List the classification of antibiotic and bacteria on which they act
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Classification of Antibiotics and Bacteria They Act On
Overview
Antibiotics can be classified along several dimensions:
- Mechanism of action (most common)
- Spectrum of activity (narrow vs. broad)
- Chemical structure / pharmacophore
- Bactericidal vs. bacteriostatic effect
I. Classification by Mechanism of Action
A. Cell Wall Synthesis Inhibitors
1. β-Lactams (Bactericidal)
All β-lactams inhibit penicillin-binding proteins (PBPs), blocking peptidoglycan cross-linking.
| Subclass | Examples | Spectrum / Target Bacteria |
|---|---|---|
| Natural Penicillins | Penicillin G, Penicillin V | Gram-positive cocci (Streptococcus, Enterococcus), some Gram-negative cocci (Neisseria) |
| Penicillinase-resistant penicillins | Nafcillin, Oxacillin, Dicloxacillin | MSSA (Staphylococcus aureus), Staphylococcus epidermidis |
| Aminopenicillins (Broad-spectrum) | Ampicillin, Amoxicillin (± clavulanate/sulbactam) | Gram-positives + H. influenzae, E. coli, Proteus mirabilis, Listeria |
| Extended-spectrum (Antipseudomonal) | Piperacillin (± tazobactam) | Pseudomonas aeruginosa, Klebsiella, E. coli, Gram-positives, anaerobes (B. fragilis) |
2. Cephalosporins (Bactericidal — broader with each generation)
| Generation | Examples | Spectrum |
|---|---|---|
| 1st | Cephalexin, Cefazolin | Primarily Gram-positive (Strep, MSSA); some Gram-negative (E. coli, Klebsiella, Proteus) |
| 2nd | Cefuroxime, Cefoxitin | Expanded Gram-negative (H. influenzae, Moraxella); anaerobes (cefoxitin covers B. fragilis) |
| 3rd | Ceftriaxone, Cefotaxime, Ceftazidime | Broad Gram-negative (Enterobacteriaceae, Neisseria, H. influenzae); ceftazidime covers Pseudomonas |
| 4th | Cefepime | Both Gram-positive & broad Gram-negative including Pseudomonas |
| 5th | Ceftaroline | Gram-positives including MRSA; some Gram-negatives (not Pseudomonas) |
| Anti-MDR (5th) | Ceftolozane/tazobactam, Cefiderocol | Highly drug-resistant Gram-negative rods, including Pseudomonas |
3. Carbapenems (Broadest-spectrum β-lactams, Bactericidal)
| Drug | Spectrum |
|---|---|
| Imipenem/cilastatin, Meropenem, Doripenem | Broadest: Gram-positive, Gram-negative (including ESBL producers), anaerobes (B. fragilis) |
| Ertapenem | Similar but not active against Pseudomonas |
4. Monobactams
| Drug | Spectrum |
|---|---|
| Aztreonam | Exclusively aerobic/facultative Gram-negative bacteria (Enterobacteriaceae, Pseudomonas, Haemophilus, Neisseria); no activity against Gram-positives or anaerobes |
5. β-Lactamase Inhibitors (used in combination)
| Drug | Combined with |
|---|---|
| Clavulanate, Sulbactam, Tazobactam | Amoxicillin, Ampicillin, Piperacillin — restores activity against β-lactamase producers |
| Avibactam, Vaborbactam, Relebactam | Newer; cover wider range including KPC and OXA β-lactamases |
6. Glycopeptides (Bactericidal)
| Drug | Spectrum |
|---|---|
| Vancomycin, Teicoplanin | Gram-positive only: MRSA, MRSE, Enterococcus, C. difficile (oral) |
7. Bacitracin, Fosfomycin
| Drug | Spectrum |
|---|---|
| Bacitracin | Gram-positive (topical: Streptococci, Staphylococci) |
| Fosfomycin | E. coli, Enterococcus faecalis (urinary tract) |
B. Cell Membrane Disruptors (Bactericidal)
| Drug Class | Examples | Spectrum |
|---|---|---|
| Polymyxins | Polymyxin B, Colistin (Polymyxin E) | Gram-negative only: Pseudomonas, Klebsiella, Acinetobacter, E. coli — reserved for MDR organisms |
| Lipopeptides | Daptomycin | Gram-positive only: MRSA, VRE, S. aureus bacteremia |
C. Protein Synthesis Inhibitors
30S Ribosomal Subunit Inhibitors
| Drug Class | Examples | Spectrum |
|---|---|---|
| Aminoglycosides (Bactericidal) | Gentamicin, Tobramycin, Amikacin, Streptomycin | Aerobic Gram-negative rods (Pseudomonas, Enterobacteriaceae); synergistic against Gram-positive with cell wall agents |
| Tetracyclines (Bacteriostatic) | Tetracycline, Doxycycline, Minocycline | Broad-spectrum: Gram-positive, Gram-negative, Rickettsia, Chlamydia, Mycoplasma, spirochetes |
| Glycylcyclines (Bacteriostatic) | Tigecycline | Very broad: Gram-positive (MRSA, VRE), Gram-negative (not Pseudomonas), anaerobes, atypicals |
50S Ribosomal Subunit Inhibitors
| Drug Class | Examples | Spectrum |
|---|---|---|
