Final answer:
A bacterium unaffected by an antibiotic is called a resistant bacterium. A semisynthetic antimicrobial is a naturally derived compound that has been chemically modified to increase its effectiveness. Antibiotic resistance poses a significant threat to global health due to the evolution of bacteria to survive exposure to these drugs.
Step-by-step explanation:
A bacterium that is unaffected by an antibiotic drug is said to be a resistant bacterium. The term resistant implies that the bacterium has developed the ability to survive in the presence of an antibiotic that was designed to kill it or inhibit its growth. This resistance can occur due to various mechanisms, such as producing enzymes that degrade the antibiotic, mutating the target of the antibiotic, preventing the antibiotic from entering the cell, or pumping the antibiotic out of the cell using efflux pumps.
Regarding the scientist who has modified an antimicrobial compound, if this new version with a hydroxyl group addition now kills both gram-negative and gram-positive bacteria, it is considered a semisynthetic antimicrobial. This is because the original compound, which was isolated from a soil bacterium and had natural antibacterial properties, was chemically modified to enhance its effectiveness against a broader range of bacteria.
The emergence of antibiotic-resistant bacteria is a serious global health threat. As bacteria develop resistance to multiple antibiotics, infections such as those caused by methicillin-resistant Staphylococcus aureus (MRSA) become harder to treat. The development of resistance is encouraged by the overuse and misuse of antibiotics, as well as by the bacteria's natural ability to adapt and defend themselves against these medicinal compounds.