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[Testing of culture media for detection of Staphylococcus aureus in bulk milk samples]
1Research Institute for Cattle Breeding, Rapotín, Czech Republic.
Abstract:
Three common selective agar culture media were tested with respect to detection of Staphylococcus aureus: Baird-Parker agar (BP), Mannitol-Salt-Phenol agar (MAN) and Vogel-Johnson agar (VJ). All media were cultivated at temperatures of 37 degrees C and 43 degrees C. Three groups of samples were used for investigations: 1, pure cultures of 52 collection strains of S. aureus received from the Czech Microorganism Collection (Tab. I), 2. pure cultures of 75 laboratory strains of S. aureus from samples of cow raw milk and 3,223 bulk samples of cow raw milk. Medium recovery and frequency of medium failure were evaluated, as well as subjective evaluation of medium selectivity and count feasibility was done. The best results of recovery and failure frequency were observed in BP/37 degrees C for all three groups; except the collection strains, in which a distinction from BP/43 degrees C was only moderately significant (P = 0.1; Tab. II), statistically significantly better results of recovery against the other media were determined for BP/37 degrees C in all cases (Tabs. III, VI, IX). No other medium with better results was found out for any other group of samples as regards failure frequency (Tabs. IV, VII, X). Recoveries of BP/43 degrees C ranged from 78 to 95% in comparison with BP/37 degrees C (Figs. 1-3). A group of three media (VJP/37 degrees C, MAN/37 degrees C, MAN/43 degrees C) showed similar results in all groups of samples, statistically significant differences were rare (Tabs. III, VI, IX); recoveries ranged from 55-85% in comparison with BP/37 degrees C (Figs. 1-3). The cultivation on VJ/43 degrees C turned out absolutely inappropriate. Subjective evaluation (Tab. IX) revealed BP/43 degrees C as the best medium, particularly due to the clearly expressed diagnostic traits and high selectivity for accompanying microflora. Enterococci were the most important accompanying microflora in cases of BP/37 degrees C, BP/43 degrees C and VJ/37 degrees C; while in MAN/37 degrees C and MAN/43 degrees C the microflora making the count difficult consisted of representatives of the genera Staphylococcus, Micrococcus and Bacillus. Determinations on different media (except VJ/43 degrees C) well correlated with each other in general (Tabs. V, VIII, XI), the differences in correlations between the pairs of media were not commonly statistically significant.
Insights
Baird-Parker agar at 37°C demonstrated superior recovery and fewer failures for detecting Staphylococcus aureus across various sample types. This selective medium is recommended for accurate bacterial identification in food safety and clinical diagnostics.
Area of Science:
- Microbiology
- Food Science
- Clinical Diagnostics
Context:
- Accurate detection of Staphylococcus aureus is crucial for public health and food safety.
- Selective agar media are commonly used for isolating and identifying S. aureus.
- Optimizing culture conditions and media choice can improve detection rates.
Purpose:
- To evaluate and compare the performance of three selective agar media (Baird-Parker, Mannitol-Salt-Phenol, Vogel-Johnson) for Staphylococcus aureus detection.
- To assess the impact of incubation temperatures (37°C and 43°C) on medium efficacy.
- To determine the best medium and temperature combination for S. aureus recovery and identification.
Summary:
- Baird-Parker agar incubated at 37°C (BP/37°C) exhibited the highest recovery rates and lowest failure frequencies for S. aureus across pure cultures and raw milk samples.
- While BP/37°C showed statistically significant advantages, BP at 43°C (BP/43°C) also performed well, particularly in subjective evaluations for selectivity.
- Mannitol-Salt-Phenol agar and Vogel-Johnson agar showed lower recovery rates, with Vogel-Johnson agar at 43°C (VJ/43°C) being unsuitable.
Impact:
- Identifies Baird-Parker agar at 37°C as the optimal selective medium for reliable Staphylococcus aureus detection.
- Provides evidence-based recommendations for microbiological laboratories, enhancing diagnostic accuracy.
- Contributes to improved food safety and clinical surveillance by optimizing bacterial detection methods.