Predominant microflora of downgraded Danish bulk tank milk.
The microflora of downgraded Danish bulk tank milk was examined to identify the main causes of increased microbial counts. Seventy-five representative samples with a microbial count exceeding 3.0 x 10(4) cfu/mL were selected for a more detailed microbial examination. A total of 1237 isolates from these samples were identified. Gram-negative, oxidase-positive bacteria were found in 72% of the samples. Coliforms were found in 20% of the samples, and non-coliforms were found in 49% of the samples. Coryneforms, other gram-positive rods, Lactococcus spp., Micrococcus spp., and coagulase-negative Staphylococcus spp. were found in 28 to 53% of the samples. Bacillus spp., Enterococcus spp., Staphylococcus aureus, Streptococcus dysgalactiae, Streptococcus uberis, and yeasts were found in <25% of the samples. Additionally, the isolates were divided into 3 groups, based on the main cause of an elevated microbial count. Microorganisms primarily associated with poor hygiene dominated the microflora in 64% of the samples; bacteria also related to poor hygiene, but in addition associated with growth at low temperatures (psychrotrophic bacteria) dominated the microflora in 28% of the samples; and bacteria mainly associated with mastitis dominated the microflora in 8% of the samples. A bulk tank milk storage period of 48 h instead of 24 h did not affect the proportion of downgraded milk samples and could not be associated with a specific group of microorganisms. Further, no relationship was found between somatic cell counts and the presence of mastitis bacteria.
Danish Dairy Board, Department of Veterinary and Milk Quality, Frederiks Allé, Arhus C, Denmark.
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Holm
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Jepsen
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Larsen
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Jespersen
D000192:Actinomycetales / Q000302:isolation & purification; D000818:Animals; D015169:Colony Count, Microbial; D003718:Denmark; D004755:Enterobacteriaceae / Q000302:isolation & purification; D006090:Gram-Negative Bacteria / Q000302:isolation & purification; D017045:Lactococcus / Q000302:isolation & purification; D008837:Micrococcus / Q000302:isolation & purification; D008892:Milk / Q000382:microbiology*; D013210:Staphylococcus / Q000302:isolation & purification; D013291:Streptococcus / Q000302:isolation & purification; D015003:Yeasts / Q000302:isolation & purification