Survival of Pseudomonas aeruginosa in modified Romanowsky staining solutions

Background Anecdotal reports suggest that rapid staining solutions can become contaminated with micro‐organisms, especially Pseudomonas aeruginosa . Hypothesis/Objectives To determine whether inoculation of rapid Romanowsky‐type stains with P. aeruginosa results in viable bacterial contamination, which could lead to cross‐contamination of slides during cytological staining. Methods Pseudomonas aeruginosa was inoculated into clean and organically contaminated staining solutions (fixative, eosin and methylene blue) and positive (broth) and negative (bleach) control solutions. Subsequent viability and survival were detected by measuring colony‐forming units per millilitre at various time points up to 2 weeks. Each sample was stained and microscopically examined to determine whether bacteria were visible. Results No bacteria could be cultured at any time point from the bleach or fixative solution. In clean eosin and methylene blue staining solutions, viable bacteria were recovered for up to 1 h, but by 24 h all bacteria were dead. In staining solutions contaminated with hair and dead skin cells, bacteria survived in methylene blue for up to 1 h, and viable bacteria persisted in the eosin stain for 2 weeks. In solutions containing viable organisms, the bacteria could be observed by microscopic examination; no bacteria were visible when the solutions contained no viable organisms. Conclusions and clinical importance Pseudomonas aeruginosa can survive in commonly used staining solutions for variable periods of time, but is unable to proliferate. Although theoretically this might complicate cytological interpretation and subsequent diagnosis, the likelihood of this in clinical practice appears remote when the correct staining technique is used.