Questions and Answers
Name some bacteria that display α, β, and γ hemolysis.
α Hemolysis: Streptococcus pneumoniae, Streptococcus viridans, some enterococci; β Hemolysis: Streptococcus pyogenes, Streptococcus agalactiae, S.aureus, Listeria monocytogenes; γ Hemolysis: some enterococci.
Name the bacteria associated with Group A Lancefield antigens.
S.pyogenes
Name the bacteria associated with Group B Lancefield antigens.
S.agalactiae
Name the bacteria associated with Group D Lancefield antigens.
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Which Group D bacteria, Streptococcus or Enterococcus, can grow in hypertonic (6.5%) saline?
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What tests can differentiate S.pneumoniae from S.viridans?
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What test can differentiate S.pyogenes and S.agalactiae?
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What are the clinically relevant gram-positive bacilli?
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Which gram-positive bacillus has metachromatic granules?
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What are the three major components of the bacterial envelope?
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Bacterial capsules are typically made from what macromolecule?
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What are the two notable examples of bacterial capsules made from a macromolecule other than polysaccharides?
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What are the two functions of a bacterial capsule?
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What test allows identification of a capsule in bacteria?
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Why are capsules an important target for medical therapy?
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Bacterial cell walls are made from what macromolecule?
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What is the major function of the cell wall?
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What is Gram staining?
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What color are gram-positive bacteria?
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What color are gram-negative bacteria?
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How do the peptidoglycan layers of gram-positive bacteria differ from those of gram-negative bacteria?
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What important enzyme is found in the periplasmic space of gram-negative bacteria?
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How do penicillins and cephalosporins work?
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Which type of Gram-staining bacteria has teichoic and lipoteichoic acid?
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What are some of the pathologic effects of teichoic acid and LPS?
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What are the three components of LPS?
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What is the only gram-positive organism that has endotoxin?
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How do the cell walls of Mycobacteria species differ from those of gram-positive and gram-negative organisms?
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What bacteria lack a cell wall?
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How do bacterial cell membranes differ from mammalian cell membranes?
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Where is the electron transport chain located in bacteria?
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What stimulus drives the direction of motion of flagellated bacteria?
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Name two bacteria with a single polar flagellum.
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What two bacteria have multiple flagella?
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What are the two types of pili and what are their functions?
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Glycocalyx, which allows bacteria to adhere to surfaces, is made of what macromolecule?
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Name some pathogenic bacteria that utilize a slime layer glycocalyx for infection.
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What metabolically inactive structure formed by certain bacteria is resistant to environmental stresses?
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What advantage does spore formation offer bacteria?
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What are the contents of an endospore?
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What are the two important spore-forming gram-positive rods?
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Why are antibiotics not effective against spores?
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What is a fomite?
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What are the four phases of bacterial growth?
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During what phase do bacteria have the highest metabolic activity but without cell division?
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During what phase is growth the fastest?
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During what phase do β-lactam drugs act?
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In what phase does bacterial growth equal that of bacterial death?
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During what phase do spores form?
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During what phase have nutrient sources been exhausted?
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How are bacteria groups separated according to their oxygen requirements?
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What are some obligate aerobe bacteria?
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What are some obligate anaerobic bacteria?
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Why do obligate aerobes require oxygen?
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How are facultative anaerobes different from obligate aerobes?
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How do microaerophilic bacteria generate adenosine triphosphate (ATP)?
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How do microaerophilic bacteria tolerate low levels of oxygen?
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Why are obligate anaerobes unable to grow in the presence of oxygen?
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What are obligate intracellular organisms?
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How do obligate intracellular organisms generate ATP?
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What are facultative intracellular organisms?
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What are some facultative intracellular organisms?
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By what process do bacteria multiply?
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Are bacteria haploid?
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Name two types of DNA forms found in bacteria.
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Name the location of chromosomal DNA in bacteria.
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Describe the DNA structure of plasmids.
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Name some genes carried on plasmids.
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How are plasmids transferred between bacteria?
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What are the size and subunits for bacterial and eukaryotic ribosomes?
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Name four ways in which bacteria are able to acquire new genetic information.
