from a wound to mimic the growth curve obtain in the laboratory? Explain.
- No. Lab conditions usually have plentiful nutrients and ideal growth temperature. In an abscess from a wound, the fact that the bacteria has our immune system fighting them, and that they have to search for nutrients, would definitely slow down their rate of growth.
B) Would you expect antibiotic therapy to be effective without any other concurrent treatment of the abscess?
- In most cases no. Antibiotic are often unable to get into the abscess due to the abscess wall formed by adjacent uninfected cells around the abscess to prevent the spread of infection. Usually incision and/or drainage is required.
C) Is generation time a useful parameter to indicate the types of media best suited to support the growth of a specific organism? Explain.
- Yes. Organisms with a faster generation time can often grow quickly due to their non-specific requirements for growth and will be able to grow in a variety of different media. Slow growing organisms often have very specific nutritional requirements and will need a more complex media. This can be determined by using generation time measurements.
page 123, 124 (Indy Graph)
Chapter 16 page 139
Page 140 (Lupe)
Page 140
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Chemotherapeutic Agent
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Spectrum of Activity
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Type(s) of Microorganisms
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Penicillin
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Narrow Spectrum
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Gram Negative
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Streptomycin
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Broad Spectrum
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Gram Negative and Gram Positive Bacteria
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Tetracycline
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Broad Spectrum
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Gram Negative and Gram Positive
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Chloramphenicol
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Broad Spectrum
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Gram Negative and Gram Positive
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Gentamicin
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Broad Spectrum
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Gram Negative and Gram Positive
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Vancomycin
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Narrow Spectrum
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Gram Positive
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Sulfanilamide
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Broad Spectrum
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Gram Negative and Gram Positive
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Review Questions
1.
Antibiotic
specially function to destroy the peptide cross-bridge of peptidoglycan (the
cell wall of bacteria). Since fungi cell wall compose of chitin, antibiotic
won't affect fungi.
Chapter 17 page 147 (Done), 148
Janelly Carrasco, page 148
4. Which of the experimental chemical compounds appear to have the broadest range of microbicidal activity? The narrowest range of microbicidal activity?
The chemical compounds that appear to have the broadest range of microbicidal activity is bleach and hydrogen peroxide. The narrowest range was LT.
Review Questions
1. Evaluate the effectiveness of a disinfectant with a phenol coefficient of 40.
It would be 40x more effective than phenol.
2. Can the disinfection period (exposure time) be arbitrarily increased? Explain.
No, not without considering the toxicity of the chemical and environmental conditions that have to be considered before altering exposure time.
3. A household cleaner is labeled germicidal. Explain what this means to you.
This means that the antimicrobial agent is microbial. However, it does not indicate the type or types of microbes that the agent will kill effectively.
