Effects of storage methods on the recovery of Mycoplasma species from milk samples

Abstract

Mycoplasma species are fastidious microorganisms causing mastitis in dairy cows. Storage by freezing milk samples affects their viability. The purpose of this study was to compare the effect of alternative storage methods on their recoverability. In Experiment I, mycoplasma counts from fresh milk samples were compared to those same samples stored for 1, 3, and 5 days at refrigerated (5 °C) temperatures. Experiment II was done to compare the mycoplasma counts of fresh milk samples with those stored frozen (−20 °C) with addition of 0%, 10%, 30% and 50% glycerol (v/v). Two strains of each of 5 species: M. bovis, M. californicum, M. bovigenitalium, M. canadense and M. alkalescens, were selected and inoculated into bulk tank milk free of this pathogen. Compared to those in fresh milk samples, counts were approximately reduced by: 0.3 log 10 CFU/ml in 5 day refrigerated milk ( P < 0.05) and by 1.0 log 10 CFU/ml in milk frozen without glycerol ( P < 0.05). Addition of glycerol (10% and 30%, v/v) to milk samples increased the number of recovered Mycoplasma by up to 0.4 log 10 CFU/ml in frozen milk samples ( P < 0.05). No significant interactions were detected between either Mycoplasma species or starting concentration and survival as effected by storage method. Refrigerating milk samples for 5 days and freezing milk samples lowers the number of recovered Mycoplasma species . The addition of glycerol to achieve 10% and 30% v/v solutions improves the recovery of Mycoplasma species from frozen milk samples. To maximize detection of this pathogen, fresh milk samples should be cultured without storage.