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Updated: Sep 21, 2026
Aseptic Laboratory Techniques: Plating Methods
Published on: May 11, 2012
[Evaluation of selective plating media for the detection of heat- or freeze-injured Staphylococcus aureus]
Yoichi Onoue1, Rie Shindo, Hiroshi Teranishi
1Kanagawa Prefectural Public Health Laboratory: 1-1-1, Nakao, Asahi-ku, Yokohama 241-0815, Japan.
Abstract:
The efficacy of Baird-Parker (BP) agar, mannitol-salt-egg yolk (MSEY) agar and mannitol salt (MS) agar in detecting Staphylococcus aureus FRI-100 heated at 52 degrees C for 20 min in 100 mmol/L potassium phosphate buffer was determined. Brain heart infusion agar with 1% pyruvate (BHIP agar) supported the highest recovery of injured cells and was used as the control medium. Of the three selective media, significantly higher recovery of heat-injured cells was observed on BP agar than MSEY agar, and the poorest recovery was observed on MS agar (p < 0.05). Low recovery of unheated cells was obtained for MS compared with other media (p < 0.05). A reduction in populations occurred gradually in reagent-grade water stored for 14 days at -20 degrees C. There was no significant difference between BHIP agar and MS agar in the number of freeze-injured cells recovered from 1 to 14 days.
Insights
Baird-Parker agar showed the best recovery of heat-injured Staphylococcus aureus cells compared to other selective media. Mannitol salt agar performed poorly for both heat- and freeze-injured cells.
Area of Science:
- Microbiology
- Food Safety
Background:
- Selective culture media are crucial for detecting bacterial pathogens like Staphylococcus aureus.
- Heat and cold stress can injure bacterial cells, affecting their recovery on selective media.
Purpose of the Study:
- To evaluate the efficacy of Baird-Parker (BP), mannitol-salt-egg yolk (MSEY), and mannitol salt (MS) agars in detecting heat-injured Staphylococcus aureus.
- To compare the recovery of unheated and injured Staphylococcus aureus cells on different selective media.
Main Methods:
- Staphylococcus aureus FRI-100 was subjected to heat injury (52°C for 20 min) and cold storage (-20°C for 14 days).
- Recovery of injured and unheated cells was assessed on BP, MSEY, MS, and Brain Heart Infusion Pyruvate (BHIP) agars.
- Statistical analysis (p < 0.05) was used to compare cell recovery rates.
Main Results:
- Baird-Parker agar demonstrated significantly higher recovery of heat-injured Staphylococcus aureus compared to MSEY agar.
- Mannitol salt agar showed the poorest recovery for both heat-injured and unheated cells.
- Brain heart infusion agar with pyruvate (BHIP agar) supported the highest recovery of heat-injured cells, serving as a control.
- No significant difference in freeze-injured cell recovery was observed between BHIP and MS agars over 14 days.
Conclusions:
- Baird-Parker agar is more effective than MSEY and MS agars for detecting heat-injured Staphylococcus aureus.
- Mannitol salt agar is not recommended for enumerating heat- or freeze-injured Staphylococcus aureus.
- BHIP agar is a suitable control medium for assessing injured cell recovery.
