Bacterial Cell Structure - Chapter 1

Bacterial Cell Structure, Physiology, Metabolism, and Genetics - Chapter 1

• Microbiologists isolate, identify, and analyze bacteria to understand human diseases
• Knowledge of microbial structure and physiology is critical to clinical microbiologists in:
  • Culturing organisms from patient samples
  • Classifying and identifying isolated organisms
  • Predicting and interpreting antimicrobial susceptibility patterns

Overview of the Microbial World

• Anton van Leeuwenhoek, a Dutch biologist/lens maker, discovered microorganisms using a homemade microscope.
• He is considered the "Father of protozoology and bacteriology" for his pioneering work.
• He observed "beasties" in water droplets

Microbes

• Microbes include bacteria, parasites, fungi, and viruses. (Images of each type are shown)

Bacteria

• Bacteria are single-celled organisms lacking a membrane-bound nucleus.
• They are categorized as prokaryotes, meaning they lack mitochondria, endoplasmic reticulum (ER), and Golgi bodies.
• These structural differences distinguish them from eukaryotes.
• Refer to Table 1-1 and Figure 1-1 for additional details (These are not included in the provided text.)

Prokaryotic Cell vs. Eukaryotic Cell

• Diagrams showcasing the distinct structures of prokaryotic and eukaryotic cells are included, highlighting differences.

Parasites

• Eukaryotic parasites can be unicellular (microscopic) or multicellular (e.g., tapeworms, which can be up to 7-10 meters long).
• Protozoa are unicellular protists that ingest food.
• Parasites can be classified based on their movement mechanisms: flagella (whip-like), pseudopodia (false feet), and cilia (eyelashes).
• Examples of parasitic organisms and their associated locomotive structures are shown.

Fungi

• Fungi are heterotrophic eukaryotes, obtaining nutrients via absorption.
• Yeasts are unicellular fungi that reproduce asexually.
• "True" yeasts do not create hyphae or mycelia.
• Most fungi are multicellular, able to reproduce both sexually and asexually.
• Multicellular fungi are composed of filaments called hyphae, which intertwine to create a mat called mycelium.
• Molds are filamentous, reproducing both ways.
• Some fungi assume both a yeast and hyphae/mycelial form, dependent on temperature.
  • Yeast form at incubator/human temperature
  • Filamentous form at room temperature
• Dimorphic fungi are capable of causing systemic diseases.

Viruses

• Viruses (virions) are microscopic infectious particles.
• They are not considered living organisms because they lack a cellular structure and cannot replicate independently.
• They require host cells to reproduce and metabolize.
• They cannot be visualized using ordinary light microscopes.
• Effects from viral infections can include changes in cell morphology (rounding up), the formation of viral inclusions within host cells, and the fusion of multiple cells to produce a syncytium (multinucleated infected forms).
• Viruses contain either DNA or RNA, but not both.
• They are acellular and have a protein coat, lacking cytoplasmic membranes

Classification/Taxonomy

• Taxonomy is the method of organizing and classifying organisms.

• The process uses the similarities and differences in phenotype (observable traits) and genotype (genetic makeup).

• It incorporates three categories:

  • Classification and taxonomy
  • Nomenclature
  • Identification

• Formal levels of bacterial classification (i.e. Domain, Kingdom, Division(Phylum), Class, Order, Family, Tribe, Genus, Species)

• The hierarchical naming structure for bacteria places genera (plural of genus) in the capitalized first-order, followed by species (lower case). Both are italicized or underlined (example: Staphylococcus aureus).

  • Family (e.g., Micrococcaceae)
  • Genus (e.g., Staphylococcus)
  • Species (e.g., aureus)

• Species can be subdivided into subspecies, serovars, and biovars, based on phenotypic characteristics.

• Phage typing is a method utilizing bacterial susceptibility to specific bacteria phages.

• Classifying organisms based on cell organization (Prokaryotic, Eukaryotic, and Archaebacteria).

• Three domains (Bacteria, Archaea, Eukarya).

Prokaryotic Cell Structure

• Describes the components of a prokaryotic cell's cytoplasmic structures, cell envelope structures, and surface polymers.
  • List of structures; Circular chromosome, Mesosome, Ribosomes, Cytoplasmic granules, Endospores, Plasma Membrane, Cell Wall (Gram positive, Gram negative, Acid-fast.), Capsule, Slime Layers, Flagella, Pili, Fimbriae

Eukaryotic Cell Structure

• Describes the components of a eukaryotic cell.
  • List of structures; Nucleus, Nucleolus, Nuclear membrane, Endoplasmic reticulum (ER), Golgi apparatus, Ribosomes, Mitochondria, Lysosomes, Peroxisomes, Chloroplasts, Microfilaments, Microtubules, Centrioles, Lysosomes, and Peroxisomes

Bacterial Morphology – Microscopic Shapes

• Shapes and arrangements of bacteria are described (e.g., coccus, bacillus, curved forms like spirillum/spirochete.).

Common Bacterial Stains

• Various staining techniques used to observe and identify bacterial organisms under a microscope are listed.

Microbial Growth and Nutrition

• Key nutritional needs for bacterial growth are: Carbon, Nitrogen, ATP (including phosphate, phospholipids, and sulfur), and mineral ions (Na+, K+, Cl-, Ca2+).
• Two basic groups of bacteria: autotrophs (lithotrophs), phototrophs, chemolithotrophs, and heterotrophs
• Various growth media (minimal media, nutrient media, enriched media, selective media, and differential media) are discussed.
• Specific examples of nutrient broths (Tryptic Soy Broth, Nutrient Broth).
• Different types of agar plates (blood agar, chocolate agar, MacConkey agar, colistin-nalidixic acid agar) and their uses are described.
• Transport media
• Environmental factors that influence bacteria growth; pH (neutral pH), temperature (psychrophiles, mesophiles, thermophiles ), gaseous composition

Bacterial Growth

• Generation and doubling time are discussed.
• The phases in the bacterial growth curve (lag phase, log phase, stationary phase, death phase) are described.
• Methods for determining cell numbers (direct microscopic count, direct plate count, and density measurement.) are stated
• Diagnostic schemes that analyze properties, including carbon source utilization, end products from various substrates, and pH changes in a medium.

Fermentation and Respiration

• Classifications of fermentation based on electron acceptors (anaerobic, aerobic).
• Metabolic pathways; glycolytic pathway (Embden-Meyerhof-Parnas = EMP), pentose phosphate pathway, and Entner-Doudoroff pathway- are identified.

Carbohydrate Utilization and Lactose Fermentation

• The catabolism of lactose is broken into two steps.
• The breakdown of lactose to release glucose is detailed using the enzymes β-galactosidase and β-galactosidase permease.

Bacterial Genetics

• Principles of bacterial genetics, including genotype, phenotype, and protein synthesis (replication, transcription, translation, and the function of codons).

• Genetic elements and alterations; bacterial genomes, extrachromosomal elements (i.e. plasmids), mobile genetic elements and mutations.

• Mechanisms of gene transfer: transformation, transduction, and conjugation.

• Processes of each mechanism are described in illustrations.