Rectal swab clarifies prostate biopsy prophylaxis

December 1, 2009

A multicenter Japanese team has proposed a method for approaching infection prophylaxis with prostate biopsy patients.

Okayama, Japan-How should urologists approach infection prophylaxis with prostate biopsy patients? In an era of increasing antibiotic resistance, it's an important question, and urologists need an accurate method of identifying whether resistant bacteria may be present. Urine cultures don't always do that.

A multicenter Japanese team has proposed a method for sampling bacteria from the rectal wall where bacteria reside that have the potential to seed the bloodstream or prostate by means of the biopsy needles. In this method, stool remaining on the glove after digital rectal examinations provided rectal swab specimens from 127 patients who had had planned transrectal prostate biopsies.

The swab specimens were used to inoculate CROMagar Orientation medium (Becton, Dickinson and Co. [BD], Tokyo) and the plates were incubated overnight at 37°C. With this medium, Escherichia coli show as reddish colonies on the plate. Investigators then sampled E. coli colonies randomly and subcultured the specimens in Torypticase Soy Agar with 5% Sheep Blood (BD) for 24 hours at 37°C. The minimum inhibitory concentration of levofloxacin (Levaquin) was then determined with BD Phoenix (BD).

Using this one-colony method, samples from 127 patients who had no antibiotic pretreatment yielded 98 E. coli isolates, of which 95% were fluoroquinolone susceptible and 5% were fluoroquinolone resistant.

Impact on prophylaxis

"This is a very important paper because usually, it is recommended to investigate only the urine," commented Kurt G. Naber, MD, PhD, of the Technical University of Munich, who is past president of the International Society of Chemotherapy for Infection and Cancer.

Commenting on the importance of the presentation, session chair John Krieger, MD, professor of urology at the University of Washington, Seattle, suggested that urologists may have to change their methods for prophylaxis to recognize increasing resistance.

The research showed that the minimum rate of fluoroquinolone resistance is likely to be 5%, Dr. Krieger said, adding, "I'd like to see a lot more data because I think 5% is going to be the low end of this."

Dr. Naber also expressed doubts about the method of sampling a single colony and suggested culturing rectal swab specimens on agar plates containing levofloxacin, 8 mg/L.

"If there is some growth, you have resistant pathogens, and if there is no growth, you have no resistant pathogens," he said. "It's much easier."

He emphasized the importance of culturing and looking for fluoroquinolone-resistant pathogens also in the fecal flora prior to prostate biopsy where the protocol indicates antibiotic prophylaxis.

Modern Medicine NETWORK

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