Assessment of Anaerobic Culture Incubation Time: A Tertiary Care Center Experience
Abstract Background Currently, there is no consensus on the ideal incubation time for anaerobic cultures. A recent survey of CliniMicroNet reported anaerobic culture incubation times from 2 to 7 days. The goal of this study is to determine the ideal anaerobic culture incubation time and to retrospectively determine if longer incubation time affected management. Methods In this prospective study at Hartford Hospital, an 869-bed level I trauma center, 838 consecutive anaerobic cultures were Gram stained and planted on anaerobic blood, colistin and nalidixic acid (CNA), and kanamycin and vancomycin (KV) agar plates (BD Diagnostic Sparks). Plates were incubated in jars at 35°C and Anoxomat system (Advanced Instruments) was used to create anaerobic conditions. Plates were checked for growth on days 2, 3, 5, and 7. Although not all patient records (EPIC) were available, the type and duration of antibiotics were recorded for more than 100 records. Results Out of 74 cultures from bronchoalveolar lavage (1), bone (2), fluid (21), tissue (14), and wound (36), 53 grew 1 isolate, 15 grew 2 isolates, 5 grew 3 isolates, and 1 grew 4 isolates, for a total of 102 isolates. Sixty percent of isolates were Gram negative and 40% were Gram positive. Of these, 43% were detected on day 2, 21% on day 3, 20% on day 5, and 17% on day 7. In a majority of cases, broad-spectrum antibiotics (vancomycin/cefepime) were administered until culture results were obtained. Conclusion Overall, 73% Gram-negative isolates and 50% Gram-positive isolates were detected on day 2 or 3. Days 5 and 7 yielded 20% and 17% of all isolates, respectively. We conclude and corroborate with CLSI recommendations that anaerobic cultures should be incubated for at least 5 to 7 days.