In vitro effects of iodinated contrast media on the growth of staphylococci

Seven commonly used arthrographic contrast media were examined in vitro for bactericidal effects against Staphylococcus aureus under various conditions simulating clinical settings, using a wide range of bacterial populations (10(1) to 10(8) colony-forming units per ml). The media tested were: sodium diatrizoate and megulumine diatrizoate (E.R. Squibb and Sons, Renogragin-60 and Renografin-76), megulumine diatrizoate (E. R. Squibb and Sons, Renografin-M-60), sodium iothalamate and megulumine iothalamate (Mallinckrodt Chemical Works, Vascoray), sodium iothalamate (Mallinckrodt Chemical Works, Conray 400), meglumine iothalamate (Mallinckrodt Chemical Works, Conray 60), and sodium diatrizoate (Winthrop Laboratories, Hypaque sodium 50%). Effects secondary to the contrast medium used, dilution ratios of the specimens, and time elapsed between the collection and cultivation of the specimens were examined. The contrast material used was found to affect bacterial growth: the Renografin materials showed a bactericidal or bacteriostatic effect, while Vascoray, the Conray materials, and Hypaque sodium 50% failed to inhibit bacterial growth. Bacterial inoculum size exhibited a direct bearing on the bactericidal or bacteriostatic effects of the Renografin but had no effect with the other media. The results indicate that Vascoray, Conray and Hypaque sodium 50% are superior to the Renografin materials for use in arthrography and other procedures in which the aspirate is submitted for microbial culture, because they interfere less with the recovery of these microorganisms.