Microbiology: Bacterial Cell Walls, Toxins, and Antibiotic Mechanisms

Which organisms have peptidoglycan in their cell walls?

Bacteria

Which bacteria have lipopolysaccharide in their cell wall?

Gram-negative bacteria

What is another name for bacterial lipopolysaccharide?

Endotoxin

Where is LPS located in Gram-negative bacteria?

Outer leaflet of the outer membrane

What does the lipid A portion of LPS cause?

Fever, shock, and DIC via cytokine release

Which antibiotics target peptidoglycan synthesis?

Beta-lactams (penicillins, cephalosporins) and vancomycin

Which antibiotics target the outer membrane of Gram-negative bacteria?

Polymyxins

What color do Gram-positive bacteria stain?

Purple

What color do Gram-negative bacteria stain?

Pink or red

What structure do Gram-positive bacteria lack?

Outer membrane

What is the function of bacterial capsules?

Prevent phagocytosis and help adhesion

What are plasmids?

Extra-chromosomal DNA carrying resistance or toxin genes

What ribosome type do bacteria have?

70S (50S + 30S)

How do bacteria reproduce?

By binary fission

Which bacterial appendage mediates conjugation?

Pilus (sex pilus)

What is conjugation?

Transfer of plasmid DNA between two bacteria via pilus

What is transformation?

Uptake of free DNA from the environment

What is transduction?

DNA transfer by bacteriophage

Which bacteria grow only at the top of broth?

Obligate aerobes

Which grow only at the bottom?

Obligate anaerobes

Which grow throughout but mostly near the top?

Facultative anaerobes

Which grow evenly throughout the medium?

Aerotolerant anaerobes

Which grow in a narrow band below the surface?

Microaerophiles

Which antibiotics inhibit DNA replication?

Fluoroquinolones

Which drug inhibits bacterial RNA polymerase?

Rifampin

Which antibiotics inhibit the 30S subunit?

Aminoglycosides and tetracyclines

Which antibiotics inhibit the 50S subunit?

Macrolides, chloramphenicol, clindamycin

What do sulfonamides and trimethoprim inhibit?

Folate synthesis

What are the major mechanisms of antibiotic resistance?

Enzyme inactivation, efflux pumps, target modification, reduced permeability

What does beta-lactamase do?

Breaks down beta-lactam antibiotics

What is the infectious dose (ID50)?

Minimum number of pathogens to cause infection

What is the lethal dose (LD50)?

Number needed to kill 50% of hosts

How is virulence related to ID50?

Lower ID50 = higher virulence

List four bacterial virulence factors.

Adherence, invasion, evasion, toxin production

What are exotoxins?

Secreted proteins causing specific tissue effects

What are endotoxins?

LPS fragments from Gram-negative cell walls

Which is more antigenic: exotoxin or endotoxin?

Exotoxin

Which bacteria produce exotoxins?

Both Gram-positive and Gram-negative

Which bacteria produce endotoxins?

Gram-negative only

Name a toxin that blocks acetylcholine release.

Botulinum toxin

Name a toxin that blocks GABA release.

Tetanus toxin

What does diphtheria toxin do?

Inhibits EF-2 and protein synthesis

What does cholera toxin do?

Increases cAMP causing watery diarrhea

What does coagulase do?

Forms fibrin clots around bacteria

What does hyaluronidase do?

Degrades hyaluronic acid in tissues

What does collagenase do?

Degrades collagen for invasion

What is a local infection?

Infection confined to a single region

What is a systemic infection?

Infection spreading through multiple systems

What is a focal infection?

Infection that seeds other sites in the body

What is a nosocomial infection?

Infection acquired in a healthcare facility

What is a zoonotic infection?

Disease transmitted between animals and humans