Management practices and forage quality affecting the contamination of milk with anaerobic spore-forming bacteria

Sources of propionic acid bacteria contamination in the milking parlor environment on Alpine Dairy Farms

High quality raw milk is an important prerequisite for the production of long ripened raw milk cheeses. This implies not only the absence of pathogenic microorganisms in raw milk, but also low levels of spoilage bacteria, including dairy propionic acid bacteria (dPAB), that can cause blowing and sensory defects in cheese, resulting in severe economic losses for producers. Raw milk contamination with dPAB has been primarily associated with improperly cleaned milking systems, but they have been detected in feed, soil, feces and on the teat skin. The objective of this study was to identify potential sources of raw milk contamination with dPAB in the barn and milking parlor environments. We also wanted to know more about the prevalence of the dPAB species in these environments and the levels of contamination. For this purpose, 16 small scale Alpine dairy farms were visited in August 2022: samples were taken from the barn environment (e.g., swab samples, air, feed, bedding), the milking system (swab samples, residual cleaning water, cleaning sponges, milk filters) and milk samples were collected at various sampling points along the milking system. Samples were analyzed for dPAB contamination, and results showed contamination at multiple sampling locations. We observed potential adverse effects of improperly set cleaning parameters of the milking system, as well as of farm specific practices. In addition, we identified cleaning water residues as an important source of contamination. Based on these findings, we propose potential mitigation strategies to reduce the risk of raw milk contamination with cheese spoilage bacteria, thereby contributing to a more sustainable food production.

Importance of Pre-Milking Udder Hygiene to Reduce Transfer of Clostridial Spores from Teat Skin to Raw Milk

Butyric acid producing clostridia (BAPC) cause the so-called late-blowing defect, a serious quality problem in semi-hard and hard cheeses. Late-blown cheeses are characterized by undesired slits and cracks, irregular eyes, and off-flavors due to excessive amounts of gas and organic acids produced by clostridia. Clostridial transfer to raw milk can occur during milking through dirty teats. Therefore, teat cleaning before milking is a key factor in preventing clostridial contamination of the milk. However, different cleaning methods are used, and little information is available on the efficacy of routine teat cleaning in reducing clostridial endospores. The main objectives of this study were to assess the extent of udder contamination with BAPC spores and to investigate the efficacy of routine teat cleaning on BAPC spore counts in milk. In a longitudinal study, eight dairy farms were visited during five sampling events. Clostridial spore counts were quantified from teat skin before and after routine teat cleaning, in pooled quarter milk samples from individual cows, and in bulk tank milk samples using a most probable number method. In addition, farm management data were collected periodically through a survey, and average cow cleanliness was assessed by a veterinarian. On average, teat cleaning resulted in a 0.6 log unit reduction in BAPC spores on teat skin, and a strong positive correlation was found between BAPC spore concentrations on teat skin after cleaning and in pooled quarter milk samples. Seasonal variations and the potential influence of differences in farm management were also noted. Interestingly, average cow cleanliness correlated strongly with BAPC spore levels in milk, suggesting the potential for a quick and rough estimation method of clostridial contamination that could be implemented by farmers.

Low-Level Clostridial Spores' Milk to Limit the Onset of Late Blowing Defect in Lysozyme-Free, Grana-Type Cheese

