Final answer:
Empiric antibiotics for a septic joint depend on the results of a gram stain, with oxacillin and cefazolin for gram-positive cocci and ceftriaxone for gram-negative bacilli. Staphylococcus aureus, a gram-positive bacterium, is the most common cause of septic arthritis and osteomyelitis.
Step-by-step explanation:
When considering an empiric antibiotic (abx) for a septic joint, broad-spectrum antibiotics are typically started. If the gram stain shows gram-positive cocci, antibiotics effective against staphylococcal and streptococcal infections, such as oxacillin and cefazolin, are frequently used. For gram-negative bacilli, third-generation cephalosporins like ceftriaxone are often prescribed.
Lab technicians determine if the infection is staphylococcal or streptococcal through direct microscopic evaluation, culture, antimicrobial susceptibility testing, and polymerase chain reaction (PCR) analysis. The most common cause of septic arthritis and osteomyelitis is Staphylococcus aureus, a gram-positive bacterium with a thick cell wall. Streptococci are classified based on their hemolysis pattern, Lancefield grouping based on cell wall carbohydrates, and by molecular typing.