Bacteria Classification and Morphology

Bacteria Classification

• Bacteria are unicellular, microscopic, free-living microorganisms that can perform essential life functions.
• They have both DNA and RNA, lack chlorophyll, and can be found in various environments, including water, food, soil, and air.
• Bacteria can survive in extreme conditions, such as pH, oxygen, temperature, and atmospheric temperature.

Morphology of Bacteria

• Bacteria have a prokaryotic cell structure, meaning they lack a nucleus and organelles bound in membranes.
• They have a single circular chromosome, no histones associated with DNA, and a cell wall made of peptidoglycan.
• They have smaller ribosomes and divide by binary fission.

Bacterial Cell Structure

• The nucleus is also called the nucleoid, nuclear body, or nuclear region.
• DNA is a single circular chromosome that is coiled up and floats in the cytoplasm.
• The cytoplasm is a watery, soft gel that contains organic and inorganic solutes, vitamins, coenzymes, ribosomes, and a network of fine fibrils.
• Plasmids are small, circular, double-stranded DNA molecules that can replicate independently.

Gram Staining Technique

• Gram staining was developed by Hans Christian Gram in 1884.
• It differentiates Gram-positive bacteria, which remain colored after staining, from Gram-negative bacteria, which do not retain the dye.
• Gram-positive bacteria are more susceptible to antibiotics due to the lack of an outer membrane.
• Gram-negative bacteria contain an outer membrane, making them less susceptible to antibiotics.

Gram-Positive Bacteria

• Examples of Gram-positive bacteria include Bacillus, Clostridia, and Actinomycetes.

Gram-Negative Bacteria

• Examples of Gram-negative bacteria include Neisseria gonorrhoeae, Neisseria meningitidis, Enteric bacteria, Pseudomonas, and Bacteroides fragilis.
• Gram-negative bacteria can be further divided into fastidious GNRs, anaerobic GNRs, and oxidase-positive or -negative GNRs.

Bacterial Cell Envelope

• The cell envelope refers to all the layers from the cell membrane outward, including the cell wall, periplasmic space, outer membrane, and capsule.
• All free-living bacteria have a cell wall, and the periplasmic space and outer membrane are found in Gram-negative bacteria.

Binary Fission

• Binary fission is a process of cell division where a single DNA molecule replicates, attaches to different parts of the cell membrane, and then divides into two identical cells.

Shapes of Bacteria

• Bacteria can have various shapes, including cocci (spherical or oval), bacilli (rod-shaped), vibros (comma-shaped), spirilla (rigid spiral forms), and spirochetes (flexible spiral forms).

Spore Germination

• Spore germination is the process by which a dormant spore becomes active and forms a vegetative cell.
• Bacteria with spores include Bacillus and Clostridia.

Capsule

• The capsule is a layer of extracellular polymeric substances surrounding the bacterial cell.
• It can protect the cell from desiccation, anti-bacterial agents, and phages, and maintain cell viscosity.
• The capsule can be stained using negative staining with India ink.

Intra-Cytoplasmic Inclusions

• Intra-cytoplasmic inclusions are rough granules that can be made up of glycogen or starch.
• They can be stained with polychrome methylene blue or toluidine blue.