Study of microbilogical flora and role of primary bacterial cultures in management of open fractures of long bones

Background: Microbiology of open fracture wounds is constantly changing. A clear understanding of the bacterial flora that could be expected is needed in order to administer a rational and effective antibiotic treatment for open fractures. The role and efficacy of primary bacterial cultures in management of open fractures is also debatable and needs further evaluation. Methods: One hundred patients with one hundred and seven open fractures of long bones were studied prospectively, from March 1st 2001 till February 28th 2002. Wound swabs were obtained at pre-debridement, intra-operative, post debridement, 1st dressing/after 24hrs intervals, subsequently every week and sent for cultures. The infecting organism, its antibiotic susceptibility and its correlation between cultures at different stages was noted. Results: An infection rate of 43.9% was noted. Most of the initial wound cultures, showed growth of Gram-negative organisms (76%), commonest being Pseudomonas (36%) and Acinitobacter(20.7%). However, majority of infections after 2nd week were caused by Gram-positive organisms. Staphylococcus aureus (93.5%) was the predominant Gram-positive organism. None of the organisms grown on admission and pre-debridemet cultures eventually caused infection; however, 28% of cases with negative cultures eventually got infected. Post debridement cultures were positive in none. Among the cultures obtained at 1st dressing 40% of organisms grown eventually caused infection whereas 60% showed growth with different organism. Conclusions: A shift in the bacterial flora occurs in compound fracture wounds from Gram-negative to Gram-positive organisms after the 2nd week. Cultures obtained at admission, predebridment, posted brid ment and at 1st dressing or after 24hrs are not reliable indicators of subsequent wound infection.