Unit 5: Agents That Target Invaders - Antibacterial Agents

Vocabulary practice flashcards covering antimicrobial classification, bacterial targets, penicillins, cephalosporins, and resistance mechanisms from Unit 5: Agents That Target Invaders.

Selective Toxicity

The ability of an antimicrobial agent to target specific microbial structures or cellular processes while minimizing harm or toxicity to host cells.

Empiric Antimicrobial Therapy

Initial antimicrobial treatment initiated immediately before the specific infecting organism is identified, which is subsequently adjusted or replaced once culture and susceptibility results become available.

Narrow-Spectrum Antimicrobial

An agent that acts selectively against a limited group of microorganisms (such as isoniazid against Mycobacterium tuberculosis) without disrupting normal host flora.

Extended-Spectrum Antimicrobial

An agent effective against Gram-positive bacteria and a significant number of Gram-negative organisms, exemplified by ampicillin.

Broad-Spectrum Antimicrobial

An antimicrobial agent active against a wide variety of microorganisms, such as tetracyclines, fluoroquinolones, and carbapenems.

Bacteriostatic Agents

Antimicrobial drugs that primarily inhibit bacterial replication and growth without directly killing the cells; examples include chloramphenicol, macrolides, clindamycin, sulfonamides, and tetracyclines.

Bactericidal Agents

Antimicrobial drugs that produce rapid bacterial killing under defined laboratory conditions; examples include aminoglycosides, $\beta$-lactams, vancomycin, quinolones, rifampicin, and metronidazole.

Bacterial Targets of Antimicrobial Action

Major microbial sites attacked by antibiotics, including cell wall synthesis, protein synthesis ($30\text{S}$, $50\text{S}$, and tRNA), nucleic acid synthesis (DNA gyrase, RNA elongation, and RNA polymerase), metabolic pathways (folic acid), and cell membrane integrity.

Gram-Positive Cell Wall

A bacterial envelope characterized by a thick peptidoglycan layer containing teichoic acid and lipoteichoic acid, making it highly susceptible to cell wall synthesis inhibitors.

$\beta$-Lactam Ring

A four-membered cyclic amide ring essential for the antibacterial activity of penicillins, cephalosporins, monobactams, and carbapenems.

Mechanism of Action of $\beta$-Lactam Antibiotics

Structural analogues of the natural D-Ala-D-Ala substrate that covalently bind to penicillin-binding proteins (PBPs), inhibiting the transpeptidation cross-linking of peptidoglycan and triggering osmotic lysis or autolysin activation.

6-Aminopenicillanic Acid

The core nucleus of penicillins, composed of a fused four-membered $\beta$-lactam ring and a five-membered sulfur-containing thiazolidine ring.

Penicillin G (Benzylpenicillin)

A natural, acid-labile penicillin administered intravenously or intramuscularly; it is the drug of choice for syphilis (Treponema pallidum) and susceptible streptococcal infections.

Probenecid

A compound that competitively inhibits the renal tubular secretion of penicillin G, thereby elevating penicillin serum concentrations and prolonging its half-life.

Benzathine Penicillin G

A long-acting, repository intramuscular depot formulation of penicillin G used to treat syphilis, streptococcal pharyngitis, and to prevent recurrent streptococcal infections.

Penicillin V (Phenoxymethylpenicillin)

An acid-stable oral natural penicillin used to treat mild-to-moderate streptococcal infections when oral therapy is preferred.

Antistaphylococcal Penicillins

Semisynthetic penicillins (nafcillin, oxacillin, dicloxacillin, methicillin) that resist staphylococcal $\beta$-lactamases; active against MSSA but inactive against MRSA, MRSE, enterococci, and Gram-negative organisms.

Nafcillin

An intravenous antistaphylococcal penicillin primarily cleared by biliary excretion (making it safe in renal failure) that is associated with adverse reactions including neutropenia and interstitial nephritis.

Methicillin

A prototype penicillinase-resistant penicillin that was withdrawn from clinical use due to nephrotoxicity presenting as interstitial nephritis.

Aminopenicillins

Extended-spectrum penicillins (ampicillin and amoxicillin) active against Gram-positive bacteria and extended to Gram-negative bacilli, yet still susceptible to degradation by $\beta$-lactamases.

Amoxicillin

An oral aminopenicillin with superior gastrointestinal absorption compared to ampicillin; widely used for otitis media, sinusitis, dental endocarditis prophylaxis, and in multi-drug regimens for Helicobacter pylori eradication.

Ampicillin

An aminopenicillin given parenterally or orally that is used in the treatment of Listeria monocytogenes meningitis, enterococcal endocarditis, and shigellosis.

Antipseudomonal Penicillins

Classes of penicillins, including carboxypenicillins (ticarcillin, carbenicillin) and ureidopenicillins (piperacillin, mezlocillin), formulated to combat Gram-negative bacilli such as Pseudomonas aeruginosa, Enterobacter, and Klebsiella species.

$\beta$-Lactamase Inhibitors

Molecules containing a $\beta$-lactam ring (clavulanic acid, sulbactam, tazobactam) with little intrinsic antibacterial activity that bind and irreversibly inactivate $\beta$-lactamase enzymes, preventing antibiotic hydrolysis.

Co-amoxiclav (Augmentin)

A fixed-dose antibacterial combination of amoxicillin and clavulanic acid that broadens antimicrobial spectrum against $\beta$-lactamase-producing pathogens.

Cephem Nucleus

The 7-aminocephalosporanic acid core of cephalosporins, composed of a four-membered $\beta$-lactam ring fused to a six-membered dihydrothiazine ring.

First-Generation Cephalosporins

Cephalosporins (e.g., cefazolin, cephalexin, cefadroxil) acting as penicillin G substitutes with excellent Gram-positive coverage; they do not cross the blood-brain barrier.

Cefazolin

A first-generation parenteral cephalosporin and the drug of choice for surgical prophylaxis due to its tissue penetration and half-life; it lacks central nervous system penetration.

Cephamycins

A subset of second-generation cephalosporins (cefoxitin, cefotetan, cefmetazole) active against mixed anaerobic intra-abdominal infections, such as peritonitis and diverticulitis.

Cefuroxime

A second-generation cephalosporin used to treat community-acquired pneumonia, otitis media, and sinusitis; it is the only second-generation agent capable of crossing the blood-brain barrier.

Third-Generation Cephalosporins

Cephalosporins (ceftriaxone, cefotaxime, ceftazidime) with expanded Gram-negative activity and high CSF penetration, making them premier choices for bacterial meningitis.

Ceftriaxone

A long-acting third-generation cephalosporin cleared predominantly via biliary excretion that achieves therapeutic CSF levels for treating bacterial meningitis and gonorrhea.

Antipseudomonal Third-Generation Cephalosporins

Ceftazidime and cefoperazone, the two third-generation cephalosporins with targeted antibacterial activity against Pseudomonas aeruginosa.

Cefepime

A fourth-generation cephalosporin administered intravenously or intramuscularly with a broad spectrum against Gram-positive cocci, Enterobacter, and Pseudomonas aeruginosa, featuring good blood-brain barrier penetration and renal clearance.

Ceftaroline Fosamil

A fifth-generation cephalosporin prodrug whose active form binds PBP 2a, conferring bactericidal activity against methicillin-resistant Staphylococcus aureus (MRSA) in complicated skin, soft tissue, and pulmonary infections.

PBP 2a

An altered penicillin-binding protein with low affinity for standard $\beta$-lactams that mediates methicillin resistance in MRSA and is targeted by ceftaroline.