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How do bacteria acquire genetic information via transformation?
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What is a bacterium that is able to utilize transformation?
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What mediates the transfer of genetic material in transduction?
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How do bacteriophages normally reproduce?
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How do bacteriophages transfer bacterial genetic material via transduction?
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What are the two types of phages?
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Which type of phage causes near-immediate lysis of bacteria?
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What is the name of the incorporated phage DNA in a temperate phage?
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Name the two types of transduction and the type of phage responsible for each.
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What part of the bacterial chromosome is transferred in generalized transduction?
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What part of the bacterial chromosome is transferred in specialized transduction?
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Name some bacterial toxins acquired through specialized transduction.
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What types of DNA can be exchanged by conjugation?
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What plasmid encodes the proteins needed to form the sex pilus?
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What is the term given when the F plasmid incorporates into the bacterial chromosomal DNA?
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Why are transposons medically relevant?
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Name a notable example of transposon-mediated drug resistance.
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What two bacteria undergo programmed rearrangement of surface antigens?
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What are the basic shape classifications of bacteria?
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What are the different pattern arrangements of cocci and common examples of each?
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What are the two main gram-positive cocci bacteria?
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Study Notes
Bacterial Envelope Components
- Major components include capsule, cell wall, and cell membrane.
Bacterial Capsules
- Typically composed of polysaccharides, which are sugar-based macromolecules.
- Exception: Bacillus anthracis has a capsule made from D-glutamic acid polypeptide, and Yersinia pestis has a capsule made from amino acids.
Functions of Bacterial Capsules
- Serve as virulence factors that protect against phagocytosis by immune cells.
- Facilitate attachment to host tissues.
Capsule Identification
- The quellung test uses anti-capsular antibodies to visualize capsular swelling under light microscopy.
Medical Relevance of Capsules
- Capsules contain polysaccharides essential for developing vaccines, such as those for S. pneumoniae and H. influenzae type B.
Bacterial Cell Walls
- Comprised of peptidoglycan (murein), a polymer of sugars and amino acids.
- Major function: provides rigidity and protects against osmotic pressure.
Gram Staining
- A classification method based on cell wall's ability to absorb crystal violet dye, followed by a counterstain.
- Gram-positive bacteria appear blue; gram-negative bacteria appear pink.
Peptidoglycan Layers
- Gram-positive bacteria have thicker layers (up to 90% of dry weight) than gram-negative bacteria (around 10% of dry weight) which also have a periplasmic space.
Key Enzymes
- β-Lactamase is found in the periplasmic space of gram-negative bacteria and confers resistance to certain antibiotics.
Antibiotics Targeting Cell Walls
- Penicillins and cephalosporins target transpeptidase enzymes, preventing peptidoglycan cross-linking.
Cell Wall Characteristics
- Gram-positive bacteria possess teichoic and lipoteichoic acids; gram-negative bacteria have lipopolysaccharides (LPS).
Pathological Effects
- Teichoic acid and LPS can induce cytokine production leading to septic shock and disseminated intravascular coagulation (DIC).
Components of Lipopolysaccharides (LPS)
- Composed of an outer polysaccharide (O-antigen), a middle core polysaccharide, and an inner lipid A that elicits toxic effects.
Unique Endotoxin
- Listeria monocytogenes is the only gram-positive organism that possesses an endotoxin.
Mycobacteria’s Cell Walls
- Contain mycolic acids, making them acid-fast and resistant to standard Gram staining techniques.
Non-Gram Staining Bacteria
- Various bacteria rely on alternative staining methods such as dark-field microscopy, Giemsa stain, and Ziehl-Neelsen stain.
Cell Wall-less Bacteria
- Mycoplasma species lack a cell wall.
Bacterial Cell Membranes
- Unique in that they do not contain sterols except in Mycoplasma species.
Location of Electron Transport Chain
- Found within the bacterial cell membrane instead of membranous organelles like mitochondria.
Bacterial Motion
- Flagella allow movement, guided by chemical gradients (chemotaxis).
Bacterial Flagella Types
- Single polar flagellum in Vibrio cholerae and Campylobacter jejuni; multiple flagella in Escherichia coli and Proteus mirabilis.
