Medical Bacteriology EXAM ONE (STUDY GUIDE + LECTURE MATERIAL) WEEK ONE

Flagella

Ropelike propeller for motility

rigid, hollow cylinder made up of flagellin

Mucosal Penetration: Enables physical movement through viscous mucus layers, inital attachemnet to host surfaces; Immune Recognition (TLR5 Activation):driving pro-inflammatory cytokine signaling

Swimming V. Tumble of Flagella

S: CCW; The flagella bundle together tightly and travels in straight line

T: CW; The flagella bundle flies apart; randomly spin in place to reorient itself.

33ft per second

Pilus

Hair-like appendages found on the surface of many bacteria, shorter and thinner than flagella.

attachment to host cells or surfaces (fimbriae) and for genetic transfer between bacterial cells (sex pilus)

Tissue Adhesion & Tropism; Biofilm Initiation; Plasmid Transfer:

Capsule

thick polysaccharide (or occasionally protein) layer located outside the cell wall.

Protects the bacterium from phagocytosis by host immune cells, prevents desiccation, and aids in surface adherence.

Antiphagocytic Shield; MAC Inhibition: blocking complement-mediated lysis

Lipopolysaccharide

A major component of the outer membrane of Gram-negative bacteria, also known as endotoxin.

of Lipid A (toxic component), Core polysaccharide, and O-antigen. It provides structural integrity and triggers a strong inflammatory response in the host.

Complement Evasion & Antigenic Variation: Long, variable O-antigen chains physically block complement access to the membrane and alter surface antigens

Peptidoglycan

polymer mesh network made of repeating disaccharides (NAG and NAM) cross-linked by short amino acid chains.

Forms the bacterial cell wall, giving the cell structural strength, maintaining its shape, and preventing osmotic lysis.

Pyrogenicity: Works synergistically with other PAMPs to induce fever and Pro-inflammatory Signaling:

virluence factor: use special enzymes (autolysins) to trim their outer wall layers. This hides the inflammatory peptidoglycan molecules from the host's detection proteins,

Gram Stain

Gram-positive bacteria stain purple/violet due to a thick peptidoglycan layer that retains crystal violet. Gram-negative bacteria stain pink/red due to a thin peptidoglycan layer and an outer membrane that lets the primary stain wash out.

Capsule Stain

A negative staining technique used to detect the presence of a bacterial capsule.

Function: Because capsules repel most stains, the background and the cell body are stained crystal violet/copper sulfate, leaving the capsule appearing as a clear halo around the cell.

SPONCH

Sulfur, Phosphorus, Oxygen, Nitrogen, Carbon, and Hydrogen. Bacteria require these macronutrients in large quantities to synthesize cellular components.

Nutritional Immunity

host defense mechanism that

limits pathogen access to critical nutrients, including iron,

zinc, vitamins, lipids, and amino acids, to repress

microbial proliferation and virulence

Nutritional Immunity Host

(a) metal sequestration

(c) nutrient competition (alternate nutrient sources)

(e) hormonal regulation

(g) siderophore interference

Siderophores

• Iron-concentrating compounds

secreted by bacteria

• Higher iron-binding activity than

transferrin

Pathogenicity Islands:

horizontally transferred loci carrying

virulence genes, GC content varies from rest of genome,

often flanked by mobile elements

large blocks of genes in bacteria that cause disease and are usually missing in harmless strains

SPI1

SPI2

SPI1: Regulatory proteins, secretion systems, Iron uptake

SPI2: Tetrathionate reductase

Ferritin

• Definition: An intracellular protein found in host cells that stores iron.

• Function: It keeps iron in a soluble, non-toxic form inside host tissues and keeps it inaccessible to invading microbes

Lactoferrin

• Definition: An iron-binding glycoprotein secreted by host mucosal epithelial cells and neutrophils.

• Function: Found in bodily fluids (tears, saliva, milk, mucus), it binds free iron with high affinity to inhibit microbial growth at mucosal surfaces

Transferrin

• Definition: A glycoprotein found in host blood plasma.

Function: Binds and transports iron safely through the circulatory system, keeping serum free-iron concentrations extremely low.

Enriched Media

• Definition: Complex media supplemented with highly nutritious materials (like blood, serum, or yeast extract).

• Function: Supports the growth of fastidious organisms (microbes with complex or demanding nutritional requirements).

Differential Media

• Definition: Growth media containing specific indicators (like dyes or pH indicators) that cause visible changes based on microbial metabolic activities.

• Function: Allows closely related organisms to be distinguished from one another on the same plate based on colony appearance or media color changes (e.g., MacConkey agar for lactose fermentation).

Selective Media

• Definition: Growth media formulated with specific chemical agents (like antibiotics, salts, or dyes) that inhibit the growth of certain microbes while allowing others to grow.

• Function: Used to isolate specific groups of bacteria from mixed samples (e.g., Mannitol Salt Agar selects for halotolerant Staphylococci).

---

How do different cell envelope structures result in different colors in the Gram stain? Gram-Positive Cell Envelope:

Thick peptidoglycan layer (20–80 nm) infused with teichoic and lipoteichoic acids. Lacks an outer membrane.

Decolorizer (alcohol) dehydrates the thick peptidoglycan layer, shrinking its pores and trapping the large Crystal Violet-Iodine (CV-I) complex inside so Cells remain Purple.

How do different cell envelope structures result in different colors in the Gram stain? Gram-negative Cell Envelope:

Thin peptidoglycan layer (2–7 nm) in the periplasmic space, surrounded by an asymmetric outer membrane containing Lipopolysaccharide (LPS).

Decolorizer (alcohol) dissolves the outer lipid membrane and extracts the CV-I complex through the thin peptidoglycan layer. Cells absorb the safranin counterstain so the Cells turn Pink/Red.

Colony Morphology: Form (Overall Shape)

Circular, Irregular, Filamentous, Rhizoid (root-like branching), Punctiform (tiny dots).

• Coccus: Spherical / round

• Bacillus: Rod-shaped

• Coccobacillus: Oval (intermediate)

• Vibrio: Comma-shaped rod

• Spirillum / Spirochete: Spiral / helical

Arrangement Prefix: Strepto- vs. Staphylo

• Strepto-: Cells attached in linear chains (division along 1 axis).

• Staphylo-: Cells in irregular, grape-like clusters (division along multiple variable planes).

Cell Arrangements: Diplo-, Tetrad, Sarcina

• diplo-: Pairs of cells.

• Tetrad: Square packet of 4 cells (division along 2 perpendicular planes).

• Sarcina: Cubical packet of 8 or 16 cells (division along 3 regular planes).

Bacterial Iron Acquisition Mechanisms

Front: Bacterial Siderophores

High-affinity iron-chelating molecules secreted by bacteria to strip ferric iron ($Fe^{3+}$) from host proteins like transferrin. Re-imported via TonB-dependent receptors.

Stealth Siderophores

Chemically modified siderophores (e.g., glycosylated salmochelin) synthesized by pathogens to evade binding by host Siderocalin.

Hemolysins & Hemophore Systems

bacterial toxins (hemolysins) lyse RBCs to release hemoglobin; secreted carrier proteins (hemophores, e.g., HasA) capture free heme and deliver it to surface receptors.

what can you draw from this graph

The graph demonstrates that RscS positively activates transcription of the syp locus (sypD and sypN), with the mutant alleles rscS1 and rscS2 acting as gain-of-function variants that drive substantially higher expression than wild-type rscS.