Bacterial Function: Motility and Resistance

Bacterial Function: Motility, Virulence Factors, and Antibiotic Resistance

• Bacteria have a remarkable ability to adapt and thrive in various ecological niches.
• This study focuses on key bacterial features and functions enabling adaptation.
• Learning objectives include describing bacterial movement, explaining virulence factors, and understanding antibiotic resistance mechanisms.

Bacterial Motility: Flagella

• Flagella are long, protein-based filaments.
• Energy is required to maintain flagella.
• Flagella enable bacteria to move in both liquids and on surfaces.
• Various flagella arrangements exist in bacteria.

Bacterial Motility: Random Walk

• Bacteria can exhibit random movement patterns.
• Reversible flagella rotate counter-clockwise (CCW) or clockwise (CW).
• Unidirectional flagella exhibit CW rotation for cell reorientation.
• Peritrichous bacteria have flagella distributed over the entire cell surface. Flagella bundle and rotate in unison for forward movement, and rotate independently for tumbling.

Bacterial Motility: Chemotaxis

• Chemotaxis is movement toward or away from a chemical signal.
• Attractants are chemicals bacteria move toward.
• Repellents are chemicals bacteria move away from.
• Phototaxis is movement toward or away from light.
• Bacteria use chemotaxis to find food sources and optimal environments

Bacterial Motility: Chemotaxis in Peritrichously Flagellated Bacteria

• Random movement occurs when no attractant is present.
• Directed movement occurs when an attractant is present, and increases the duration of the cell movement (run).

Biofilms

• Biofilms are communities of bacteria on a surface.
• A biofilm protects bacteria from death and biocides.
• Biofilms are a cause of infection in medical devices.

Quorum Sensing

• Quorum sensing is the ability of some bacterial species to sense the density of bacteria in their local area and adjust their behavior appropriately.
• Bacteria communicate via signaling molecules.
• Quorum sensing can occur between the same or different bacterial species, based on the density of signaling molecules in the local area.

Microbes and the Human Body

• The human body contains 10 times more bacteria than human cells.
• There are 10 times more viruses than bacteria in the human body, mostly in the gut.
• Most bacteria are commensals (part of the normal flora).
• Some bacteria are opportunistic pathogens, meaning they cause harm only in specific circumstances or locations.

Pathogens

• Bacteria (and other microbes) that can cause disease are called pathogens.
• Virulence is a pathogen's disease-causing potential.
• Virulence factors are bacterial traits enabling pathogenicity.

Virulence Factors: Adhesion

• Adhesion is a virulence factor allowing bacteria to attach to surfaces.
• Some bacteria adhere to surfaces via capsules and pili.

Virulence Factors: Toxins

• Toxins are molecules secreted by microorganisms that inhibit host cells, or kill host cells.
• Endotoxins are released during bacterial cell division or lysis (rupturing), and affect their surroundings.
• Exotoxins have a wider range of impact, including cells in locations other than microbial sites of infection. Exotoxins are secreted by the bacteria.

Endotoxins

• Endotoxins are lipopolysaccharides (LPS) and lipoteichoic acid which are components of the bacterial cell wall.
• Released during bacterial cell division or lysis, they cause harmful effects.

Exotoxins Example

• Exotoxins, such as hemolysins, destroy red blood cells.
• Different hemolysins cause varying levels of blood cell damage/ destruction in cultures.

AB Exotoxins Example

• Botulinum and tetanus toxins are AB exotoxins.
• AB toxins include a binding domain and a catalytic domain. The binding domain attaches the toxin to a target, while the catalytic domain carries out the toxin's damaging effects.

Antiobiotic Resistance

• Intrinsic resistance is the ability of some bacteria to resist certain antibiotics through chromosomal DNA. This involves mechanisms such as lacking the target for the antibiotic or actively pumping the antibiotic out of the cell. Such resistance is often only effective against gram-positive bacteria.
• Acquired resistance is shown through mutations or acquiring plasmids from other bacteria, which lead to high antibiotic resistance.

Horizontal Gene Transfer

• Horizontal gene transfer is the method by which antibiotic resistance genes can be spread among different bacteria. This is achieved through transduction (phage), transformation (DNA), or conjugation (physical contact).