Pili Functions
- Common pili (fimbriae) assist in adhesion; sex pili facilitate genetic material exchange.
Glycocalyx Composition
- Made of polysaccharides; tightly associated glycocalyx is a capsule, while loosely associated is a slime layer.
Slime Layer Pathogens
- Pathogens like Streptococcus mutans and Staphylococcus epidermidis use slime layers to adhere in their respective environments.
Spores
- Metabolically inactive structures that help bacteria endure environmental stresses; require autoclaving for sterilization due to heat, chemical, and radiation resistance.
Endospore Contents
- Composed of bacterial DNA, sparse cytoplasm, a cell membrane, peptidoglycan, and a protective keratin-like coat.
Clinical Relevance of Spores
- Antibiotics are ineffective against spores due to their impermeable coats and inactivity.
Fomites
- Inanimate objects that can harbor and transmit infections (e.g., contaminated hospital surfaces).
Bacterial Growth Phases
- Consist of lag, logarithmic, stationary, and death phases; each has distinct metabolic activities and growth dynamics.
Bacterial Oxygen Requirements
- Classified as obligate aerobes, facultative anaerobes, microaerophilic, aerotolerant anaerobes, and obligate anaerobes based on oxygen utilization.
Aerotolerant Organisms
- Can survive in both oxygen-rich and anaerobic environments but only metabolize anaerobically.
Intracellular Bacteria
- Obligate intracellular organisms (e.g., Chlamydia, Rickettsia) depend on host cells for ATP, while facultative intracellular organisms can exist both inside and outside host cells.
Bacterial Multiplication
- Occurs via binary fission, and bacteria are haploid.
Bacterial DNA Forms
- Contain chromosomal DNA (in nucleoid) and plasmid DNA (circular, double-stranded).
Gene Transfer Mechanisms
- Include transformation, transduction, conjugation, and transposon insertion.
Transformation Process
- Involves uptake of free DNA from the environment by competent bacteria.
Bacteriophage Function
- Mediate gene transfer through transduction by infecting bacteria and packaging bacterial DNA into new phages.
Types of Transduction
- Generalized transduction (virulent phage) transfers any part of the bacterial genome; specialized transduction (temperate phage) transfers specific adjacent segments.
Toxins from Specialized Transduction
- Includes diphtheria toxin and cholera toxin, highlighting the exchange of genetic factors.
Conjugation and Plasmids
- The F plasmid facilitates the formation of sex pili for genetic exchange, leading to Hfr strains when integrated into the bacterial genome.
Medical Implications of Transposons
- They contribute to antibiotic resistance spread, illustrated by the vanA transposon linked to vancomycin resistance.
Antigenic Variation
- Organisms like Neisseria gonorrhoeae undergo programmed rearrangements to evade the immune system.
Bacterial Shape Classifications
- Bacteria are categorized into cocci, bacilli, and spirochetes based on their shapes.
Cocci Arrangements
- Examples include diplococci (e.g., Neisseria), chains (e.g., streptococci), and clusters (e.g., staphylococci).
Gram-Positive Cocci Differentiation
- Streptococcus species are catalase negative, while Staphylococcus are catalase positive; tests can differentiate between them.
Clinical Identification Tests
- Utilize selective media like sheep blood agar and additional biochemical tests (e.g., coagulase, bacitracin sensitivity) to identify specific bacterial species.
Lancefield Classification
- Group A (S. pyogenes), B (S. agalactiae), and D (Streptococcus bovis and enterococci) are classified based on carbohydrate antigens in their cell walls.
Enterococci Characteristics
- Enterococcus faecalis can grow in hypertonic saline while S. bovis cannot, highlighting a key distinction in the group.
Differentiation of Streptococcus Species
- Tests like the optochin sensitivity and bacitracin sensitivity are vital for identifying specific Streptococcus species, linking back to their clinical relevance.
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Description
Test your knowledge on the bacterial envelope components, the composition of bacterial capsules, and specific examples of capsules. This quiz includes key concepts in bacteriology and helps reinforce essential microbiology terms.