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Short communication: Improved method for centrifugal recovery of bacteria from raw milk applied to sensitive real-time quantitative PCR detection of Salmonella spp.1

Brewster, Jeffrey D., Paul, Moushumi
Journal of dairy science 2016 v.99 no.5 pp. 3375-3379
EDTA (chelating agent), Salmonella, agitation, bacteria, calcium, centrifugation, chelating agents, cream, detergents, homogenization, homogenized milk, lipids, microbial detection, milk, pasteurization, pathogens, quantitative polymerase chain reaction, raw milk, somatic cells, sugars, whey
Centrifugation is widely used to isolate and concentrate bacteria from dairy products before assay. We found that more than 98% of common pathogenic bacteria added to pasteurized, homogenized, or pasteurized homogenized milk were recovered in the pellet after centrifugation, whereas less than 7% were recovered from raw milk. The remaining bacteria partitioned into the cream layer of raw milk within 5 min, and half-saturation of the cream layer required a bacterial load of approximately 5×108 cfu/mL. Known treatments (e.g., heat, enzymes or solvents) can disrupt cream layer binding and improve recovery from raw milk, but can also damage bacteria and compromise detection. We developed a simple, rapid agitation treatment that disrupted bacteria binding to the cream layer and provided more than 95% recovery without affecting bacteria viability. Combining this simple agitation treatment with a previously developed real-time quantitative PCR assay allowed the detection of Salmonella spp. in raw milk at 4 cfu/mL within 3 h. To our knowledge, this is the first report of an effective method for achieving high centrifugal recovery of bacteria from raw milk without impairing bacterial viability.