Podcast
Questions and Answers
The Gram stain was discovered by ______ in 1884.
The Gram stain was discovered by ______ in 1884.
H.C. Gram
Bacteria that are spherical or elliptical in shape are called ______.
Bacteria that are spherical or elliptical in shape are called ______.
cocci
The coagulase test is used specifically for ______.
The coagulase test is used specifically for ______.
staphylococci
The bacilli are bacteria that have a ______ shape.
The bacilli are bacteria that have a ______ shape.
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Mycobacteria are difficult to stain due to their high content of ______.
Mycobacteria are difficult to stain due to their high content of ______.
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Staphylococcus aureus divides in ______ planes forming an irregular configuration.
Staphylococcus aureus divides in ______ planes forming an irregular configuration.
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The vibrio bacteria are known for their ______, comma shape.
The vibrio bacteria are known for their ______, comma shape.
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The ______ test is used for Gram-positive cocci.
The ______ test is used for Gram-positive cocci.
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Spirilla are bacteria that have a ______ shape.
Spirilla are bacteria that have a ______ shape.
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Actinomycetes resemble radiating rays of the ______ when viewed in tissue lesions.
Actinomycetes resemble radiating rays of the ______ when viewed in tissue lesions.
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Mycoplasmas are unique because they are ______ wall deficient.
Mycoplasmas are unique because they are ______ wall deficient.
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Phototrophs obtain energy from ______.
Phototrophs obtain energy from ______.
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Chemotrophs cannot perform ______.
Chemotrophs cannot perform ______.
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Autotrophs utilize carbon dioxide (CO2) to prepare their own ______.
Autotrophs utilize carbon dioxide (CO2) to prepare their own ______.
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Heterotrophs use organic compounds as their carbon ______.
Heterotrophs use organic compounds as their carbon ______.
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Fastidious heterotrophs require ______ nutrients for their growth.
Fastidious heterotrophs require ______ nutrients for their growth.
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The classification of bacteria is important to distinguish them from one type to another, and can be used to serve a variety of ______.
The classification of bacteria is important to distinguish them from one type to another, and can be used to serve a variety of ______.
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Wet-mounted and properly stained bacterial cell suspensions can differentiate bacteria based on their ______ characteristics.
Wet-mounted and properly stained bacterial cell suspensions can differentiate bacteria based on their ______ characteristics.
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The Gram reaction of the organism is a method used in ______ staining.
The Gram reaction of the organism is a method used in ______ staining.
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Bacteria may be grouped based on their growth characteristics, such as whether they grow aerobically or ______.
Bacteria may be grouped based on their growth characteristics, such as whether they grow aerobically or ______.
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Cell wall (O), flagellar (H), and capsular (K) ______ are used to classify certain organisms at the species level.
Cell wall (O), flagellar (H), and capsular (K) ______ are used to classify certain organisms at the species level.
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Phage typing has been used primarily as an aid in epidemiologic surveillance of diseases caused by ______ aureus.
Phage typing has been used primarily as an aid in epidemiologic surveillance of diseases caused by ______ aureus.
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Bacteria can be identified and classified largely based on their reactions in a series of ______ tests.
Bacteria can be identified and classified largely based on their reactions in a series of ______ tests.
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Campylobacter jejuni grows well at 42° C in the presence of several ______.
Campylobacter jejuni grows well at 42° C in the presence of several ______.
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Bacteria that can grow at 0°C or below are called ______.
Bacteria that can grow at 0°C or below are called ______.
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Most human pathogens are classified as ______.
Most human pathogens are classified as ______.
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Bacteria that can grow best above 45°C are known as ______.
Bacteria that can grow best above 45°C are known as ______.
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Bacteria that can tolerate oxygen but do not require it are called ______ anaerobes.
Bacteria that can tolerate oxygen but do not require it are called ______ anaerobes.
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Organisms that cannot survive in the presence of oxygen are known as ______ anaerobes.
Organisms that cannot survive in the presence of oxygen are known as ______ anaerobes.
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Archeobacteria that grow at extremely high temperatures are referred to as ______ thermophiles.
Archeobacteria that grow at extremely high temperatures are referred to as ______ thermophiles.
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Acidophiles grow best at an ______ pH.
Acidophiles grow best at an ______ pH.
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Microorganisms that require low concentrations of oxygen are termed ______ microphiles.
Microorganisms that require low concentrations of oxygen are termed ______ microphiles.
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Bacteria that can break down toxic forms of oxygen but do not use it for respiration are called ______ tolerant anaerobes.
Bacteria that can break down toxic forms of oxygen but do not use it for respiration are called ______ tolerant anaerobes.
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The optimum pH of growth for Vibrio cholerae is ______.
The optimum pH of growth for Vibrio cholerae is ______.
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Bacteria that grow best at neutral pH (6.5-7.5) are called ______.
Bacteria that grow best at neutral pH (6.5-7.5) are called ______.
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Halophiles require moderate to large salt ______.
Halophiles require moderate to large salt ______.
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Extreme halophiles require salt concentrations between ______ to ______%.
Extreme halophiles require salt concentrations between ______ to ______%.
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Bacteria that have no flagella are classified as ______.
Bacteria that have no flagella are classified as ______.
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Endospore forming bacteria, like Bacillus, produce spores ______ the bacterial cell.
Endospore forming bacteria, like Bacillus, produce spores ______ the bacterial cell.
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Bacteria that do not produce spores are classified as ______ spore forming bacteria.
Bacteria that do not produce spores are classified as ______ spore forming bacteria.
