Butyric acid-producing bacterial spore levels in conventional raw milk vary by farm

Abstract

Graphical Abstract Summary: The levels of anaerobic butyric acid-producing sporeforming bacteria (BAB) in bulk tank raw milk from 7 similarly managed conventional dairy farms were studied. It is important to control and minimize BAB spores in raw milk to prevent late blowing defect in certain styles of cheese during aging. Different farm management practices such as bedding type used, cleaning agents, and udder clipping frequency may affect BAB spore concentrations in raw milk. We employed statistical models to test the relationship between farm-level factors and BAB spore concentrations. No significant association between management practices surveyed (i.e., bedding management, milking preparation procedures, teat and udder cleanliness scoring, holding area cleaning procedures, and udder clipping or flaming frequency) and BAB spore concentration was found, with one possible reason being the small sample size used. The minimum number of individual samples required was calculated using parameters from this study, demonstrating how this research can be used for future study design.

A machine learning approach reveals that spore levels in organic bulk tank milk are dependent on farm characteristics and meteorological factors

“…These values are very similar to data collected from previous studies, in which a positive rate of 87% with a mean of 0.36 log 10 CFU/mL and a standard deviation of 0.51 log 10 CFU/mL (Martin et al, 2019) and a positive rate of 85% with a mean of 0.26 log 10 CFU/mL and a standard deviation of 0.52 log 10 CFU/mL (Murphy et al, 2019) were reported. Similar to TSC, BAB data from our study are not substantially different from previous studies (Vissers et al, 2007a;Shi et al, 2023). Organic milk samples evaluated in this study had a 94.4% positive rate with a mean of 2.19 log 10 MPN/L and a standard deviation of 0.65 log 10 MPN/L.…”

“…Organic milk samples evaluated in this study had a 94.4% positive rate with a mean of 2.19 log 10 MPN/L and a standard deviation of 0.65 log 10 MPN/L. By comparison, Vissers et al (2007a) reported a mean of 2.10 log 10 MPN/L with a standard deviation of 0.71 log 10 MPN/L while Shi et al (2023) reported a positive rate of 87% with a mean 1.79 log 10 MPN/mL and a standard deviation of 0.59 log 10 MPN/L for 12 NY farms enrolled in the study. Similar to the other spore levels reported here, the levels and variance in psychrotolerant spore count found in this study were in line with what research on conventional raw milk has reported.…”

“…Any tubes with observed movement of the wax plug, indicating gas formation, were scored as positive. The number of positive and negative tubes for each sample was used to calculate the final BAB MPN/mL as previously described (Shi et al, 2023).…”

Sources, transmission, and tracking of sporeforming bacterial contaminants in dairy systems

“…Despite these high spore concentrations in key sources, spores are generally present in raw milk at much lower levels. For example, recent studies indicate that the mean psychrotolerant spore count ( PSC ), MSC, and thermophilic spore count are −0.72 ( Buehler et al, 2018 ), 0.26 and 0.26 log cfu/mL ( Murphy et al, 2019 ), respectively, whereas the butyric acid bacteria most probable number ( MPN ) for enumeration of anaerobic gas–producing spores is 1.79 log MPN/L ( Shi et al, 2023 ). The level of spore contamination in the bulk tank raw milk is ultimately driven by the practices implemented at the point of milk harvest, including teat and udder hygiene ( Zucali et al, 2015 ), milking routine ( Bava et al, 2017 ), and consistently applied procedures by milking parlor employees ( Evanowski et al, 2020 ).…”