Purpose: To describe the population dynamics of sporeforming bacteria and spores in milk from farm to packing plant.
Methods: A systematic review was conducted to identify and summarize primary research studies that describe the prevalence and/or concentration of spore-forming bacteria and spores at more than one production/processing point in the same study. Relevant studies are considered from countries implementing similar processing procedures as the United States without publication year restriction.
Results: Literature searches retrieved 9,778 citations, among which data were extracted from 31 relevant citations for meta-analysis. Due to variant milk sampling points recorded in citations, we standardized the sampling points by clustering similar ones as follows: on farm, during transportation, at plant before pasteurization and after pasteurization. Bacillus cereus was the most reported organism. Concentrations were more abundant with 582 data points for both vegetative cells and spores, compared to prevalence data with 68 points. In general, great heterogeneity was observed among studies in the contamination of milk samples. Spore concentrations remain stable until pasteurization, in a range of 0-2.5 log spores/ml. After pasteurization, spore concentrations decrease in accordance with an increase in vegetative cells.
Significance: Although considerable research has been conducted on this topic, there are limited studies to holistically describe the population dynamics of sporeforming bacteria under the current milk production system. Findings of this study can provide insights regarding steps where spore-forming bacteria could be introduced for potential effective management, as well as further research needs to increase the quality and shelf life of milk products in the United States.