Lecture 3: Glycocalyx and Cell Wall

Any material found external to the cell wall; includes S-layers, capsules, exopolysaccharides (EPS), and slime

Glycocalyx

Loosely adhered polysaccharide or glycoprotein; transiently produced and important for adhesion and biofilm formation

Exopolysaccharide (EPS)/Slime

Tightly adhered protein or glycoprotein lattice

S-Layer

Thick structured layer of repeating polysaccharide units or glycoproteins at the cell surface covalently attached to the cell

Capsule

T/F: Capsule play significant roles in bacterial virulence and are used for serotyping

True

Capsules that prevent recognition by neutrophils and macrophages

Immune Evasion

Capsules block C3b deposition, reducing opsonization

Complement Resistance

Encapsulated bacteria survive longer in blood/tissue

Persistence and Dissemination

What is the essential function of the cell wall?

• mechanical protection from osmotic stress (turgor pressure)

• maintain cell shape

• prevent osmotic lysis

What does turgor result from?

Solute concentration difference between the inside and outside the cell

T/F: Molecules only found in the bacterial cell wall, such as peptidoglycan, are a common antibiotic target

True

Bacteria that have a thick peptidoglycan layer which contains teichoic and lipoteichoic acids; stain PURPLE

Gram-Positive Bacteria

Bacteria that have a thin peptidoglycan layer surrounded by an outer membrane; stain PINK

Gram-Negative Bacteria

Bacteria that have a thin layer of peptidoglycan, arabinoglycan, and mycolic acid all covalently linked

Acid-Fast Bacteria

The amount of ___ in the cell wall largely determines the gram reaction of the bacterium

peptidoglycan

Complex polymer that provides strength and rigidity to the bacterial cell wall; units are made of glycan crosslinked with peptides

Peptidoglycan

T/F: Peptidoglycan forms a 3D network surrounding the cell membrane, covalently bonded throughout by glycosidic and peptide linkages

True

Precursor to lysine that is unique to prokaryotes and required for cell wall synthesis

Diaminopimelic acid (DAP)

Gram (+/-) bacteria have a direct crosslinking between L-R3 and D-alanine while gram (+/-) bacteria have an additional peptide bridge connecting L-R3 and D-alanine

-;+

Why is it important that the amino acids in the tetrapeptide are D-form?

Most amino acids are L-form, so enzymes target L-form amino acids; this prevents the breakdown of tetrapeptides

What is found in all gram(+) bacteria and is covalently bound to peptidoglycan? It performs a role in attachment and stabilization

Teichoic Acid

What teichoic acid bound to membrane lipids is NOT covalently bound to peptidoglycan?

Lipoteichoic Acid

Waxy lipids that provide protection from dessication, hydrophobic antimicrobials, acids, and bases; they are found in the cell wall of acid-fast bacteria

Mycolic Acids

T/F: Acid-fast bacteria stain pink on a Gram stain

False; do not stain