Final answer:
The causative 'bug' in septic arthritis for a young female with purpuric skin lesions is most commonly Staphylococcus aureus, with Neisseria gonorrhoeae also being important in sexually active individuals. Diagnosis is made via synovial fluid analysis, and treatment includes targeted antimicrobial therapy.
Step-by-step explanation:
The student is inquiring about the causative bug in septic arthritis, especially in the context of a young female with purpuric skin lesions. Septic arthritis, also known as infectious arthritis, is most often caused by bacterial infection within the joint. While several pathogens can cause septic arthritis, the most common causative bacterium in the general population, including adults and young children, is Staphylococcus aureus (S. aureus). Particularly in sexually active individuals, Neisseria gonorrhoeae is another important cause. Considering the mention of purpuric skin lesions, it is also pertinent to consider Neisseria meningitidis, as it can be associated with purpura in the setting of disseminated infection.
Diagnosis of infectious arthritis is typically confirmed by aspiration and analysis of synovial fluid to identify the culpable pathogen. The chosen treatment usually involves administration of antimicrobial agents that are effective against the identified bacterium, taking antimicrobial susceptibility into account.