Antibiotic resistance, initially a problem in hospitals and in developing countries, today affects the world at large. Given sufficient time and drug use, antibiotic resistance will inevitably emerge. There are no antibiotics to which bacterial resistance has not eventually appeared. The penicillin-resistant Strep. Fluoroquinolone-resistant Enterobacteriaceae took 10 years to emerge clinically.
Antibiotic resistance is progressive, evolving from low levels through intermediate to high levels.
Fluoroquinolone resistance among Escherichia coli requires several sequential mutations to reach a high, clinically relevant level. The few vancomycin-insensitive strains of Staph. Organisms that are resistant to one antimicrobial drug are likely to become resistant to others. The first tetracycline-resistant gonococcus appeared among strains that were already resistant to penicillin. Fluoroquinolone resistance emerged among gonococcal strains that were resistant to both tetracycline and penicillin.