Predominant Microflora of Downgraded Danish Bulk Tank Milk

Abstract

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.

Contamination of cow's raw milk by psychrotrophic and mesophilic microflora in relation to selected factors

“…But the results cannot be generalised because this technology was used on one farm only in our investigation (Cd1). Nevertheless, the influence of deficiencies in herd management and milking on the microbial quality of milk was confirmed (Holm et al, 2004;Jayarao et al, 2004). The influence of milking technology on the rate of microbial contamination of milk (Table 4) confirmed the finding (Gonzalo et al, 2006) that milking in a milking parlour is done under more hygienic conditions of milk acquirement compared to the in-stall milking pipeline system.…”

“…It was also confirmed by the identification of microflora in bulk milk samples with higher bacterial counts than 3.0 × 10 4 CFU/ml in Denmark. Microorganisms primarily associated with poor hygiene dominated in 64% of samples; bacteria also associated with poor hygiene and growth at low temperatures (psychrotrophic bacteria) were dominant microflora in 28% of samples and bacteria connected mainly with mastitis were dominant microflora in 8% of samples (Holm et al, 2004).…”

A flow cytometric technique for quantification and differentiation of bacteria in bulk tank milk

“…The isolates of the 75 bulk tank milk samples were identified with traditional microbiological analyses and grouped according to the main cause of elevated bacterial counts as previously reported (Holm et al 2004). Based on these groups, three regions in the flow cytometric plot were defined: region 1 includes bacteria mainly associated with poor hygiene, region 2 includes psychrotrophic hygiene bacteria and region 3 includes bacteria mainly related to mastitis.…”

“…The detailed procedures used for counting colonies, selecting colonies and identifying isolates are previously described (Holm et al 2004). …”

“…and Streptococcus spp. (Holm et al 2004). Thus, a technique for differentiating micro-organisms related to poor cleaning of the udder or milking equipment, bacteria related to poor cleaning of the bulk tank and bacteria mainly associated with mastitis will help the farmer to locate a problem.…”