Antibiotic Resistance Quiz

Microbiology & Antibiotics

• Learning Outcomes: Students should be able to:
  • Discuss differences between prokaryotes, eukaryotes, and viruses
  • Discuss differences and significance between gram-positive and gram-negative bacteria
  • Describe features of normal flora
  • Outline reproductive and DNA transfer processes of bacteria
  • Outline major groups of antimicrobials
  • Discuss mechanisms of action of a range of antimicrobials and anti-viral agents
• Relevance to Courses:
  • Audiology: Bacterial infections can lead to otitis (middle ear infection)
  • Cardiac Physiology: Infections of the endocardium (inner lining of heart chambers and heart valves) can occur via bacteria spreading through the bloodstream.

Microbiology

• Phylogenetic Tree of Life: Based on ribosomal RNA sequencing, showing prokaryotes (Bacteria and Archaea) and eukaryotes (animals, fungi, plants) branching from a common ancestor.

Prokaryotes and Eukaryotes

• Prokaryotic Cells:

  • Smaller, typically less than 2µm
  • Simple internal structure
  • No membrane-bound organelles
  • Circular DNA (nucleoid)
  • One chromosome plus plasmids
  • Small ribosomes (70S)
  • Reproduce via binary fission

• Eukaryotic Cells:

  • Larger, typically greater than 2µm
  • Complex internal structure
  • Membrane-bound organelles
  • DNA within a nucleus
  • More than one chromosome
  • Larger ribosomes (80S)
  • Reproduce via mitosis and meiosis

• Prokaryotic Cell Structure:

  • Diagrams depicting capsule, cell wall, cytoplasmic membrane, chromosomal region, ribosomes, pili (attachment structures), and flagella (motility)

• Bacteria Structure: (Diagram Shown)

  • Illustrates the key components of a bacterial cell including the chromosome (nucleoid region) , ribosomes , food granules, flagella, cell wall, capsule/slime layer and plasmid.

Bacteria Cell Wall

• Peptidoglycan: A unique bacterial cell wall component composed of alternating sugars (NAM and NAG) cross-linked by peptides.

• Gram-Positive Bacteria: Thicker peptidoglycan layer and teichoic acids.

• Gram-Negative Bacteria: Thinner peptidoglycan layer, outer membrane with lipopolysaccharides (LPS).

Gram- and Gram+ Bacteria

• Gram Staining Procedure: The steps of the staining protocol to differentiate between gram + (purple) and gram - bacteria (pink).

Bacteria Found at Anatomical Sites

• A table listing various anatomical locations, and the prevalent bacteria commonly found there.

Normal Flora/Indigenous Microbiota

• Normal Flora: Composed typically of staphylococci and corynebacteria.
• Protection: Lactobacillus vaginalis provides protection against mucocutaneous infection.
• Opportunistic Pathogens: Some normal flora members can become opportunistic pathogens.

Growth and Reproduction

• Binary Fission: The primary method of bacterial reproduction, occurring typically when the cell reaches a critical size. It requires suitable environment, including temperature, pH, and nutrients. Growth continues exponentially until resources become scarce or growth inhibitors accumulate. This triggers sporulation.
• E. coli: Generation time of approximately 20 minutes.

Sporulation

• Spores: Dormant structures that allow bacteria to survive adverse conditions (e.g., extreme temperatures, lack of nutrients). Spores can last centuries and require specific conditions for germination to occur.

Antibiotics

• Classes: (Diagram showing examples and their mechanisms of action). Various classes of antibiotics; including beta-lactams, aminoglycosides, chloramphenicol, tetracyclines, macrolides, ansamycins, streptogramins, lipopeptides and their common mechanisms of action.

Antibiotic-Mechanisms of Action

• Cell Wall Synthesis Inhibition: Penicillins and Bacitracin target enzymes crucial for peptidoglycan cross-linking, disrupting cell wall integrity.

• Cell Membrane Function Disruption: Polymyxins target the bacterial outer membrane, causing leakage and death.

• Protein Synthesis Inhibition: Aminoglycosides and macrolides disrupt protein synthesis within bacterial ribosomes, interfering with peptide chain elongation and bacterial growth.

• Nucleic Acid Synthesis Inhibition: Quinolones target DNA gyrase in bacteria, while rifamycins target RNA polymerase, thus hindering DNA replication and reproduction.

• Action as Antimetabolites: Sulfonamides and trimethoprim interfere with bacterial metabolic processes for DNA synthesis by inhibiting folic acid synthesis.

MRSA - Methicillin-Resistant Staphylococcus Aureus

• Classification: Gram-positive, spherical (coccus), forms clusters, aerobic, coagulase-positive and producing toxins.
• Resistance mechanism: Presence of a β-lactamase enzyme degrading methicillin, and other β-lactam antibiotics.

Antibiotic Resistance

• Natural: The inability of antibiotics to penetrate or target a specific bacteria because of biochemical differences.
• Acquired: The development of resistance in bacteria owing to mechanisms, including genetic variations.

