TABLE 1.
Total antibiotics tested and their respective properties
| Biochemical property | Site of action | Class and subclass | Origin | Antibiotic (Ab) | Ab concentrationa | Resistanceb | No. of clonesc |
|---|---|---|---|---|---|---|---|
| Hydrophilic | Cell wall | Beta-lactams | |||||
| Penicillins | Natural | Penicillin | 64 | + | 16 | ||
| Cephalosporins | Semisynthetic | Ampicillin | 8 | + | 50 | ||
| Cephalothin | 32 | + | 15 | ||||
| Cefoxitin | 64 | − | 0 | ||||
| Cefotaxime | 0.25 | + | 67 | ||||
| Cefepime | 0.125 | + | 45 | ||||
| Monobactams | Synthetic | Aztreonam | 0.25 | + | 19 | ||
| d-cycloserine | Natural | d-cycloserine | 32 | + | 24 | ||
| Amphipathic | Cytoplasmic membrane | Polymyxins | Natural | Polymyxin B | 0.5 | + | >1,000 |
| Hydrophobic | Protein synthesis | Chloramphenicol | Synthetic | Chloramphenicol | 8 | + | 16 |
| Aminoglycosides | Natural | Gentamicin | 4 | − | 0 | ||
| Semisynthetic | Amikacin | 16 | − | 0 | |||
| Tetracyclines | Natural | Tetracycline | 4 | − | 0 | ||
| Natural | Chlortetracycline | 4 | − | 0 | |||
| Semisynthetic | Doxycycline | 4 | − | 0 | |||
| DNA synthesis | Fluoroquinolones | Synthetic | Nalidixic Acid | 4 | − | 0 | |
| Synthetic | Norfloxacin | 0.125 | − | 0 | |||
| Nitrofurans | Synthetic | Nitrofurantoin | 1 | − | 0 |
a
The minimum concentration of antibiotic (μg/ml) needed to inhibit the growth of E. cloni cells (Lucigen). This concentration (MIC) was used to screen clones for cryptic antibiotic resistance.
b
If resistance occurred in our study, this is denoted as “+”.
c
The number of clones indicates the number of colonies that appeared if resistance occurred at the MIC.