[Testing of culture media for detection of Staphylococcus aureus in bulk milk samples].
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.
Benda
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Research Institute for Cattle Breeding, Rapotín, Czech Republic.
Vyletĕlová
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M
D000818:Animals; D003470:Culture Media; D005516:Food Microbiology; D008892:Milk / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000302:isolation & purification*
D003470:Culture Media