Final answer:
Bacteria like S. aureus have developed resistance to antibiotics such as penicillin through several mechanisms, leading to strains like MRSA and VRSA that are resistant to multiple drugs including methicillin and vancomycin.
Step-by-step explanation:
The characteristics of bacteria that are resistant to penicillin and other antibiotics involve various defense mechanisms. One such bacterium is Staphylococcus aureus, which in its methicillin-resistant (MRSA) and vancomycin-resistant (VRSA) forms, has adapted to survive in the presence of these antibiotics.
Some strains of S. aureus were initially treated with penicillin, but have since developed resistance. This resistance has arisen due to mechanisms such as production of ß-lactamase enzymes that degrade the antibiotic, mutations that change the target site of the antibiotic, prevention of antibiotic entry into the cell, or efflux pumps that remove the antibiotic from the cell. This has resulted in strains of S. aureus that are now resistant to nearly all available antibiotics, including methicillin and vancomycin.