Bacterial Anatomy Shapes and Sizes

Bacterial Shapes and Size

• Bacteria exhibit three main shapes: cocci (spherical), bacilli (rod-shaped), and spirilla (spiral).
• Most bacteria range in size from 0.2 to 10 micrometers in diameter, allowing them to be viewed under a microscope.

Structural Components

• The cell wall provides structural support and maintains the characteristic shape of a bacterial cell.

Cell Structure

• Bacteria that are bounded only by a cell membrane and lack a cell wall are typically categorized as Mycoplasma.

Cocci Arrangements

• Cocci can be arranged in three patterns: singles (scattered), pairs (diplococci), and clusters (staphylococci).

Escherichia coli and Diseases

• Escherichia coli is commonly associated with diseases such as urinary tract infections (UTIs) and foodborne illnesses.
• Habitats for Escherichia coli include the intestines of humans and animals, where it usually resides as part of the normal flora.

Transmission in Neonates

• In neonatal meningitis, Escherichia coli can be acquired during birth, particularly when it passes through the birth canal.

Colony Formation

• On Eosin-Methylene Blue (EMB) or MacConkey’s agar, Escherichia coli forms distinctive colonies that can appear dark and metallic green on EMB and pink on MacConkey’s agar due to lactose fermentation.

Laboratory Differentiation

• Escherichia coli can be differentiated from other lactose-positive organisms through its unique growth patterns and biochemical reactions, such as producing indole.

Characteristics of Escherichia coli

• Escherichia coli is a rod-shaped, facultative anaerobe that ferments lactose and produces gas, contributing to its classification in laboratories.
• Strains of Escherichia coli can vary, with some being pathogenic and others being harmless, highlighting the importance of identifying specific strains for diagnosis.