A note on inoculum reproducibility: a comparison between solid and liquid culture.

The level of reproducibility for replicate determinations of drug sensitivity was significantly greater for liquid than for solid cultures and decreased markedly with the density of colonies upon seeded agar plates. Inocula of Escherichia coli and Pseudomonas aeruginosa were significantly less sensitive towards chlorhexidine when derived from liquid rather than solid culture. We therefore suggest that only liquid cultures be used for the preparation of challenge inocula for regulatory tests of antimicrobial activity.

A laboratory evaluation of a new disinfectant cleaner for fibreoptic instruments.

The antimicrobial activity of Dettox ABC (DTX), a new disinfectant cleaner, developed for use in endoscopy, has been evaluated against sixteen strains of micro-organisms, nine of which were clinical isolates obtained from endoscope washings. In all cases the maximum growth inhibitory and lethal dilutions were considerably greater than those recommended for use (1/25). Time-survival data was determined for DTX (1/750), in hard water, against Pseudomonas aeruginosa, and the effects of horse blood, yeast cells, serum and porcine mucin evaluated. These date indicated that the activity of the product was adversely affected at this dilution by organic matter. Levels of organic debris, which were found capable of neutralizing a 1/750 DTX dilution were included in a multiple challenge of the product with P. aeruginosa at dilutions of 1/25, 1/50 and 1/100 prepared in hard water. Its performance was satisfactory. Similarly, the activity of DTX at these dilutions upon Staphylococcus aureus cells dried in blood and mucin on glass surfaces was satisfactory. The levels of organic debris used in this study were considerably greater than those expected in practice with endoscopes.