Eukaryotes vs. Prokaryotes

• Agents of human infectious diseases include bacteria, fungi, protozoa, helminths, and viruses.

Eukaryotes

• Eukaryotes are organisms with cells containing complex structures inside membranes alongside a nucleus, or nuclear envelope, in which genetic material is carried.
• Eukaryotes also contain membrane-bound organelles like mitochondria, chloroplasts, and the Golgi apparatus.
• Almost all species of large organisms are eukaryotes, including animals, plants, and fungi, although most species of eukaryotic protists are microorganisms.

Prokaryotes

• Prokaryotes are a group of organisms that lack a cell nucleus or any other membrane-bound organelles.
• Most prokaryotes are unicellular.
• Prokaryotes are divided into two domains: bacteria and archaea.

Biologic Relationships of Pathogenic Microorganisms

• Animals in the Kingdom are classified under type Eukaryotic cells and include Helminths as pathogenic microorganisms.
• Plants are classified under type Eukaryotic cells and include None as pathogenic microorganisms.
• Protists are classified under type Eukaryotic cells and include Protozoa and Fungi as pathogenic microorganisms.
• Prokaryotes are classified under type Prokaryotic cells and include Bacteria as pathogenic microorganisms.
• Viruses are classified under type Noncellular cells.

Bacteria

• Bacteria is the plural form of the Latin word bacterium.
• Bacteria is the smallest living cells with a size range from 0.1 – 5 μm.

Classification of Medically Important Bacteria

• One way to classify bacteria is based on Gram's stain: Gram-positive, Gram-negative, and acid-fast bacteria.
• Bacteria can also be classified based on morphology as Cocci (spherical) or Bacilli (rod-shaped).
• Bacteria can be classified based on oxygen requirement as Aerobic (lives with oxygen) or Anaerobic (lives without oxygen).
• Bacteria can be classified based on shape and spore-forming ability to form Clusters, chains, and pairs or Spore forming, non spore forming.

Bacterial Shape & Cell Arrangement

• Bacteria exhibit a variety of shapes and cell arrangements.

• Cocci are spherical or oval-shaped.

• Bacilli are rod-shaped.

• Coccobacilli are very short rods.

• Fusiform are rod-shaped with tapered ends.

• Spirilla are spiral-shaped rigid, while spirochetes cells are flexible.

• Cocci arrangement includes pairs (diplococci), chains (streptococci), and irregular clusters (staphylococci).

Naming of Bacteria

• Bacterial names have two parts
• Genus name comes first followed by species name
• Example: Staphylococcus aureus

Viruses Nomenclature

• Viruses are named with a single name such as poliovirus, measles virus, or rabies virus, or names with two words, such as herpes.

Characteristics of Prokaryotic and Eukaryotic Cells

• DNA is not within a nuclear membrane for Prokaryotic Bacterial Cells, but within for Eukaryotic Human Cells.
• Mitotic division does not occur in Prokaryotic Bacterial Cells, but does occur in Eukaryotic Human Cells.
• DNA is not associated with histones in Prokaryotic Bacterial Cells, but is in Eukaryotic Human Cells.
• The chromosome number for Prokaryotic Bacterial Cells is one compared to Eukaryotic Human Cells that is more than one.
• Membrane-bound organelles, such as mitochondria and lysosomes, are found in Eukaryotic Human Cells however they are not found in Prokaryotic Bacterial Cells.
• Ribosomes have a size of 70S in Prokaryotic Bacterial Cells compared to 80S in Eukaryotic Human Cells.
• Prokaryotic Bacterial Cells contain a cell wall containing peptidoglycan, whereas Eukaryotic Human Cells do not.
• Mitosis is the process where a eukaryotic cell separates the chromosomes in the cell nucleus into two identical sets in two nuclei.
• Histones are strongly alkaline proteins found in eukaryotic cell nuclei, which package and order the DNA into structural units called nucleosomes.

Protozoa

• Protozoa characteristics include that they are Single-celled eukaryotes. 
• Protozoa lack a cell wall. 
• Protozoa often live in the digestive tract of animals. 
• They are grouped according to how they move and use one or more flagella, cilia, or a cytoplasmic extension (pseudopodia). 
• Protozoa for the most part are harmless to humans.  A few are pathogenic in nature, where examples are malaria, sleeping sickness, giardiasis, and amoebic dysentery.

Fungi

• Fungi are eukaryotes that contain chitin in the cell wall
• Yeasts (e.g., Candida sp.) cause oral thrush. 
• Molds (e.g., Aspergillus sp.) cause opportunistic infections.

Viruses

• Viruses are neither eukaryotes nor prokaryotes. 
• They don't grow and do not display any metabolic activity. 
• Viruses only perform replication within living cells. 
• Viruses contain either DNA or RNA, and nucleic acid is packed inside a protein shell.
• Viral DNA is either double or single stranded and is an intracellular obligatory parasite.
• Viral infections include AIDS, influenza, hepatitis, and herpes infections.

Comparison of Medically Important Organisms

• Viruses, Bacteria, Fungi, Protozoa, and Helminths are all medically important organisms
• Viruses contain either DNA or RNA, while Bacteria, Fungi, Protozoa, and Helminths contain both.
• Viruses have no nucleus, while bacteria are Prokaryotic, and Fungi, Protozoa and Helminths are eukaryotic.
• Viruses lack Ribosomes, and Bacteria have 70S, while Fungi, Protozoa, and Helminths have 80S. 
• Viruses and Bacteria are absent of Mitochondria while Fungi, Protozoa, and Helminths posses it
• Viruses surface is Protein capsid and lipoprotein envelope, while Bacteria is Rigid wall containing peptidoglycan.
• Fungis have a Rigid wall containing the outer surface of chitin and Protozoa and Helminths have a Flexible membrane outer surface
• Viruses dont have mobility ,Bacteria some, and Fungi None. Protozoa and Helminthat have the most mobility .
• Viruses, Bacteria, Fungi, Protozoa, and Helminths all replicate differently
• Viruses use Not binary fission,
• Bacteria use Binary fission,
• Fungi use Budding or mitosis2 
• Protozoa use3 Mitosis.

Key Points

• Agents of human infectious diseases are bacteria, fungi (yeasts and molds), protozoa, helminths, and viruses.
• Bacterial cells have a prokaryotic nucleus, while human, fungal, protozoan, and helminth cells have a eukaryotic nucleus; viruses are not cells and do not have a nucleus.
• All cells contain both DNA and RNA, whereas viruses contain either DNA or RNA, not both.
• Bacterial and fungal cells are surrounded by a rigid cell wall, whereas human, protozoan, and helminth cells have a membrane.
• The bacterial cell wall contains peptidoglycan, whereas the fungal cell wall contains chitin.

Explore eukaryotic microorganisms and their characteristics, focusing on membrane-bound organelles. Compare eukaryotes with other microorganisms, including their classification and domain. Understand the common features of large organisms and their cellular structures.