The culture of sterile urine for detection of anaerobic bacteria—not necessary for standard evaluation

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EXAMINATION of urine specimens for aerobic bacteria is a well-established procedure in the clinical microbiology laboratory. The method used at the Cleveland Clinic is as follows. Catheter or clean catch-voided urine specimens are cultured with minimal delay. A MacConkey agar plate is used for the isolation and preliminary identification of gram-negative bacteria. A colony count is prepared by uniformly streaking a sheep-blood agar plate with 0.001 ml of well-mixed, undiluted urine delivered by a calibrated platinum loop. This plate also serves for isolation of gram-positive bacteria. The plates are incubated aerobically at 37 C overnight. Those cultures demonstrating aerobic pathogenic bacteria are identified by means of appropriate differential media.1 In standard sterile urine cultures, a search for anaerobic bacteria is not usually undertaken. Our study was designed to determine whether or not anaerobic bacteria are important factors in urinary tract infection; if they are, to identify them would be mandatory.

Materials and methods

In addition to culturing urine specimens by the previously described method, 0.5 ml of undiluted, well-mixed urine was placed in 7.5 ml of freshly prepared thioglycollate medium, incubated at 37 C, and examined daily for macroscopic and microscopic growth. All specimens that grew aerobic pathogens by the routine method, as well as those that did not demonstrate growth in the thioglycollate medium at the end of 72 hours were discarded and studied no further. Each of the remaining specimens was then transferred to two blood agar plates. Each plate was incubated for 48 hours at 37 C,. . .



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