Bacterial spore levels in bulk tank raw milk are influenced by environmental and cow hygiene factors

Abstract

Sporeforming bacteria are responsible for the spoilage of several dairy products including fluid milk, cheese, and products manufactured using dried dairy powders as ingredients. Sporeforming bacteria represent a considerable challenge for the dairy industry because they primarily enter the dairy product continuum at the farm, survive processing hurdles, and subsequently grow in finished products. As such, strategies to reduce spoilage due to this group of bacterial contaminants have focused on understanding the effect of farm level factors on the presence of spores in bulk tank raw milk with the goal of reducing spore levels in raw milk, as well as understanding processing contributions to spore levels and outgrowth in finished products. The goal of the current study was to investigate sources of spores in the farm environment and survey farm management practices to identify variables using multimodel inference, a model averaging approach that eliminates the uncertainty of traditional model selection approaches, that affect the presence and levels of spores in bulk tank raw milk. To this end, environmental samples including feed, bedding, manure, soil, water, and so on, and bulk tank raw milk were collected twice from 17 upstate New York dairy farms over a 19-mo period and the presence and levels of various spore types (e.g., psychrotolerant, mesophilic, thermophilic, highly heat resistant thermophilic, specially thermoresistant thermophilic, and anaerobic butyric acid bacteria) were assessed. Manure had the highest level of spores for 4 out of 5 aerobic spore types with mean counts of 5.87, 5.22, 4.35, and 3.68 log cfu/g of mesophilic, thermophilic, highly heat resistant thermophilic, and specially thermoresistant thermophilic spores, respectively. In contrast, bulk tank raw milk had mean spore levels below 1 log cfu/mL across spore types. Multimodel inference was used to determine variables (i.e., management factors, environmental spore levels, and meteorological data from each sampling) that were important for presence or levels of each spore type in bulk tank raw milk. Analyses indicated that variables of importance for more than one spore type included the residual level of spores in milk from individual cows after thorough teat cleaning and forestripping, udder hygiene, clipping or flaming of udders, spore level in feed commodities, spore level in parlor air, how often bedding was topped up or changed, the use of recycled manure bedding, and the use of sawdust bedding. These results improve our understanding of how spores transfer from environmental sources into bulk tank raw milk and provide information that can be used to design intervention trials aimed at reducing spore levels in raw milk.

Reservoirs of antimicrobial resistance genes in retail raw milk

“…2b and c). This is consistent with the fact that HTST milk commonly comes from multiple dairies and bacteria that remain after heat-treatment are likely also diverse [26,27]. Interestingly, the diversity estimated in HTST milk fluctuated over the RT incubation, during which both alpha diversities exhibited decreases at 4 h and 24 h (LMM, P < 0.01, Fig.…”

Paenibacillus odorifer, the Predominant Paenibacillus Species Isolated from Milk in the United States, Demonstrates Genetic and Phenotypic Conservation of Psychrotolerance but Clade-Associated Differences in Nitrogen Metabolic Pathways

“…Reducing contamination with P. odorifer spores may be achieved at the farm level by implementing management practices aimed at reducing the transfer of bedding material, soil, and manure into raw milk, as these sources have been previously shown to harbor psychrotolerant spore-forming bacteria like Paenibacillus spp. (42,45,46). Finally, as Paenibacillus spp.…”

Optimizing Pasteurized Fluid Milk Shelf-Life Through Microbial Spoilage Reduction

“…There are two primary routes through which spoilage bacteria enter the fluid milk supply chain: (i) contamination of raw milk on farms with psychrotolerant Gram-positive sporeforming bacteria (Martin et al, 2019) and (ii) contamination of milk at the processing level with Gram-negative bacteria after pasteurization (i.e., post-pasteurization contamination) (Martin et al, 2018). When post-pasteurization contamination is prevented (e.g., through Good Manufacturing Practices), psychrotolerant Gram-positive spore-forming bacteria (e.g., Bacillus spp.…”

“…are the primary causes of pasteurized fluid milk spoilage. This is because spores (i.e., the resistant structure produced by the spore-forming bacteria) can survive commonly used pasteurization methods (e.g., HTST) (Martin et al, 2019) and subsequently grow at refrigeration temperatures over a period of 14-17 days after pasteurization (Ranieri and Boor, 2009). Some technologies such as ultra-high pasteurization [e.g., pasteurization at 138 • C (280 • F) for 2 s (International Dairy Food Association, n.d.)] are known to effectively reduce bacterial spores in fluid milk.…”