Mechanisms of Antimicrobial Resistance

• Alter/Degrade Antibiotic: Bacterial defense mechanisms that modify or destroy the antibiotic to prevent its action.

• Pump Out Antibiotic: Active efflux pumps remove the antibiotic from the cell, rendering the drug ineffective

• Decrease Permeability: Modifications in the bacterial cell wall that prevent antibiotic entry.

• Mutate Target Gene: Bacterial mutations that change the antibiotic's targeted protein or enzyme, thus reducing the antibiotic sensitivity.

Porins:

• Proteins in the outer bacterial membrane that form channels for molecules to pass through. Their presence influences antibiotic permeability and is closely linked to antibiotic resistance mechanisms.

Efflux Pumps:

• Active transporters in the bacterial cell membrane, expelling antibiotics from the cell, thus avoiding antibiotic action. RND, MATE, MFS and SMR efflux pumps are identified in the mechanisms of active expulsions of antibiotics.

Degradation:

• Bacterial enzymes such as penicillinases degrade antibiotics, rendering the drug chemically ineffective.

Mutation of target genes:

• Genetic changes to proteins or enzymes that the drug targets. These changes can render the affected protein or enzyme insensitive to antibiotics.

Origin and spread of resistance genes

• Genes can be found on the chromosome or on plasmids. Transfer of genetic material between bacteria occurs through horizontal gene transfer mechanisms, such as conjugation, transduction, or transformation.

Mechanisms of Plasmid-Encoded Antibiotic Resistance

• Various bacterial mechanisms of resistance conferred by plasmids (transferable genetic elements) are outlined, such as resistance to ẞ-lactam, Chloramphenicol, Aminoglycosides, Tetracycline, and Erythromycin.

Gene Transfer between Bacteria

• Transformation: Bacterial cells take up free DNA from their surroundings.
• Transduction: Phage (viruses) transfer bacterial DNA to other cells.
• Conjugation: A direct transfer of DNA from one cell to another usually via a conjugation pilus.

Search for New Antibiotics: Selective Toxicity

• Selective toxicity is the key concept for antimicrobial therapy, in which the drug is toxic towards microbes but not to humans.
• Exploiting differences in bacterial structures, processes, and metabolism enables targeting of microbial cells and avoiding harm to host cells .

Specific Targets

• Cell Wall: Drugs targeting bacterial cell walls inhibit peptidoglycan synthesis (penicillins, cephalosporins, and vancomycin) to avoid disruption of structural integrity.
• Cell Membrane: Targeting bacterial membranes with drugs that disrupt their function or permeability (e.g., polymyxins) or targeting sterol biosynthesis (e.g., nystatin) for antifungal activity.
• Ribosomes: Antibiotic targeting bacterial ribosomes (e.g., aminoglycosides, tetracyclines, macrolides, Chloramphenicol) to inhibit protein synthesis, interfering with bacterial growth.
• Metabolism: Various antibacterial drugs interfere with bacterial metabolic processes like folic acid synthesis (e.g., sulfonamides, and trimethoprim), or the production of other essential metabolites.
• Nucleic Acid Synthesis: Antibiotics targeting bacterial DNA replication or RNA polymerase (e.g., quinolones, rifamycins) ultimately hindering bacterial growth.

Two Main Mechanisms of Action

• Bactericidal: Killing the microorgansim directly, by targeting essential structural components (cell wall, membranes).
• Bacteriostatic: Inhibiting bacterial growth, relying on the host's immune system to eliminate them.

Spectrum of Activity

• Narrow spectrum: Effective against a limited range of species.
• Broad spectrum: Effective against a wide range of species.

General Unwanted Effects

• Alteration of Gut Flora: Introducing secondary infections, superinfection (potentially more severe bacterial infections).
• Hypersensitivity Reactions: Allergies due to antigenicity of the antibiotic; could manifest as anaphylaxis.
• Gastrointestinal effects: Diarrhea, antibiotic-associated colitis (inflammation).

How long should antibiotic be taken

• Full course of recommended dosage and time as prescribed.
• Length can vary based on the severity of infection or condition.

Virology

• Virus: An intracellular parasite requiring a host cell to replicate, thus unable to reproduce outside of a host cell. Composed of nucleic acid core (DNA or RNA) that is surrounded by a protein coat or capsid. Some viruses have an external lipid envelope.

Antiviral Drugs

• Selective Toxicity: Difficult to achieve to avoid harm to hosts, because of the close structural similarity of viral and host components.
• Acyclovir: Incorporated into viral DNA synthesis.
• Relenza: Inhibits viral penetration into host cells.
• HIV and HAART: Reverse transcriptase inhibitors prevent viral replication and aids host immune system response to recover.
• Interferons: Naturally produced in infected host cells that defend against viral infections.

References

• A list of relevant publications and resources is provided.