Final answer:
Penicillin G is chosen as an effective treatment most likely for infections caused by gram-positive bacteria, capable of treating diseases like diphtheria and pneumonia, but less effective against gram-negative bacteria, viruses, and fungi.
Step-by-step explanation:
If penicillin G is chosen as the best treatment for a given infection, the microorganisms most likely causing the infection are gram-positive bacteria. Penicillin G is particularly effective against this group of bacteria, which includes pathogens that can cause diseases such as diphtheria, gonorrhea, pneumonia, and syphilis. While penicillin G also affects a few gram-negative bacteria like Escherichia coli, it is not considered as effective against most gram-negative pathogens or against viruses and fungi.
In the 1940s, infections by the bacterium Staphylococcus aureus could be treated with penicillin, but today, there are strains completely resistant to this antibiotic, highlighting the importance of correct diagnostic to ensure effective treatment.
Gram-positive bacteria have distinct features that can be targeted by antibiotics like penicillin G, which is produced by fungi of the genus Penicillium and typically administered intravenously or intramuscularly due to its instability in acidic conditions such as those found in the stomach.