Short communication: Can the mammopathogenic Escherichia coli P4 strain have a direct role on the caseinolysis of milk observed during bovine mastitis?

A) Growth curves of Escherichia coli P4 in LPS-fresh milk (△), noninfused fresh milk (▴), minimum synthetic medium (MS, ●), and Luria Bertani broth (LB, ■). Arrows indicate times at which extracellular bacterial protein samples from milks and LB (solid line), and MS (dotted line) were recovered for zymogram analyses. B) Growth curves of E. coli K12 MG1655 in LPS-fresh milk (△) and noninfused fresh milk (▴).

Sodium dodecyl sulfate-PAGE zymogram analysis of Escherichia coli P4 extracellular content culture from minimum synthetic medium. Clear zones indicate protease activities on Coomassie Blue R250 stained gel. M = molecular mass standard.

Sodium dodecyl sulfate-PAGE electrophoretograms of total caseins (A), α_S1-casein (B), α_S2-casein (C), and β+κ-caseins (D) alone (Ctr) or mixed with an equal quantity of Escherichia coli P4 extracellular proteins from 13h minimum synthetic medium (EP-MS) and 10h Luria Bertani (EP-LB) cultures, and incubated for 0, 24, and 48h at 37°C. Gel was stained with Coomassie Blue R250.

Evolution of each casein fraction, determined by fast protein liquid chromatography analysis, from noninfused fresh milk (NIFM) inoculated with Escherichia coli P4 (bars with white background) or not (bars with gray background), and incubated for 2, 7, and 24h at 37°C.

Sodium dodecyl sulfate-PAGE electrophoretogram of proteose-peptone fraction from noninfused fresh milk (NIFM) inoculated with Escherichia coli P4 (P) or not (C), and incubated for 2, 7, and 24h at 37°C. Gel was stained with Coomassie Blue R250. M = molecular mass standard.

Growth curve of Escherichia coli P4 in minimum synthetic medium devoid of (NH₄)₂SO₄ and glycerol, but supplied with 0.15% (wt/vol) sodium caseinate (initially prepared in a 0.05 M pH 7 sodium phosphate buffer) and SDS-PAGE electrophoretogram of caseins in culture medium after 0 (1) and 200h (2) of incubation at 37°C. Gel was stained with Coomassie Blue R250.