The growth of clostridial spores during ripening leads to late blowing (LB), which is the main cause of spoilage in Grana Padano Protected Designation of Origin (PDO) cheese and other hard, long-ripened cheeses such as Provolone, Comté, and similar cheeses. This study aimed to verify the cause-effect relationship between the level of clostridial butyric spores (BCS) in milk and the onset of the LB defect. To this end, experimental Grana-type cheeses were produced without lysozyme, using bulk milk with different average BCS content. The vat milk from the so-called "virtuous" farms (L1) contained average levels of BCS of 1.93 ± 0.61 log most probable number (MPN) L^-1, while the vat milk from farms with the highest load of spores (L2), were in the order of 2.99 ± 0.69 log MPN L^-1. Cheeses after seven months of ripening evidenced a strong connection between BCS level in vat milk and the occurrence of LB defect. In L2 cheeses, which showed an average BCS content of 3.53 ± 1.44 log MPN g^-1 (range 1.36-5.04 log MPN g^-1), significantly higher than that found in L1 cheeses (p < 0.01), the defect of LB was always present, with Clostridium tyrobutyricum as the only clostridial species identified by species-specific PCR from MPN-positive samples. The L1 cheeses produced in the cold season (C-L1) were free of defects whereas those produced in the warm season (W-L1) showed textural defects, such as slits and cracks, rather than irregular eyes. A further analysis of the data, considering the subset of the cheesemaking trials (W-L1 and W-L2), carried out in the warm season, confirmed the presence of a climate effect that, often in addition to the BCS load in the respective bulk milks (L1 vs. L2), may contribute to explain the significant differences in the chemical composition and some technological parameters between the two series of cheeses. Metagenomic analysis showed that it is not the overall structure of the microbial community that differentiates L1 from L2 cheeses but rather the relative distribution of the species between them. The results of our trials on experimental cheeses suggest that a low-level BCS in vat milk (<200 L^-1) could prevent, or limit, the onset of LB in Grana-type and similar cheeses produced without lysozyme.

Clostridium tyrobutyricum occurrence in silages and cattle feed: Use of molecular and simulation data to optimize predictive models

Introduction

Poor quality silage can derive from the presence of deleterious microorganisms such as clostridia. Their dissemination along the food chain, especially in milk, causes issues such as the cheese late-blowing defect, particularly triggered by Clostridium tyrobutyricum. The scope of our study was to determine the C. tyrobutyricum occurrence in three different farms across four time periods in relation to the animal diets, specifically the Total Mixed Ration (TMR), by using real-time PCR.

Methods

For this purpose, molecular-derived data were exploited to optimize a predictive model that simulated the farm conditions favoring the growth of butyric acid bacteria such as C. tyrobutyricum.

Results

Our results showed that the originally utilized predictive model strongly underestimated the growth of C. tyrobutyricum in comparison to the molecular data. At the same time, our findings uncovered an additional source of contamination in the TMR related to silage and dietary residues that represent a reservoir of microbial contamination during successive TMR preparation. Based on these findings, the optimization of the model parameters such as growth rate range and the inclusion of the residues in the model, allowed a more accurate prediction of the contamination levels. Therefore, this study revealed that proper hygiene practices such as the removal of silage and TMR residues within the farm environment is essential to control the contamination by C. tyrobutyricum and avoid food waste and economic losses.

Graduate Student Literature Review: Farm management practices: Potential microbial sources that determine the microbiota of raw bovine milk

Environmental and herd-associated factors such as geographical location, climatic conditions, forage types, bedding, soil, animal genetics, herd size, housing, lactation stage, and udder health are exploited by farmers to dictate specific management strategies that ensure dairy operation profitability and enhance the sustainability of milk production. Along with milking routines, milking systems, and storage conditions, these farming practices greatly influence the microbiota of raw milk, as evidenced by several recent studies. During the past few years, the increased interest in high-throughput sequencing technologies combined with culture-dependent methods to investigate dairy microbial ecology has improved our understanding of raw milk community dynamics throughout storage and processing. However, knowledge is still lacking on the niche-specific communities in the farm environment, and on the factors that determine bacteria transfer to the raw milk. This review summarizes findings from the past 2 decades regarding the effects of farm management practices on the diversity of bacterial species that determine the microbiological quality of raw cow milk.

Inoculation of mother's own milk could personalize pasteurized donor human milk used for feeding preterm infants

BACKGROUND

Human milk is a vehicle for bioactive compounds and beneficial bacteria which promote the establishment of a healthy gut microbiome of newborns, especially of preterm infants. Pasteurized donor human milk (PDHM) is the second-best option when preterm mother's own milk is unavailable. Since pasteurization affect the microbiological quality of donor milk, PDHM was inoculated with different preterm milk samples and then incubated, in order to evaluate the effect in terms of bacterial growth, human milk microbiome and proteolytic phenomena.

