305 week 9 bacteria

Why are bacteria important in healthcare?

Most are harmless or beneficial, but some cause disease; understanding them supports infection control.

Prokaryotes vs. eukaryotes

Prokaryotes lack a nucleus and membrane-bound organelles, have circular DNA, and are smaller; eukaryotes have a nucleus and organelles, linear DNA, and are larger.

What structures do all cells share?

Plasma membrane, cytoplasm, DNA, and ribosomes.

How is bacterial size measured?

In micrometres (µm); bacteria are much smaller than human cells and require a microscope to visualize.

Cocci

Spherical-shaped bacteria.

Bacilli

Rod-shaped bacteria.

Spirilla and spirochetes

Spiral-shaped bacteria.

Common bacterial arrangements

Cocci: pairs, chains, clusters, and tetrads. Bacilli: single rods or chains.

Binary fission

Bacterial reproduction involving DNA replication, cell elongation, and division into two genetically identical cells.

How do bacterial populations grow?

Exponentially, often with short generation times; each division can double the population.

What are the major bacterial cell structures?

Capsule, cell wall, plasma membrane, cytoplasm, ribosomes, nucleoid, flagella, and pili.

What is the bacterial cell envelope?

The protective boundary that includes the plasma membrane and cell wall; Gram-negative bacteria also have an outer membrane.

Functions of the bacterial cell envelope

Protection, shape, and selective transport.

Gram-positive bacteria

Have a thick peptidoglycan cell wall, stain purple, and lack an outer membrane.

Gram-negative bacteria

Have a thin peptidoglycan cell wall, an outer membrane, and stain pink or reddish.

What determines Gram-stain colour?

Gram-positive bacteria retain the purple stain; Gram-negative bacteria appear pink or reddish.

Capsule vs. slime layer

Both are glycocalyces involved in adherence, protection, and biofilm formation. Capsules are organized and firmly attached; slime layers are loose and easily removed.

What is the glycocalyx?

An external bacterial coating that can occur as a capsule or slime layer and supports adherence, protection, and biofilm formation.

Flagella

Long, whip-like appendages that provide movement and help bacteria respond to chemical gradients through chemotaxis.

Fimbriae

Short, hair-like projections primarily used for bacterial attachment.

Pili

Longer projections involved in attachment and DNA transfer during conjugation.

Cytoplasm

The internal material of the bacterial cell where cellular components are located.

Ribosomes

The structures responsible for protein synthesis.

Nucleoid

The region containing the bacterial chromosome; it is not enclosed by a nuclear membrane.

Endospores

Dormant, highly resistant structures that allow certain bacteria to survive unfavourable conditions.

Which bacteria produce endospores?

Bacillus and Clostridium.

Bacterial chromosome

Usually a single circular DNA molecule located in the nucleoid that contains essential genetic information.

Plasmids

Small circular DNA molecules separate from the chromosome that replicate independently.

What can plasmids carry?

Genes for antibiotic resistance, virulence factors, and metabolic advantages.

Transposons

Mobile genetic elements, or “jumping genes,” that move within DNA, rearrange genetic information, and can transfer resistance genes.

What are the three mechanisms of bacterial gene transfer?

Transformation, transduction, and conjugation.

Why is bacterial gene transfer important?

It increases genetic diversity, spreads beneficial traits, and can promote antibiotic resistance.

Transformation

The uptake of free DNA from the environment, including DNA released by dead bacteria, allowing new genetic traits to be acquired.

Transduction

The transfer of bacterial DNA between cells by bacteriophages.

Bacteriophage

A virus that infects bacteria and can transfer bacterial DNA through transduction.

Conjugation

Direct cell-to-cell DNA transfer requiring physical contact and a sex pilus; often transfers plasmids and resistance genes.

Transformation vs. transduction vs. conjugation

Transformation: uptake of free environmental DNA. Transduction: DNA transfer by bacteriophages. Conjugation: direct transfer between bacterial cells.

F plasmid

The fertility plasmid that enables bacterial conjugation.

Hfr cell

A bacterial cell in which the F plasmid is integrated into the chromosome, allowing larger segments of DNA to be transferred during conjugation.

Operons

Groups of genes controlled together to coordinate gene expression and conserve energy.

Lac operon

An example of an operon that coordinates the expression of a group of genes.

Colonization vs. infection

Colonization means microorganisms are present without tissue damage or symptoms; infection involves tissue invasion, tissue damage, and symptoms.

Example of bacterial colonization

Staphylococcus aureus in the nose or Escherichia coli in the intestine without disease.

Examples of bacterial infection

Wound infection, urinary tract infection (UTI), and pneumonia.

What are opportunistic pathogens?

Microorganisms that cause disease when host defences weaken, bacteria enter abnormal locations, or normal flora become imbalanced.

Examples of opportunistic pathogens

Escherichia coli, Staphylococcus aureus, and Candida species.

What makes a bacterium pathogenic?

The ability to cause disease through virulence factors, toxins, adhesion, invasion, and immune evasion mechanisms.

Virulence factors

Features that help bacteria cause disease, including capsules, adhesins, toxins, biofilms, extracellular enzymes, and antigenic variation.

Stages of infection

Exposure → attachment → colonization → invasion → disease.

Adhesion factors

Pili, fimbriae, glycocalyx, and surface adhesion proteins that help bacteria attach to host tissues.

How do capsules contribute to pathogenicity?

They can help bacteria adhere to surfaces and evade immune destruction.

How do biofilms contribute to bacterial survival?

They support adherence and can help bacteria avoid immune destruction.

Immune evasion strategies

Capsules, intracellular survival, biofilm formation, and antigenic variation.

Antigenic variation

Changes in bacterial antigens that can help bacteria evade recognition by the immune system.

Bacterial toxins

The two major types are exotoxins and endotoxins.

Exotoxins

Protein toxins secreted by living bacteria; they often have specific targets and potent biological effects.

Examples of exotoxins

Botulinum toxin, tetanus toxin, and cholera toxin.

Endotoxins

The lipid A component of lipopolysaccharide (LPS), found in Gram-negative bacteria and released during bacterial cell death.

Exotoxins vs. endotoxins

Exotoxins are secreted proteins with often specific, potent effects; endotoxins are lipid A components of LPS that are released during cell death and cause general inflammation.

Hyaluronidase

An extracellular enzyme that aids tissue invasion and infection.

Collagenase

An extracellular enzyme that aids tissue invasion and infection.

Coagulase

An extracellular enzyme associated with bacterial infection and tissue interactions.

Streptokinase

An extracellular enzyme that aids infection by affecting blood clots.