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Survival of Staphylococcus pseudintermedius in modified Romanowsky staining solutions
Angus Misan1, Wei Yee Chan1, Darren Trott1
1School of Animal and Veterinary Sciences, University of Adelaide, Roseworthy, South Australia, 5371, Australia.
Background:
Stains that are used regularly for patient-side diagnosis to rapidly identify bacterial and fungal infections could become contaminated by common pathogens, such as Staphylococcus pseudintermedius, during slide immersion.
Hypothesis/Objectives:
To determine whether the inoculation of S. pseudintermedius into modified Romanowsky type stains (Quick Dip® ) results in viable bacterial contamination and whether this is influenced by the addition of organic debris (canine hair and skin).
Methods:
A clinical isolate of S. pseudintermedius was inoculated into clean and organically contaminated Quick Dip® solutions (methanol fixative, eosin, methylene blue), and positive (broth) and negative (bleach) controls. Each solution was tested for the presence of viable bacteria by counting the number of colony forming units (CFU/mL) at various time points. Solutions also were examined under high power microscopy to count the number of visible bacteria at each time point.
Results:
Staphylococcus pseudintermedius was able to survive in the clean and contaminated Quick Dip® stains for at least one hour, but by 24 h no viable bacteria remained. Survival of the bacteria was not supported in the fixative at any time point. Staphylococcus pseudintermedius remained visible under high power microscopy for up to 2 weeks in all organically contaminated solutions of the Quick Dip® set.
Conclusions And Clinical Importance:
Staphylococcus pseudintermedius only remains viable in eosin and methylene blue for short periods of time, but the prolonged visibility of dead organisms could theoretically lead to the misdiagnosis of cytology samples.
Insights
Bacterial contamination of diagnostic stains by Staphylococcus pseudintermedius is possible, but viable bacteria do not persist long-term. However, dead bacteria can remain visible, potentially leading to misdiagnosis in patient-side cytology.
Area of Science:
- Veterinary Microbiology
- Diagnostic Cytology
- Clinical Pathology
Background:
- Diagnostic stains used for rapid patient-side identification of bacterial and fungal infections are susceptible to contamination.
- Common pathogens like Staphylococcus pseudintermedius can contaminate stains during slide immersion, posing a risk to diagnostic accuracy.
Purpose of the Study:
- To investigate the potential for viable bacterial contamination of modified Romanowsky stains (Quick Dip®) by Staphylococcus pseudintermedius.
- To determine if organic debris (canine hair and skin) influences bacterial survival and contamination within these stains.
Main Methods:
- Inoculation of Staphylococcus pseudintermedius into clean and organically contaminated Quick Dip® stain solutions (fixative, eosin, methylene blue).
- Quantification of viable bacteria using colony-forming units (CFU/mL) at various time points.
- Microscopic examination to assess the visibility of bacteria over time.
Main Results:
- Staphylococcus pseudintermedius survived in clean and contaminated stains for at least one hour, but not after 24 hours.
- No bacterial survival was observed in the methanol fixative component.
- Dead Staphylococcus pseudintermedius remained microscopically visible for up to two weeks in organically contaminated stain solutions.
Conclusions:
- While Staphylococcus pseudintermedius viability in eosin and methylene blue stains is short-lived, the prolonged visibility of dead bacteria presents a theoretical risk.
- This prolonged visibility of non-viable organisms could lead to misdiagnosis in patient cytology samples.
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