A practicing general physician (GP) notices that several of her patients have come to see her because their bacterial infections will not clear.
A practicing general physician (GP) notices that several of her patients have come to see her because their bacterial infections will not clear. She asks a pathologist in her practice to characterize the bacteria strains that her patients have. The pathologist’s report summarized in Table 1. With that information, the GP creates a short list of antibiotics that she could prescribe. Table 2 lists those antibiotics, their spectrum characteristics, and their mechanism of action. Using both of these tables, which antibiotic(s) might the GP prescribe for each patient, and why? (6 points)
There is more than one correct answer for each patient, but you only need to report one.
Table 1. Pathologist’s report.
| Patient | Bacteria Characteristics | Antibiotic prescribed | Rationale for antibiotic choice |
| #1 | Gram (-), cell wall present, Polymixin B resistant | ||
| #2 | Gram (+), cell wall present, Streptomyocin and Gentamicin resistant | ||
| #3 | Gram (+), cell wall present, Oxacillin resistant, patient allergic to tetracycline |
Table 2. Common antibiotics and their properties.
Remember: Broad-spectrum antibiotics work against both Gram-positive and Gram-negative bacteria. Narrow-spectrum antibiotics are only effective against specific families of bacteria.
| Antibiotic | Spectrum | Mechanism of Action |
| Penicillin | Broad | Inhibits functioning of transpeptidase |
| Oxacillin | Narrow (Gram +) | Inhibits functioning of transpeptidase |
| Amoxicillin – clavulanic acid | Broad | Amoxicillin inhibits peptidoglycan formation; clavulanic acid inhibits beta-lactamases that destroy amoxicillin |
| Cefazolin | Broad | Inhibits peptidoglycan formation |
| Vancomycin | Narrow (Gram +) | Inhibits synthesis of peptidoglycan |
| Gentamicin | Narrow (Gram -) | Inhibits protein synthesis |
| Tetracyclins | Broad | Inhibits protein synthesis |
| Trimethoprim-sulfa-methoxazole | Broad | Inhibits synthesis of folic acid which is needed for bacteria to survive |
| Polymyxin B | Narrow (Gram -) | Disrupts cell membrane structure and therefore permeability |
| Streptomyocin | Broad | Inhibits protein synthesis |
