Microbiology Quiz on Antibiotics and Resistance

Antibiotics Resistance Mechanisms

• Antibiotics resistance genes are located on plasmids which can be transferred between bacteria during conjugation.
• Transformation is the uptake of genes from the environment.
• Transduction is horizontal gene transfer by bacteriophages. Bacteriophages inject their DNA into a bacterial cell. The bacteriophage's DNA takes over the bacterial cell's machinery, causing the bacteria to produce new phage particles.
• Accidental packaging occurs if bacterial DNA fragments are mistakenly packaged along with phage DNA. This leads to the transfer of genetic material from the infected bacterium to new bacteria.

Antimicrobial Susceptibility Testing

• Disk diffusion (Kirby-Bauer Test): Antibiotic-impregnated disks are placed on an inoculated agar plate with bacteria. The effectiveness of the antibiotic is determined by the size of the inhibition zone around the disk. Zones of inhibition are used to identify antibiotic-resistant bacteria.
• Broth Dilution: Bacteria are exposed to different concentrations of an antibiotic in a liquid medium, and the lowest concentration that prevents visible growth is called the MIC (minimum inhibitory concentration). This indicates the antibiotic's effectiveness.

History of Microbiology

• Antonie van Leeuwenhoek made the first microscope.
• Louis Pasteur formulated the germ theory of fermentation.

Fermentation Pathways

• Anaerobic bacteria perform fermentation in the absence of oxygen, converting sugars into lactic acid, acetic acid, and propionic acid.
• Lactobacillus bacteria in dairy products produce lactic acid, used in yogurt and cheese production.
• Yeast (Saccharomyces cerevisiae) is essential in baking and brewing, converting sugars into carbon dioxide and alcohol.

Pasteurisation

• A process that heats milk to 70°C, then cools, and stores it to reduce bacterial numbers, but does not kill all bacteria.
• Ultra-High-Temperature (UHT) milk is sterilized, increasing its shelf life.

Koch's Postulates

• The microbe must be present in every case of the disease.
• The microbe must be isolated and grown in pure culture.
• The disease must be reproduced when the pure culture is inoculated into a healthy host.
• The same microbe must be re-isolated from the infected host.

Characteristics of Living Things (in bacteria)

• Movement (some bacteria use flagella)
• Reproduction (conjugation, transduction, or transformation)
• Sensitivity (such as chemotaxis)
• Growth
• Respiration (some bacteria are anaerobic)
• Excretion
• Nutrition

Subdivision of cellular organisms

• Prokaryotes (Bacteria and Archaea)
• Eukaryotes (Protists, Animals, Plants, Fungi)
• Bacteria and archaea cells lack membrane-bound organelles.

Prokaryotes

• Genetic material in the cytoplasm.
• Eubacteria (Bacteria).
• Archaebacteria (Archaea).
• Biological membranes usually contain a phospholipid bilayer with fatty acid tails. Archaea also have complex lipid (i.e., isoprene-based) that can form a monolayer.

Bacteria and Archaea Membrane

• Lipids have a hydrophilic head and hydrophobic tails, forming a bilayer.
• Archaea membrane lipids have ether bonds instead of ester bonds.
• Lipid bilayer as seen in some Archaea and all Eucarya and Bacteria
• Lipid monolayer as found only in some Archaea—especially in extreme thermophiles.

Bacterial Classification

• Classification based on genetic information is a more recent approach.
• Previously, morphological differences and biochemical characteristics were used.
• Newer methods include multi-locus enzyme electrophoresis (MLEE).
• Prokaryotes have no nucleus characterized by a single cell
• Diverse metabolism

Characteristics of Bacteria

• Heterotrophic / photoautotrophs
• Aerobic / anaerobic
• Typical size: 1-2 mm
• No membrane-bound organelles
• Internal structures without membranes

Classifying Bacteria

• Types of bacteria are eubacteria, archaebacteria, and gram-positive, gram-negative
• Morphology (cell shapes), including cocci, bacilli, spirals
• Nutrient type (chemoheterotrophs, photoheterotrophs, chemoautotrophs, photoautotrophs)
• Existence of endospores
• Diseases caused by bacteria (e.g., tetanus, botulism, gonorrhea, Chlamydia, tuberculosis)
• Ecological requirements (oxygen, temperature, and pH) Energy capturing metabolism, autotrophs and heterotrophs

Ecological Diversity

• Bacteria show great diversity in their ecological requirements like pH, temperature, oxygen, and osmotic pressure.

