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Effect of diluents on the enumeration of Vibrio vulnificus
P V Azanza1, K A Buckle, G H Fleet
1Department of Food Science and Technology, University of New South Wales, Sydney, Australia.
Abstract:
Peptone (0.1%) solution containing 3% NaCl (PS) was a more suitable diluent than phosphate buffered saline (PBS) solution for the enumeration of Vibrio vulnificus in both broth cultures and oyster homogenates. PBS caused significant underestimation of the viable population of the species by plate counts on either selective or non-selective media. Dilution in PS is recommended in methods for the enumeration of V. vulnificus.
Insights
Peptone-salt solution is a better diluent than phosphate-buffered saline for counting Vibrio vulnificus in oysters and broths. Using phosphate-buffered saline leads to underestimating the viable Vibrio vulnificus population.
Area of Science:
- Microbiology
- Food Safety
- Bacteriology
Background:
- Accurate enumeration of Vibrio vulnificus is crucial for food safety, particularly in seafood like oysters.
- Standard laboratory diluents may impact the viability of certain bacterial species during enumeration.
Purpose of the Study:
- To compare the suitability of peptone-salt (PS) solution versus phosphate-buffered saline (PBS) as diluents for enumerating Vibrio vulnificus.
- To determine the impact of diluent choice on the accuracy of bacterial plate counts.
Main Methods:
- Enumeration of Vibrio vulnificus in broth cultures and oyster homogenates.
- Comparison of plate counts using selective and non-selective media after dilution in PS and PBS.
Main Results:
- Peptone-salt solution (0.1% peptone, 3% NaCl) provided more accurate counts of Vibrio vulnificus.
- Phosphate-buffered saline (PBS) caused significant underestimation of viable Vibrio vulnificus populations.
- Underestimation occurred regardless of whether selective or non-selective media were used.
Conclusions:
- Peptone-salt solution is a more suitable diluent for enumerating Vibrio vulnificus.
- Recommended use of PS in standard methods for Vibrio vulnificus quantification to ensure accurate results.