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Questions and Answers
Which bacterium is diagnosed using both direct microscopy and serology?
Where can Mycobacterium leprae primarily be identified?
What is the primary characteristic of diploocci bacteria?
What method is NOT typically used for identifying bacteria?
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What type of staining is particularly good for visualizing capsules?
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Which method can identify bacteria directly from clinical samples like blood?
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What type of bacteria typically exhibits spiral shapes with many turns?
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What characteristic is analyzed to identify bacteria through biochemical tests?
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What is the process by which a single bacterial cell divides to form two cells?
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What is the term for the time it takes for one bacterial cell to divide into two?
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In which phase of the bacterial growth curve do cells experience the maximum growth rate?
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How many bacterial cells will be present after 3 generations if you start with 3 cells?
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What method can be used to measure microbial growth directly?
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What occurs during the stationary phase of bacterial growth?
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Which of the following bacteria has the longest generation time?
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Which phase of bacterial growth is characterized by a slow start and preparation for exponential growth?
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What does optical density (OD) measure in bacterial cultures?
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Which microscopy technique allows the visualization of bacteria against a dark background?
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What is the purpose of using propidium iodide in microscopy?
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Which method is used to determine the amount of CO2 produced as an indicator of bacterial respiration?
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What does each colony on an agar plate represent?
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What is the characteristic feature of sloppy agar?
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Which of the following is NOT a method for estimating bacterial growth?
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What is one disadvantage of using optical density as a measurement of bacterial growth?
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Study Notes
Bacterial Identification
- Treponema pallidum is diagnosed by direct microscopy and serology.
- Mycobacterium leprae is found in the footpads of mice and nine-banded armadillos.
- Chlamydia trachomatis only grows within eukaryotic cells.
Microscopy
- Coccobacillus shaped bacteria include Chlamydia.
- Rod shaped bacteria include Bacillus.
- Palisades are a characteristic arrangement of bacteria like Corynebacteria.
- Diplobacillus shaped bacteria include Moraxella.
- Cocci include Diplococci like Pneumococcus, Chains like Streptococci and Bunches of grapes like Staphylococci.
- Comma shaped bacteria include Vibrios.
- Spiral-few turns bacteria include Spirillium.
- Spiral-many turns bacteria include Spirochaetes.
Staining and Microscopy
- Simple stain is usually one colour.
- Negative stain is good for observing capsules.
- Fluorescent stain can be used for visualization.
- Differential stain is a technique for distinguishing between different types of bacteria.
Biochemical Tests
- Biochemical tests analyze sugar fermentation products like acids, alcohol, or gas.
- Tests determine the ability to utilize specific sugars.
- Tests analyze bacterial enzymes.
- Growth under aerobic and anaerobic conditions can be tested.
Other Identification Methods
- API system uses a series of biochemical tests to quickly identify bacterial species.
- Catalase test determines whether an organism produces the enzyme catalase.
- Molecular techniques are increasingly used for bacterial identification.
- Matrix Assisted Laser Desorption Time of Flight (MALDI-TOF) can be used to identify bacteria directly from clinical samples like blood.
Growth of Bacteria
- Bacteria divide by binary fission.
- Growth rate varies greatly between bacterial species.
- Generation time refers to the time it takes for one bacterial cell to divide into two.
- Bacterial growth is logarithmic.
- The formula N = 2n calculates the number of bacteria (N) after a certain number of generations (n).
Growth Curve
- The bacterial growth curve depicts the phases of bacterial growth.
- Lag phase is a period of slow growth where bacteria adapt to the new environment.
- Exponential phase is a period of rapid growth where bacteria divide at their maximum rate (µmax).
- Stationary phase is a period of stable population where the rate of cell division is equal to the rate of cell death.
- Death phase is a period where the rate of cell death exceeds the rate of cell division.
Measuring Bacterial Growth
- Direct methods involve counting bacterial cells.
- Microscopy can be used to visually count bacteria.
- Flow cytometry counts cells passing through a light detector.
- Plate counts quantify the number of viable bacteria in a sample.
Indirect Methods
- Optical density measures the turbidity of a bacterial culture.
- Measuring respiration quantifies the metabolic activity of the bacteria.
Bacterial Growth Media
- Broth is a liquid media used for enrichment and growth curve analysis.
- Agar is a solid media used for bacterial identification and assessing culture purity.
- Sloppy agar is a semi-solid media used to demonstrate bacterial motility and preserve bacterial cultures.
Bacterial Identification Based on Colony Morphology
- Color can be indicative of bacterial species.
- Shape can help distinguish bacteria.
- Size can be a determining factor.
- Smell is sometimes a characteristic feature.
- Effect on media can indicate specific bacterial features like haemolysis or color change.
Non-culturable Bacteria
- Some bacteria, like Treponema pallidum, have never been successfully grown in culture.
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