METHODS

In an in-vitro study PDHM was inoculated at 10% v/v using ten preterm milk samples. Microbiological, metataxonomic and peptidomic analyses, on preterm milk samples at the baseline (T0), on PDHM and on inoculated milk (IM) samples at T0, after 2 h (T1) and 4 h (T2) of incubation at 37 °C, were conducted.

RESULTS

IM samples at T2 showed a Total Bacterial Count not significantly different (p > 0.01) compared to preterm milk samples. At T2 lactic acid bacteria level was restored in all IM. After inoculation, metataxonomic analysis in IM samples showed that Proteobacteria remained the predominant phylum while Firmicutes moved from 3% at T1 to 9.4% at T2. Peptidomic profile of IM resembled that of PDHM, incubated for the same time, in terms of number and type of peptides.

CONCLUSION

The study demonstrated that inoculation of PDHM with mother's own milk could restore bacterial growth and personalize human milk microbiome in PDHM. This effect could be beneficial because of the presence of maternal probiotic bacteria which make PDHM more similar to mother's own milk.

Farm Silage Facilities and Their Management for the Prevention of Anaerobic Bacteria Spore Contamination in Raw Milk

At feed-out, aerobic spoilage of silage enables an increase in anaerobic spore-forming bacteria (ANSB) that may enter the total mixed ration (TMR). The aim of our study was to understand whether in hot summers the silage structures and management may affect the level of ANSB in milk for long-ripening cheese production. A survey of silage facilities, management, and their relationships with silage, TMR, feces, and milk ANSB most probable number (MPN) content was conducted in the Po Valley during summer months. Silo type did not affect the mean ANSB, but only the wideness of their value distributions, with a narrow range for bags and a wider range for bunkers. The unloading equipment affected the ANSB count; the front-end loader with cutter was associated with a lower ANSB count—probably as a result of the reduced surface left after daily silage removal. Silo length and daily removed face width were the main factors affecting contamination of silage by spore-forming bacteria during summer, with longer silos and wider surface removal reducing ANSB contamination—probably as a consequence of reduced aerobic spoilage at the silage surface. The silage contamination by spore-forming bacteria within a log10 2 MPN g−1 allowed a low concentration of spore-forming bacteria at the farm bulk milk tank level. Fecal ANSB levels did not factor into the regression that explains the ANSB in farm milk. It has been found that silage facilities’ features and their management are an important first step to reduce the extent of ANSB contamination at the farm level.

Colorimetric Point-of-Care Detection of Clostridium tyrobutyricum Spores in Milk Samples

Clostridium tyrobutyricum represents the main spoiling agent responsible for late blowing defects (LBD) in hard and semi-hard cheeses. Its spores are resistant to manufacturing procedures and can germinate during the long ripening process, causing the burst of the cheese paste with a consequent undesirable taste. The lower quality of blown cheeses leads to considerable financial losses for the producers. The early identification of spore contaminations in raw milk samples thus assumes a pivotal role in industrial quality control. Herein, we developed a point of care (POC) testing method for the sensitive detection of C. tyrobutyricum in milk samples, combining fast DNA extraction (with no purification steps) with a robust colorimetric loop-mediated isothermal amplification (LAMP) technique. Our approach allows for the sensitive and specific detection of C. tyrobutyricum spores (limit of detection, LoD: ~2 spores/mL), with the advantage of a clear naked-eye visualization of the results and a potential semi-quantitative discrimination of the contamination level. In addition, we demonstrated the feasibility of this strategy using a portable battery-operated device that allowed both DNA extraction and amplification steps, proving its potential for on-site quality control applications without the requirement of sophisticated instrumentation and trained personnel.

Effect of Different Farming Practices on Lactic Acid Bacteria Content in Cow Milk

The natural load of lactic acid bacteria (LAB) in milk is the basis of the production of raw milk cheeses, such as Grana Padano PDO. In the last decades, improvements in livestock hygiene management resulted in bulk cow milk with less than 20,000 colony forming units (CFU) of bacterial count, unable to ensure a sufficient supply of LAB, with a negative impact on cheese quality. This study investigated the relations between farm management practices and prevalence of different groups of bacteria in cow milk. Sixty-two intensive dairy farms located in Lombardy (Italy) where involved, most of them destined as milk for the production of Grana Padano. Season had no significant effect on the content of most of the bacterial groups, except for coliforms. A strong relation among standard plate count (SPC) and other bacterial groups was evidenced. Cluster analysis showed that the most productive farms applied a complete milking routine and produced milk with the lowest value of SPC, the lowest count of the other bacteria, including LAB, but the highest LAB/SPC. The study suggests that complexity of farming practices can affect the microbial population of milk.

