Bacteriology Flashcards

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.

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.