Abstract
Dairy biofilms as a source of contamination of milk and its products are of great concern in the dairy industry. For a reliable risk assessment, knowledge about the microbial community composition of biofilms in the milking systems of dairy farms must be improved. In this work, swab samples of milking machine biofilms of two dairy farms were investigated by a combination of culture-dependent and -independent methods. Spots in the milking system with enhanced microbial colonization were identified by quantification on selective and non-selective media. In addition, stainless steel coupons were placed into the piping system of a milking machine, removed after several milking intervals, and investigated for colonization by cultivation and culture-independently. Isolates were differentiated and identified by a combination of chemotaxonomical methods and 16S rRNA sequencing. The culture-independent approach involved treatment of the samples with the viability dye propidium monoazide prior to direct DNA-extraction by enzymatic cell lysis and cloning to exclude bias from dead biomass. The milking equipment retainers and the outlet of the milk bulk tank were identified as highly colonized spots on both farms. A high bacterial diversity was detected covering the phyla Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria. Presence of biofilms was demonstrated on several materials including stainless steel and plastic, which are frequently used in milking machines, but also in dairy processing plants. Growth of mainly Gram-positive bacteria with high percentages of the phylum Actinobacteria was detected on the stainless steel coupons after exposition in the milking system for two to three days. Knowledge about the heterogenic microbial load on different parts of the milking machines and the stainless steel coupons will help to identify primary colonizers of the milking system, to assess the risk potential of biofilms for raw milk, to improve sanitation processes and to identify parts of the milking machine, which should be improved by hygienic design.
Highlights
Biofilms are accumulations of microbial cells attached to surfaces and embedded in self-produced matrices [1]
The highest mean total microbial count (TMC) of 6.3 log10 cfu/cm2 was detected on the milking equipment retainers of farm 1, followed by the plastic pipe at the end of the pressure line and the outlet of the milk bulk tank with TMCs about 2 log levels lower
High TMCs on the milking equipment retainers could be an essential source of contamination of the milking system with biofilm formers, pathogenic bacteria and/or spoilage organisms, while high TMCs on the outlet of the bulk tank could lead to the transfer of these organisms to the dairy industry
Summary
Biofilms are accumulations of microbial cells attached to surfaces and embedded in self-produced matrices [1]. Attachment of cells and subsequent biofilm formation can be influenced by surface material, roughness, and hydrophobicity, which can in turn be affected by surface conditioning with food ingredients [2, 3]. Bacterial biofilms are a major problem in the food industry. Biofilm cells can withstand unfavorable environmental conditions, such as nutrient depletion or treatment with antimicrobial substances [4, 5]. For the dairy industry biofilm formation is a fundamental problem, because raw milk contains a wide variety of microorganisms and dairy products are susceptible to microbial spoilage. The secretion of heat-resistant spoilage enzymes such as proteases and lipases by biofilm inhabitants into the raw milk can lead to reduced shelf-life of UHT milk [3, 10]
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
