MICROBIO 1.2

Basic Characteristics of Pathogens

• Pathogens cause disease and students will treat diseases.
• The CDC reports over 2.8 million antibiotic-resistant infections annually in the US, resulting in over 35,000 deaths.
• In 2017, there were at least 12,800 deaths related to Clostridioides difficile infections.
• The 2019 Antibiotic Resistance Threat Report (CDC, 2019) identifies 21 bacteria and fungi as threats to the US, categorized as "urgent, serious, concerning, watch-list."
• A recent PNAS publication highlights a group of H1N1 swine influenza viruses showing potential for human pandemic concern.

G4 Swine Flu Viruses

• The CDC is taking action to deal with the G4 swine flu viruses in China, which pose a pandemic risk.
• This recent publication in the Proceedings of the National Academy of Science (PNAS) describes H1N1 swine influenza viruses having the potential to infect humans.
• These viruses are of major pandemic concern.

Mysterious Respiratory Illness in Dogs

• Many US states are reporting unusual respiratory illnesses in dogs.
• The illnesses were detected in October 2021.
• There's no evidence of human-to-human spread.

Is It the Flu or COVID?

• An at-home test can distinguish between the flu and COVID-19.

Class Objectives

• Compare and contrast prokaryotes and eukaryotes (including cell walls).
• Understand the advantages and disadvantages of being a prokaryote and identify adaptive strategies.
• Identify fundamental differences among bacterial types (gram-positive, gram-negative, acid-fast).
• Define fungi, distinguishing them from viruses and bacteria, and explain their organizational structure.
• Define parasites and their basic organizational structure.
• Understand how viruses are categorized.

Prokaryotes vs. Eukaryotes

• Prokaryotes have free-floating DNA, while eukaryotes have DNA bound to protein.
• Prokaryotic DNA is circular, and eukaryotic DNA is linear.
• Prokaryotes typically lack a nucleus and membrane-bound organelles.
• Prokaryotic ribosomes are 70S, and eukaryotic ribosomes are 80S.
• Prokaryotes reproduce through binary fission, whereas eukaryotes reproduce through mitosis or meiosis.
• Prokaryotic cells are generally smaller (1-5 μm) than eukaryotic cells (10-100μm).
• Prokaryotes are haploid, while eukaryotes can be diploid or higher.

Pros of Being Prokaryotic

• Coupled transcription and translation, leading to faster processes.
• Simpler and faster binary fission compared to mitosis.
• Reduced space requirements.
• High metabolic rates, allowing microbes to double in size every 20 minutes due to high surface area to volume ratio.

Bacteria in the Large Intestine

• The human large intestine contains trillions of bacteria, contrasting with only 7.6 billion people on Earth.

Cons of Being Free-Living

• The three main challenges for microbes are resistance (to damaging agents), occupancy (finding a suitable environment), and nutrition (intermittent availability).

Goal: Adapt and Survive (Efficiently)

• The intrinsic nature of microbes is to adapt and survive efficiently.

Mechanisms of Survival

• The bacterial cell wall protects the cytoplasmic membrane.
• Bacteria protect their cytoplasmic membrane through techniques like being gram-positive, gram-negative, or acid-fast.

Gram-Positive vs. Gram-Negative Bacteria

• Gram-positive bacteria retain the crystal violet-iodine complex after alcohol decolorization.
• Gram-negative bacteria do not retain the crystal violet-iodine complex.
• Gram-positive bacteria have a thick peptidoglycan layer, while Gram-negative bacteria have a thin layer.

Peptidoglycan

• Peptidoglycan, also known as murein, protects against osmotic pressure.
• Bacterial shapes (cocci, bacilli, spirilla) are determined by peptidoglycan structure.
• Certain antibiotics impede peptidoglycan synthesis.

Lipopolysaccharide (LPS)

• LPS anchors itself to the outer membrane.
• It is responsible for eliciting fever in the host.
• It contains hydrophilic side chains that prevent hydrophobic compounds from entering the cell.

Periplasmic Space

• The periplasmic space is located between two membranes, containing enzymes and proteins that aid in transport and nutrition.

Acid-Fast Bacteria

• Acid-fast bacteria have waxy cell walls that prevent standard Gram staining.
• Special stains are required for identification.

Occupancy

• Microbes must find hospitable environments.
• Development of mechanisms to evade common environmental behaviors.
• Employing biofilms for attachment and protection are examples of adapting to an environment.

Movement

• Capsule for protection against phagocytosis.
• Flagella for motility, chemotaxis toward favorable environments.
• Pili for attachment.

Nutrition

• Bacteria require readily available nutrients in their environments.
• The bacterial growth cycle demonstrates that nutrients ebb and flow in the environment.

Cytoplasmic Membrane and Transport

• The cytoplasmic membrane contains permeases to facilitate entry of most metabolites.
• Facilitated diffusion-molecules move along the concentration gradient.
• Active transport-molecules move against the concentration gradient, requiring energy.
• Group translocation-molecules are chemically modified during transport.

Viral Classification

• Viruses are classified based on morphology and replication.

What are Fungi?

• Fungi are usually multicellular eukaryotic organisms.
• They are heterotrophs (cannot make their own food).
• Fungi play crucial roles in nutrient cycling.
• They reproduce both sexually and asexually.

Basics of Fungi

• Fungi are eukaryotic, with a nucleus, mitochondria, Golgi, and endoplasmic reticulum.
• Fungal cells have rigid walls composed of chitin and glucans.
• The cell membrane contains ergosterol.
• Multiple forms (unicellular, multicellular, or dimorphic) exist.
• Reproduction is dependent on environmental factors (temperature, pH, CO2).
• Fungi produce spores, use budding, or both.

Parasites

• Parasites live on or in a host and obtain nutrients from the host.
• Two main groups: protozoa and helminths.
• Protozoa include amoebas, flagellates, ciliates, and apicomplexans.
• Helminths include nematodes, trematodes, and cestodes.

What About Viruses?

• Viruses are neither prokaryotic nor eukaryotic
• Viruses cannot reproduce by themselves