A 10-year study of membrane filter system versus blood culture bottles in culturing vitrectomy cassette vitreous in infectious endophthalmitis

Purpose: To compare the microbiological outcomes of membrane filter system and blood culture bottle techniques in culturing diluted vitrectomy cassette vitreous. Design: Retrospective comparative case series. Methods: Diluted vitrectomy cassette vitreous specimens from March 25, 2002 to July 11, 2012 were cultured using both membrane filter system and blood culture bottles. The isolates were divided into 3 groups: ones that had positive cultures with (1) both membrane filter system and blood culture bottles, (2) membrane filter system only, and (3) blood culture bottles only. The 48-hour as well as 2-week results were documented. Results: A total of 447 patients with 168 positive cultures were studied. At the 48-hour time point, 126 isolates were documented. Of those, 104 (82%) were culture positive with both membrane filter system and blood culture bottles, 15 (12%) were culture positive only with membrane filter system, and 7 (6%) were culture positive only with blood culture bottles. At the 2-week time point, an additional 42 organisms were isolated. Of those, 19 (45%) were culture positive with both membrane filter system and blood culture bottles, 11 (26%) with membrane filter system only, and 12 (29%) with blood culture bottles only. Out of 168 total isolates, 123 (73%) were culture positive with both membrane filter system and blood culture bottles, 26 (16%) with membrane filter system only, and 19 (11%) with blood culture bottles only. Among all microbiological outcomes, there was no significant difference between membrane filter system and blood culture bottle (P =.37). Of those organisms that were culture positive only with either membrane filter system or blood culture bottle, mold and Mycobacterium species were culture positive more commonly with membrane filter system (P =.034 and P =.016, respectively), and gram-positive organisms were culture positive more commonly with blood culture bottles (P =.021). Conclusions: In the current study, a combination of membrane filter system and blood culture bottles for culture of diluted vitrectomy cassette vitreous provides the highest number of positive culture outcomes. The blood culture bottle method is technically easier and represents a viable alternative to the more complex membrane filter system technique.