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Study Notes
Introduction to Bacterial Classification
- Bacterial classification is crucial for distinguishing different types
- It serves various functions, including identification
- Bacteria can be grouped using diverse typing schemes
Morphological Characteristics
- Wet-mounted and stained bacterial suspensions aid differentiation
- Methods should be simple and straightforward
- Examples include Gram stain, acid-fast staining, motility, flagellar arrangement, spore presence, capsule presence, inclusion bodies, and shape
- This information helps identify organisms to the genus level, minimizing misclassification
Growth Characteristics
- Bacterial growth can occur aerobically, anaerobically, facultatively, or microaerobically
- Proper atmospheric conditions are essential for isolation and identification
- Other important growth assessments include: incubation temperature, pH, required nutrients, and resistance to antibiotics
- Specific examples like Campylobacter jejuni growth at 42°C are given. Escherichia coli and other members of Enterobacteriaceae can grow on minimal media.
Antigens and Phage Susceptibility
- Cell wall (O), flagellar (H), and capsular (K) antigens aid species and serotype identification
- Serotyping helps determine strains with exceptional virulence or public health significance (e.g. Vibrio cholerae O1, various E. coli serotypes)
- Phage typing aids in epidemic surveillance (e.g. Staphylococcus aureus, mycobacteria, Vibrio cholerae, Salmonella typhi)
Biochemical Characteristics
- Bacteria are often identified and classified based on biochemical reactions
- Key tests commonly used include: oxidase, nitrate reduction, amino acid degradation, fermentation, carbohydrate utilization
- Other tests are specific to certain families, genera, or species (e.g. coagulase test for staphylococci, pyrrolidonyl arylamidase test for Gram-positive cocci)
Classification by Gram Stain and Cell Wall
- Gram stain, discovered by Hans Christian Gram in 1884, remains a vital technique
- Gram stain classifies bacteria as Gram-positive or Gram-negative based on their morphology and differential staining
- Some bacteria, such as mycobacteria, are not easily stained due to lipid content in peptidoglycan
- Alternative techniques (e.g., Kinyoun stain) overcome limitations by targeting the resistance to destaining
Classification Based on Shape
- Spherical (cocci)
- Monococcus (single cell)
- Diplococcus (paired cells)
- Streptococcus (chain-like cells)
- Tetrad (four cells)
- Sarcina (eight or sixteen cells in a cubical arrangement)
- Staphylococcus (clusters)
- Rod-shaped (bacilli)
- Spiral-shaped (spirilla)
- Vibrio (comma-shaped)
- Specific examples are provided within the shape categories like Streptococcus pyogenes, Bacillus anthracis, Vibrio cholerae, Helicobacter pylori etc.
Classification Based on Bacterial Cell Shape
- Cocci: Spherical or elliptical bacteria that may remain single or aggregate in various configurations
- Bacilli: Rod-shaped or cylindrical
- Vibrios: Curved, comma-shaped
- Spirilla: Spiral shape
Classification of Other Group
- Actinomycetes: Branching filamentous bacteria resembling radiating sunrays
- Mycoplasms: Bacteria lacking a cell wall with round or oval structures or interlacing filaments
Classification Based on Mode of Nutrition
- Phototrophs: Gain energy from light
- Photolithotrophs: Use reduced inorganic compounds as electron sources
- Photoorganotrophs: Use organic compounds as electron sources
- Chemotrophs: Gain energy from chemical compounds
- Chemolithotrophs: Oxidize inorganic compounds for energy
- Chemoorganotrophs: Use organic compounds for energy
Classification on the Basis of Carbon Requirement
- Autotrophs: Use carbon dioxide (CO2) as their sole carbon source
- Photoautotrophs: Obtain energy from light to fuel CO2 assimilation
- Chemoautotrophs: Derive energy from chemical reactions to incorporate CO2
- Heterotrophs: Use preformed organic molecules as their carbon source
Classification Based on Temperature Requirements
-
Psychrophiles: Thrive in cold environments
-
Psychrotrophs: Can adapt to varying cold to moderate temps
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Mesophiles: Optimum growth in moderate temperatures (25-40° C) - includes many human pathogens
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Thermophiles: Adapt to high temperatures
-
Hyperthermophiles: Thrive in extremely high temperatures
Classification Based on Oxygen Requirements
- Obligate aerobes: Require oxygen
- Facultative anaerobes: Can grow with or without oxygen
- Obligate anaerobes: Cannot grow in the presence of oxygen or oxygen-derived compounds
- Aerotolerant anaerobes: Do not need oxygen for metabolism but are unaffected by its presence
- Microaerophiles: Tolerate very low concentrations of oxygen
Classification based on pH
- Acidophiles: Adapted to acidic environments
- Alkaliphiles: Thrive in alkaline environments
- Neutrophiles: Prefer neutral conditions
Classification Based on Osmotic Pressure Requirements
- Halophiles: Thrive in high salt concentrations
- Extreme or Obligate Halophiles: Require very high salt concentrations
- Facultative Halophiles: Tolerate moderate salt concentrations
Classification Based on Flagella Number
- Atrichous: Lack flagella
- Monotrichous: Single flagellum
- Lophotrichous: Multiple flagella at one end
- Amphitrichous: Multiple flagella at opposite ends
- Peritrichous: Multiple flagella distributed over the entire cell surface
Classification Based on Spore Formation
- Spore-forming bacteria produce spores under adverse conditions; endospores are formed within the cell (e.g., Bacillus, Clostridium)
- Non spore-forming bacteria do not produce spores (e.g., E. coli, Salmonella)
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Description
This quiz explores the fundamentals of bacterial classification, including morphological and growth characteristics. Learn about the techniques for identifying bacteria, from staining methods to growth conditions essential for isolation. Test your knowledge on how different typing schemes help avoid misclassification.
