Use of the isolator 1.5 microbial tube for culture of synovial fluid from patients with septic arthritis

Synovial fluid specimens obtained from patients with arthritis were plated onto solid media (conventional cultures) or inoculated into an Isolator 1.5 microbial tube (Isolator cultures), and the yield and time to detection of organisms were compared. Overall, 144 specimens obtained from 137 patients were processed, and 31 (21.5%) cultures obtained from 29 patients were positive by at least one method. Staphylococcus aureus was isolated from 12 patients, Streptococcus pneumoniae and Kingella kingae were isolated from 4 patients each, group G streptococci were isolated from 3 patients, Staphylococcus epidermidis and members of the family Enterobacteriaceae were isolated from 2 patients each, and Streptococcus mitis and Peptostreptococcus prevotii were isolated from 1 patient each. Overall, the causative organism was detected in 31 of 31 (100.0%) Isolator cultures and 24 of 31 (77.4%) conventional cultures (P < 0.02). Twenty-nine of 31 (93.5%) positive Isolator cultures and 20 of 24 (83.3%) conventional cultures were positive by the second day of incubation. Among the 24 cultures positive by both methods, higher numbers of CFU per milliliter were detected with the Isolator system in 13 cultures and with conventional cultures in 2 cultures (P < 0.002). Inoculation of synovial fluid into an Isolator 1.5 microbial tube improves the recovery of organisms causing septic arthritis.