| Macrolides (Bacteriostatic) | Erythromycin, Azithromycin, Clarithromycin | Gram-positive cocci, atypicals (Mycoplasma, Chlamydia, Legionella), H. influenzae |
| Ketolides | Telithromycin | Respiratory pathogens including macrolide-resistant Streptococcus |
| Clindamycin (Bacteriostatic) | Clindamycin | Gram-positive (Streptococcus, MSSA, MRSA skin infections), anaerobes (B. fragilis) |
| Chloramphenicol (Bacteriostatic) | Chloramphenicol | Broad: Gram-positive, Gram-negative, anaerobes, Rickettsia; rarely used due to toxicity |
| Oxazolidinones (Bacteriostatic) | Linezolid, Tedizolid | Gram-positive only: MRSA, VRE, MDRSA |
| Streptogramins | Quinupristin/Dalfopristin | Gram-positive: VRE (E. faecium), MRSA |
D. Nucleic Acid Synthesis Inhibitors
| Drug Class | Examples | Spectrum |
|---|---|---|
| Fluoroquinolones (Bactericidal) | Ciprofloxacin, Levofloxacin, Moxifloxacin | Broad: Gram-negative (Cipro best for Pseudomonas), Gram-positive (Levo/Moxi cover MRSA-susceptible Strep, Staph), atypicals |
| Rifamycins (Bactericidal) | Rifampin | Gram-positive (Staph, Strep), Mycobacterium tuberculosis; always used in combination |
| Metronidazole (Bactericidal) | Metronidazole | Anaerobes only (B. fragilis, C. difficile, C. perfringens) + protozoa |
| Nitroimidazoles | Tinidazole | Anaerobes, protozoa |
E. Folate Synthesis Inhibitors (Bacteriostatic)
| Drug Class | Examples | Spectrum |
|---|---|---|
| Sulfonamides | Sulfamethoxazole | Broad Gram-positive + Gram-negative; used with trimethoprim |
| Diaminopyrimidines | Trimethoprim (TMP) | Broad; TMP-SMX together: E. coli, H. influenzae, Pneumocystis jirovecii, MRSA (skin) |
II. Classification by Spectrum
| Spectrum | Drug Examples |
|---|---|
| Narrow — Gram-positive only | Penicillin G, Vancomycin, Daptomycin, Linezolid |
| Narrow — Gram-negative only | Aztreonam, Polymyxins |
| Narrow — Anaerobes only | Metronidazole |
| Broad-spectrum | Carbapenems, Tetracyclines, TMP-SMX, Fluoroquinolones, Tigecycline |
| Anti-MRSA | Vancomycin, Daptomycin, Linezolid, Ceftaroline, TMP-SMX (skin) |
| Anti-Pseudomonal | Piperacillin/tazobactam, Ceftazidime, Cefepime, Ceftolozane/tazobactam, Carbapenems (not Ertapenem), Ciprofloxacin, Aminoglycosides, Aztreonam |
| Anti-atypical (Intracellular) | Macrolides, Doxycycline, Fluoroquinolones |
| Anti-mycobacterial | Rifampin, Isoniazid, Ethambutol, Pyrazinamide |
III. Quick Reference: Key Bacteria & First-Line Antibiotics
| Bacterium | Gram Stain | First-line Antibiotic(s) |
|---|---|---|
| Staphylococcus aureus (MSSA) | Gram + cocci | Nafcillin, Oxacillin, Cefazolin |
| Staphylococcus aureus (MRSA) | Gram + cocci | Vancomycin, Daptomycin, Linezolid |
| Streptococcus pyogenes (Group A) | Gram + cocci | Penicillin G/V, Amoxicillin |
| Streptococcus pneumoniae | Gram + cocci | Penicillin (if susceptible), Ceftriaxone, Vancomycin |
| Enterococcus faecalis / faecium | Gram + cocci | Ampicillin ± gentamicin; Vancomycin (VRE: Linezolid, Daptomycin) |
| Escherichia coli | Gram − rod | TMP-SMX, Fluoroquinolones, Cephalosporins |
| Klebsiella pneumoniae | Gram − rod | Cephalosporins, Carbapenems (if ESBL) |
| Pseudomonas aeruginosa | Gram − rod | Piperacillin/tazobactam, Cefepime, Carbapenems, Ciprofloxacin |
| Haemophilus influenzae | Gram − rod | Amoxicillin/clavulanate, Azithromycin, Ceftriaxone |
| Neisseria meningitidis | Gram − cocci | Penicillin G, Ceftriaxone |
| Neisseria gonorrhoeae | Gram − cocci | Ceftriaxone |
| Bacteroides fragilis | Gram − anaerobe | Metronidazole, Piperacillin/tazobactam, Carbapenems |
| Clostridium difficile | Gram + anaerobe | Vancomycin (oral), Fidaxomicin |
| Mycoplasma pneumoniae | No cell wall | Azithromycin, Doxycycline |
| Chlamydia trachomatis | Intracellular | Azithromycin, Doxycycline |
| Legionella pneumophila | Gram − intracellular | Azithromycin, Levofloxacin |
| Mycobacterium tuberculosis | Acid-fast | Isoniazid + Rifampin + Pyrazinamide + Ethambutol |
Sources:
- Sherris & Ryan's Medical Microbiology, 8th Ed. — Table 23-1: Characteristics of Antibacterial Drugs
- Goodman & Gilman's The Pharmacological Basis of Therapeutics — Classification of Penicillins and Antimicrobial Chemotherapy chapters
- Goodman & Gilman's — Antimicrobial Chemotherapy: Classes and Actions
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