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

TY - JOUR

T1 - A flow cytometric technique for quantification and differentiation of bacteria in bulk tank milk

AU - Holm, C.

AU - Mathiasen, T.

AU - Jespersen, Lene

PY - 2004

Y1 - 2004

N2 - AIMS: The present study describes a flow cytometric technique for quantification and differentiation of bacteria in bulk tank milk according to the main cause of elevated counts.METHODS AND RESULTS: A total of 75 Danish bulk tank milk samples exceeding the grading level of 3.0 x 10(4) CFU ml(-1) were examined by both flow cytometry and traditional microbiological analyses. The correlation coefficient (r) between the two methods was 0.71. For the differential analyses of the dominant bacterial populations four different parameters were used to give a species-characteristic pattern. The four parameters were as follows: staining with Oregon Green conjugated wheat germ agglutinin that binds to the cell wall of bacteria, staining with hexidium iodide that binds to all bacterial DNA, the flow cytometric forward scatter and the flow cytometric side scatter. 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 ability of the flow cytometric technique to predict the main cause of elevated bacterial counts on routine samples was examined. Comparing these results with results obtained by traditional microbiological analyses for identification showed that for 81% of the samples the two techniques agreed on the main cause of an elevated bacterial count.CONCLUSIONS: The ability of the presented flow cytometric technique to enumerate and differentiate bacteria in bulk tank milk according to the main cause of elevated counts was demonstrated.SIGNIFICANCE AND IMPACT OF THE STUDY: This study described the first step in development of a technique suitable for routine analyses of bulk tank milk samples. A technique indicating the main cause of an elevated count will enable the farmer to eliminate the contamination source within a short time limit.

AB - AIMS: The present study describes a flow cytometric technique for quantification and differentiation of bacteria in bulk tank milk according to the main cause of elevated counts.METHODS AND RESULTS: A total of 75 Danish bulk tank milk samples exceeding the grading level of 3.0 x 10(4) CFU ml(-1) were examined by both flow cytometry and traditional microbiological analyses. The correlation coefficient (r) between the two methods was 0.71. For the differential analyses of the dominant bacterial populations four different parameters were used to give a species-characteristic pattern. The four parameters were as follows: staining with Oregon Green conjugated wheat germ agglutinin that binds to the cell wall of bacteria, staining with hexidium iodide that binds to all bacterial DNA, the flow cytometric forward scatter and the flow cytometric side scatter. 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 ability of the flow cytometric technique to predict the main cause of elevated bacterial counts on routine samples was examined. Comparing these results with results obtained by traditional microbiological analyses for identification showed that for 81% of the samples the two techniques agreed on the main cause of an elevated bacterial count.CONCLUSIONS: The ability of the presented flow cytometric technique to enumerate and differentiate bacteria in bulk tank milk according to the main cause of elevated counts was demonstrated.SIGNIFICANCE AND IMPACT OF THE STUDY: This study described the first step in development of a technique suitable for routine analyses of bulk tank milk samples. A technique indicating the main cause of an elevated count will enable the farmer to eliminate the contamination source within a short time limit.

KW - Animals

KW - Bacteria

KW - Bacterial Typing Techniques

KW - Cattle

KW - Colony Count, Microbial

KW - Flow Cytometry

KW - Food Microbiology

KW - Hygiene

KW - Industrial Microbiology

KW - Mastitis, Bovine

KW - Milk

U2 - 10.1111/j.1365-2672.2004.02346.x

DO - 10.1111/j.1365-2672.2004.02346.x

M3 - Journal article

C2 - 15479408

SN - 0370-1778

VL - 97

SP - 935

EP - 941

JO - Proceedings of the Society for Applied Bacteriology

JF - Proceedings of the Society for Applied Bacteriology

IS - 5

ER -