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Staphylococcus aureus recoveries on various brands of membrane filters
Abstract:
Six commercial brands of membrane filters were compared using staphylococcus aureus obtained from pure cultures and from swimming pool water. The following brands of filters were tested: Gelman, Millipore, Nuclepore, Oxoid, Sartorius, and Selectron. Standard membrane filter (MF) procedures and m-Staphylococcus broth were used in the evaluation. Analysis of the results was performed by comparing filter recoveries to the standard plate count using the t-test and the coefficient of variation. The data revealed that recovery on Nuclepore filters was consistently lower than the other brands and showed a wider degree of variation from the mean. All organisms recovered from the pool were gram-positive cocci, and the colonies ranged from white to yellow-gold in color. Approximately 15% of both the white and yellow-gold colonies were coagulase-positive, indicating that colony color alone does not denote the presence of coagulase-positive S. aureus. Since there was no correlation between colony color of the organisms recovered on membrane filters and the presence of coagulase, the feasibility of coagulase testing only the yellow-gold colonies for bathing water analysis is questionable.
Insights
Nuclepore membrane filters showed lower Staphylococcus aureus recovery rates and higher variability compared to other brands. Colony color is not a reliable indicator for identifying coagulase-positive bacteria in water analysis.
Area of Science:
- Microbiology
- Environmental Science
- Filtration Technology
Background:
- Membrane filtration is crucial for water quality testing, particularly for detecting bacterial contaminants like Staphylococcus aureus.
- Standardized methods are essential for reliable microbial recovery and accurate water safety assessments.
- Variability in filter performance can impact the accuracy of microbiological analyses.
Purpose of the Study:
- To compare the recovery efficiency of six commercial membrane filter brands for Staphylococcus aureus.
- To evaluate the reliability of colony color as an indicator for coagulase-positive Staphylococcus aureus in environmental samples.
- To assess the suitability of specific membrane filters for routine water quality monitoring.
Main Methods:
- Six membrane filter brands (Gelman, Millipore, Nuclepore, Oxoid, Sartorius, Selectron) were tested using Staphylococcus aureus from pure cultures and swimming pool water.
- Standard membrane filter (MF) procedures and m-Staphylococcus broth were employed for bacterial recovery.
- Statistical analysis included t-tests and coefficient of variation to compare filter recoveries against standard plate counts.
Main Results:
- Nuclepore filters exhibited consistently lower Staphylococcus aureus recovery rates and greater variation compared to Gelman, Millipore, Oxoid, Sartorius, and Selectron filters.
- Recovered bacteria from pool water were gram-positive cocci with white to yellow-gold colonies.
- Approximately 15% of both white and yellow-gold colonies tested positive for coagulase, indicating colony color is not a definitive marker.
Conclusions:
- Nuclepore filters are less suitable for accurate Staphylococcus aureus enumeration due to lower recovery and higher variability.
- Relying solely on yellow-gold colony color for coagulase-positive Staphylococcus aureus detection in bathing water is unreliable.
- Further validation of filtration methods and diagnostic criteria is necessary for effective water safety monitoring.