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Aseptic Laboratory Techniques: Volume Transfers with Serological Pipettes and Micropipettors
Published on: May 31, 2012
Should we care about transmission of infectious bacterial agents through serum handling?
Pezhman Mahmoodi1, Abdolmajid Mohammadzadeh1, Shadi Baniardalani1
1Department of Pathobiology, Faculty of Veterinary Science, Bu-Ali Sina University, Hamedan, Iran.
Insights
Serum samples from healthy humans and animals are generally safe for immunological assays, as bacterial contamination levels tested did not lead to growth. Routine centrifugation does not significantly reduce bacterial presence in sera.
Area of Science:
- Microbiology
- Immunology
- Veterinary Diagnostics
Background:
- Immunological assays rely on serum antibodies for diagnosing bacterial infections.
- The safety of using common serum samples, particularly regarding potential bacterial contamination, requires thorough investigation.
Purpose of the Study:
- To assess the risk of bacterial transmission from serum samples used in immunological assays.
- To determine the viability of common bacterial species (Staphylococcus aureus, Bacillus cereus, Escherichia coli) in human and animal serum.
Main Methods:
- Bacterial species were serially diluted and spiked into blood samples from humans and various animal species (sheep, goat, cattle, horse).
- Serum samples were analyzed for bacterial growth using colony counts before and after centrifugation.
- Scanning electron microscopy was employed for direct observation of bacterial cells in sera.
Main Results:
- No bacterial growth was observed in serum samples containing up to 7.5 × 10^2 CFU/ml of S. aureus, 7.5 × 10^5 CFU/ml of B. cereus, and 7.5 × 10^5 CFU/ml of E. coli.
- Standard centrifugation procedures did not significantly reduce the bacterial load in the serum samples.
- Bacterial viability was confirmed in both centrifuged and non-centrifuged serum samples across different concentrations.
Conclusions:
- Serum samples from apparently healthy humans and animals can likely be handled without significant risk of transmitting common bacterial agents.
- While the risk appears low, complete exclusion of potential infectious bacterial agent transmission from serum samples should not be assumed.
Abstract:
Immunological assays are valuable diagnostic tools to detect infections due to most of bacterial microorganisms. However, the question is how much safe are the common serum samples used as sources of antibodies in these assays? Here, we experimentally followed the issue. 10-fold serial dilutions of two Gram-positive, Staphylococcus aureus and Bacillus cereus, and one Gram-negative bacteria, Escherichia coli, were prepared and spiked into freshly taken blood samples of human and four animal species including sheep, goat, cattle, and horse. After blood clotting, serum samples were examined by colony count method before and after a centrifugation step followed by an observation with a scanning electron microscope. No bacteria grew from both centrifuged and non-centrifuged serum samples contained at least 7.5 × 102, 7.5 × 105, and 7.5 × 105 CFU/ml of S. aureus, B. cereus, and E. coli, respectively. Moreover, routine centrifugation criteria did not show any significant effect on decrease of bacterial cells in sera. The results suggest that we can handle serum samples of apparently healthy humans and animal species without deep concern for possibility of transmission of infectious bacterial agents. However, this supposition should not completely be excluded.
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