Enumeration of coagulase and thermonuclease-positive Staphylococcus spp. in raw milk and fresh soft cheese: an evaluation of Baird-Parker agar, Rabbit Plasma Fibrinogen agar and the Petrifilm Staph Express count system.
Staphylococcus spp. are microorganisms that are naturally present in milk and dairy products and are often associated with food-borne diseases outbreaks due to the ability of some strains to produce thermostable enterotoxins. This ability is usually associated with coagulase and thermonuclease production, characteristics that are considered in the microbiological analyses for the control of such microorganisms. The objective of this study was to evaluate the culture media and the methodologies used for the enumeration of coagulase and thermonuclease-positive Staphylococcus spp. in raw milk and fresh soft cheese. Samples of artificially contaminated milk (with coagulase-positive Staphylococcus reference strains) and samples of naturally contaminated raw milk and cheese were submitted for enumeration in Baird-Parker agar (BP), Rabbit Plasma Fibrinogen agar (RPFA) and in the Petrifilm Staph Express count system (STX). No significant differences (P > 0.05) were observed between the mean counts obtained in all of the evaluated culture media. RPFA and STX had good correlation indices between the total and typical colony counts as well as with coagulase and the thermonuclease-positive colony counts. Thus, there is a better association between coagulase and thermonuclease production to typical colony morphology developed on these culture media, leading to more accurate and reliable results than with BP, which demonstrated lower correlation indices between these counts.
Viçosa
Gabriela Nogueira
GN
Departamento de Veterinária, Universidade Federal de Viçosa, Campus UFV, 36570 000 Viçosa, MG, Brazil.
Moraes
Paula Mendonça
PM
Yamazi
Anderson Keizo
AK
Nero
Luís Augusto
LA
D000362:Agar; D000818:Animals; D001431:Bacteriological Techniques; D002611:Cheese / Q000382:microbiology*; D003030:Coagulase / Q000378:metabolism; D015169:Colony Count, Microbial / Q000379:methods*; D003470:Culture Media / Q000737:chemistry; D005506:Food Contamination / Q000032:analysis*; D005516:Food Microbiology; D006801:Humans; D008836:Micrococcal Nuclease / Q000378:metabolism; D008892:Milk / Q000382:microbiology*; D013210:Staphylococcus / Q000201:enzymology / Q000302:isolation & purification* / Q000378:metabolism
D003030:Coagulase; D003470:Culture Media; D000362:Agar; D008836:Micrococcal Nuclease