Introduction to Microbiology

Microbiology Definition

• Microbiology focuses on the study of organisms too small to be seen without magnification.

Types of Microbes

• Microbes include TSEs (Transmissible Spongiform Encephalopathies), viruses, bacteria, and eukaryotes like fungi and protozoa.

Transmissible Spongiform Encephalopathies (TSEs)

• TSEs cause sponge-like lesions in the brain.
• Examples of TSEs include Kuru, Scrapie, and Creutzfeld-Jacob disease.

Size Comparison

• Eukaryotes are larger than bacteria, which are in turn larger than viruses.

Eukaryotes vs. Bacteria

• Eukaryotes feature internal compartmentalization with organelles like mitochondria, whereas bacteria do not.

Viruses Distinctions

• Viruses are not visible with a light microscope; an electron microscope is needed.
• Viruses require a host to grow and divide.
• Viruses are metabolically inactive outside a host.
• Unlike bacteria and eukaryotes, viruses contain both DNA and RNA in their genome.

Viral Protein Coats

• Viruses have two types of protein coats: icosahedral (20 faces) and helical.

Viral Replication Steps

• Viruses enter cells via receptors.
• They release their genome into the host cell.
• Viruses replicate by using the host cell's machinery.
• Reverse transcription is then used to transcribe the genome to produce viral proteins (capsid).
• The virus either leaves to infect other cells or integrates into the host genome as a pro-virus.

Bacterial Replication

• Bacteria replicate through binary fission.

Bacterial DNA Storage

• Bacterial DNA is stored in chromosomes and plasmids.

Bacterial Protein Production

• mRNA enters the cell and associates with ribosomes to form proteins in bacteria.

Bacterial Morphology

• Bacteria have various shapes and arrangements.
• Bacilli are rod-shaped, cocci are spherical, and spirochaetes are spiral-shaped.
• Some bacteria are curved, like the ones that cause cholera.
• Streptococci form chains of spheres, while staphylococci form bunches of spheres.

Gram-Positive vs. Gram-Negative Bacteria

• Both Gram-positive and Gram-negative bacteria have a capsule, peptidoglycan layer, and a cytoplasmic membrane.
• Gram-negative bacteria possess additional structures: LPS (lipopolysaccharide), an outer membrane, lipoprotein, and a periplasmic space.

Alpha Haemolysis

• Alpha haemolysis results in a green tinge due to the breakdown of haemoglobin.

Beta Haemolysis

• Beta haemolysis is characterized by a clear zone around each colony.

Bacterial Typing Definition

• Typing refers to defining the organism.

Serotyping

• Serotyping uses antisera to identify antigens present on the bacteria.

Phage Typing

• Phage typing uses bacteriophages (bacterial viruses) to recognize surface proteins.

Genetic Typing

• Genetic typing involves sequencing DNA properties.

Genetic Typing Methods

• Plasmid profiling, RFLP (restriction fragment length polymorphism), probes, and PCR (polymerase chain reaction) are types of genetic typing.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic cells lack internal membranes, while eukaryotic cells have DNA encased in a nucleus.
• Prokaryotic cells have rigid cell walls, whereas some eukaryotic cells lack a cell wall.
• Prokaryotic cells have 70S ribosomes, while eukaryotic cells have 80S ribosomes.

Fungi vs. Protozoa

• Fungi can be single-celled or multicellular.
• Protozoa are exclusively single-celled.

Types of Fungi

• Yeasts grow as single cells or as hyphae, and examples include candida spp and cryptococcus spp.
• Moulds grow only as hyphae, with examples such as aspergillus spp, penicillium spp, and fusarium spp.

Fungal Cell Wall

• Fungal cell walls consist of manoproteins, a B-glucan layer, chitin layer, a cell membrane and ergosterol within the cell membrane.

Pathogenic Bacteria

• Bacteria that cause disease are referred to as pathogenic bacteria.

Commensal Bacteria

• 'Good' bacteria are known as commensals or normal flora.

Disruption of Commensals

• Antibiotics, HIV, and trauma can disrupt commensals.
• Antibiotics can lead to salmonella and C. difficile infections.
• HIV can lead to TB and Candida infections.
• Trauma can lead to s. aureus entering through cuts.

Pathobionts

• Opportunistic bacteria are termed pathobionts.
• Changes in the environment can cause them to emerge.

Bacteria with Opposite Reactions

• Escherichia coli O157 is harmful to humans but beneficial to cattle.
• Salmonella typhimurium is harmful to humans but non-pathogenic to chickens.