Toxic effect of calcium alginate swabs on Neisseria gonorrhoeae

Abstract

Calcium alginate (CA)-tipped swabs have been reported to interfere with the recovery of herpes simplex virus, Chlamydia trachomatis, and Ureaplasma urealyticum and may cause cytotoxicity in cell culture. To determine whether CA swabs also inhibit the growth of Neisseria gonorrhoeae, we carried out a series of experiments using either CA swabs that were toxic or nontoxic in a cell culture cytotoxicity assay or nontoxic rayon or cotton swabs. Leaving a toxic CA swab in 3 ml of Mueller-Hinton broth inoculated with 104 CFU/ml caused rapid killing within 6 h at 37°C; colony counts of five strains were <1% of those of Mueller-Hinton broth controls. When the tips of toxic CA swabs were inoculated directly and kept at 37°C without holding medium, the swabs were sterile at 6 h. If the same swabs were placed in Amies medium with charcoal, organisms could still be recovered at 6 h. Toxicity was less at room temperature than at 37°C. Inhibition of growth of N. gonorrhoeae was not seen with rayon or cotton swabs. The toxic component was neither the CA fiber nor the aluminum wire but probably the glue used to attach the fibers. We concluded that some lots of CA swabs kill N. gonorrhoeae in vitro. Survival of N. gonorrhoeae is improved with nontoxic swabs, particularly cotton swabs, and Amies medium with charcoal regardless of swab type.