The drug bacitracin consists of a group of structurally similar peptide antibiotics originally isolated from Bacillus subtilis . Bacitracin blocks the activity of a specific cell-membrane molecule that is responsible for the movement of peptidoglycan precursors from the cytoplasm to the exterior of the cell, ultimately preventing their incorporation into the cell wall. Bacitracin is effective against a wide range of bacteria, including gram-positive organisms found on the skin, such as Staphylococcus and Streptococcus . Although it may be administered orally or intramuscularly in some circumstances, bacitracin has been shown to be nephrotoxic (damaging to the kidneys). Therefore, it is more commonly combined with neomycin and polymyxin in topical ointments such as Neosporin .
| Drugs that Inhibit Bacterial Cell Wall Synthesis | ||||
|---|---|---|---|---|
| Mechanism of Action | Drug Class | Specific Drugs | Natural or Semisynthetic | Spectrum of Activity |
| Interact directly with PBPs and inhibit transpeptidase activity | Penicillins | Penicillin G, penicillin V | Natural | Narrow-spectrum against gram-positive and a few gram-negative bacteria |
| Ampicillin, amoxicillin | Semisynthetic | Narrow-spectrum against gram-positive bacteria but with increased gram-negative spectrum | ||
| Methicillin | Semisynthetic | Narrow-spectrum against gram-positive bacteria only, including strains producing penicillinase | ||
| Cephalosporins | Cephalosporin C | Natural | Narrow-spectrum similar to penicillin but with increased gram-negative spectrum | |
| First-generation cephalosporins | Semisynthetic | Narrow-spectrum similar to cephalosporin C | ||
| Second-generation cephalosporins | Semisynthetic | Narrow-spectrum but with increased gram-negative spectrum compared with first generation | ||
| Third- and fourth-generation cephalosporins | Semisynthetic | Broad-spectrum against gram-positive and gram-negative bacteria, including some β-lactamase producers | ||
| Fifth-generation cephalosporins | Semisynthetic | Broad-spectrum against gram-positive and gram-negative bacteria, including MRSA | ||
| Monobactams | Aztreonam | Semisynthetic | Narrow-spectrum against gram-negative bacteria, including some β-lactamase producers | |
| Carbapenems | Imipenem, meropenem, doripenem | Semisynthetic | Broadest spectrum of the β-lactams against gram-positive and gram-negative bacteria, including many β-lactamase producers | |
| Large molecules that bind to the peptide chain of peptidoglycan subunits, blocking transglycosylation and transpeptidation | Glycopeptides | Vancomycin | Natural | Narrow spectrum against gram-positive bacteria only, including multidrug-resistant strains |
| Block transport of peptidoglycan subunits across cytoplasmic membrane | Bacitracin | Bacitracin | Natural | Broad-spectrum against gram-positive and gram-negative bacteria |