Microbiology Chapter on Gram Negative Bacteria

Microbiology Overview

• Microbiology is the study of microorganisms, organisms too small to be seen with the naked eye.
• Major groups include viruses, bacteria, fungi, and parasites (protozoa).
• Microbes vary in shape, size, and genetic and metabolic characteristics.

Microbial Size and Microscopy

• Microbes are very small, ranging from atoms to cells.
• Electron microscopes have a higher resolution than light microscopes.
• Electron microscopes can magnify objects thousands of times more than light microscopes.

Comparing Light and Electron Microscopes

• Light microscopes use visible light.
• Electron microscopes use electrons.
• Light microscopes magnify images up to 1500x.
• Electron microscopes magnify images up to 500,000x.
• Light microscopes use glass lenses.
• Electron microscopes use electromagnets.
• Light microscopes can view living and non-living things.
• Electron microscopes can mainly view non-living things.
• Light microscopes are cheap.
• Electron microscopes are expensive.
• Light microscopes are portable.
• Electron microscopes are static.

Microscopy Overview

• The light microscope uses visible light and a system of lenses to produce magnified images of small objects.
• The parts of a microscope include the eyepiece, arm, rack stop, stage clip, coarse focus, fine focus, revolving nosepiece, objective lens, stage, condenser, illuminator, and base.
• Gram positive and negative bacteria can be visually distinguished via a staining procedure when using a light microscope.

Viruses

• Small size (18-600 nm)
• Subcellular structural organization.
• True parasites.

Bacteria

• Prokaryotic cells.
• Lack a nucleus.
• Lack intracellular compartments.
• Typically smaller than eukaryotes (1-10 μm).
• Possess various structural components: capsule, fimbriae, ribosomes, pili, slime, mesosome, cytoplasm, flagella, membrane, plasmid, cell wall, and nucleoid.

Fungi

• Eukaryotic cells.
• Contain a nucleus and have intracellular compartments.
• Larger than bacteria.
• Yeasts (unicellular) are typically 15-10 μm.
• Moulds (multicellular) can reach up to 50 μm.

Protozoa

• Eukaryotic cells.
• Nucleus and intracellular compartmentalization.
• Some exhibit motility via pseudopods, flagella, or cilia.
• Larger than bacteria (typically up to 100 μm).
• Complex life cycles often involving biological vectors.

Eukaryotes and Prokaryotes

• Key differences in size, nuclear structures (nucleus presence), chromosomes (number and structure), and cytoplasmic structures (e.g., mitochondria).
• Eukaryotic ribosomes are 80S, and prokaryotic ribosomes are 70S.

Microbial Distribution

• Microbes are ubiquitous; they live almost everywhere on Earth (in various environments, including high/low temperatures, acidic/alkaline conditions, and high pressure).
• Microbes can live in nearly any kind of environment.

Microbial Impact on the Environment

• Critical role in sustainability (conversion of nitrogen, carbon, and sulfur into usable forms for plants).
• Useful in cleaning up some environmental pollutants.

Microbial Impact on Human Health

• Essential for food production (fermentation).
• Important participants in the human microbiota (skin, oral, vaginal, and gastrointestinal tracts).
• Roles in human health and disease.
• Colonization begins at birth. It's of two types: permanent or transient colonization.

Microbial Impacts on the Human Body

• Different types of microbes live on/in different parts of the body.
• Human microbiota affects health by maintaining balance.
• Imbalances in the microbiota can lead to various health issues.

Fecal Microbiota Transplantation

• Fecal microbiota transplantation (FMT) involves transferring fecal microbiota from a healthy donor to a recipient with a disrupted gut microbiota.
• FMT is thought to work by restoring gut microbial diversity and function.

The Intestine Microbiota

• Microbes that live on/in the different parts of the intestinal tract vary greatly.
• The intestinal microbiota affects human health.
• The intestinal microbiota and its diversity change from infancy to adulthood.

The Skin Microbiota

• Second-largest microbiota in the human body.
• Made up of 10^8 – 10^10 microbes per square cm of skin.
• Restructured during puberty.
• Microbial communities stabilize after puberty.

Disruption of Microbial Balance

• Imbalance in the skin microbiota can cause issues like acne.
• Other microbial imbalances can cause various health conditions.

Importance of Gram and Ziehl-Neelsen Stains

• Both techniques identify bacteria based on their cell wall structure.
• Gram stain differentiates Gram-positive and Gram-negative bacteria.
• Ziehl-Neelsen stain identifies acid-fast bacteria.

Bacterial Cell Wall Structure

• Gram-positive bacteria have a thick cell wall composed of peptidoglycan.
• Gram-negative bacteria have a thin cell wall with an additional outer membrane. The outer membrane contains lipopolysaccharide (LPS).

Bacterial Cell Wall Components

• Peptidoglycan (or murein), a major component of bacterial cell walls.
• Teichoic and lipoteichoic acids strengthen the cell wall in Gram-positive bacteria.
• Lipopolysaccharide (LPS) is a major component in Gram-negative bacterial cell walls.

Bacterial External Structures: Capsules, Flagella, Fimbriae

• Capsules are protective polysaccharide layers that enhance microbial survival and biofilm formation.
• Flagella are whip-like appendages for motility.
• Fimbriae are hair-like appendages that aid in attachment to surfaces.

Biofilms

• Biofilms are well-organized communities of microbes encased in a self-produced extracellular matrix.
• Biofilms can cause problems in industrial processing equipment.

Bacterial Shapes and Arrangements

• Common bacterial shapes include coccus (spherical), bacillus (rod-shaped), spiral.
• Bacterial arrangements can include diplococci, streptococci, staphylococci, tetrads, and sarcinae.

Bacterial Structures: DNA Chromosome and Plasmids

• Bacterial DNA chromosome is single, circular, and supercoiled.
• Plasmids are extrachromosomal circular DNA molecules.

Bacterial Structures: Cytoplasmic Structures:

• Cytoplasmic membrane is a lipid bilayer that encloses the cytoplasm. Other cytoplasmic structures are ribosomes, involved in protein synthesis, an important location for various key cellular activities.