Detection of bacteriophage-infected cells of Lactococcus lactis by using flow cytometry.
Bacteriophage infection in dairy fermentation constitutes a serious problem worldwide. We have studied bacteriophage infection in Lactococcus lactis by using the flow cytometer. The first effect of the infection of the bacterium is a change from cells in chains toward single cells. We interpret this change as a consequence of a cease in cell growth, while the ongoing cell divisions leave the cells as single cells. Late in the infection cycle, cells with low-density cell walls appear, and these cells can be detected on cytograms of light scatter versus, for instance, fluorescence of stained DNA. We describe a new method for detection of phage infection in Lactococcus lactis dairy cultures. The method is based on flow cytometric detection of cells with low-density cell walls. The method allows fast and early detection of phage-infected bacteria, independently of which phage has infected the culture. The method can be performed in real time and therefore increases the chance of successful intervention in the fermentation process.
Michelsen
Ole
O
BioCentrum-DTU, Technical University of Denmark, Building 301, DK-2800 Kgs. Lyngby, Denmark.
Cuesta-Dominguez
Alvaro
A
Albrechtsen
Bjarne
B
Jensen
Peter Ruhdal
PR
D000818:Animals; D001435:Bacteriophages / Q000254:growth & development*; D005434:Flow Cytometry / Q000379:methods*; D013294:Lactococcus lactis / Q000821:virology*; D008892:Milk / Q000382:microbiology; D015203:Reproducibility of Results