Strain-Dependent Cheese Spoilage Potential of Clostridium tyrobutyricum

Clostridium tyrobutyricum, a Gram-positive, anaerobic, spore-forming bacterium, is considered as one of the main causative agents for spoilage of hard and semihard cheeses. Growth of C. tyrobutyricum in cheese is critically influenced by ripening temperature and time, pH, salt and lactic acid concentration, moisture and fat content, and the presence of other microorganisms. Previous studies revealed high intraspecies diversity of C. tyrobutyricum strains and variable tolerance toward pH, temperatures, and salt concentrations. These findings indicate that strain-dependent characteristics may be relevant to assess the risk for cheese spoilage if clostridial contamination occurs. In this study, we aimed to compare the phenotypes of 12 C. tyrobutyricum strains which were selected from 157 strains on the basis of genotypic and proteotypic variability. The phenotypic analysis comprised the assessment of gas production and organic acid concentrations in an experimental cheese broth incubated at different temperatures (37, 20, and 14 °C). For all tested strains, delayed gas production at lower incubation temperatures and a strong correlation between gas production and the change in organic acid concentrations were observed. However, considering the time until gas production was visible at different incubation temperatures, a high degree of heterogeneity was found among the tested strains. In addition, variation among replicates of the same strain and differences due to different inoculum levels became evident. This study shows, that, among other factors, strain-specific germination and growth characteristics should be considered to evaluate the risk of cheese spoilage by C. tyrobutyricum.

Dairy farm management practices and the risk of contamination of tank milk from Clostridium spp. and Paenibacillus spp. spores in silage, total mixed ration, dairy cow feces, and raw milk

The occurrence of Paenibacillus and Clostridium spores in silage is of great concern for dairy producers because their spores can contaminate milk and damage processed milk and semi-hard cheeses. Spoiled silage is considered to be the main contamination source of the total mixed ration (TMR), feces of dairy cows, and consequently bulk tank milk via the contamination of cow teats by dirt during milking. The presence of an anaerobic and facultative anaerobic sporeformer population in different matrices (soil, corn silage, other feeds, TMR, feces, and milk) and its transmission pathway has been studied on 49 dairy farms by coupling plate count data with 16S-DNA identification. The different matrices have shown a high variability in the anaerobic and facultative anaerobic spore count, with the highest values being found in the aerobically deteriorated areas of corn silages. Clostridium tyrobutyricum, Paenibacillus macerans, and Paenibacillus thermophilus were detected in all the matrices. The TMR spore count was influenced by the amount of spoiled corn silage in the TMR and by the care taken when cleaning the spoiled silage before feed-out. Most of the farms that prevent the presence of visible moldy silage in the silo and carefully clean to remove molded spots were able to maintain their TMR spore counts below 4.0 log spores/g. When a level of 4.5 log spores/g of TMR was exceeded, the feces presented a greater contamination than 3.0 log spores/g. Moreover, the higher the number of spores in the feces was, the higher the number of spores in the milk. Most of the farms that presented a feces contamination greater than 5.0 log spores/g had a higher milk spore contamination than 1,000 spores/L. Careful animal cleaning and good milking practices have been found to be essential to maintain low levels of contamination in bulk tank milk, but it has emerged that only by coupling these practices with a correct silage management and cleaning during TMR preparation can the contamination of milk by spores be kept at a low level. It has been found that aerobically deteriorated silage has a great capacity to contaminate TMR and consequently to increase the risk of milk spore contamination, even when routine milking practices are adopted correctly.

