Final answer:
The steady increase in antibiotic-resistant bacteria since the discovery of penicillin is primarily due to increased antibiotic use, which leads to natural selection favouring resistant strains. Both medical over-prescription and agricultural over-use contribute to this problem, posing a significant global health threat.
Step-by-step explanation:
Ever since the discovery of penicillin in 1928, the incidence of resistant bacteria has increased significantly. The primary driver behind this trend is A. Increased Antibiotic Use. Antibiotic resistance occurs due to the process of natural selection; the antibiotic kills susceptible bacteria, leaving behind those with resistance traits that continue to multiply. This evolutionary pressure has been exacerbated by the imprudent and excessive use of antibiotics, both in human medicine and in agriculture. In human medicine, antibiotics are sometimes prescribed unnecessarily or are not taken as directed, which may lead to incomplete eradication of the infectious bacteria and the development of resistance. In agriculture, 70% of antibiotics produced are fed to animals in sub-therapeutic doses, fostering the development of resistance that can be transferred to humans.
Data show that infections like those caused by Staphylococcus aureus, once treatable with penicillin, now include strains like MRSA that are completely resistant. The misuse of antibiotics poses a global health threat, with multidrug-resistant strains causing an increasing number of infections. This resistance has serious implications, including worse clinical outcomes, more complex and expensive treatments, and higher mortality rates.