Studies on the mechanism of gel formation in the California mastitis test reaction

Abstract

SummaryThe effects of various factors on gel formation in the California Mastitis Test (CMT) were studied to obtain information on the mechanism of the reaction. Death of the leucocytes in milk, produced either by storing the milk at 5°C or by freezing and thawing, markedly reduced the viscosity of the gel formed by the milk with CMT reagent. Samples of skim-milk to which leucocytes were added gave increasingly viscous gels with CMT reagent as the pH was increased to 10·0. Soluble casein increased the viscosity of the gel formed by leucocytes with CMT reagent. The viscosity of the gel was decreased by the addition of CaCl2 and NaCl. On microscopic examination the gel formed in the CMT appeared as an irregularly arranged fibrillar network containing DNA. Deoxyribonuclease I rapidly eliminated the gel-forming property of leucocyte nuclei with CMT reagent, and EDTA inhibited this enzyme activity. Crude protease, trypsin, papain and bacterial protease decreased the gelforming property to different degrees. The presence of EDTA with these enzymes resulted in the formation of a viscous, ropy gel before the addition of CMT reagent. It was concluded that at least a part of the protein of the DNA-protein complex of leucocyte nuclei, in addition to the native polymer of DNA, was necessary for gel formation in the CMT reaction.