Bacterial Shapes

• Two most common: Spherical (cocci), and Rods (bacilli).
• Cocci can aggregate into chains (streptococci) or clumps (staphylococci).
• Bacilli can be straight rods / comma-shaped rods / corkscrew-shaped

Bacterial Cell Structures

• Cell walls: Bacteria have rigid cell walls made of peptidoglycan or murein. Gram-positive bacteria have thick cell walls with high peptidoglycan concentrations and other polymers (like teichoic acids), and gram-negative bacteria have thin cell walls with less peptidoglycan and an outer membrane.
• Flagella: The structure used for movement in some bacteria, composed of protein.
• Fimbriae / pili: structures utilized for attachment, composed of a singular protein.
• Capsule / mucilage layer: an external protective layer.

Bacterial Ribosomes

• Particulate organelles within the cell
• Function in protein synthesis
• Composed of 70-S subunits (large + small)

Bacterial Genomes

• Nucleoid contains the bacterial chromosome in a region without a membrane.
• Plasmids: are small circular DNA molecules in addition to the chromosome.
• Plasmids function includes antibiotic resistance, heavy metal tolerance, and pathogenicity (carrying toxin genes).

Bacterial Spores

• Bacteria produce endospores under adverse environmental conditions.
• Endospores allow for survival.
• Spore formation and structure involve several steps including initiation, DNA replication, septum formation, engulfment, cortex formation, coat synthesis, and maturation. These then lead to dormancy and germination.

Viruses (a general overview – not comprehensive)

• Viruses are intracellular obligatory parasites—infectious agents that consist of nucleic acid (DNA and/or RNA) and protein.
• Virions are infectious form with a nucleic acid core surrounded by a protein capsid, sometimes with an envelope.
• They can infect all organisms, driving global biogeochemical cycles,
• Viruses impact various ecosystem roles and human health, impacting human health.
• Viruses (in general) have varying sizes (20 to 300 nm).

Viral Genome and Replication

• Viruses may contain DNA or RNA.
• Various different types of RNA and DNA strands can be present, each with different pathways needed to replicate.
• Viral genomes include instructions that, when translated into protein, are responsible for replication. This may involve host cell resources or utilize host-independent systems to perform the steps for viral replication.

Viral Life-Cycle Stages

• Attachment/Adsorption
• Penetration (membrane fusion or endocytosis)
• Uncoating (release of viral nucleic acids)
• Synthesis (replication of genetic material and protein synthesis)
• Assembly (virion components are collected)
• Release (new viruses are released from infected cell)

Viral Tropisms

• Specific host cells, tissues and organisms are targeted by different classes of viruses – the result of specific cell receptors.
• SARS-CoV-2 (COVID-19) exemplifies cell receptor specificity.

Viral Genomes and Mutations

• All viruses mutate, some at much faster rates than others.
• Mutations can be synonymous (no change in amino acid sequence) or non-synonymous (change in amino acid sequence), altering the virus's shape, structure and surface proteins, impacting the host's recognition and immune response.

Infectious Diseases and Reproduction Number

• The basic reproduction number (Ro) represents the average number of people infected by a single infectious individual.
• Higher Ro values correlate with more contagious viruses.

Outcomes of Natural Viral Infections

• Asymptomatic infection.
• Acute infection (immunological resolve).
• Chronic infection (e.g., HIV or HCV infections).
• Emerging conditions like long Covid or other autoimmune diseases.

Immune Response and Viral Infections

• Immune system components (innate and adaptive).
• Roles of phagocytes, NK cells and cytokines.

Viral Classification

• Different classes of viruses can be categorized using the Baltimore classification system.
• This system classifies viruses based on their genome type (DNA or RNA, and if the strand is single or double stranded), and if (+) or (-) polarity, which allows predictive modelling.

Viral Shapes/Structures

• Viruses vary in their shapes; helical (Tobacco Mosaic Virus), icosahedral (Adenovirus), and complex (Bacteriophages).
• Structural proteins include capsomeres, glycoproteins, and matrix proteins.
• Lipid envelopes are also present in some viruses impacting interaction with the host cell.

Vaccine Developments

• Methods for vaccine development include inactivated vaccines, live attenuated vaccines, genetic vaccines, and synthetic peptides.

Fungal characteristics and structures

• Fungal cell walls are complex structures containing mannoproteins, glucans, and chitin.
• Fungal cells have a cell membrane containing ergosterol.
• Some fungi are heterotrophic (saprophytes, parasites , or symbiotes)
• Fungal reproduction (asexual and/or sexual). Spores are involved in the reproduction.
• Fungal structures (hyphae, sporangiospores, mycelium, conidia)

Antifungal mechanisms

• Polyenes, azoles (inhibit ergosterol synthesis) disrupt the cell membrane, causing increased permeability and ultimately cell death.
• Specific fungal targets are used to selectively target the pathogen.

Test your knowledge on key concepts related to microbiology, including antibiotic resistance mechanisms, determining Minimum Inhibitory Concentration (MIC), and the historical context provided by Koch's postulates. This quiz covers important topics and significant figures in the field of microbiology.