Bedding and bedding management practices are associated with mesophilic and thermophilic spore levels in bulk tank raw milk

Mesophilic and thermophilic spore-forming bacteria represent a challenge to the dairy industry, as these bacteria are capable of surviving adverse conditions associated with processing and sanitation and eventually spoil dairy products. The dairy farm environment, including soil, manure, silage, and bedding, has been implicated as a source for spores in raw milk. High levels of spores have previously been isolated from bedding, and different bedding materials have been associated with spore levels in bulk tank (BT) raw milk; however, the effect of different bedding types, bedding management practices, and bedding spore levels on the variance of spore levels in BT raw milk has not been investigated. To this end, farm and bedding management surveys were administered and unused bedding, used bedding, and BT raw milk samples were collected from dairy farms (1 or 2 times per farm) across the United States over 1 yr; the final data set included 182 dairy farms in 18 states. Bedding suspensions and BT raw milk were spore pasteurized (80°C for 12 min), and mesophilic and thermophilic spores were enumerated. Piecewise structural equation modeling analysis was used to determine direct and indirect pathways of association among farm and bedding practices, levels of spores in unused and used bedding, and levels of spores in BT raw milk. Separate models were constructed for mesophilic and thermophilic spore levels. The analyses showed that bedding material had a direct influence on levels of spores in unused and used bedding as well as an indirect association with spore levels in BT raw milk through used bedding spore levels. Specific bedding and farm management practices as well as cow hygiene in the housing area were associated with mesophilic and thermophilic spore levels in unused bedding, used bedding, and BT raw milk. Notably, levels of spores in used bedding were positively related to those in unused bedding, and used bedding spore levels were positively related to those in BT raw milk. The results of this study increase the understanding of the levels and ecology of mesophilic and thermophilic spores in raw milk, emphasize the possible role of bedding as a source of spores on-farm, and present opportunities for dairy producers to reduce spore levels in BT raw milk.

Efficient milking hygiene reduces bacterial spore contamination in milk

Clostridia in the milk can lead to late blowing, a cheese defect. Clostridia are ubiquitous, deriving from both the farm environment and the feed ingested by the cows, and are transferred into the milk through faecal contamination. Our aim was to investigate the effect of different in-parlour practices on the content of anaerobic spore-forming bacteria in milk, and to monitor the variation in spore content in the feed and environment. The experiment, conducted in an experimental dairy during autumn, was repeated in exactly the same way for two consecutive years. The experimental design applied three different milking routines in three consecutive 7-d periods: forestripping alone (F); forestripping and post-dipping (F+Post); pre-dipping, wiping, forestripping and post-dipping (Pre+F+Post). Teat skin swabs and samples of feed, faeces, bedding materials and milk were collected for microbiological analyses. The dietary forage of the lactating cows included maize silage, which, in both years, was found to have the highest level of clostridial spore contamination. Pre-dipping with a detergent/emollient solution, and drying with a disposable paper towel, proved much more efficient in reducing spore contamination than forestripping alone, both on the teats (1·30 vs. 2·20 log10 MPN/swab; P < 0·001) and in the milk (1·82 vs. 2·47 log10 MPN/L, P < 0·02), while post-dipping had little influence on spore count. The standard plate count in milk was significantly lower with Pre+F+Post treatment than with F (3·80 vs. 4·51 log10 CFU/mL, P < 0·01). The teat preparation procedure did not influence the lactic acid bacterial levels in the milk, which is very positive in that decreased lactic acid bacterial content can lessen raw milk cheese quality.

Relationships among ensiling, nutritional, fermentative, microbiological traits and contamination in corn silages addressed with partial least squares regression

