Introduction to Microbiology

• Microbiology studies microorganisms, a diverse group of microscopic, single-celled or clustered organisms; it also includes microscopic but non-cellular viruses.
• Microbial cells differ from animal and plant cells in that they can live alone in nature, unlike animal and plant cells which exist as part of multicellular organisms.

Reasons to Study Microbiology

• It is a basic biological science.
• It is an applied biological science.
• Microbiology addresses practical issues in medicine, agriculture, and industry.
• Microorganisms significantly impact soil fertility and animal production.
• Microorganisms are responsible for some of the most serious diseases in humans, animals, and plants.

Microbiology Disciplines

• Mycology studies fungi.
• Bacteriology studies bacteria.
• Virology studies viruses.
• Protozoology studies protozoa.
• Related disciplines include Parasitology, Immunology, Pathology, Epidemiology, Public Health and Hygiene, and Biotechnology.

Historical Background

• Humans utilized microbial products before they knew of the organisms' existence.
• Foods like mushrooms were consumed.
• Fermented beverages like beer and wine were produced.
• Medicines with antibacterial properties were available.
• Food was preserved through salting and drying.

Advent of the Microscope

• Anton van Leeuwenhoek (Netherlands) created his own microscopes.
• He was also the first person to observe bacteria, yeasts, and protozoa.
• Paul Ehrlich introduced vital staining of bacteria with methylene blue in 1881.
• Hans Christian Gram introduced Gram staining in 1884.

Pasteur and Industrial Microbiology

• Before Pasteur, there was debate over spontaneous generation.
• Spontaneous generation: living organisms arise in decaying matter without a pre-existing eg structure.
• Louis Pasteur (Father of Microbiology) disproved the spontaneous generation theory in 1861 using a swan-necked flask.
• Pasteur boiled a liquid in the flask, leaving it open to the air.
• He showed fermentation ceased to occur, disproving spontaneous generation.

Robert Koch and Medical Microbiology

• Robert Koch's studies greatly advanced medical microbiology.
• Koch demonstrated that microorganisms grown outside the body could cause disease.
• Alexander Fleming discovered the antibacterial properties of Penicillium cultures in 1929.
• Fleming named the active ingredient penicillin.

Classification of Organisms (Woese, 1980)

• Kingdom of Archaebacteria includes one-celled organisms lacking organelles.
• Kingdom of Eubacteria consists of one-celled organisms lacking organelles.
• Kingdom of Eukaryotes includes uni- or multi-cellular organisms with organelles.

Alternate Classification

• Archaebacteria and Eubacteria are classified together as Prokaryotes.
• Eukaryote constitutes a separate class.
• Prokaryote refers to cells lacking a true nucleus structure (primitive nucleus).
• Eukaryote refers to cells with a membrane-enclosed nucleus (true nucleus) and often other organelles.

Prokaryotic vs. Eukaryotic Cells

Prokaryote

• Phylogenetic groups: Bacteria and Archaea.
• Nuclear structure: Absent.
• Nuclear membrane: Absent.
• Nucleolus: Absent.
• DNA: Often a single molecule that is circular and not complexed like DNA in plasmids.
• Division: No mitosis.
• Introns in genes: Rare.
• Cytoplasmic structure and organization: (no information given)
• Cytoplasmic membrane: Usually lacks sterols; hopanoids MAY be present
• Internal membranes: Relatively simple; limited to specific groups
• Ribosomes: 70S in size
• Membranous organelles: Absent.
• Respiratory system: Part of cell membrane
• Photosynthetic pigments: In internal membranes or chloroplasts
• Cell walls: Most, peptidoglycan (Bacteria), glycoprotein (Archaea)
• Forms of motility: Flagella composed of a single type of protein; arranged in a fiber
• Size: Usually small < 2ųm diameter

Eukaryote

• Phylogenetic groups: Eukarya: Algae, Fungi, Protozoa, plants, animals
• Nuclear structure: Present
• Nuclear membrane: Present.
• Nucleolus: Present.
• DNA: present in several chromosomes, complexed with histones
• Division: Mitosis; mitotic apparatus with microtubular spindle.
• Introns in genes: Common.
• Cytoplasmic structure and organization: (no information given)
• Cytoplasmic membrane: Usually PRESENT sterols; hopanoid is absent
• Internal membranes: Complex; reticulum
• Ribosomes: 80S, except for ribosomes of mitochondria and chloroplasts which are 70S
• Membranous organelles: Present

Eukaryotic Cells Vs Prokaryotic Cells Continued

• Respiratory system: is in Mitochondria
• photosynthetic pigments: in chloroplasts when present
• Cell walls: polysaccharide in plants, usually absent in animals and protozoa
• Flagellar movement: composed of microtubules
• Non-Flagellar: cytoplasmic amoeboid movement.
• Cytoskeleton: present, microtubules, cilia spindle
• Size: much larger 2 >100 ųm diameter