Microbiology: Antibiotics and Antimicrobial Agents

This flashcard set covers the mechanisms of action, classes, resistance factors, and sensitivity testing for antibiotics and antimicrobial agents as presented in the BIOL2368 Microbiology lecture notes.

Antibiotics

Derived from 'anti bios' meaning 'anti life'; these are naturally occurring or man-made (synthetic) agents that kill or inhibit the growth of microorganisms.

Bactericidal

Doses of antibiotics or agents that function by killing microorganisms.

Bacteriostatic

Antimicrobial agents that inhibit or stop the growth of microorganisms rather than killing them.

Narrow spectrum

Antimicrobial activity that is effective against a specific or limited range of microorganisms.

Broad spectrum

Antimicrobial activity that covers a wide range of microorganisms, though it may have less efficacy.

Penicillium notatum

The fungus identified by Alexander Fleming that secretes a compound (penicillin) capable of killing the bacteria Staphylococcus aureus.

Beta-lactams

A large class of antibiotics, including penicillins, cephalosporins, carbapenems, and monobactams, that work by inhibiting bacterial cell wall synthesis.

Beta-lactamases

Enzymes produced by some bacteria, particularly Gram negatives, that split open the beta-lactam ring of antibiotics to render them ineffective.

NAM and NAG

$N-acetylmuramic acid$ and $N-acetylglucosamine$; these are the components of the peptidoglycan layers in bacteria whose crosslinking is interrupted by cell wall inhibitors.

Augmentin

A generic antibiotic that combines amoxicillin with the beta-lactamase inhibitor clavulanic acid.

Carbapenems

Beta-lactam cell wall inhibitors where the carbon atom in the nucleus is switched for a sulfur atom; they are extremely broad spectrum and resistant to beta-lactamases.

Cephalosporins

Antibiotics structurally similar to penicillins but with slight changes to their beta-lactam ring; they are categorized into five generations based on their primary targets.

Bacitracin

A polypeptide antibiotic derived from Bacillus that inhibits the linear strands of peptidoglycan before the crosslinking process; it is typically used topically.

Isoniazid

An antimycobacterial antibiotic used against Gram positives with mycolic acid; it inhibits the incorporation of mycolic acid into the bacterial cell wall.

Penicillin binding proteins

Proteins in the bacterial chromosome that cross-link NAM-NAM chains; mutations in these can lead to resistance by decreasing their affinity for penicillin.

Chloramphenicol

An antibiotic that binds to the $50S$ portion of the ribosome and inhibits the formation of peptide bonds; it is small and diffuses into tissues but can suppress bone marrow formation.

Aminoglycosides

Antibiotics like streptomycin that alter the shape of the $30S$ ribosomal subunit, causing the mRNA code to be misread and interfering with the start of protein synthesis.

Tetracyclines

Agents that interfere with the attachment of tRNA to the mRNA-ribosome complex, preventing translation; effective against rickettsia and chlamydias.

Macrolides

Antibiotics containing a macrocyclic ring, such as erythromycin, which are effective in Gram positives and typically function as bacteriostatic agents.

Fluoroquinolones

Bactericidal agents that inhibit DNA synthesis; they target DNA gyrase in Gram negative bacteria and topoisomerase IV in Gram positive bacteria.

Rifampins

Antibiotics that inhibit mRNA synthesis, particularly useful for treating tuberculosis and leprosy due to their ability to access deep tissue in tubercules.

Daptomycin

A lipopolypeptide that attacks the cell membrane of Gram positive bacteria, leading to a dysfunctional membrane and stopping the synthesis of DNA, RNA, and proteins.

Antimetabolite

A chemical that competes with the actual substrate for an enzymatic process, such as sulfonamides and trimethoprim replacing PABA ($para-aminobenzoic acid$).

Ergosterol

The chemical found in fungal plasma membranes that is targeted by anti-sterol antifungal agents, whereas humans possess cholesterol.

Interferons

A class of cytokines produced by human cells in response to viral infection that inhibit viral multiplication; alpha-interferon is a common drug of choice.

Neuraminidase

An enzyme that assists influenza virus in releasing from host cells; it is the target of antiviral drugs like Relenza and Tamiflu.

Metronidazole (Flagyl)

A universal treatment covering both protozoa and obligate anaerobic bacteria, commonly used for conditions like vaginitis.

Disk diffusion method (Kirby-Bauer test)

A sensitivity test where disks containing known concentrations of an agent are placed on a lawn culture; effectiveness is measured by the diameter of the zone of inhibition.

Minimal Inhibitory Concentration (MIC)

The lowest dose of an antimicrobial reagent that is effective against a pathogen, often determined using an E (Epsilometer) test strip.

Minimal Bactericidal Concentration (MBC)

The specific concentration of an antibiotic required to kill bacteria, determined using the broth dilution test.