The objective of this work was to reduce the predictor dimensionality and to develop a model able to forecast contamination in corn silages. A survey on 33 dairy farms was performed, and samples from core, lateral, and apical parts of the feed-out face of corn silage bunkers were analyzed for chemical, biological (digestible and indigestible NDF), fermentative (pH, ammonia nitrogen, lactic acid, VFA, and ethanol), and microbiological (yeasts and molds) traits. Corn silage samples were analyzed for cell and spore counts by adoption of a molecular DNA-based method. A partial least squares (PLS) regression with a leave-one-out cross-validation method was used to reduce the dimensionality of the original predictors ( = 30) by projecting the independent variables into latent constructs. In a first step of the model development, the importance of independent variables in predicting contamination was assessed by plotting factor loadings of both dependent and independent variables on the first 2 components and by verifying for each predictor the variable influence on projection values adopting the Wold's criterion as well as the entity of standardized regression coefficients. Three ensiling characteristics (bunker type, presence of lateral wrap plastic film, and penetration resistance as a measurement of the ensiled mass density), a chemical trait (DM), 9 characterizations of the fermentative profile (pH, ammonia nitrogen, acetic acid, butyric acid, isobutyric acid, valeric acid, isovaleric acid, ethanol, and lactic acid), and 2 microbiological traits (yeasts and molds) were retained as important terms in the PLS model. Three reduced-variable PLS (rPLS) regressions-the first based on ensiling, chemical, fermentative, and microbiological retained important variables (rPLSecfm); the second based on chemical, fermentative, and microbiological retained important traits (rPLScfm); and the last based on only chemical and fermentative retained important variables (rPLScf)-were performed. The model that best fit the measurements was rPLSecfm. The rPLScfm and rPLScf models had similar regression performances but higher mean square errors of prediction than rPLSecfm. However, all tested models seemed adequate to rank corn silages for low, medium, and high risks of contamination. To avoid the visit on farm by trained people required to measure penetration resistance, the use of the rPLScf model is suggested as a useful tool to assess the risk of in corn silage.

Application of high pressure processing for controlling Clostridium tyrobutyricum and late blowing defect on semi-hard cheese

In this study we evaluated the application of different high pressure (HP) treatments (200-500 MPa at 14 °C for 10 min) to industrial sized semi-hard cheeses on day 7, with the aim of controlling two Clostridium tyrobutyricum strains causing butyric acid fermentation and cheese late blowing defect (LBD). Clostridium metabolism and LBD appearance in cheeses were monitored by sensory (cheese swelling, cracks/splits, off-odours) and instrumental analyses (organic acids by HPLC and volatile compounds by SPME/GC-MS) after 60 days. Cheeses with clostridial spores HP-untreated and HP-treated at 200 MPa showed visible LBD symptoms, lower concentrations of lactic, citric and acetic acids, and higher levels of pyruvic, propionic and butyric acids and of 1-butanol, ethyl and methyl butanoate, and ethyl pentanoate than cheeses without spores. However, cheeses with clostridial spores and HP-treated at ≥ 300 MPa did not show LBD symptoms and their organic acids and volatile compounds profiles were comparable to those of their respective HP-treated control cheeses, despite HP treatments caused a low spore reduction. A decrease in C. tyrobutyricum spore counts was observed after curd pressing, which seems to indicate an early spore germination, suggesting that HP treatments ≥300 MPa were able to inactivate the emerged C. tyrobutyricum vegetative cells and, thereby, prevent LBD.

New assessment based on the use of principal factor analysis to investigate corn silage quality from nutritional traits, fermentation end products and mycotoxins

BACKGROUND

A survey on 68 dairy farms was carried out to evaluate the ensiling procedures adopted to store corn silage. Samples from core, lateral and apical zones of the feed-out face of silos were analysed. A principal factor analysis (PFA) was carried out on the entire database (196 silage samples and 36 variables) and 11 principal factor components (PCs) were retained and interpreted.

RESULTS

Ensiling procedures influenced the area exposed to risk of air penetration. Cores had higher dry matter, starch and lactic acid content or lower pH, fibre, propionate and butyrate concentrations than peripheral samples (P < 0.05). The highest (P < 0.05) mycophenolic acid and roquefortina C concentrations were detected in lateral samples. Chemical and digestibility variables loaded on two PCs; four PCs were characterized by end-products associated with clostridia, heterolactic, homolactic and aerobic fermentations; two PCs were associated with mycotoxins, whereas three PCs explained ensiling procedures.

CONCLUSION

The main quality traits of corn silages differed throughout the entire silo face. Minimization of the area exposed to risk of air penetration represents the best strategy to preserve the nutritional value and safety of corn silages. PFA allowed a clusterization of original variables into 11 PCs, appearing able to discriminate well and poorly preserved corn silages.