Reply by Authors: “Prospective Monitoring and Adapting Strategies for Prevention of Infection Following Transrectal Prostate Procedures”

After instituting a policy of screening high risk patients for fluoroquinolone resistance, approximately half of the patients in whom infection developed were not screened. This underscores the importance of proper screening criteria. One could argue that in the context of a rising incidence of FQ resistance, clinical risk factors may soon lack the discriminatory ability to differentiate which patients might benefit from selective screening. However, at present, screening all men who are to undergo a transrectal ultrasound guided prostate procedure would be a costly and unproven venture.

FQ resistance was determined by screening the rectal swab culture against a 10 μg/ml ciprofloxacin concentration on MacConkey agar plates. While this commonly used formulation has been the most extensively studied,¹ the minimum inhibitory concentration of antibiotics is not determinable from such a screening study. If FQ resistance is noted, confirmatory testing is performed by inoculating bacteria on plates with increasing concentrations of antibiotics. Resistance to FQs for the bacterial family Enterobacteriaceae (includes E. coli) is defined as a minimum inhibitory concentration of 4 μg/ml ciprofloxacin or greater while susceptibility is defined as a minimum inhibitory concentration of 1 μg/ml or less. Of all the patients who screened positive for FQ resistance, none was subsequently found to have FQ susceptibility based on this lower antibiotic concentration threshold on confirmatory testing. Decreasing the FQ concentration in the screening assay might very well increase the yield of FQ resistance but may also yield a higher false-positive rate or overgrowth of normal bacterial flora. Further studies are required to determine the limitations and better define the threshold of rectal swab antibiotic resistance screening.