Microbio Exam 4

Mutualism (obligatory)

A relationship where both organisms benefit and depend on each other for survival

Example of mutualism

Buchnera aphidicola and aphids

What does aphid provide Buchnera?

Amino acids Buchnera cannot synthesize

What does Buchnera provide aphid?

Tryptophan (Trp)

Cooperation

A non-obligatory relationship where both organisms benefit

Commensalism

One organism benefits, the other is unaffected

Example of commensalism

Staphylococcus epidermidis on skin

Predation

One organism kills and consumes another

Bdellovibrio mechanism

Enters periplasm and consumes cytoplasm of Gram-negative bacteria

Parasitism

One organism benefits, host is harmed

Amensalism

One organism harmed, other unaffected

Example of amensalism

Streptomyces producing antibiotics

Competition

Organisms compete for same resources

Attenuation

Regulation causing premature termination of transcription

When transcription continues Region 2 pairs with

Region 3

When transcription terminates Region 3 pairs with

Region 4

Sigma factor cascade

F → E → G → K activation sequence

Spore cortex composition

NAG, NAM, muramic delta-lactam

Stage 1 germination

Ca²⁺ DPA release, partial hydration

Stage 2 germination

Cortex hydrolysis, further hydration

Outgrowth

Metabolism resumes, cell emerges

What controls attenuation?

Translation of leader peptide

C. difficile characteristics

Gram+, spore-forming anaerobe

C. difficile cause of infection

Antibiotic disruption of microbiota

C. difficile pathogenesis

Spores germinate → toxins → inflammation & diarrhea

C. difficile toxins

TcdA and TcdB

C. difficile treatment

Vancomycin, fidaxomicin, fecal transplant

Innate immunity

Nonspecific, no memory, first line defense

Adaptive immunity

Specific, has memory

Antimicrobial peptides

Cationic peptides that disrupt membranes

Defensins

Disulfide-rich peptides in immune cells

Cathelicidin (LL-37)

Broad-spectrum antimicrobial peptide

Lysozyme

Breaks peptidoglycan (muramidase)

Lactoferrin

Sequesters iron to inhibit growth

Pattern Recognition Receptors (PRRs) Recognize

PAMPs on pathogens

TLRs Recognize

extracellular PAMPs

NOD-like receptors (NLRs) Recognize

intracellular PAMPs

Complement system

Cascade leading to opsonization, inflammation, MAC formation

Opsonization

Coating pathogen to enhance phagocytosis

Phagocytosis

Process of engulfing and destroying microbes

Phagosome + lysosome

Fuse to destroy pathogen

Neutrophils

Phagocytic, form NETs

Macrophages

Phagocytic, antigen presentation

Dendritic cells

Antigen presentation to T cells

Granulocytes

Contain antimicrobial granules

NETs

Extracellular traps that kill microbes

Adaptive immunity characteristics

Specificity, diversity, memory, self/non-self recognition

Antigen

Substance that triggers immune response

Epitope

Specific region recognized by antibody

Active immunity

Body produces immune response

Passive immunity

Receives preformed antibodies

MHC Class I Found on

all nucleated cells, presents endogenous antigens to CD8+ T cells

MHC Class II Found on

APCs, presents exogenous antigens to CD4+ T cells

T helper cells (CD4+)

Activate immune responses

Cytotoxic T cells (CD8+)

Kill infected cells

Th1

Promotes inflammation

Th2

Stimulates antibody production

Th17

Responds to bacteria in tissues

Treg

Suppresses immune response

B cells

Produce antibodies

B cell receptor

Membrane-bound antibody

Antibody classes

IgM, IgG, IgA, IgE, IgD

First antibody produced

IgM

V(D)J recombination

Combines gene segments for diversity

Somatic hypermutation

High mutation rate in antibody genes

Class switching

Changes antibody type (IgM → IgG)

Endemic

Constant low-level disease presence

Incidence

New cases

Prevalence

Total cases

Outbreak

Sudden increase

Epidemic

Large outbreak

Pandemic

Global spread

Index case

First identified case

Morbidity rate

New cases / population

Mortality rate

Deaths / infected population

Herd immunity

Population protection due to widespread immunity

Antigenic drift

Small changes in pathogen

Antigenic shift

Major changes

Direct contact

Physical transfer

Indirect contact

Surface transmission

Droplet

Respiratory spread

Inactivated vaccine

Killed pathogen

Attenuated vaccine

Weakened pathogen

Subunit vaccine

Specific antigen components

DNA vaccine

Host produces antigen

mRNA vaccine

Host translates RNA into antigen

Adjuvant

Enhances immune response

Selective toxicity

Kills pathogen, not host

Therapeutic index

Toxic dose / therapeutic dose

MIC

Lowest concentration preventing growth

MLC

Lowest concentration killing bacteria

β-lactams

Inhibit cell wall synthesis

Resistance mechanism to B-lactams

β-lactamase enzymes

Clavulanic acid

Inhibits β-lactamase

Vancomycin Binds

D-Ala-D-Ala to block cell wall synthesis

Vancomycin resistance

D-Ala → D-Lactate change

Aminoglycosides

Bind 30S subunit

Tetracyclines

Bind 30S, block tRNA

Macrolides

Bind 50S subunit

Sulfonamides

Block folic acid synthesis (PABA analog)